Tale of quadriceps and hamstring muscle strength after ACL reconstruction: a systematic review with longitudinal and multivariate meta-analysis

Abstract

ObjectiveThis study aimed to investigate how knee extensor and flexor strength change over time after anterior cruciate ligament reconstruction (ACLR).DesignSystematic review with longitudinal meta-analysis.Data sourcesMedline, Embase, CINAHL, Scopus, Cochrane CENTRAL and SPORTDiscus to 28 February 2023.Eligibility criteriaStudies of primary ACLR (n≥50), with mean participant age 18–40 years, reporting a quantitative measure of knee extensor or flexor strength were eligible. Muscle strength had to be reported for the ACL limb and compared with: (1) the contralateral limb (within-person); and/or (2) an uninjured control limb (between-person).ResultsWe included 232 studies of 34 220 participants. Knee extensor and flexor strength showed sharp initial improvement postoperatively before tailing off at approximately 12–18 months post surgery with minimal change thereafter. Knee extensor strength was reduced by more than 10% compared with the contralateral limb and approximately 20% compared with uninjured controls at 1 year for slow concentric, fast concentric and isometric contractions. Knee flexor strength showed smaller deficits but was still 5%–7% lower than the contralateral limb at 1 year for slow concentric, fast concentric and isometric contractions. Between-person comparisons showed larger deficits than within-person comparisons.ConclusionKnee extensor muscle strength is meaningfully reduced (>10%) at 1 year, with limited improvement after this time up to and beyond 5 years post surgery. Many people likely experience persistent and potentially long-term strength deficits after ACLR. Comparison within person (to the contralateral limb) likely underestimates strength deficits in contrast to uninjured controls.