Minimally Invasive Total Knee Arthroplasty 

Updated: Jul 09, 2019
Author: Derek F Amanatullah, MD, PhD; Chief Editor: Erik D Schraga, MD 

Overview

Background

In addition to conventional surgical approaches, total knee arthroplasty (TKA) may be done by means of minimally invasive surgery (MIS). Minimally invasive TKA (MIS-TKA) is often portrayed in the lay community and press as involving a small skin incision. Actually, MIS-TKA is defined by limited soft-tissue and bony dissection. MIS-TKA was developed after the description of unicondylar knee arthroplasty.[1, 2]

Conventional TKA is a successful operation for patients suffering from arthritis of the knee, with a reported complication rate of less than 2% and an implant survivorship of 95% at 10 years. The aim of MIS-TKA is to decrease postoperative pain and shorten the rehabilitation period.

Indications

MIS-TKA is used as an alternative to conventional TKA. However, there are conflicting data on whether MIS-TKA is an acceptable replacement for or even an improvement on conventional TKA, and no definitive answer to this question is available at present.

Contraindications

No absolute contraindications exist for MIS-TKA; this procedure is defined by limited soft-tissue and bony dissection. Conventional TKA is probably a more suitable choice for the following patients[3, 4, 5] :

  • Patients with a body mass index (BMI) greater than 40 kg/m 2
  • Patients with severe fixed valgus deformity
  • Patients with severe osteoporosis
  • Patients who have previously undergone knee arthrotomy
  • Patients with rheumatoid arthritis

Technical Considerations

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

  • Appropriate preoperative screening and clearance
  • Preoperative templating and planning
  • Preoperative administration of antibiotics as recommended by the American Academy of Orthopaedic Surgeons (AAOS)

Outcomes

Early series comparing MIS-TKA with conventional TKA reported successful outcomes.[6, 7] A randomized controlled trial (RCT) showed significantly shorter hospital stays after MIS-TKA than after conventional TKA.[8] In a retrospective review of 48 knees, MIS-TKA patients were able to complete an active straight leg raise earlier than conventional TKA patients could.[9]  A similar conclusion was reached in a study comparing computer-assisted approaches.[10] A case-control study comparing 32 knees after conventional TKA and after MIS-TKA reported mean Knee Society Scores (KSS) of 94 and 96 and mean functional scores of 90 and 99, respectively.[11]

An RCT that investigated extensor and flexor muscle function after conventional TKA and MIS-TKA found that the MIS-TKA group had a higher knee extensor peak torque at 3, 6, and 12 months postoperatively.[12]  Similarly, another RCT found that the MIS-TKA group had greater hamstring and quadriceps strength at 4 weeks after surgery; however, this difference was not observed at 12 weeks, and no benefit was documented with regard to longer-term strength or functional performance.[13]

Another prospective RCT, which compared conventional TKA with MIS-TKA by using an accelerometer, found that MIS-TKA patients were significantly more active on all postoperative days and that MIS-TKA patients achieved 80% of their preoperative acceleration in about half of the time that conventional TKA patients took to reach this level.[14]

Additionally, a systematic review of 13 randomized controlled trials found that the mean KSS at 6 and 12 weeks postoperatively was higher in the MIS-TKA group but that this difference was lost at 6 months.[15] Finally, a long-term cohort study of a group of 192 patients determined that there was a 95% 10-year implant survival rate, with excellent functionality and clinical outcomes according to the Oxford Knee Score (OKS).[16]

Conflicting conclusions demonstrate why there is still no consensus regarding either the noninferiority or the superiority of MIS-TKA as compared with conventional TKA. A prospective RCT found that as expected, incisions were significantly shorter in the MIS-TKA group, but there were no significant differences in the Knee Injury and Osteoarthritis Outcome Score (KOOS), the OKS, the KSS, and the Short Form (SF)-12 score at 6-week, 1-year, 2-year, and 5-year follow-up evaluations in comparison with conventional TKA.[17]

A meta-analysis of 30 RCTs (2500 TKAs) examined short- to midterm results (< 36 months) for MIS-TKA as compared with conventional TKA.[18] The authors concluded that the MIS-TKA group had better outcomes with respect to KSS, range of motion (ROM), days to straight leg-raise, and total blood loss. However, this benefit was associated with longer operating and tourniquet times, as well as wound-healing complications. Overall, though, there were no significant differences between MIS-TKA and conventional TKA with regard to radiographic evaluation of component positioning.

