Minimally Invasive Total Hip Arthroplasty 

Updated: Oct 01, 2018
Author: Derek F Amanatullah, MD, PhD; Chief Editor: Erik D Schraga, MD 

Overview

Practice Essentials

In addition to conventional surgical approaches, total hip arthroplasty (THA) may be done via minimally invasive surgery (MIS). Minimally invasive THA (MIS-THA) is often portrayed in the lay community and press as involving a small skin incision; actually, it is limited soft-tissue and bony dissection. Existing MIS-THA techniques are based on variations of conventional surgical approaches that have been used by surgeons for decades.

To date, no single technique has been proved superior to the others. The benefits of a shorter incision (see the image below) must outweigh the added technical difficulty caused by reduced visualization. The choice of operative approach depends on surgeon preference and experience.

Minimally invasive total hip arthroplasty. Shown a Minimally invasive total hip arthroplasty. Shown are skin incisions for direct anterior (black), miniposterior/lateral/anterolateral (dark blue), conventional posterior (dark blue plus red extensions), direct superior (green), and SuperPATH (purple) approaches to hip. Conventional posterior incision is usually 10-25 cm long. Single incisions for minimally invasive approaches are usually less than 10 cm long. In two-incision approach, both incisions are usually less than 5 cm long.

Indications and contraindications

A minimally invasive approach may be suitable for the following:

  • Patients with a straightforward anatomy
  • Patients who are not obese (ie, body mass index [BMI] lower than 30 kg/m 2)

No absolute contraindications to MIS-THA have been definitively established, but conventional THA is probably a more suitable choice for the following patients:

  • Patients with pathologic conditions that necessitate enhanced exposure (eg, revision THA, complex primary THA, complete hip dislocation, Crowe type III or IV dysplasia, or severe acetabular protrusion)
  • Patients who have previously undergone certain surgical procedures (eg, malunion or prior osteotomy or fracture repair requiring removal of hardware)
  • Patients undergoing surgery involving the use of a cemented prosthesis (eg, for osteoporotic bone, metastatic cancer, metabolic disorder, or femoral anatomy)
  • Patients with bony ankylosis
  • Patients with rheumatoid arthritis
  • Patients with a BMI higher than 30 kg/m 2
  • Patients with severe hip contracture
  • Patients who are exceedingly muscular

See Overview for more detail.

Preparation for procedure

A routine preoperative workup is necessary, including the following:

  • Complete medical workup
  • Radiography (eg, affected extremity and chest radiographs)
  • Basic laboratory evaluation (eg, type and screen, complete blood count, basic metabolic panel, and urine analysis)
  • Electrocardiography (ECG) for patients older than 50 years
  • Additional studies, as warranted by any comorbid conditions that may be present
  • Dental evaluation and treatment for dental diseases should be done before THA is performed; routine cleaning of the teeth should be delayed for several weeks after surgery

Preoperative templating may be used to guide determination of the following:

  • Implant size
  • Leg length restoration
  • Femoral stem offset

The following specialized surgical instrumentation and implants may be helpful during MIS-THA:

  • Modified versions of conventional instrumentation to access a limited operative field
  • Additional equipment for visualization (eg, fiberoptic light cables, cutaway reamers, angled reamers and broach handles, Hohmann retractors with light sources, or flexible acetabular reamers)
  • Special operating room table for hip dislocation (eg, Judet Orthopaedic Table, PROfx Fracture Table, or Jupiter Table)

See Periprocedural Care for more detail.

Procedural technique

The choice of operative approach depends on the surgeon’s preference and experience. The basic surgical approaches to the hip include the following:

  • Direct anterior approach (eg, modified Smith-Petersen) - Performed in the supine position and uses the internervous plane between the femoral and superior gluteal nerves
  • Anterolateral approaches (eg, modified Watson-Jones) - Performed in the supine or lateral position and divides the anterior portion of the gluteus medius muscle
  • Direct lateral approach (eg, modified Hardinge) - Performed in the supine or lateral position and uses the intramuscular interval between the tensor fasciae latae and gluteus medius muscles
  • Posterior approach (eg, modified Southern) - Performed in the lateral position and divides the gluteus maximus muscle and the short external rotators of the hip (eg, piriformis, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris)
  • Piriformis-sparing posterior approach - Performed in the lateral position and divides the gluteus maximus, the iliotibial band, and the short external rotators of the hip (eg, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris) except the piriformis
  • Direct superior approach – Performed in the lateral position and divides the gluteus maximus and the short external rotators of the hip (e.g., piriformis, superior gemellus, obturator internus, and inferior gemellus) while leaving the iliotibial band and quadratus femoris intact
  • Two-incision approach - Combines an anterior approach to the acetabulum with a posterior approach to the proximal femoral shaft
  • SuperPATH approach – Performed in the lateral decubitus position and divides the gluteus maximus, medius, and minimus

The complication rate is twice as high for surgeons who perform fewer than 50 MIS-THAs a year. Complications after MIS-THA are more common in the following individuals:

  • Patients older than 65 years
  • Patients with a BMI higher than 30 kg/m 2
  • Women with osteoporosis
  • Patients with altered femoral or acetabular anatomy

Common adverse events include the following:

  • Dislocation
  • Damage to the sciatic, femoral, or lateral femoral cutaneous nerve
  • Impaired postoperative wound healing
  • Hematoma
  • Infection

See Technique for more detail.

Background

In addition to conventional surgical approaches, total hip arthroplasty (THA) may be done via minimally invasive surgery (MIS).[1] Minimally invasive THA (MIS-THA) is often portrayed in the lay community and press as involving a small skin incision; actually, it is limited soft-tissue and bony dissection. Existing MIS-THA techniques are based on variations of traditional direct anterior, anterolateral, direct lateral, and posterior surgical approaches that have been used by surgeons for decades. To date, no single technique has been proved definitively superior to the others.

For surgeons, the benefits of a shorter incision must outweigh the added technical difficulty from reduced visualization. A thorough knowledge of the relevant anatomy is important for any elective procedure but takes on added significance for MIS-THA. The hip consists of a ball (femoral head) that fits into a socket (acetabulum); the joint capsule and the surrounding ligaments and muscles provide stability to the joint. Ideally, for MIS-THA to be considered, there should be little or no anatomic deformity of the femoral head and acetabulum. Surgeons may try to progressively shorten their incisions while on the upward portion of the learning curve.

Indications

Degenerative arthritis of the hip can often be managed medically by means of reasonable exercise, therapy, analgesics, assistive devices to unload the diseased hip, and alternative pain management techniques that work for a particular patient. If medical therapy fails, then surgical therapy can be considered.

Specific indications for MIS-THA vary by author and by type of surgical approach. Most authorities cite the presence of a straightforward anatomy and the absence of obesity (ie, body mass index [BMI] lower than 30 kg/m2) as desirable factors in choosing patients for MIS, especially early in the surgeon’s learning curve.

Although MIS-THA is increasingly being used as an alternative to conventional THA, there is still some debate as to whether MIS-THA is an acceptable replacement for or even an improvement on conventional THA. At present, although there is support for MIS-THA in the literature, no definitive answer to this question is available.

Contraindications

No absolute contraindications for MIS-THA have been definitively established; this procedure is defined by limited soft-tissue and bony dissection. The probability of converting an MIS-THA approach to a conventional approach should be discussed with the patient, and patient expectations should be appropriately managed. A conventional approach to the hip is more suitable for the following patients[2, 3, 4] :

  • Patients with pathologic conditions that necessitate enhanced exposure (eg, revision THA, complex primary THA, complete hip dislocation, Crowe type III or IV dysplasia, or severe acetabular protrusion)
  • Patients who have previously undergone certain surgical procedures (eg, malunion or prior osteotomy or fracture repair requiring removal of hardware)
  • Patients undergoing surgery involving the use of a cemented prosthesis (eg, for osteoporotic bone, metastatic cancer, metabolic disorder, or femoral anatomy)
  • Patients with bony ankylosis
  • Patients with rheumatoid arthritis
  • Patients with a BMI higher than 30 kg/m 2
  • Patients with severe hip contracture
  • Patients who are exceedingly muscular

Technical Considerations

Best practices

Before undertaking MIS-THA, surgeons need to gain specialized hands-on training by operating on cadavers and by visiting experienced surgeons. A double-blinded, randomized, controlled trial determined that the risks associated with MIS-THA were doubled in a surgeon’s first 60 cases but that this increased risk was not present in the surgeon’s next 60 cases.[5] These data give some idea of the learning curve associated with MIS-THA and suggest that surgeons should not undertake this procedure without appropriate training and mentorship.

