Summary

The cross-sectional study determined long-term deficits in lower limb muscle strength and performance after ACL surgery.

Abstract

Athletes often complain about persistent instability after anterior cruciate ligament (ACL) reconstruction and rarely reach their previous level of performance. There is an increased risk of re-rupture or injury on the contralateral side, probably due to proprioception deficits and inadequate muscle function. For this study, we hypothesized that athletes would have long-term deficits in lower limb muscle strength and performance after ACL surgery. Maximal strength deficits during isometric and isokinetic exercises were investigated. In addition, an isoinertial single-leg jump and a strength endurance test were performed to identify the nature of the deficits. In a cross-sectional study, 17 judokas (26±3.9 years old) were examined at a mean time of 5.1+1.1 years after ACL rupture (group A) and 27 judokas (27±2.4 years old) without knee injury (group B). All judokas were currently training at the national or international competition level. Single-leg countermovement jumps, isokinetic (0.2 and 0.6m/s) and isometric test procedures (6s in 30° knee flexion) for maximum strength and a strength endurance test with 30 repetitions at 0.2m/s in the closed chain were performed. A piezoelectric force plate and a Contrex leg press were used. The individual force parameters were recorded in a performance index to determine the direction of these. Subjects in group A showed significantly lower maximum strength values in all isokinetic (87.3% at 0.6m/s, 92.56% at 0.2m/s concentric, 89.7% at 0.2m/s eccentric), isometric (80.6%) and isoinertial strength tests (83.8%) after 5 years compared to the unaffected lower extremity (p<.01). The judo-specific strength index also showed serious deficits. The stronger leg of the athletes in group B had a higher index than the weaker one with a 95%CI of {1.04-1.08}. The uninjured leg achieved a value of 1.18 with a 95%CI of (1.12-1.24) compared to the formerly injured leg. The athletes showed lower maximum forces but significantly less fatigue in a logarithmic regression coefficient of strength endurance on the ACL rupture side (-23.71x+1604N) compared to the contralateral side (y=-30.98x+1828N)(p<0.05). Thus, 5 years after ACL rupture, athletes showed significant deficits in all relevant maximal strength tests. These findings could explain the poor performance of these athletes and the higher risk of a new ACL rupture without deficits in strength endurance. Changes in the composition of muscle fibres from type II to type I thus seem likely. Further studies are needed to assess the impact of this phenomenon on athletes' performance, especially with regard to sport-specific tasks and injury potential.