An RCT that evaluated medium-term results demonstrated that at a mean of 6 years' follow-up, there were no differences between MIS-TKA and conventional TKA in terms of pain, function, malalignment, or revision rates.[19]

 

Periprocedural Care

Patient Education and Consent

It is imperative to ensure appropriate patient education before either conventional total knee arthroplasty (TKA) or minimally invasive TKA (MIS-TKA). Such education should address the patient’s postoperative expectations, as well as inform the patient regarding the administration of anticoagulation.[20]  Preoperative counseling with respect to the patient’s postoperative activity level is left to the discretion of the surgeon.

Preprocedural Planning

Preoperative evaluation and preparation for MIS-TKA are exactly the same as they would be for conventional TKA, except for the specialized surgical instrumentation and implants involved in the minimally invasive surgery (MIS) technique. Because exposure may be limited, many retractors are designed to protect the soft tissues during osteotomy. An example is a two-pronged retractor that serves to protect the collateral ligaments while the distal femoral cuts are made.

Special MIS-TKA instrumentation has been developed to facilitate either a medial or a lateral approach; left medial instruments can be used as right lateral instruments, and vice versa.[21, 22]  Manufacturers have also developed smaller cutting blocks to facilitate access through a smaller surgical window. Ultimately, the size of the implant limits the size of the skin incision and the arthrotomy.

The tibial tray has been designed with a shortened or modular keel; this decreases the need for subluxation of the tibia and makes placement of the tibial tray easier at cementing. This minimodular keel affords excellent radiographic positioning and high component survivorship.[23, 24] With cemented components, a meticulous effort must be made to remove excess cement with a limited exposure. The lateral femoral condyle and the lateral tibial plateau are common areas of residual cement that should be routinely explored.

Equipment

Starting in 1940, metallic implant materials were developed, and metal or ceramic prostheses have been part of knee reconstruction ever since. The term knee replacement was descriptive of some early attempts when hinge-type prostheses were used. Today, all contemporary prostheses just resurface the degraded joint surfaces, yet the procedure is still described as knee joint replacement.

All knee prostheses today utilize polyethylene for the tibial and, often, the patellar articulating surfaces. Metal-on-metal implants were used originally, but corrosion occurred in situ and limited their success. Polyethylene has been in constant use for more than 40 years for knee replacement surgery.

The knee prostheses can be secured to the underlying bone either with a porous metal surface or with the use of acrylic resins as an anchoring cement. Both methods are quite successful. Currently, more than 150 types of knee replacement implants, made by several manufacturers, are available.

Computer- and robotic arm–assisted navigation is increasingly popular. A systematic review and meta-analysis studying MIS techniques demonstrated that this technology may prove superior in terms of radiographic tibial component positioning, but as yet, there is no evidence that this improves clinical outcomes.[25] Patient satisfaction and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores at an average of 10 years postoperatively do not differ between computer-assisted and traditional MIS-TKA.[26] Although incisions can be shorter with computer navigation, this approach significantly increases operating time.[27]

 

Technique

Minimally Invasive Approaches to Total Knee Arthroplasty

In a minimally invasive total knee arthroplasty (MIS-TKA), the midline skin incision is approximately twice the length of the patella (ie, 6-14 cm), and a parapatellar arthrotomy is performed (see the image below).

Minimally invasive total knee arthroplasty (MIS-TK Minimally invasive total knee arthroplasty (MIS-TKA). Midline skin incision is performed. Mini-incision is approximately twice length of patella, 6-14 cm (blue); conventional incision is longer (red extensions).

For varus knees, a curvilinear medial skin incision extending from the superior pole of the patella to the tibial joint line provides better exposure. For valgus knees, a curvilinear lateral skin incision extending from the superior pole of the patella to the tibial joint line provides better exposure.[22] If necessary, a second lateral incision may be made from the lateral femoral epicondyle to just above the Gerdy tubercle.[7]

A limited (or mini-) medial parapatellar arthrotomy is favored (see the image below). This familiar approach facilitates a natural transition from conventional TKA to MIS-TKA.[4] MIS-TKA limits the proximal extension into the quadriceps tendon to 2-4 cm and still allows sufficient lateral subluxation of the patella.[28] Patellar eversion should be avoided, and the infrapatellar fat pad may be retained to limit anterior knee pain and potential wound complications.[29, 30, 31, 32]  Because of the unique incisions of specific MIS procedures, converting to the standard medial parapatellar arthrotomy can be problematic and may require an entirely new incision.