Computer or robotic guidance is currently advocated by some and may allow virtual visualization of the minimally exposed surgical anatomy. The advantage of such guidance is that the proper medialization for correct coverage of the cup can be both qualitatively and quantitatively achieved.

Procedural planning

Advantages of minimally invasive approach

The growth of interest in MIS-THA is related to market- and patient-driven demand for the procedure. In one study, 53% of hip surgeons admitted feeling pressured to use a specific surgical technique or implant as a result of a patient request, in some cases in a way that they believed could be harmful to their patients. Surgeons should consider whether they are prepared to subject themselves to the increased stress and learning curve associated with MIS-THA, especially if the desire for MIS-THA does not exist among their patients. The learning curve connected with MIS-THA is steep, and mastering the skill is frequently an ongoing process.

Young, active members of the work force tend to prefer MIS because of the shorter recovery time and earlier return to work. The proposed benefits of MIS-THA are better incisional cosmesis (as perceived by the patient only), increased patient satisfaction, and possibly a shorter hospital stay.[2, 6, 7]

Preoperative and postoperative gait analysis in 10 patients who had undergone posterior MIS-THA demonstrated 85% recovery of gait velocity, 90% recovery of single-leg stance time, 90% recovery of cadence, and 70% return of stride length, as well as less dependence on walking aids.[3] Moreover, 97% of patients attained standard physical therapy goals (transferring in and out of bed from standing, rising from a chair to standing, moving from standing to sitting, walking 100 feet, and negotiating a full flight of stairs) within 1 day of surgery.[8] Decreased blood loss, decreased postoperative pain, and decreased need for postoperative ambulatory walking aids have also been reported with MIS-THA.[9]

Limitations of minimally invasive approach

Trauma to the bone itself is the same for MIS-THA and conventional THA. Trauma to the skin can vary. The pressure on the wound from modified retractors is approximately double that of conventional retractors. In a study of 34 THAs, plastic surgeons rated six of 20 MIS-THA scars as poor but rated only one of 14 conventional THA scars as poor. Thirty of 31 patients also stated that pain relief and implant longevity were more important than scar cosmesis after 2 years of follow-up.[10]

MIS-THA is associated with a 6% increase in local wound complications.[11] This increase may be secondary to increased soft-tissue and cutaneous trauma from the retraction or reamers abrading the skin.[12] However, two meta-analyses found that the increase in cutaneous trauma was not statistically significant.[13, 14]

Damage to surrounding structures, especially nerves, is one of the main concerns with MIS-THA. The anterolateral approach places the superior gluteal nerve at significant risk; four of five superior gluteal nerves were cut during a cadaveric study.[15] A meta-analysis demonstrated a fivefold increase in the risk of lateral femoral cutaneous nerve (LFCN) palsy after anterior MIS-THA, as well as a statistically significant increase in the risk of any nerve palsy.[14]

Poor visibility during MIS-THA contributes to implant malposition, femoral fracture from anteverting the femoral component more than the proximal femoral geometry allows, and insufficient implant seating. Other complications of MIS-THA include proximal femoral fracture (3% for the two-incision approach), hematoma (2% in one study), acetabular component malposition (an abduction angle of < 35° or >50° was seen in 4% and 11%, respectively, with posterior MIS-THA), and varus femoral component malposition (14% with posterior MIS-THA).[2, 3, 11, 16] Acetabular cup anteversion was three times more likely to be outside the acceptable range with the posterior MIS-THA.[17]

Comorbid conditions (eg, obesity, diabetes mellitus, alcoholism, and hypertension) influence rehabilitation more than incision length. Any functional advantages of MIS-THA disappear by 6 weeks to 6 months after surgery. It is yet to be determined whether good pain scores and functional recovery are due to MIS or to newer anesthesia and pain-management techniques. Studies suggest that young patient age and high preoperative hemoglobin levels are the only factors associated with shorter hospital stays; incision size is not.

Multiple other studies have found no differences in operating time, pain control, transfusion rates, low-grade heterotopic ossification, estimated blood loss, length of hospital stay, gait (ie, stride length, cadence, or walking speed), or Harris Hip Score between MIS-THA and conventional THA.[11, 13, 14, 18, 19]

Complication prevention

Complication prevention measures recommended for MIS-THA are exactly the same as those recommended for conventional THA and should include the following:

  • Appropriate preoperative screening and operative clearance
  • Preoperative templating and planning
  • Preoperative administration of antibiotics as recommended by the American Academy of Orthopaedic Surgeons (AAOS)
  • Postoperative anticoagulation as recommended by the AAOS
  • Instruction regarding physical restrictions and limitations as indicated

Outcomes

Direct anterior approach

Kennon et al described the results of 2132 consecutive anterior MIS-THAs, of which 1281 were cemented and 851 cementless, and reported that complications included dislocations (1.3%), hematomas (1.5%), infections (0.23%), fractures (4.1%), and nerve injuries (0.4%).[20]

Siguier et al, in a retrospective review of 1037 anterior MIS-THAs, reported a 0.96% rate of dislocation and a 0.77% rate of revision surgery due to septic loosening, aseptic loosening, and recurrent dislocations. No patients developed significant heterotopic ossification, clinical limp, or Trendelenburg gait.[21]

Matta et al, in a study of 506 conservative anterior MIS-THAs (386 primary THAs, 92 THAs after previous hip surgery, and 22 revision THAs), reported one infection, two anterior dislocations, one posterior dislocation, and one temporary femoral nerve palsy. The average leg-length discrepancy was 3 mm.[22]

Rachbauer et al, in a prospectively study of 100 consecutive anterior MIS-THAs without exclusion criteria, reported three complications: one proximal femur fracture, one acetabular perforation, and one deep infection.[23]

Poehling-Monaghan et al, in a study of 222 patients receiving either direct anterior or miniposterior THAs, found no differences in mean length of stay, operative or in-hospital complications, maximum feet walked in hospital, or percent discharged to home.[24] Direct anterior patients had longer mean operating times than miniposterior patients (114 vs 60 minutes). In addition, they had greater need for gait aids at 2 weeks (92% vs 68%) but higher Harris Hip Scores at 8 weeks (95 vs 89). Direct anterior patients had lower rates of return to work and driving but did not differ in regard to use of gait aids, narcotics, activities of daily living, or walking 0.5 miles. Fewer wound problems occurred in the direct anterior group.

Maratt et al compared dislocation rates between direct anterior and posterior THA in 2147 patients.[25] There was no reported difference in dislocation rates (0.84% for direct anterior vs 0.79% for posterior). They also agreed with the previous literature in noting a slightly shorter length of stay with the direct anterior approach but a higher risk of fracture, increased blood loss, and increased hematoma risk.

Tripuraneni et al, in a matched cohort of 132 hip procedures, compared 66 direct anterior THAs with 66 posterior THAs.[26] Average acetabular abduction angle was 41.9° (range, 32-60°) in the posterior group and 43.8° (range, 30-62°) in the direct anterior group. The percentage of outliers (outside the Lewinnek safe zone, 30-50°) was 9.1% in the posterior group and 13.6% in the direct anterior group. There were two anterior dislocations in the direct anterior group and one anterior dislocation in the posterior group. Overall, it was concluded that there was no observable difference in hip stability or acetabular abduction between the direct anterior and posterior approaches.

