Muscle composition is not a prognostic factor for muscle strength recovery after anterior cruciate ligament surgery by hamstring tendon autograft.

Purpose: For the athlete, anterior Cruciate Ligament (ACL) rupture and its surgical management are often a turning point in their career. Success and time to return to sport are essential parameters for athletes and their support staff, so it is critical to understand the prognostic factors influencing return to sport after anterior cruciate ligament reconstruction (ACLR). The aim of this study was to determine the influence of hamstring muscle composition on muscle power following ACLR with autogenous hamstring grafts.

Methods: 24 patients with chronic torn ACL were included at a single-center over a period of 17 months. They underwent surgical repair and during this procedure grafts were harvested from the gracilis and the semitendinosus. Muscle composition was assessed on the remaining proximal part of the semitendinosus muscle, which is usually discarded, by immunostaining. Muscle power was defined by comparing the strength of the operated leg and the healthy leg on an isokinetic dynamometer at 6 months according a standardized protocol after 6 months of outpatient rehabilitation. Various other intrinsic and extrinsic factors were also studied, such as body mass index (BMI), age, sex, smoking, or sport practiced, to determine factors influencing isokinetic strength test after ACLR.

Results: No statistical relationship was identified between muscle composition and the muscle power between the operated and healthy leg. Smoking and female gender were associated with worse muscle recovery. Age and BMI had no influence on isokinetic performance at 6 months.

Conclusion: Following ACLR muscle composition is not associated with difference in strength between the two legs at 6 months. Determining muscle fiber composition of the patient does not inform the rehabilitation protocol or predict muscle strength recovery. Larger series data is required to understand the influence of gender or tobacco on muscle fiber characteristic.

Level of evidence: I; Prospective prognostic study.