A Comparison of Subvastus and Midvastus Approaches in Minimally Invasive Total Knee Arthroplasty

Background: The mini-subvastus and the mini-midvastus approaches are among the most common alternatives to the medial parapatellar approach for total knee arthroplasty. The purpose of this study was to compare the early clinical outcomes of these two approaches. Methods: In this prospective, randomized study of fifty-one patients who underwent bilateral total knee arthroplasty, the mini-subvastus approach was used in one knee and the mini-midvastus approach, in the contralateral knee. There were forty-two women and nine men who had a mean age of seventy years at the time of the index arthroplasties, and they were followed for two years postoperatively. Clinical outcome was assessed and compared with use of the Knee Society pain and function scores, the straight-leg-raising test, range of motion, and isokinetic strength testing. Operating time and blood loss for each approach were also compared. In addition, patients were surveyed concerning which knee they preferred. Results: Comparisons of postoperative Knee Society scores between both approaches at the time of the two-year follow-up did not yield a significant difference in outcome. Isokinetic strength testing at twelve weeks postoperatively revealed no significant differences in muscle strength, with a mean extensor peak torque-to-body weight ratio of 0.14 Nm/kg for both groups. No significant difference was found with respect to total blood loss, straight-leg-raising test, range of motion, or patient preference. There was no clinically relevant difference in operative times between the two approaches. Conclusions: The minimally invasive subvastus and midvastus approaches for total knee arthroplasty were both associated with excellent short-term clinical results. Some surgeons believe that the subvastus approach completely avoids damage to the quadriceps mechanism and therefore would be associated with improved muscle function. This prospective series did not identify a substantive difference between the two approaches. We believe that the decision between these surgical approaches should be based on surgeon preference and experience.