Minimally invasive total knee arthroplasty (MIS-TK Minimally invasive total knee arthroplasty (MIS-TKA). Parapatellar (ie, medial parapatellar, midvastus, subvastus, or lateral) arthrotomy is performed to access knee joint and perform arthroplasty.

Other options for the arthrotomy include the midvastus, subvastus, and lateral approaches.[6, 33, 34, 35]

A midvastus (or midvastus split) approach involves cutting 1-3 cm of the vastus medialis obliquus (VMO).[17] However, the VMO is the only muscle that prevents lateral displacement of the patella when the knee is actively extended.[19]  A prospective study found that the midvastus approach does not afford a better gait pattern than conventional TKA does at 8 weeks postoperatively.[36]  A study comparing MIS techniques found no difference between the medial parapatellar and midvastus approaches in terms of patellar tracking and anterior knee pain.[37]

A subvastus arthrotomy avoids disturbing the quadriceps mechanism but may make it difficult to evert the patella. However, with satisfactory dissection and smaller instrumentation, patellar translation alone is sufficient. A retrospective study found that the subvastus approach provides adequate exposure and excellent early recovery in valgus native knees.[38] However, employing this technique also requires proper patient selection, in that it becomes increasingly difficult to retract the quadriceps tendon laterally in larger and more muscular patients.[28]  

The quadriceps-sparing technique is essentially a subvastus approach with no patellar translation; it necessitates modified instrumentation. Both the subvastus approach and the quadriceps-sparing approach often provide limited visibility of the lateral tibial condyle and have longer learning curves for the surgeon.[29]  A retrospective study comparing the quadriceps-sparing and medial parapatellar approaches found no clinical or radiographic differences at a minimum follow-up of 5-years, demonstrating no apparent long-term benefits to the more challenging quadriceps-sparing approach.[31]

A randomized, double-blind study by Tomek et al compared a quadriceps-sparing subvastus approach with the medial parapatellar approach.[39] The investigators found that the quadriceps-sparing approach yielded no significant advantages over the medial parapatellar approach in terms of either time to recovery of knee function or opioid utilization. However, patients who underwent the quadriceps-sparing procedure reported slightly lower mean pain scores at rest on postoperative day 1 and during activity on postoperative day 3.

Another randomized study, by Wegrzyn et al, compared the gait of patients 2 months after a subvastus approach or a standard medial parapatellar approach and found no differences between the groups with respect to outcome scores, activity scores, patient milestone diary of activities, isometric quadriceps strength, or gait parameters.[40]

The lateral approach is a newer technique for MIS-TKA that involves an incision through the iliotibial band. It often requires computer navigation and has been associated with a higher incidence of postoperative complications.[41]  A disadvantage of a lateral arthrotomy is the reduced access to the tibia and the posteromedial soft-tissue attachments that results from the position of the incision approximately 7 mm lateral to the tibial tubercle.[19]  Potential advantages of the lateral approach include the following[7] :

  • It obviates the need for an intramedullary guide for femoral component positioning
  • It does not violate the quadriceps mechanism
  • It permits eversion of the patella
  • It does not dislocate the knee joint

Although the limited skin incision and arthrotomy hinder simultaneous visualization of every component of the joint, the mobile window concept allows all portions of the joint to be visualized during MIS-TKA—but not at the same time. Accordingly, the surgeon must be vigilant to avoid placing undue stress on the soft tissue through aggressive retraction.

MIS-TKA is facilitated by 10-35° of knee flexion.[42] In addition, gravity can be used to assist in visualizing the knee joint and minimizing soft-tissue trauma through what is known as the suspended leg technique. By flexing the hip to 20-30° and allowing the knee to flex to 90-100° of flexion, the target portion of the knee can be manipulated into the surgical field.

Familiarity with techniques of soft-tissue and bony manipulation is essential for a successful MIS-TKA, but the specific techniques used may vary, depending on the surgical approach used.[21]

Patellar capsular release enhances the lateral mobility of the patella and the exposure of the anterior knee joint. Subluxation or retraction of the patella results in minimal postoperative quadriceps dysfunction as compared with the complete patellar eversion used in conventional TKA.[43, 32] Joint dislocation is avoided during bone cuts to prevent capsular damage, which affects postoperative recovery. Progressive bone cuts increase the volume of available surgical space through which to operate. They may be done in either of the following sequences[6, 19] :

  • First the tibia, then the femur, and finally the patella
  • First the patella (if it is to be resurfaced), then the distal femur, then the tibia, and finally the remaining femur

Even when this tactic is used, however, surgeons may need to complete bone cuts freehand and remove bone piecemeal after the initial osteotomy.