Berend et al investigated the incidence of early periprosthetic fractures associated with primary THA in the direct anterior approach.[27] After identifying 2689 primary THAs, they reported 26 (0.9%) early periprosthetic femoral fractures, with 23 requiring revision. Analyzing risk factors, including age, gender, body mass index, and stem length, they noted that only increased age was associated with an increased risk of femoral fracture. Finally, logistic regression analysis revealed a significant age-fracture association for female gender only, which remained when controlled for BMI, stem length, or both.

Anterolateral approach

Pflüger et al, in a comparison of 50 conventional THAs with 50 MIS-THAs performed via the anterolateral approach with the patient in a supine position, found the two groups to be virtually identical with respect to average blood loss, operating time, and implant positioning.[28]

Xu et al, in a case-control study of 149 patients, compared the anterolateral approach with the posterolateral approach in terms of hip abductor strength and function.[29] At 3 months after surgery, the anterolateral group had significantly better hip abduction angles. At 6 months after surgery, the anterolateral group had significantly better hip abductor strength. No differences were observed in Harris Hip Scores at any time point up to 1 year after surgery. The observed differences were attributed to the fewer muscles interrupted in the anterolateral approach.

Tsai et al reported on outcomes in 1077 primary THAs performed in 1003 patients.[30] Median wound length was 6 cm (range, 4.8-9.2), median operation time was 68 minutes (range, 45-112). Mean perioperative blood loss was 422 mL (range, 56-990). The median cup inclination angle was 44º (range, 33-54º), median acetabular version angle was 17° (range, 12-24º), and median hospital stay was 4 days (range, 3-8).

A total of 22 (2.0%) complications were noted, including five cases of stem subsidence, four of cup loosening, five greater trochanter fractures, four infections, two intraoperative proximal femur fractures, and two iliopsoas impingements.[30] In all, 13 (1.2%) received additional surgery. No neurovascular injury or dislocation was noted. The Harris Hip Score improved from 53 (range, 33-67) preoperatively to 94 postoperatively (range, 87-100).

Nakai et al compared 103 anterolateral-approach THAs with 98 posterolateral-approach THAs. In the anterolateral group, intraoperative fracture was observed in six hips, three in the greater trochanter and three in the calcar femorale.[31] One hip was subjected to irrigation because postoperative infection was suspected. In the posterolateral group, intraoperative fracture was demonstrated in four hips in the calcar femorale. No postoperative dislocation and no pulmonary embolism or nerve paralysis were observed in either group. The authors noted that by their measurements, the anterolateral approach was not superior to the posterolateral approach.

Direct lateral approach

Ilizaliturri et al reported one pulmonary embolism and 19 small skin abrasions in 40 patients who underwent MIS-THA via the lateral approach; there were no cases of dislocation, but in 7.5% of cases, initial exposure difficulty necessitated conversion to standard-length incisions.[32]

Higuchi et al, in a retrospective study of 212 MIS-THAs done via the direct lateral approach, reported decreases in operating time, intraoperative blood loss, and total blood loss with MIS. There were no differences in postoperative bleeding and other complications between the standard-incision group and the short-incision group. The overall dislocation rate was 2.4%, and the rate of acetabular loosening was 1.9%.[33]

De Beer et al, in a comparison of matched-pair cohorts comprising 30 patients who underwent primary MIS-THA and 30 who underwent conventional THA via the direct lateral approach, reported no significant differences in operating time, opioid consumption, postoperative blood loss, complications, length of hospital stay, and Harris and Oxford hip scores 6 weeks after the procedure.[18] .

Howell et al, in a prospective comparison of 50 MIS-THAs with 57 conventional THAs done via the direct lateral approach, reported that MIS-THA increased the average length of surgery, but they noted no differences in the rate of blood transfusion. The mean length of hospital stay was shorter with MIS-THA. There were two intraoperative proximal femur fractures and hematomas in the MIS group, compared with one hematoma in the conventional group.[2]

De Anta-Diaz et al compared muscle damage and functional outcomes between 50 lateral-approach patients and 49 direct anterior patients in a randomized controlled study.[34] Postoperatively, there were significantly higher mean levels of interleukin (IL)-6, IL-8, and tumor necrosis factor alpha (TNF-α) in the lateral group up to postoperative day 4. By magnetic resonance imaging (MRI) at postoperative month 6, the lateral group showed greater fatty atrophy in the gluteus muscles but similar degrees in the other muscles. The mean thickness of the tensor fasciae latae (TFL) was significantly higher in the lateral group. Functional outcome was similar between groups at 3 and 12 months postoperatively.

Eto et al, in a retrospective review of revision THAs, found that the direct anterior approach was associated with early revision surgery when compared with the posterior and anterolateral (nondirect anterior) approaches.[35] Aseptic loosening occurred in 30% of the direct anterior cases, whereas the rate was 8% for the nondirect anterior approaches.

Posterior approach

Mardones et al, in a cadaveric study, compared the extent and location of damage to the abductor and external rotator muscles and tendons after two-incision and miniposterior THA.[36] Damage to the muscle of the gluteus medius and gluteus minimus was substantially less with the miniposterior technique than with the two-incision technique. Every miniposterior hip replacement caused the external rotators to detach during the exposure and caused additional measurable damage to the abductor muscles and tendon. None of the two-incision hip replacements were done without cutting, reaming, or damaging the gluteus medius or gluteus minimus muscle or external rotators.

A cadaveric study by Meneghini et al compared direct anterior and posterior approaches in 12 hips.[37] The mean amount of damage to the gluteus medius was 2.62% of its muscular area (range, 0-7.94%) in the direct anterior group and 2.85% (range, 0-8.9%) in the posterior group. Muscle damage to the TFL occurred in all six specimens in the direct anterior group and was a mean of 31.32% (range, 18.31–58.48%) of its muscular area. The direct head of the rectus femoris was damaged a mean of 12.24% (range, 0-24%) of its muscular area in the direct anterior group, with preservation of its origin on the anterior superior iliac spine (ASIS) in each specimen. Neither site of damage was noted in the posterior group.

Swanson analyzed 1000 consecutive MIS-THAs in 759 patients (none of whom were excluded on the basis of BMI) via the posterior approach. After a mean follow-up of 37 months, there was a 3% dislocation rate, a 0.3% incidence of deep wound infection, a 0.5% incidence of superficial infection, and a 1% incidence of delayed wound healing. The revision rate was of 2.1% (for dislocations, loosening, deep infection, and periprosthetic femoral shaft fractures). Radiographic follow-up revealed acceptable component positioning for 95.3% of the patients.[38]

Sculco et al studied 1000 patients undergoing posterior THA and reported only one deep infection, 12 dislocations, one revision (for recurrent dislocation), and two sciatic nerve palsies. There was a wide range in acetabular component positioning.[4]

Wenz et al compared a posterior approach to MIS-THA with a conventional direct lateral approach (>25 cm) and found that the former led to a significant decrease in transfusion requirements, shorter operating time, earlier ambulation, and improvements in discharge disposition and functional recovery during physical therapy.[39]

Pagnano et al, in a comparison of two-incision THA with posterior MIS-THA in 26 patients who underwent staged bilateral MIS-THA (with two-incision MIS-THA on one hip and posterior MIS-THA on the other), found that the majority of patients preferred the latter.[40] The added surgical technical difficulty of the two-incision MIS-THA was not rewarded with an earlier return to functional activities. There were no differences in the times to discontinue ambulatory aids, to return to driving, to climb stairs, to return to work, or to walk half a mile. Many patients were annoyed by the mere presence of the anterior incision during simple daily activities (eg, bathing or changing clothes) because the incision was clearly visible.

