Lower-Extremity Compensations Following Anterior Cruciate Ligament Reconstruction
ABSTRACT & COMMENTARY
Synopsis: The hip and/or ankle can compensate for knee extensor moment deficits during weight-bearing activities in the involved extremity of patients after ACL reconstruction.
Source: Ernst GP, et al. Lower extremity compensations following anterior cruciate ligament reconstruction. Phys Ther 2000;80:251-260.
Weight-bearing tests such as the vertical jump are often used to assess overall function of patients following knee injury or surgery. This study evaluated lower-extremity kinetics following autograft bone-patellar tendon-bone anterior cruciate ligament (ACL) reconstruction in 20 subjects an average of 9.8 months postreconstruction, and 20 comparison subjects matched by sex, age, weight, and activity level (using the Tegner and Lysholm activity scales). Knee laxity was assessed with a KT1000, and any subjects with an involved-uninvolved side difference greater than 4 mm were excluded to avoid the potential confounding effects of knee instability. The ACL reconstruction subjects followed similar rehabilitation protocols that included both weight-bearing and non-weight-bearing exercises. A Vicon Motion Analysis System was used to determine the knee extensor moment and summated extensor moment (hip + knee + ankle extensor moments) for the lower extremity during a single leg vertical jump (take-off and landing) and lateral step-up exercise on an 18-cm-high step. Performance was measured on both the involved and uninvolved sides in the ACL reconstruction group, and both matched extremities in the comparison group.
For the knee extensor moments, the findings indicated the difference between the involved and uninvolved extremities for each of the three activities was different for the experimental and comparison groups. The knee extension moment of the involved side in the ACL reconstruction group was less than the uninvolved side, and of the matched extremity for the comparison group. There was no difference between the uninvolved extremity of the ACL reconstruction subjects and the matched extremity of the comparison subjects, and no differences between extremities of the comparison group.
For the summated extensor moments, the involved lower extremity of the ACL reconstruction group was less than the uninvolved side and the matched side of the comparison group only for vertical jump landing. No other differences were found for the summated extensor moments between groups or extremities.
COMMENT BY DAVID H. PERRIN, PhD, ATC
Rehabilitation following ACL reconstruction should include both weight-bearing (closed-chain) and non-weight-bearing (open-chain) exercises. Some clinicians have moved to almost exclusive use of closed-chain exercise for rehabilitation of ACL reconstruction patients, and many clinicians use weight-bearing performance tests to assess functional outcome. This study found that the hip and ankle extensors are capable of compensating for a knee extensor moment deficit in the involved extremity of ACL reconstruction patients. The implications of these findings are twofold as they relate to rehabilitation and functional assessment.
The subjects in this study participated in rehabilitation programs that incorporated both closed- and open-chain exercise, and still displayed knee extensor moment deficits at an average of 9.8 months postsurgery. One would expect rehabilitation protocols that use exclusively closed-chain exercise would result in knee extensor strength deficits of an even greater magnitude than found for subjects in this study. These findings would seem to support the importance of both closed- and open-chain exercise for rehabilitation of ACL reconstruction patients. Given the compensation found in this study, it is likely the only way to isolate the quadriceps muscle group for strengthening is with open-chain knee extension exercise.
This study also illustrates that normal function on closed-chain exercises such as the vertical jump (take-off) and step-up maneuver don’t necessarily indicate a normal knee extensor mechanism. While weight-bearing performance is certainly an important component of overall lower extremity functional assessment, clinicians should not overlook non-weight-bearing isolated strength assessment of the knee extensor mechanism during and following rehabilitation of ACL reconstructed patients.
This study reinforces the need for both open- and closed-chain exercise and assessment following ACL reconstruction. Ernst and colleagues correctly identify the need for additional research to determine how long these deficits remain, the implication of the deficits on performance and reinjury, and the need for studies to determine the best rehabilitation program to restore the entire lower extremity to preinjury levels of strength and performance.
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