Most MIS TKAs do not fail early. MIS TKRs performed through a mini midvastus approach are not predisposed to early failure.

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By Richard S. Laskin, MD
ORTHOPEDICS TODAY 2008; 28:61
January 2008

It has been alleged that minimally invasive total knee replacements may tend to fail early. Our use of MIS techniques of the past 5 to 6 years does not substantiate this. When one reviews the literature as to why total knees in general may tend to fail early we find the basic causes to be infection, instability, malposition and stiffness. We have not found these problems in our MIS patients using a mini midvastus approach.

Our infection rate performing total knee replacement (TKR) surgery both through a MIS approach and through a standard median parapatellar approach has been the same, about 0.2%. One might assume that if the MIS approach took longer to perform the infection rate would rise. Indeed, several years ago we received the Insall Award from the Knee Society for a study we performed evaluating infection after primary TKR. We determined that if the surgical time goes longer than 2.2 hours, the infection rate goes up as well. Our average operative time with the midvastus approach was 56 minutes. Furthermore, with this approach one can easily visualize all the structures so that inordinate retraction is not required. Strong retraction has been shown in the past also to cause problems with tissue viability and infection rates.

Instability
In a study comparing patients having a median parapatellar incision with those having a mini midvastus MIS incision there was no difference in instability rates in either the sagittal or coronal planes. This was true because with the mini midvastus approach you can still expose the posterior recesses as well as the medial and lateral sides of knee in a way to enable flexion and extension space balancing. You also can visualize all the femoral landmarks (posterior-condyles, transepicondylar line, and mid trochlear line) to enable proper rotatory position of the femoral component. In a comparative study, the Knee Society Scores for stability in both coronal and sagittal planes were similar for both the mini midvastus MIS and standard median parapatellar groups.

Malposition
The positions of both femoral and tibial components were measured on PACS computerized radiographs in patients who had undergone mini midvastus MIS TKR. There were very few outliers found from the optimal position of the two components and these numbers were no greater than that seen in patients with standard median parapatellar incisions.

Stiffness
In our published study the patients who had a MIS TKA through a mini midvastus approach seemed to get their motion back faster than those who had had a standard median parapatellar incision.

Putting all of this together, we did not discover any findings which would suggest that using that MIS TKRs performed through a mini midvastus approach would predispose to early failure. However, that is not the case with other MIS approaches.

One particular approach, the quad-sparing approach, has been shown to have a high rate of complications. Aglietti and others reported on fractured femoral condyles, tears in the patellar ligament and other technical problems attendant to the fact that it is very difficult to visualize all the soft structures properly through that MIS approach. When surgeons state that “MIS TKRs have a high complication rate” they usually are referring to surgeries done through that exposure. The surgery is done from the medial side of the knee making visualization of the patellar tendon and lateral femoral condyle difficult and leads to the described potential complications. As more of these problems have been noted surgeons have gradually abandoned that approach in favor of the more traditional MIS approaches such as the mini midvastus, the mini subvastus, or the mini quad split. All three of those exposures are not associated with a higher complication rate and should not be expected to cause early failure of TKRs.

For more information:
Richard S. Laskin, MD, can be reached at Hospital for Special Surgery, 535 E. 70th St., New York, NY 10021-4892: 212-606-1041; e-mail: laskinr@hss.edu. He is a consultant for and receives speaking and teaching fees from Smith & Nephew Orthopaedics.
References:

Laskin RS. Mini-incision: In opposition to the premise that mini-incision for TKR is occasionally desirable and rarely necessary. J Arthroplasty. 2006;21(Supp.1):19-21.
Laskin RS. Minimally invasive knee replacement: The results justify its use. Clin Orthop Relat Res. 2005;440:54-59.
Laskin RS. Phongkunakorn A. Becsac B et al. Minimally invasive total knee arthroplasty total knee replacement: An outcome study. Clin Orthop Relat Res. 2004;428:74-82.
Laskin RS. Reduced-incision total knee arthroplasty. J Knee Surg. 2006;19:46-51.