Hamstring muscle function following anterior cruciate ligament reconstruction using semitendinosus and gracilis autografts

Background: The effect of anterior cruciate ligament reconstruction (ACLR) using hamstring tendon grafts on residual hamstring muscle strength and function remains unclear, while the relationship between pre-operative and post-operative hamstring strength has not been established. Objective: To assess hamstring strength before and after ACLR using semitendinosus and gracilis tendon grafts (STG), and to evaluate the relationships between pre-operative and post-operative hamstring strength, and between hamstring strength and knee function. Methods: This study consisted of three parts: Firstly, a systematic review of current literature that investigated hamstring strength. Secondly, a retrospective analysis of isokinetic hamstring strength pre-operatively and six months following ACLR over five years. Thirdly, subjective assessment of current hamstring and knee function using the Tegner scale, Knee Self-Efficacy Scale (K-SES) and a hamstring questionnaire developed for this study based on the K-SES (K-SES Ham). Results: (1) Eleven studies met the inclusion criteria for the systematic review. Between limb hamstring peak torque (PT) deficits ranged from 10-19% and 6.4-12.6% at six and 12 months, respectively. Only three of the studies reported both pre and post-operative results. Absolute PT values were found to be low at 96Nm at 60°/s (Range 77-121.8Nm) with just one study normalising PT to body weight (PTBW). (2) Fifty-four patients agreed to participate in the retrospective data analysis. Low between limb PT deficits were identified pre-operatively (5.87%) and post-operatively (7.25%). Statistically significant improvements were found post-operatively for both the injured and uninjured limbs compared to pre-operative values. Strong correlations were identified between pre and post-operative scores for PT, PTBW, Total work and average PT. The mean absolute PT at 60°/s of 103.02Nm was higher than previously reported but lower than expected, when normalised to body weight (PTBW). (3) The median score for the Tegner was 7.0, K-SES 8.27 and K-SES Ham 8.66 at a mean of 3.66 years post-operatively. PTBW consistently correlated with the Tegner scale and K-SES across both speeds of 60 and 180°/s. Conclusion: ACLR with STG grafts resulted in good patient outcomes in terms of comparative objective hamstring strength and subjective knee and hamstring muscle performance. Hamstring strength actually improved post-operatively, with small deficits of less than 10% detected between limbs. The strong relationship between pre-operative and post-operative scores supports the need for more intensive pre-habilitation to gain optimal post-operative results. PTBW may be a more beneficial parameter than relative PT deficits in terms of predicting patient subjective performance, and future studies need to fully examine the importance of PTBW to assess its links to injury prevention and performance.