After the procedure, the patient should be followed at the same time intervals that would be appropriate for a conventional TKA. Clinical and radiographic examinations should be done at 2 weeks, 6 weeks, 3 months, and 6 months and then yearly for the life of the TKA to monitor for aseptic loosening and late infection.

Complications

The more difficult surgical approaches required for MIS-TKA are associated with a prolonged surgical learning curve. This learning curve can affect operating time, as well as infection rate.[44, 45, 46]  In addition, the limited visibility inherent in MIS-TKA exacerbates the technical difficulty of performing accurate osseous cuts and can result in cement retention. Otherwise, the complications of MIS-TKA are similar to those of conventional TKA. Infection, aseptic loosening, implant malposition, and arthrofibrosis remain potential complications.

To prevent deep venous thrombosis (DVT), as well as pulmonary embolism (PE), patients should be on an appropriate anticoagulation regimen, as recommended by the American Academy of Orthopaedic Surgeons (AAOS). At present, there does not appear to be a consensus among orthopedic surgeons regarding the choice of a pharmacologic agent for prophylaxis. A retrospective study of 113 patients found no difference in thromboembolic events or bleeding complications among MIS-TKA and conventional TKA patients treated postoperatively with either enoxaparin or rivaroxaban.[47]

Lateral skin numbness due to intraoperative injury of the infrapatellar branch of the saphenous nerve is expected after TKA and has an impact on patient satisfaction.[48] A clinical study by Tanavalee et al found no difference in skin numbness between MIS-TKA and conventional TKA; this result was explained by the cadaveric finding that all branches of the infrapatellar branch of the saphenous nerve appear to cross the midline from medial to lateral between the superior pole of the patella and the tibial tubercle.[49]

MIS-TKA does not result in any improvement in component survivorship. Attempts to determine whether it yields any significant improvements in postoperative knee function or long-term component longevity have yielded conflicting reports.[50, 51]

MIS-TKA may not actually be atraumatic to the knee. One study found that serum levels of creatinine phosphokinase (CPK), myoglobin, aldolase, lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase, and creatinine were equal in conventional TKA and MIS-TKA soft tissues.[52] Another study found no differences between conventional TKA and MIS-TKA with regard to preoperative and postoperative C-reactive protein (CRP) or interleukin (IL)-6 levels.[14]

As a result of the high cost of the new instruments required, the significant potential for complications, and the substantial learning curve, MIS-TKA is currently recommended only for high-volume surgeons who receive specialized training.[22]

 

Medication

Medication Summary

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Antibiotics

Class Summary

The American Academy of Orthopaedic Surgeons (AAOS) has recommended the use of prophylactic antibiotics that include cefazolin, cefuroxime, or vancomycin. The antibiotics should be administered 60 minutes prior to the procedure and discontinued within 24 hours after the procedure. However, for outpatient/office-based procedures, a single dose before the procedure is sufficient.

Cefazolin

Cefazolin is a first-generation semisynthetic cephalosporin that arrests bacterial cell wall synthesis, inhibiting bacterial growth.

Cefuroxime (Ceftin, Zinacef)

Cefuroxime is a second-generation cephalosporin that maintains the gram-positive activity of first-generation cephalosporins; it adds activity against Proteus mirabilis, Haemophilus influenzae, Escherichia coli, Klebsiella pneumoniae, and Moraxella catarrhalis. The condition of the patient, the severity of the infection, and the susceptibility of the microorganism determine the proper dose and route of administration.

Vancomycin

Vancomycin is a potent antibiotic that is directed against gram-positive organisms and that is active against Enterococcus species. It is useful in the treatment of septicemia and skin structure infections. Vancomycin is indicated for patients who cannot receive or have not responded to penicillins and cephalosporins and for patients who have infections with resistant staphylococci.

Anticoagulants, Hematologic

Class Summary

To prevent deep venous thrombosis, as well as pulmonary embolism, patients should be on an appropriate anticoagulation regimen, as recommended by the AAOS. Currently, there is no consensus among orthopaedic surgeons regarding the choice of pharmacologic prophylaxis. A retrospective study of 113 patients found no difference in thromboembolic events or bleeding complications between minimally invasive and conventional total knee arthroplasty TKA patients treated postoperatively with either enoxaparin or rivaroxaban.[47]