Hartzband reported on 100 THAs done via the posterior approach and observed no dislocations, though a 15% incidence of acetabular component malpositioning was documented.[16]

Wright et al prospectively compared 42 patients who underwent posterior MIS-THA with a matched cohort who underwent conventional THA and reported no dramatic clinical benefits, aside from an improved cosmetic appearance.[9]

Dorr et al, reporting on 105 posterior MIS-THAs with uncemented components, found that on gait analysis of 10 patients at 10 weeks’ follow-up, gait velocity was 80-85% of normal, cadence was 82-90% of normal, and stride length was 62-74% of normal.[41, 42]

Goldstein et al, in a retrospective comparison of 85 posterior MIS-THAs with 85 conventional THAs, reported that operating times, acetabular inclination angles, Harris Hip Scores, dislocation rates, and transfusion rates were similar in the two groups. Patient satisfaction was 96% in the MIS group and 90% in the conventional group.[6, 43]

Oganda et al, in a prospectively randomized study of 219 posterior THAs performed by a single experienced surgeon (109 via MIS and 110 via standard incision), reported no significant differences between the two groups with respect to postoperative hematocrit, rate of blood transfusion, pain scores, analgesic use, length of hospital stay, functional outcomes (Western Ontario and McMaster University [WOMAC], Oxford, and Harris hip scores), component placement (inclination angle 45.6° and 46.7°), or grade of cement mantle.[19]

When 100 of the patients in this study were selected randomly for gait analysis, no differences related to incision length were demonstrated in average stride length, cadence, or walking speed.[19] The main determinant for discharge home was adequate family support; age and preoperative hematocrit correlated with length of hospital stay.

Woolson et al, in a retrospective comparison of 50 posterior MIS-THAs and 85 conventional THAs, found no differences in transfusion rate, estimated blood loss, operating time, or length of hospital stay.[11] They did note an increased number of malpositioned components in the MIS-THA cohort. Acetabular inclination was less than 30° or more than 50° in 30% of the MIS-THAs, compared with 15% of the conventional THAs. The femoral stem was in varus in 12% of the MIS-THAs, compared with 4% of the conventional THAs.

When hemodialysis patients were excluded, there was a significant increase in wound complications in the MIS-THA cohort as compared with the conventional THA cohort.[11] Of the MIS-THAs, 33% were graded as having poor fit and fill, compared with 14% of conventional THAs. The MIS-THA cohort reported a significantly higher incidence of wound edges curling into the scar.

Winther at al conducted a prospective cohort study comparing the direct anterior, posterior, and lateral approaches.[44] At 6 weeks after surgery, the posterior approach allowed greater hip abduction strength than the direct anterior approach and allowed greater muscle strength than the lateral approach. At 3 months post surgery, however, no significant differences in muscle strength were found between the three groups.

Piriformis-sparing posterior approach

Khan et al initially described the piriformis-sparing approach in a study comparing 100 patients undergoing this procedure with 100 patients undergoing a standard posterior approach.[45] With a minimum follow-up of 2 years, they reported lower mean blood loss in the piriformis group, shorter inpatient stay, and greater improvement in WOMAC scores for up to 1 year.

Khan et al later compared the piriformis-sparing and standard posterior approaches in a randomized controlled study of 100 patients.[46] In the piriformis-sparing group, there was a trend towards a better 6-minute walk test at 2 weeks and greater patient satisfaction at 6 weeks, and the acetabular components were less anteverted and had a lower mean inclination angle. In both groups, mean component positions were within Lewinnek's safe zone. Surgeons perceived the piriformis-sparing approach as significantly more difficult, particularly in obese patients, leading them to conclude that as compared with the standard posterior approach, it is more difficult while providing only short-term benefits.

Direct superior approach

A cadaveric study comparing the direct anterior and direct superior approaches found no statistically significant difference in the rate of gluteus medius and quadratus femoris muscle injury in terms of percentage of surface area.[47] The direct superior approach was associated with less damage to the gluteus minimus, the TFL, and the rectus femoris. Finally, there was no statistically significant difference in the percentage of surface area of damage to the gluteus medius tendon between these approaches; however, it was noted that the direct superior approach had a statistically reduced transected length of the gluteus minimus tendon as compared with the direct anterior approach.

Roger et al retrospectively analyzed outcomes of 135 patients undergoing the direct superior approach.[48] There were no dislocations, no sciatic nerve palsies, no wound complications, and low transfusion rates (8%). The postoperative Harris Hip Score averaged 96.5 (range, 87-100). Overall acetabular cup abduction angle averaged 41 (range, 21-49), and anteversion averaged 21 (range, 15-27). Four percent and 2% of femoral components were inserted into more than 2º varus and 2º valgus alignment, respectively.

Two-incision approach

Berger, reviewing the first 100 cases of the two-incision MIS-THA, reported a 1% complication rate and no instances of dislocation, failure of biologic fixation, or reoperation; he also reported rapid recovery and an 85% rate of same-day discharge.[7]

Bal et al, in a comparison of 89 consecutive primary THAs using the fluoroscopy-guided two-incision MIS-THA with data from historical controls (96 direct lateral mini-incision THAs performed by the same surgeon), reported a 42% complication rate in the two-incision group, compared with 6% in the direct lateral incision group; a 10% repeat surgery rate in the two-incision group, compared with 3% in the direct lateral incision group; and significant radiographic malpositioning of components.[49, 50]

Of these patients, 25% sustained an LFCN injury, and one patient had neurapraxia of the femoral nerve.[49] Surgical experience proved highly significant: The rate of complications associated with the two-incision approach decreased substantially after the initial learning curve had been completed, resulting in a reliably safe and predictable operation.

Pagnano et al, comparing 80 consecutive patients who underwent two-incision MIS-THAs with retrospective data from the same surgeon’s previous 120 conventional posterior THAs, reported an 14% complication rate in the two-incision group, compared with a 3.75% rate in the conventional group.[40]

Irving, in a study of 192 direct two-incision MIS-THAs without fluoroscopic guidance after 2 years of follow-up, reported a 2.6% incidence of intraoperative proximal femur fractures that were fixed with cerclage wire and a 1.6% incidence of anterior dislocations.[51]

Nivbrant et al, in a clinical and cadaveric study documenting anatomic variations of LFCN injury during minimally invasive two-incision MIS-THA, reported a 38% incidence of paresthesia in the nerve’s distribution postoperatively, with almost 50% resolution at 6-month follow-up. Upon cadaveric dissection (97 specimens), the investigators identified a significant variation in the lateral branch of the LFCN in 31% of cases, which correlated with proximal and lateral thigh sensory loss.

Archibeck et al, reviewing results of the first 10 cases performed by surgeons who had completed the two-incision MIS-THA training course, noted a challenging learning curve.[52] Investigators observed no complications in 47% of cases, one complication in 37%, and more than one complication in 22%. Femur fractures occurred in 6.5% of cases. Nerve injury occurred in 3.2%, consisting mostly of lateral femoral cutaneous nerve injury and an isolated case of sciatic nerve injury. Early revisions were seen in 0.9% of patients (seven for infection and eight for dislocation). Patients with BMIs greater than 30 kg/m2 had a higher complication rate (16.3%) than those with BMIs less than 30 kg/m2 (8.3%).

The most striking finding of this study was that the number of complications did not significantly decrease from the first to the tenth case in a single surgeon’s experience, which suggests the learning curve may extend beyond the first 10 cases.[52] Accordingly, this procedure may be best performed by specially trained surgeons who perform a high volume of these cases.

In a randomized controlled trial comparing the miniposterior and two-incision approaches, Sershon et al found no significant differences in Harris Hip Scores or 12-item Short Form Survey physical and mental composite scores.[53] However, a longer operating time, increased operative complexity, and need for fluoroscopy in the two-incision approach were found to be significant disadvantages. 

SuperPATH approach

Penenberg et al, in a study of 250 consecutive hip implants with the SuperPATH approach, found no increased risk of component malposition, dislocation, or other adverse effects at the time of short-term evaluation or follow-up for 24 months.[54] The authors cite improvements made with regard to instrumentation, which allow this technique to be user-friendly and likely to be associated with a shorter learning curve than the two-incision approach.

Torre et al, in a case series, had an independent third party analyze postoperative radiographs in 66 of the first 100 patients who underwent the SuperPATH approach for component positioning and seating, femoral offset, and leg length.[55] Analysis deemed all components in the case series to be well seated and positioned. Leg lengths were measured to within 5 mm of the contralateral side, and mean acetabular abduction angle was 40.13°. It was concluded that implant position was optimal within the learning curve of the first 100 cases for described THA safe zones.

