Improvement of voluntary quadriceps muscle activation after total knee arthroplasty

Objective: To evaluate the maximal voluntary contraction (MVC) force and the voluntary activation of the quadriceps femoris muscle in patients with knee osteoarthritis (OA) before and after total knee arthroplasty (TKA). Design: A prospective intervention study. Setting: University hospital clinic in Germany. Patients: Fifty patients (32 women, 18 men; mean age standard deviation, 65.8+/-5.6y) with knee OA and 23 healthy age- and gender-matched control subjects. Intervention: Unilateral TKA without patella resurfacing. Main Outcome Measures: Voluntary activation, MVC, and true maximal contraction forces of the bilateral quadriceps femoris muscles, using the twitch interpolation technique before and 33+/-8 months after TKA. Assessment of postoperative knee pain by the Lewis score. Results: Voluntary activation increased bilaterally after surgery (P<.01 operated side, P=.02 nonoperated side) but remained lower than the voluntary activation of the controls. MVC (P<.001) and true maximal contraction forces (P=.01) increased significantly on the operated side. MVC remained unchanged (P=.45), and true maximal contraction forces decreased significantly (P=.04) on the nonoperated side. Conclusion: Patients with knee OA have significant bilateral voluntary activation deficits that are, at least in part, reversible within 3 years after TKA. Rehabilitation programs immediately after TKA should focus on reduction of voluntary activation deficits. After voluntary activation improves, physical therapy should target the augmentation of quadriceps femoris muscle strength.