Minimally Invasive Total Hip Arthroplasty

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] < 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 remains some debate as to whether MIS-THA is an acceptable replacement for or even an improvement on conventional THA. At present, although there continues to be support for MIS-THA in the literature, there are no definitive data establishing MIS-THA as superior to standard THA. ^[4]

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 ^{[5, 6, 7]} :

• 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

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. ^[8] 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. ^{[5, 9, 10]}

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. ^[6] 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. ^[11] Decreased blood loss, decreased postoperative pain, and decreased need for postoperative ambulatory walking aids have also been reported with MIS-THA. ^[12]

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. ^[13]

MIS-THA is associated with a 6% increase in local wound complications. ^[14] This increase may be secondary to increased soft-tissue and cutaneous trauma from the retraction or reamers abrading the skin. ^[15] However, two meta-analyses found that the increase in cutaneous trauma was not statistically significant. ^{[16, 17]}

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. ^[18] 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. ^[17]

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). ^{[5, 6, 14, 19]} Acetabular cup anteversion was three times more likely to be outside the acceptable range with posterior MIS-THA. ^[20]

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. ^{[14, 16, 17, 21, 22]}

In a systematic review and meta-analysis that included only level I studies, Clesham et al found that there was no difference between minimally invasive (anterior and anterolateral; n = 1282) and conventional (posterolateral and direct lateral; n = 1351) approaches in relation to all clinical outcomes. ^[23] These outcomes included all-cause revision, aseptic revision, instability, infection, and periprosthetic fracture. 

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

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%). ^[24]

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. ^[25]

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. ^[26]

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. ^[27]

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. ^[28] Direct anterior patients had longer mean operating times than miniposterior patients (114 vs 60 min). 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. ^[29] 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. ^[30] 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. ^[31] 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.

Dietrich al investigated whether the intraoperative femoral fracture rate associated with the direct anterior approach could be reduced with the use of a short-stem design. ^[32] In 457 patients with the standard-length stem, the intraoperative fracture rate was 11.8%, compared with 4.4% in 183 patients receiving the short stem. Additionally, in comparison with the standard-length stems, the short stems were associated with fewer postoperative hematomas and wound-healing problems.

Rykov et al performed a randomized controlled trial in 46 patients to compare the changes in postoperative serum markers of muscle damage (creatine kinase and C-reactive protein) between the direct anterior and posterolateral approaches. ^[33] At 2 hours, 1 day, 2 weeks, and 6 weeks after operation, there were no significant differences in serum measurements between the two approaches. Therefore, despite the muscle-sparing internervous path of the direct anterior approach, the extent of soft-tissue damage may be similar to that seen with the intermuscular path of the posterolateral approach.

Thaler al performed a 2-year postoperative gait analysis in 16 patients who underwent undergoing direct anterior THA as compared with 17 who underwent anterolateral THA. ^[34] The study indicated that the direct anterior approach had significantly better stride time and cadence; however, the study did not evaluate functional outcomes. 

Reichert et al performed a prospective single-center randomized controlled trial to compare the outcomes of the direct anterior and lateral approaches to THA in 123 patients. ^[35] The direct anterior approach was associated with higher patient activity levels than the lateral approach at 1 year, but there was no significant difference in hip function. The radiographic positions of the THA components in the two approaches were similar.

This latter finding was also duplicated by Brun et al in a randomized controlled trial of 164 patients who underwent THA via either the direct anterior or the lateral approach. ^[36]  

Sang et al conducted a prospective randomized study investigating the incidence of LFCN injury between bikini incisions (n = 99) and conventional incisions (n = 96) in the direct anterior approach. ^[37] The percentage of clinically reported LFCN injuries was significantly higher in the bikini group (36.36%) than in the conventional group (21.88%).

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. ^[38]

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. ^[39] 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. ^[40] 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. ^[40] 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. ^[41] 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.

Liu et al compared minimally invasive anterolateral (MAL) and direct anterior (DA) approaches in 90 patients and found improved early (≤ 6 wk) patient-reported outcomes, shorter operating times (62.4 vs 71 min), less blood loss (132.6 vs 159.23 mL), and lower postoperative hemoglobin drops (29.56 vs 36.4 g/L) in the MAL group. ^[42] Additionally, there was a 14.6% rate of LFCN injury in the DA group versus 0% in the MAL group.

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. ^[43]

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. ^[44] 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%.

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. ^[21] .

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. ^[5] 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.

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. ^[45] 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. ^[46] 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. ^[47] 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. ^[48] The mean 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. ^[49] 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.

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. ^[7]

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. ^[50]

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. ^[51] 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. ^[19]

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. ^[12]

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. ^{[52, 53]}

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. ^{[9, 54]}

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. ^[22]

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. ^[22] 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. ^[14] 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. ^[14] 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. ^[55] 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. ^[56] 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. ^[57] 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.

Amanatullah et al used an instrumented retractor to determine the applied force to the piriformis during the piriformis-sparing posterior approach in 23 hips. ^[58] Whereas in 96% of patients, the piriformis tendon was not damaged in the approach to the hip capsule, partial or complete damage to the sacral origin, muscle belly, or musculotendinous junction occurred in 91% of patients. Thus, the piriformis-sparing approach may not be as minimally invasive as was previously described.

A randomized controlled trial of 110 patients found that at 10 years post surgery, the piriformis-sparing approach appeared to provide significantly better piriformis volume and muscle composition than the posterior approach; however, outcomes were similar in the two cohorts, with both reporting excellent pain relief and hip function. ^[59]

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. ^[60] 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. ^[61] 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.

LeRoy et al retrospectively analyzed 676 patients treated with primary THA by a single surgeon to determine whether differences exist in the perioperative outcomes of the direct superior approach as compared with the posterior approach. ^[62]  The superior approach was associated with a significantly shorter hospital length of stay (1.71 vs 2.17 d) and a lower rate of discharge to a rehabilitation facitlity (8.8% vs 17.9%). There were no differences in blood transfusion rates or operating time.

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. ^[10]

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. ^{[63, 64]}

Of these patients, 25% sustained an LFCN injury, and one patient had neurapraxia of the femoral nerve. ^[63] 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. ^[51]

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. ^[65]

Nivbrant et al, in a clinical and cadaveric study documenting anatomic variations of LFCN injury during 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. ^[66] 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 LFCN 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. ^[66] 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. ^[67] However, a longer operating time, increased operative complexity, and need for fluoroscopy in the two-incision approach were found to be significant disadvantages.

Abdel et al also found no significant differences between the miniposterior and two-incision approaches at 10-year follow-up with respect to mean revision or reoperation rates. ^[68]

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. ^[69] 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. ^[70] 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 and 101.7 ± 18.3 min, respectively). ^[71] 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 d).

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°). ^[71] 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. ^[72] They concluded that use of this tissue-sparing technique has the potential to significantly reduce postdischarge costs.

Meng et al compared the outcomes of the SuperPATH approach with those of the posterior approach in four patients with bilateral osteonecrosis of the femoral head. ^[73] Whereas the side on which the SuperPATH approach was taken had a shorter incision length, that side also had a longer operating time, greater blood loss, and less improvement in the mean Harris Hip Score at 12 months than the side on which THA was performed via the posterior approach. Length of stay, postoperative range of motion, and 12-month patient satisfaction scores were similar in the two groups.