Rasuli et al, comparing the first consecutive 49 PATH cases with the first 50 SuperPATH cases, reported the mean operating times for the two procedures (114.5 ± 17.5 minutes and 101.7 ± 18.3 minutes, respectively).[56] They noted that PATH operating time reached a plateau by case 40, whereas SuperPATH operating time continued to decrease by case 50. In addition, mean length of stay was shorter for SuperPATH (2.2 vs 3.0 days).

Finally, Rasuli et al noted that acetabular cups were significantly more anteverted and less abducted in the SuperPATH cohort (anteversion, 23.5° ± 8.2°; abduction, 39.0° ± 8.4°) than in the PATH cohort (anteversion, 13.1° ± 7.1°; abduction, 42.9° ± 7.6°).[56] Despite the learning curve, these results indicate that PATH and SuperPATH approaches can be adopted with minimal complications and outcomes consistent with innovator outcomes.

Gofton et al, in a retrospective study of healthcare databases at three institutions, found that patients implanted using the SuperPATH technique experienced reduced 30-day all-cause readmission rates (2.3% vs 4.2%) and were more routinely discharged home (91.5% vs 27.3%) than was previously reported for patients in the United States.[57] They concluded that use of this tissue-sparing technique has the potential to significantly reduce postdischarge costs.

 

Periprocedural Care

Patient Education and Consent

It is imperative to ensure appropriate patient education before either conventional total hip arthroplasty (THA) or minimally invasive THA (MIS-THA). Such education should address the patient’s postoperative expectations, as well as inform the patient regarding the administration of anticoagulation. Preoperative counseling with respect to the patient’s postoperative activity level is left to the discretion of the surgeon.

Preprocedural Planning

Provided that the disadvantages caused by limited visualization during MIS-THA can be overcome, there is no logical reason to use a longer incision and create more surgical trauma if a shorter incision with less trauma would achieve the same end result. The skin incision can limit component insertion. A 10-cm (4-in.) incision is appropriate for inserting a 56-mm acetabular component while avoiding contact between the component and the skin or subcutaneous tissues.[6]

The most important factors allowing early discharge appear to be related to patient selection, patient motivation, anesthesia, acute pain-management techniques, and the postoperative protocol. The specific operative approach used does not appear to be an independent factor in early discharge. There are no data to indicate how the surgical approach interacts with the other variables in affecting discharge.

Factors such as family education, patient preconditioning, preemptive analgesia, and accelerated preoperative rehabilitation—rather than the surgical technique per se—may play a major role in fostering better outcomes after MIS-THA. Careful scientific study and evaluation are warranted before MIS techniques are widely accepted.

Preprocedural evaluation

No special workup is indicated for MIS-THA patients as compared with conventional THA patients. If the diagnosis of hip disease is in doubt, magnetic resonance imaging (MRI) or a diagnostic injection into the hip joint may be useful. If a fluoroscopically guided hip-joint injection relieves pain, the pathology is probably localized to the intra-articular joint. Careful examination and selected diagnostic modalities may be needed to rule out spinal stenosis, herniated lumbar disk, vascular claudication, incarcerated hernia, meralgia paresthetica, psoas impingement, hip bursitis, transient osteoporosis, malignancy, stress fracture, and other diseases that can mimic the symptoms of hip degeneration.

A routine preoperative workup is necessary, including the following:

  • Complete medical workup
  • Radiography (eg, affected extremity and chest radiographs)
  • Basic laboratory evaluation (eg, type and screen, complete blood count, basic metabolic panel, and urine analysis)
  • Electrocardiography (ECG) for patients older than 50 years
  • Additional studies, as warranted by any comorbid conditions that may be present

Dental evaluation and treatment for dental diseases should be done before THA is performed. Routine cleaning of the teeth should be delayed for several weeks after surgery. In older patients with prostate problems or urinary retention issues, urinalysis should be done and cultures obtained to check for urinary infections; any infections diagnosed should be treated before THA.

Because of the limited surgical exposure afforded by MIS-THA, preoperative templating is critical. Templating may be used to guide determination of the following:

  • Implant size
  • Leg length restoration
  • Femoral stem offset

If there is uncertainty about leg lengths, computed tomography (CT) can provide definitive evaluation. The opposite hip joint should be evaluated on the anteroposterior radiograph for comparison of leg lengths and assessment of existing offset relations. In selected patients, other studies (eg, vascular indices, spinal radiographs, MRI of the hip or spine, and evaluation of the ipsilateral knee joint) may be required.

Intraoperative radiographic imaging may or may not be necessary, depending on surgeon experience. Intraoperative radiography may prolong operating time and complicate the procedure, but it may reduce the risk of component malpositioning and facilitate the estimation of leg length.

Equipment

Specialized surgical instrumentation and implants are commonly required for MIS-THA. Because exposure may be limited, MIS-THA may necessitate modification of conventional instrumentation and possibly the use of additional equipment (eg, fiberoptic light cables, cutaway reamers, angled reamers and broach handles, Hohmann retractors with light sources, or flexible acetabular reamers).[58, 59, 60]

Particular operating room tables make certain MIS-THA approaches more accessible and may be required to provide the requisite traction and permit rotation of the lower extremity. For example, a Judet Orthopaedic Table (Tasserit, Sens, France) or a PROfx Fracture Table (OSI, Union City, CA) can facilitate an anterior approach, and a Jupiter Table (Trumpf, Charleston, SC) may be especially suitable for an anterolateral approach.[21, 59, 61]

Monitoring & Follow-up

After an MIS-THA procedure, the patient should be followed at the same time intervals that would be appropriate for a conventional THA. Periodic clinical and radiographic examinations are indicated to monitor for aseptic loosening, wear, and late infection.

 

Technique

Approach Considerations

Among the first alternatives to the transtrochanteric approach to total hip arthroplasty (THA) were the conventional posterior and lateral approaches.[62] These early alternative approaches sought to limit disturbance to osseous and soft-tissue anatomy, thereby avoiding unnecessary complications (eg, trochanteric nonunion).[63, 64] The conventional posterior and lateral approaches were nevertheless reported to be associated with nerve injury.[65]

Beginning in the 1990s, these conventional surgical approaches were further modified to limit the amount of soft-tissue dissection and minimize damage to healthy surrounding structures. Minimally invasive THA (MIS-THA) actually is not a single approach but a collective term that encompasses multiple distinct minimally invasive surgical (MIS) approaches. For example, the surgeon may use a single mini-incision, which is usually shorter than 10 cm, or may prefer to use two incisions, each of which is shorter than 5 cm (see the image below).

Minimally invasive total hip arthroplasty. Shown a Minimally invasive total hip arthroplasty. Shown are skin incisions for direct anterior (black), miniposterior/lateral/anterolateral (dark blue), conventional posterior (dark blue plus red extensions), direct superior (green), and SuperPATH (purple) approaches to hip. Conventional posterior incision is usually 10-25 cm long. Single incisions for minimally invasive approaches are usually less than 10 cm long. In two-incision approach, both incisions are usually less than 5 cm long.

Basic approaches currently employed for MIS-THA include the following[3] :

  • Direct anterior approach (eg, modified Smith-Petersen) - Performed in the supine position and uses the internervous plane between the femoral and superior gluteal nerves
  • Anterolateral approaches (eg, modified Watson-Jones) - Performed in the supine or lateral position and divides the anterior portion of the gluteus medius
  • Direct lateral approach (eg, modified Hardinge) - Performed in the supine or lateral position and uses the intermuscular interval between the tensor fasciae latae (TFL) and the gluteus medius
  • Posterior approach (eg, modified Southern) - Performed in the lateral position and divides the gluteus maximus and the short external rotators (eg, piriformis, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris) of the hip
  • Piriformis-sparing posterior approach - Performed in the lateral position and divides the gluteus maximus, the iliotibial band, and the short external rotators of the hip (eg, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris) except the piriformis
  • Direct superior approach – Performed in the lateral position and divides the gluteus maximus and the short external rotators of the hip (e.g., piriformis, superior gemellus, obturator internus, and inferior gemellus) while leaving the iliotibial band and quadratus femoris intact
  • Two-incision approach - Combines an anterior approach to the acetabulum with a posterior approach to the proximal femoral shaft
  • SuperPATH approach – Performed in the lateral decubitus position and divides the gluteus maximus, medius, and minimus

The choice of operative approach depends on surgeon preference and experience. Any small incision during MIS-THA should be used as a mobile window, so that pressure is not exerted on any single surgical area long enough to compromise muscle and soft tissue. Specialized instruments (see Periprocedural Care) and trained assistants facilitate MIS-THA enormously. Such instruments keep the assistants’ hands out of the operative field while generating less tension on the soft tissues.

