Abstract
BACKGROUND: The hamstring graft used in anterior cruciate ligament (ACL) reconstruction has been shown to lead to changes to the semitendinosus and gracilis musculature. This study further evaluated the effect of the surgery on hamstring muscle morphology and knee muscle strength at 2 years post-surgery. HYPOTHESES: (1) Loss of donor muscle size would significantly correlate with knee muscle strength deficits (2) Loss of donor muscle size would be greater for muscles that do not experience tendon regeneration, and (3) Morphological adaptations would also be evident in non-donor knee muscles. STUDY DESIGN: Cross sectional evaluation. METHODS: 20 participants (14 male, 6 female, 29 ± 7 years, 82 ± 15 kg) that had undergone a hamstring graft in ACL reconstruction at least two years previously, underwent bilateral MRI and subsequent strength testing. Muscle and tendon volumes, peak CSA’s and lengths were determined for 12 muscles and 6 functional muscle groups of the surgical and contralateral limbs. Peak isokinetic concentric strength was measured in knee flexion/extension and internal/external tibial rotation. RESULTS: Only 50% of the patients regenerated both the semitendinosus and gracilis tendons. The regenerated tendons were longer with larger volume and CSA compared to the contralateral side. Deficits in semitendinosus and gracilis muscle size were greater for tendons that did not regenerate. In addition, combined hamstrings (semitendinosus, semimembranosus, biceps femoris) and combined medial knee muscles (semitendinosus, semimembranosus, gracilis, vastus medialis, medial gastrocnemius, sartorius) on the surgical side were reduced in volume by 12% and 10% respectively. A 7% larger volume was observed in the surgical leg for the biceps femoris and corresponded with a lower internal/external tibial rotation strength ratio. The difference in volume, peak CSA and length of the semitendinosus and gracilis correlated significantly with the deficit in knee flexion strength with Pearson correlations of 0.51, 0.57 and 0.61 respectively. CONCLUSION: The muscle-tendon properties of the semitendinosus and gracilis are substantially altered following harvesting, and these alterations may contribute to knee flexor weakness in the surgical limb. These deficits are more pronounced in tendons that do not regenerate and are only partially offset by compensatory hypertrophy of other hamstring muscles. CLINICAL RELEVANCE: Surgeons should consider muscle retraction of the hamstring following tendon harvest in their choice of graft option for ACL reconstruction.