Hamstring muscle strength before and after anterior cruciate ligament reconstruction: A systematic review

BACKGROUND: The effect of hamstring tendon grafting during anterior cruciate ligament reconstruction (ACLR) on residual hamstring muscle strength remains unclear. OBJECTIVES: To identify if hamstring muscle strength deficits exist after ACLR using the ipsilateral semitendinosus and gracilis tendons (STG) in absolute and relative terms, and ascertain if pre-operative strength influences post-operative strength outcomes. METHODS: A search was performed using five databases; MEDLINE, SPORTSdiscus, Cinahl, AMED and Cochrane. Original articles that reported both absolute and relative hamstring muscle strength on isokinetic testing after ACLR with STG grafts were evaluated, selected and critically appraised. RESULTS: Eleven studies that met the inclusion criteria were included in the review. Hamstring peak torque (PT) deficits in the reconstructed leg compared to the contralateral side ranged from 10-19% and 6.4-12.6% at six and 12~months, respectively. Minimal deficits were reported at five to six year follow up. For absolute strength values the mean PT identified in absolute terms was low at 96 Nm at 60°/s (Range 77-121.8 Nm) with just one study normalising PT to body weight (PTBW). Only three of the included studies reported both pre- and post-operative results with two studies identifying similar reductions in PT of 8.6-9% in the operated limb from pre-operative to six months. CONCLUSION: Deficits in hamstring strength were found to exist up to one year post-operatively but appear to resolve by five to six years. It is recommended that future studies report PTBW to allow for better interpretation of results to allow for comparisons against normative data. More research is needed to examine the influence of pre-operative hamstring muscle strength on post-operative results.