Some authors recommend using fluoroscopy to verify the correct location of the skin incisions; others consider this measure unnecessary.[60, 66] Given the decreased visualization characteristic of MIS-THA, surgeons may find high-technology computer navigation, custom guides, or robotics extremely useful for correctly positioning the components.[67] However, the precise role of these technologies in MIS-THA remains to be demonstrated.

In some cases, it may prove necessary to osteotomize the femoral neck in situ or piecemeal rather than dislocating the hip and removing the femoral head en bloc.[8, 59]

Direct Anterior Approach

The anterior approach uses the internervous plane between the femoral nerve (lateral border of the sartorius) and the superior gluteal nerve (medial border of the TFL). The space between the TFL and the sartorius is developed by splitting the fascia of the anterior TFL and then sliding medially. Access to the joint capsule is achieved through the interval between the TFL and gluteus medius muscles and the rectus femoris muscle of the quadriceps femoris.

Because this approach requires no splitting of muscles or formal cutting of tendons, it is considered the optimal MIS-THA approach.[3, 21] According to its proponents, the direct anterior approach is the only true MIS-THA technique because the hip joint is closest to the anterior skin and the overlying fat tissue is thin in this part of the thigh.

An advantage to the anterior approach is that the operation is done with the patient in the supine position, which means that a bilateral procedure can be performed without any need for redraping or repositioning. Carefully selected and otherwise healthy patients may be candidates for simultaneous bilateral elective THA.

To avoid transecting branches of the lateral femoral cutaneous nerve (LFCN), the skin incision is placed more laterally than in the traditional Smith-Petersen approach (see the images below). The proximal femur can be easily exposed by extending the incision distally, and proximal femur fractures are easy to access.

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct anterior approach. Photograph of right anterior thigh after draping on fracture table. Note metal spar with square holes; this device attaches to fracture table and allows elevation of femur during femoral preparation.
Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct anterior approach. Left femoral head is dislocated anteriorly before osteotomy of femoral neck.
Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct anterior approach. View of proximal femur and right hip in supine position, showing lesser trochanter femoral neck resection marked with pen.
Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct anterior approach. Proximal femoral exposure and rasp is introduced into femoral canal facilitated by fracture table via metal spar elevating femur anteriorly.
Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct anterior approach. Insertion of acetabular component after acetabular component reaming in supine position.
Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct anterior approach. Circumferential view of acetabular component is shown with visual confirmation of orientation. Insertion guides and radiographs also may be used to assess positioning.

Kennon et al described a direct anterior MIS-THA in the supine position using accessory portals as needed.[20] In addition to the primary incision in line with the femoral neck, a distal lateral or a posterior superior accessory portal is created to allow the introduction of a reamer or a broach. Preparation of the femur can be difficult with this approach. Even though both cemented and uncemented implants have been performed safely, cementless components are generally preferred by most authors.

Michel et al described a “MicroHip” procedure that represents a modification of the Smith-Petersen approach.[68] This operation is performed with the patient in the lateral decubitus position, using standard instrumentation on a regular operating table without placing any traction on the leg. Regardless of patient positioning, the use of the intermuscular plane is thought to contribute to faster recovery as compared with a conventional muscle-splitting approach.

The direct anterior approach has the advantage of preventing injury to muscles and their attachments to the pelvis and femur, thereby helping restore their normal tension and the dynamic muscular stabilization of the hip joint immediately after the procedure is completed. Patients do not require hip dislocation precautions postoperatively.

In cadaver studies, this assumption has not held true.[37, 36, 47] Surgeons do not routinely repair posterior structures if they release during the direct anterior approach, whereas repair is routine with the other approaches.

A potential disadvantage of the direct anterior approach is that it is more technically demanding and requires extensive knowledge of hip-joint anatomy in the supine position. Additionally, the LFCN is at risk and, rarely, the femoral nerve. Potential complications associated with fracture table use include intraoperative femoral and ankle fractures. The major contraindications for direct anterior MIS-THA are related to previous acetabular fracture associated with posterior heterotopic ossification (HO), pelvic deformity, or posterior acetabular defects for which extensive posterior access may be necessary.

Anterolateral Approach

In the anterolateral approach, the skin incision proceeds from the anterior tubercle of the greater trochanter and angles toward the anterior superior iliac spine. Like the anterior approach, this approach uses the plane between the gluteus medius and the TFL and usually only requires elevation of the anterior third of the gluteus medius.[59, 69] Abductor muscle function is maintained, and the posterior capsule is left intact.

Bertin et al reported on anterolateral MIS-THA and noted decreased muscle damage and difficulty with achieving femoral exposure and obtaining consistent acetabular component positioning.[59]

Pflüger et al reported on anterolateral MIS-THA and noted that the gluteal insufficiency or dehiscence seen with the conventional anterolateral approach was eliminated by preserving the muscle attachments.[28]

The anterolateral approach provides good visualization of the acetabulum. Compared with the direct lateral approach, it results in less abductor weakness; compared with the posterior approach, it yields lower dislocation rates. Sectioning of muscle and tendon or the greater trochanter is not required for implantation of components.

The anterolateral approach places the superior gluteal nerve at risk during proximal dissection.[15]

Direct Lateral Approach

The direct lateral approach was initially described by Kocher and subsequently modified by Hardinge and Millikan et al. The anterior one third to one half of the gluteus medius is released from the greater trochanter. The procedure can be performed with the patient in a supine, semilateral, or  lateral decubitus position.

The skin incision runs from a point 2 cm proximal to the greater trochanter to a point located 5-8 cm distally along a line parallel to the long axis of the femur. There is no true internervous plane, and the dissection involves splitting the gluteus medius and the vastus lateralis. After the TFL is incised, the gluteus medius fibers are cut to expose the joint capsule.[32]

Division of the gluteus medius is limited to 5 cm proximal to the greater trochanter or 4 cm proximal to the superior acetabulum; further extension places the superior gluteal neurovascular bundle at risk for injury. Division of the abductor musculature may be manifested in a prolonged or even permanent limp after surgery. The extent of denervation of the abductors after the direct lateral approach is controversial.

The main disadvantage of the direct lateral approach is the necessity of detaching the gluteus minimus and a portion of the gluteus medius from the greater trochanter, which can lead to a delay in functional recovery or, in some cases, incomplete healing of the abductor musculature back to the greater trochanter. Damage to the superior gluteal nerve can cause a limping gait due to impaired abduction.

In most studies, the direct lateral MIS-THA has failed to show significant improvements over other approaches, aside from a slight reduction in hospital stay. However, some authors have reported favorable outcomes for this approach in comparison with a conventional direct lateral approach to THA.

Posterior Approach

The posterior approach (also referred to as the posterolateral approach by some authors) is the workhorse for conventional THA.[62, 69] It is the most commonly used approach among US surgeons and is technically the easiest, requiring only one assistant.

An 8-cm incision is made over the posterior trochanter, the gluteus maximus, and the capsule. The dissection proceeds to the gluteus maximus fascia and the TFL. The TFL is incised laterally, and the fibers of the gluteus maximus are split in line with the muscle fibers. The short external rotators (eg, piriformis, superior gemellus, obturator internus, and inferior gemellus) are elevated as a single flap from the femur and reflected posteriorly; this, along with the posterior hip capsule, is repaired at the completion of the operation.

