Factors explaining chronic knee extensor strength deficits after ACL reconstruction

Abstract

Persistent quadriceps muscle weakness is common after anterior cruciate ligament (ACL) reconstruction. The mechanisms underlying these chronic strength deficits are not clear. This study examined quadriceps strength in people two to fifteen years post ACL reconstruction and tested the hypothesis that chronic quadriceps weakness is related to levels of voluntary quadriceps muscle activation, antagonistic hamstrings moment, and peripheral changes in muscle. Knee extensor strength and activation were evaluated in fifteen ACL reconstructed and fifteen matched uninjured control subjects using an interpolated triplet technique. Electrically evoked contractile properties were used to evaluate peripheral adaptations in the quadriceps muscle. Antagonistic hamstrings moments were predicted using a practical mathematical model. Knee extensor strength and evoked torque at rest were significantly lower in the reconstructed legs (P < 0.05). Voluntary activation and antagonistic hamstrings activity were similar across legs and between groups (P > 0.05). Regression analyses indicated that side-to-side differences in evoked torque at rest explained 71% of the knee extensor strength differences by side (P < 0.001). Voluntary activation and antagonistic hamstrings moment did not contribute significantly (P > 0.05). Chronic quadriceps weakness in this sample was primarily related to peripheral changes in the quadriceps muscle, not to levels of voluntary activation or antagonistic hamstrings activity.

Quadriceps Function and Hamstrings Co-Activation After Anterior Cruciate Ligament Reconstruction

“…Our findings support our hypothesis and agree with those of previous researchers who examined hamstrings activity during muscle contractions 28 and functional tasks such as gait 30 in individuals with ACLR. However, our results differed from those of Krishnan and Williams, 43 who found no difference in hamstrings coactivation between injured and uninjured individuals. Yet Krishnan and Williams 43 evaluated hamstrings co-activation at 908 of knee flexion and noted that their results were specific to joint angle.…”

“…However, our results differed from those of Krishnan and Williams, 43 who found no difference in hamstrings coactivation between injured and uninjured individuals. Yet Krishnan and Williams 43 evaluated hamstrings co-activation at 908 of knee flexion and noted that their results were specific to joint angle. Furthermore, they did not report the graft types in their sample, which may have influenced their findings.…”

Young Athletes Cleared for Sports Participation After Anterior Cruciate Ligament Reconstruction: How Many Actually Meet Recommended Return-to-Sport Criterion Cutoffs?

“…This method has been used to reliably quantify quadriceps and hamstring torque in healthy individuals and individuals with ACL injury and reconstruction. 19,21,31,32,37,40,50,55 Single-Leg Hop Tests Participants performed the 4 single-leg hop tests in the following order: single hop for distance, triple hop for distance, crossover hop for distance, and 6-meter timed hop. 42 These hop tests are commonly used clinically and have good measurement reliability in noninjured individuals and in those following ACL reconstruction.…”

“…12,14,20, 32,49 Each participant completed a practice trial before performing 2 measured trials for each limb, with limbs being tested in random order. The averages of the 2 trials for the involved and uninvolved limbs were used to calculate an LSI for distance measures as (involved score/uninvolved score) × 100%, and for the 6-meter timed hop as (uninvolved score/involved score) × 100%.…”

Avaliação Do Perfil Da Arquitetura Neuromuscular Em Pacientes Submetidos a Cirurgia Do Ligamento Cruzado Anterior

“…Dentre os mecanismos propostos para a perda de força, a alteração na arquitetura muscular tem sido proposta como um dos fatores a serem estudados (LOPPRESTI et al, 1988;KRISHNAN;WILLIAMS 2001). Os resultados de diversos estudos sobre a força muscular apontam que as diferenças encontradas após RLCA podem estar relacionadas a alterações morfológicas do músculo.…”