Muscle torques in total knee arthroplasty with subvastus and parapatellar approaches.

The current study was designed to compare muscle torques when using the subvastus and parapatellar approaches for unilateral total knee arthroplasty. Twelve female patients had unilateral total knee arthroplasty with the subvastus approach from January 1997 to June 1998. The historic control group consisted of 16 female patients who had unilateral total knee arthroplasty with the parapatellar approach from July 1994 to January 1997. Six and 12 months after surgery, a Cybex dynamometer was used to measure isometric and isokinetic muscle strength. Two parameters were used to compare the two approaches, the first parameter was the difference in peak torque between the surgically treated knee and the baseline value for the healthy knee, and the second parameter was the hamstring to quadriceps peak-torque ratio, again using the value for the healthy knee as baseline. The subvastus approach resulted in an initial higher peak torque in the quadriceps 6 months after surgery, but this difference became insignificant 12 months postoperative. Using the subvastus approach, the hamstring to quadriceps peak-torque ratio reached the normal range (0.50-0.80) sooner than was the case using the parapatellar approach. There is a phenomenon of cross adaptation of the untreated knee to the surgically treated knee, and knees operated on by the subvastus approach showed functional recovery at an earlier date than those operated on by the parapatellar approach.