Knee flexor and extensor strength during concentric and eccentric muscle actions after anterior cruciate ligament...

The purposes of this study were to compare operated and nonoperated knees after anterior cruciate ligament reconstruction using the semitendinosus tendon and a polypropylene ligament augmentation device, and to determine the interrelationships among strength, knee stability, and current activity levels. Isokinetic tests for knee flexion (prone position) and extension (sitting position) strength during concentric-eccentric muscle action cycles were completed at 60 and 180 deg/sec angular velocities, and passive anterior displacement were determined for 15 male and 15 female patients (mean age, 27 +/- 8 years; mean time since surgery, 21 +/- 3 months). With the exception of eccentric muscle actions during knee extension, peak torque and work done were significantly greater on the nonoperated leg (P < 0.05). Passive anterior displacement was significantly greater in the operated than the nonoperated knee (P < 0.01). Strength measurements tended to be modestly related to current activity level (R > 0.40 in 24 of 32 correlations; P < 0.05), whereas anterior displacement was not related to current activity level (R = -0.19, operated knee; R = -0.09, nonoperated knee; P > 0.05). Greater emphasis should be directed toward strengthening the knee flexors and knee extensors after this surgery. Although joint-specific tests (completed actively via isokinetic dynameter) are more related to activity levels than are knee laxity tests (completed passively via knee arthrometer), neither test should be relied on as the only predictor of activity level in this patient population.