Posterior MIS-THA uses the same plane of dissection as the conventional posterior approach but is designed to minimize the soft-tissue dissection.[60, 70] The gluteus maximus split should be kept to a minimum, and release of the gluteus maximus tendon insertion and quadratus femoris muscles should be avoided. Anterior capsular release is critical: releasing the anterior capsule facilitates femoral mobilization and easy delivery of the femur into a small wound.[58]

The following four differences in muscle damage have been observed between posterior MIS-THA and conventional posterior THA:

  • In posterior MIS-THA, no incision is made in the TFL
  • In posterior MIS-THA, the gluteus maximus muscle is split less than 6 cm, whereas in conventional posterior THA, this muscle is split 10-12 cm
  • In posterior MIS-THA, the gluteus maximus tendon is not released, whereas in conventional posterior THA, this tendon is released and repaired
  • In posterior MIS-THA, the quadratus femoris muscle is not released, whereas in conventional posterior THA, this muscle is released and repaired

With posterior MIS-THA, the femoral preparation is compromised in relation to what it would be with conventional posterior THA because the quadratus femoris muscle is kept intact and the lesser trochanter is not visible, but the acetabular landmarks are the same and are in the visual field. For both the posterior MIS-THA and the conventional posterior THA, meticulous posterior capsular closure with the short external rotator reattachment is critical. This repair reduces the risk of postoperative dislocation from 3% to 0.85%.[71]

Curved inserters facilitate correct acetabular cup positioning and help avoid a more vertical inclination of the acetabular component. Femoral components must be aligned with the posterior cortical bone of the neck for correct version, and the lateral edge of the stem must be under the tip of the greater trochanter to avoid a varus position.

Posterior MIS-THA does result in less pain and better function in the first 3 months than conventional posterior THA does. In gait studies, the posterior incision yields results equivalent to those of the anterior approach.

The major disadvantage of the posterior approach is the cutting off of the external rotators of the joint and opening of the posterior hip capsule (which may result in posterior hip dislocation). Intraoperative damage to the inferior gluteal nerve may lead to a limp as a result of impaired abduction. In cadaver studies, abductor muscle damage occurred in every posterior MIS-THA despite direct visualization and placement of retractors to protect the gluteus medius and gluteus minimus muscles.[37, 36]

A major factor in the pathogenesis of thromboembolic disease during THA is intraoperative distortion of the femoral vein as a result of retraction and limb positioning, which is thought to be especially likely with any posterior approach.

Two-Incision Approach

Two-incision MIS-THA uses the direct anterior approach, which facilitates osteotomy of the femoral neck, preparation of the acetabulum, and insertion of the acetabular component. The anterior incision is about 5 cm long, passing obliquely from the intertrochanteric line to the center of the femoral head, which are identified with fluoroscopy (see the image below).

Minimally invasive total hip arthroplasty: two-inc Minimally invasive total hip arthroplasty: two-incision approach. Photograph of right hip in supine position showing outlines of anterior superior iliac spine and greater trochanter. Dotted line marks anterior incision.

The superficial plane between the TFL and the sartorius and the deeper plane between the rectus femoris and the TFL are the same as in the direct anterior approach.

A second incision is placed posteriorly to prepare the femur and allow insertion of the femoral component. This incision is 3-4 cm long and is made in line with the femoral canal. The gluteus maximus fascia is split superficially, and a direct pathway to the femoral canal is found with blunt dissection posterior to the abductor tendons and anterior to the piriformis tendon, as in blind nailing of femur fractures (see the image below).

Minimally invasive total hip arthroplasty: two-inc Minimally invasive total hip arthroplasty: two-incision approach. Surgeon can guide femoral broaches through small posterior incision while palpating through anterior incision.

Irving developed a double-incision technique without fluoroscopy, adopting both the posterior approach and the direct anterior approach.[51] The method has been described without fluoroscopy by other authors as well.

The incidence of proximal femoral fractures is three times higher with two-incision MIS-THA than with conventional THA. This difference is related to several factors, including the direction and magnitude of forces delivered to the broach and implant, the loss of visual and tactile feedback, and an increased tendency toward component malalignment. As in the direct anterior approach, injury to the LFCN can lead to lateral thigh numbness.

In one study, patients undergoing two-incision MIS-THA recovered slower than those undergoing posterior MIS-THA, as measured by mean time to discontinue use of a walker or crutches, discontinue use of all ambulatory aids, and return to normal daily activities.[72] Substantially more muscle damage occurs to the gluteus medius and minimus muscles in two-incision MIS-THA than in posterior MIS-THA. The location of the gluteus medius muscle damage typically is along the posterior border of the muscle belly proximal to the tendinous portion of the gluteus medius.

Two-incision MIS-THA also damages the short external rotators. Patients appeared to be more satisfied with the appearance and functional results of posterior MIS-THA than with those of two-incision MIS-THA.[72] It should be noted, however, that several other authors have obtained exactly the opposite results, with dramatically better clinical outcomes and a significant patient preference for two-incision MIS-THA.

The difficulty inherent in the two-incision approach is reflected in the longer mean operating times associated with this procedure. As a result, many surgeons are reluctant to learn two-incision MIS-THA.

Direct Superior Approach

In the direct superior approach, the skin incision proceeds from the posterosuperior corner of the greater trochanter, extending proximally in line with the fibers of the gluteus maximus. The gluteus maximus fascia is incised sharply, exposing the gluteus maximus muscle. (See the image below.)

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct superior approach. Gluteus maximus fascia is incised sharply to expose gluteus maximus muscle.

These fibers are divided longitudinally with a Cobb elevator, and the deep fascia of the gluteus maximus is gently divided, exposing pericapsular fat. The piriformis tendon is detached close to its insertion. (See the image below.)

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct superior approach. Gluteus maximus muscle fibers are divided longitudinally, and deep gluteus maximus fascia is divided to expose pericapsular fat; prirformis tendon is detached close to its insertion.

The capsule is then incised in the inferior aspect of the wound, and the capsulotomy is extended posterior and superior to the superior acetabulum. (See the image below.)

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct superior approach. Capsule is incised in inferior aspect of wound; capsulotomy is extended posterior and superior to superior acetabulum.

The hip is dislocated, the femoral neck is osteotomized with an oscillating saw, and the femoral head is removed. (See the image below.)

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct superior approach. Hip is dislocated, femoral neck osteotomized, and femoral head removed.

A sharp curved Hohmann retractor is placed over the anterior acetabular rim. A second bent 90º Hohmann retractor is then placed at the inferior margin of the acetabulum. A 90º handheld retractor is placed in the superior aspect of the wound to delineate the margin between the superior labrum and the superior capsule. A 90º sharp Hohmann retractor is placed deep to the superior capsule and gently tapped into the ilium. An optional retractor is placed on the posterior aspect of the acetabulum. (See the image below.)

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct superior approach. Sharp curved Hohmann retractor is placed over anterior acetabular rim; second bent 90-degree Hohman at inferior margin; 90-degree handheld retractor in superior aspect of wound; and 90-degree sharp Hohmann deep to superior capsule. Optional retractor may be placed on posterior aspect of acetabulum.

The acetabular labrum is excised, and the acetabulum is reamed with a 55º angled acetabular reamer. The leg is placed in 40º flexion, 40º adduction, and 40º internal rotation. A 90º handheld retractor is placed in the inferior aspect of the wound to retract the quadratus femoris away from the proximal femur.

Minimally invasive total hip arthroplasty: direct Minimally invasive total hip arthroplasty: direct superior approach. Acetabular labrum is excised; acetabulum is reamed. Retractor is placed in inferior aspect of wound to retract quadratus femoris away from proximal femur.

A 90º Hohmann retractor is then placed over the superior femoral neck. A third retractor is placed under the calcar to expose the proximal femur. A box chisel may be used to remove the bone from the lateral neck. The acetabulum is reamed under direct vision to a size 1 mm smaller than the anticipated hemispheric implant. A single hand-powered reamer is used in femoral preparation to locate the direction of the femoral diaphysis. Hand reaming is performed to lateralize the proximal femoral canal. Sequential broaching is performed with an offset handle until maximal cortical contact in the mediolateral dimension is obtained.

