ISOKINETIC MUSCLE PERFORMANCE AFTER ANTERIOR CRUCIATE LIGAMENT SURGERY - LONG-TERM RESULTS AND OUTCOME PREDICTING FACTORS AFTER PRIMARY SURGERY AND LATE-PHASE RECONSTRUCTION

The purpose of this study was to evaluate the long-term isokinetic mus cle performance after ACL surgery and to analyze by a multiple stepwis e regression which factors (if any) predict the overall outcome. The s tudy subjects were 119 patients who had 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 betw een the injury and the ACL surgery. The isokinetic strength measuremen ts 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 degre es/s. The measurements revealed that after the ACL surgery there was s till a considerable thigh muscle strength deficit especially in extens ion of the injured extremity, the average extension strength deficit r anging from 9 to 20 %. The extension strength deficit was significantl y more prominent in the chronic (18-20 %) than in the acute group (9-1 5 %). The extension strength deficit was also significantly greater at the slower (15-20 %) than higher (9-18 %) speed of the isokinetic mov ement. In both the acute and chronic groups, a multiple stepwise regre ssion analysis indicated that patellofemoral pain and flexion deficit of the knee were the factors that most frequently and significantly as sociated with the strength deficits. At the higher speed of the isokin etic movement, these two factors accounted 20 % and 21 % for the varia tion seen in the quadriceps strength deficit of the acute group and th e chronic group. No correlation could be found between age, sex, heigh t, weight, body mass index, length of the follow-up time, injury type, athletic activity level, immobilization method, knee stability, and t he isokinetic muscular performance.