Asymmetries In Quadriceps And Hamstring Strength And Fatigability In Patients 6-months After Acl Reconstruction

Abstract

Muscle dysfunctions are common after anterior cruciate ligament reconstruction (ACL-R) and may contribute to functional limitations and return to play readiness; however, the severity of lingering muscle dysfunction following rehabilitation is not well understood. Bilateral comparisons of quadriceps and hamstring muscle function are common practice to evaluate rehabilitation progress. The role of muscle fatigue is not well understood in patients recovering from ACL-R. PURPOSE: To compare quadriceps and hamstring muscle strength and fatigability between ACL-R and contralateral limbs in patients 6-months after ACL-R. METHODS: Participants included thirty-five patients with a history of primary, unilateral ACL-R an average of 6.3 ± 1.1 months post-surgery (18.2 ± 2.8 years, 74.2 ± 18.2 kg, 1.72 ± 8.7 m, sex: 20 F/15 M) that had completed a post-surgical rehabilitation program. Strength was quantified using measures of normalized (mass) peak knee extension and flexion torques (Nm/kg) during maximal isometric contractions (90 degrees flexion). Fatigability was quantified using the percent (%) decline in torque during 30-second maximal isometric knee extension and flexion contractions (90 degrees flexion). All measures were performed bilaterally. Comparisons between ACL-R and contralateral limbs were made using paired t-tests. Limb symmetry index (LSI) was used to describe strength asymmetries (=ACL-R limb / contralateral limb × 100). RESULTS: Quadriceps strength was significantly lower (P< .001) in the ACL-R limb (1.5±0.5) compared to contralateral limb (2.3±0.5), with a strength LSI of 64.8±16.4%. There was no difference in hamstring strength (P=.17) between the ACL-R (0.8±0.3) and uninvolved (0.9±0.2) limbs, with a strength LSI of 94.7±2.6%. Quadriceps fatigability was significantly lower (P= .02) in the ACL-R limb (15.3±13.0) compared to the contralateral limb (22.3±9.1). There was no significant difference in hamstring fatigability (P=.59) between the ACL-R limb (23.0±10.6) and contralateral limb (23.9±8.7). CONCLUSION: Patients demonstrated large quadriceps strength asymmetries (65%) at an average of 6-months post-surgery. The ACL-R limb demonstrated less quadriceps fatigability compared to the contralateral limb. Hamstring strength and fatigability were symmetrical.