Piriformis-Sparing Approach

A piriformis-sparing MIS-THA is performed by one surgeon with one or two assistants. No specialized instruments are required. The patient is placed in the lateral decubitus position. Leg lengths are noted and the leg positioned in 45° of flexion at the hip and 90° of flexion at the knee. Landmarks for the skin incision are identified, with the tip, the anterior border, and the posterior border of the greater trochanter forming an equilateral triangle with sides of approximately 4-6 cm.

A 6-cm incision is made, starting one fingerbreadth anterior to the posterior corner of the triangle and extending cranially and posteriorly at an angle of 30° to the long axis of the femur, so that two thirds of the incision is distal to the tip of the greater trochanter and one third proximal. In all but the very slimmest of patients, the incision is extended distally if there is inadequate access to the acetabulum or proximally if better access to the femur is desired. In nonobese patients, an incision of 7-10 cm is the norm. In obese or highly muscular patients, longer incisions are needed, and the surgeon should not hesitate to extend the incision in such cases.

Once the femoral head has been dislocated, the neck is osteotomized. A Hohmann retractor is placed just distal to the lesser trochanter to retract the distal part of the quadratus femoris distally and provide better visualization of the calcar (for accurate positioning of the osteotomy site); a second Hohmann may be required to prevent fascia lata from sliding over the greater trochanter.

After the neck is cut, the proximal femur is retracted anteriorly with a curved Hohmann retractor placed in front of the anterior column. The anterior capsule may have to be released if it is tight, though this is seldom necessary in a routine osteoarthritic hip. A second curved Hohmann retractor is placed under the transverse ligament to hold the inferior capsule out of the way, and a Norfolk and Norwich retractor is placed in the proximal part of the wound between the fibers of the gluteus maximus (superficially) and the posterior capsular flap (deep).

The retractor positions at this stage are crucial to obtaining good exposure of the acetabulum. Occasionally, the Norfolk and Norwich retractor fails to retract the posterior capsular flap (with stay sutures attached) adequately, thus obscuring the view of the posteroinferior edge of the acetabulum. In this case, a pointed Hohmann retractor may be placed carefully between the acetabular margin and the posterior capsule to retract the latter posteriorly.

The labrum is excised with a long-handled scalpel, with care taken to preserve the capsule and piriformis. If the piriformis or the superior capsule obscures the view into the roof of the acetabulum (eg, with a valgus femoral neck), these structures may be retracted by means of a Charnley pin fixed into the ilium. With correctly placed retractors, adequate soft-tissue release, a correctly located incision, and, in the obese patient, a sufficiently long incision, the view into the acetabulum should be good, with a 360° view of the acetabular margin.

The inferior capsule may be incised to facilitate entry of the reamers. The acetabulum is then reamed in the normal manner, and the cup is inserted (40-45° of abduction and 25° of anteversion). Care is taken to prevent the reamers from exerting leverage on the femur or retractor and thereby contributing to the creation of an eccentric socket.

The femur is presented by flexing, adducting, and internally rotating the hip; the incision “mobile window” is moved appropriately. A Hohmann retractor is placed medially (just proximal to the lesser trochanter) to afford access to the femoral canal. A second retractor may be placed under the femur to elevate it. A Langenbeck retractor is often required to prevent fascia lata from subluxating over the greater trochanter. At this point, the intact piriformis tendon may be seen and palpated as a tight cord exiting its insertion and passing posteriorly.

The femur is then prepared with broaches, placed in 20° of anteversion. With an overhanging greater trochanter, the piriformis tendon may be damaged by the broach if care is not taken. In obese patients, retraction of the proximal part of the incision with a Langenbeck retractor is required to prevent skin abrasion from the femoral broaches. With trial components in place, hip stability is tested, leg lengths are checked, and the definitive components are inserted. This approach does not preclude normal balancing of the hip when required (eg, capsulotomy, tendon release, or osteophyte removal).

Closure commences with repair of the posterior capsule, which is sutured to the back of the greater trochanter (by using the stay sutures already in place) through two drill holes in the bone. At this stage, the entire posterior envelope has been reconstructed. The remaining tissues are closed in layers. Neither a hip abduction wedge nor a pillow is used. Patients are mobilized without restrictions.[45]

SuperPATH Approach

The SuperPATH approach was developed to promote early mobilization and greater range of motion, physiologic gait kinematics, and improved pain control. It is a hybrid of the superior capsulotomy (SuperCap) approach and the percutaneously assisted total hip (PATH) technique.

Preparation of the hip in situ allows the operative leg to rest on a Mayo stand during the entire procedure, obviating the need for a second assistant. Additionally, because the hip is not dislocated, the interval between the gluteus medius and the piriformis is utilized, and the piriformis can be preserved in a majority of cases.

Using the percutaneous accessory portal for acetabular preparation ensures that visualization of the wound is not obscured by tooling. This allows the procedure to be done safely through the smaller window created by an intact piriformis. The accessory portal also provides in-line access to the cup, simplifying the insertion of screws and facilitating impaction of bone-ingrowth components.[73]

As is the case for the SuperCap and PATH techniques, any available implant can be used for the SuperPATH technique, including both press-fit and cemented styles for either femoral or acetabular components. This allows the surgeon to make the choice of implant on the basis of the patient’s disease and deformity, without being unduly influenced by the choice of incision.[73]

Complications

The complication rate is twice as high for surgeons who perform fewer than 50 MIS-THAs a year. Complications after MIS-THA are more common in the following individuals:

  • Patients older than 65 years
  • Patients with a body mass index (BMI) higher than 30 kg/m 2
  • Women with osteoporosis
  • Patients with altered femoral or acetabular anatomy

Common adverse events include the following:

  • Dislocation
  • Damage to the sciatic nerve, femoral nerve, or LFCN
  • Impaired postoperative wound healing
  • Hematoma
  • Infection
  • Venous thrombosis or thromboembolism

The most common errors during MIS-THA are vertical positioning of the acetabulum due to noncentric drilling and varus placement of the femoral stem, leading to a higher incidence of early or late dislocation. Proximal femoral fractures, fractures of the greater trochanter, and torsional fractures of the femoral shaft and its condyles are associated with problems related to femoral head dislocations. Damage to the sciatic nerve or the femoral nerve can occur.

Less significant risks include skin rupture caused by excessive tension from the hooks and impaired postoperative wound healing. The incidence of hematomas, as well as superficial and deep infection, is also higher. Early or late dislocation of the hip-joint endoprosthesis is more likely after MIS-THA. It has been suggested that the greater retraction pressure associated with MIS techniques causes muscle and wound damage and poor healing, though there is little clinical evidence to support this suggestion.

The reason for the high probability of complications after MIS-THA may be that only one surgery team member has good access to the treated area; this restricted access limits assistant support and also inhibits the transfer of experience from surgeon to surgeon. The use of a special set of instruments can facilitate implantation of the endoprosthesis and reduce the number of complications.

Because the posterior approach carries an increased risk of posterior dislocation, it is reasonable to be especially alert for this complication with this procedure. However, a study of 1000 hips treated with miniposterior MIS-THA reported a posterior dislocation rate of 1.2%, compared with 5.8% for the standard posterior approach.[4, 74] Despite sufficient soft-tissue mobilization in properly selected patients, limited surgical visualization may necessitate conversion of MIS-THA to conventional THA in a minority (< 10%) of patients.[32]

Because the two-incision technique uses unique dissection planes, it has a significant learning curve that results in a higher-than-anticipated complication rate.[40] One study found that the rate of complications did not decrease over a surgeon’s first 10 cases, which suggested that the learning curve may be longer than expected.[52]

The two-incision technique is supposed to spare cutting muscles and tendons, though cadaveric studies of 10 hips showed that in every case, the abductors, external rotators, or both were injured.[36] Moreover, unlike standard mini-incisions, which use large dissection planes, the two short incisions have limited extensibility. Given the increased level of skill and experience required to perform the two-incision approach safely and correctly, many surgeons feel that this approach is best left to high-volume surgeons who receive specialized training.[3]