Muscle atrophy contributes to quadriceps weakness after anterior cruciate ligament reconstruction

Objectives: Quadriceps weakness persists after anterior cruciate ligament reconstruction. Muscle atrophy and activation failure may contribute. This study examined the roles of atrophy and activation failure in quadriceps weakness after anterior cruciate ligament reconstruction. Design: Case series. Methods: Twenty patients six months post-anterior cruciate ligament reconstruction participated. Atrophy was determined as peak quadriceps cross sectional area from magnetic resonance images. Quadriceps activation was quantified via the central activation ratio, while muscle strength was measured isometrically. All testing was performed bilaterally. Hierarchical linear regression and one-way ANOVAs were performed to examine the relation of muscle strength with activation and atrophy. Results: Cross sectional area (R-2 = 0.307; = 0.011) explained more of the variance in quadriceps strength than central activation ratio (R-2 < 0.001; p = 0.987). Strength and cross sectional area were lower in the injured (strength: 2.03 +/- 0.51 N m/kg; cross sectional area: 68.81 +/- 17.80 cm(2)) versus uninjured limb (strength: 2.89 +/- 0.81 N m/kg; cross sectional area: 81.10 +/- 21.58 cm(2); p < 0.001). There were no side-to-side differences in central activation ratio; however, quadriceps activation failure was present bilaterally (injured: 0.87 +/- 0.12; uninjured: 0.85 +/- 0.14; p = 0.571). Conclusions: Quadriceps cross sectional area was strongly related to muscle strength six months after anterior cruciate ligament reconstruction and substantial injured versus uninjured limb deficits were demonstrated for strength and cross sectional area. Patients may benefit from exercises aimed at improving quadriceps cross sectional area post-operatively. (C)) 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.