The purpose of this study was to evaluate the validity of the simple measurements of the muscle performance of the lower extremity, one legged hop testing for distance and the measurement of the circumference of the thigh 15 cm proximal to the joint line, by comparing them to the isokinetic strength testing 5 to 9 years after an ACL reconstruction with a bone-patellar tendon-bone (BTB) autograft. The measurements were performed on 86 patients on average 7 years after the surgery. The clinical evaluation was performed using the standard knee ligament evaluation form of the International Knee Documentation Committee (IKDC) and the Lysholm and the Marshall knee scores. At seven years, the isokinetic mean strength deficit of knee extension at the 60 degrees per second was 10 % in the operated limb as compared to the contralateral limb (NS). In the knee flexion, the differences were even smaller and statistically not significant either. The strength deficit of the knee extension at all knee angle velocities (p < 0.005), and flexion at 60 degrees per second (p < 0.05), correlated to the one legged hop testing, so that the patients with the greatest strength deficit also had the worst outcome in the one legged hop test. Also, the correlation between thigh atrophy and the deficit in the isokinetic strength test was significant in knee extension at all knee angle velocities (p < 0.001), and in knee flexion at 180 degrees per second (p < 0.005). In the final evaluation of the IKDC, 21 patients were rated as "normal", 51 as "nearly normal", 13 as "abnormal", and one as "severely abnormal". The mean of the Lysholm score was 83, classified as good, and that of Marshall score 43, classified as good. In conclusion, the one legged hop testing, as a functional muscle strength testing after an anterior cruciate ligament reconstruction, seems to correlate well with the isokinetic strength testing of the knee, especially in the knee extension. Because the hop testing can be easily performed and without extra equipment, we recommend its use for the evaluation of the functional muscle performance after an anterior cruciate ligament reconstruction. The measurement of the thigh atrophy is also easy to perform, and should be used beside the one legged hop testing, especially if the isokinetic strength testing is not available.

The purpose of this study was to evaluate the long-term isokinetic muscle performance after ACL surgery and to analyze by a multiple stepwise regression which factors (if any) predict the overall outcome. The study subjects were 119 patients who had a complete rupture of the ACL and had been treated surgically at the Tampere University Hospital between 1981 and 1990. They were divided into the acute group (N = 62) and into the chronic group (N = 57) according to the time delay between the injury and the ACL surgery. The isokinetic strength measurements of the quadriceps and hamstring muscles were performed on average 4 years after the operation using Cybex II and Cybex 6000 dynamometers (Lumex Inc., Ronkokoma, NY, USA). The peak torques were determined at speeds of 60 and 180 degrees/s and the peak work at speed of 180 degrees/s. The measurements revealed that after the ACL surgery there was still a considerable thigh muscle strength deficit especially in extension of the injured extremity, the average extension strength deficit ranging from 9 to 20%. The extension strength deficit was significantly more prominent in the chronic (18-20%) than in the acute group (9-15%). The extension strength deficit was significantly greater ar the slower (15-20%) than higher (9-18%) speed of the isokinetic movement. In both the acute and chronic groups, a multiple stepwise regression analysis indicated that patellofemoral pain and flexion deficit of the knee were the factors that most frequently and significantly associated with the strength deficits. At the higher speed of the isokinetic movement, these two factors accounted 20% and 21% for the variation seen in the quadriceps strength deficit of the acute group and the chronic group. No correlation could be found between age, sex, height, weight, body mass index, length of the follow-up time, injury type, athletic activity level, immobilization method, knee stability, and the isokinetic muscular performance.

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