Objective: The objective of this study was to use magnetic resonance (MR) imaging to investigate long-term changes in muscle and tendon morphology following a hamstring strain injury.
Materials and methods: MR images were obtained from 14 athletes who sustained a clinically diagnosed grade I-II hamstring strain injury between 5 and 23 months prior as well as five healthy controls. Qualitative bilateral comparisons were used to assess the presence of fatty infiltration and changes in morphology that may have arisen as a result of the previous injury. Hamstring muscle and tendon-scar volumes were quantified in both limbs for the biceps femoris long head (BFLH), biceps femoris short head (BFSH), the proximal semimembranosus tendon, and the proximal conjoint biceps femoris and semitendinosus tendon. Differences in muscle and tendon volume between limbs were statistically compared between the previously injured and healthy control subjects.
Results: Increased low-intensity signal was present along the musculotendon junction adjacent to the site of presumed prior injury for 11 of the 14 subjects, suggestive of persistent scar tissue. The 13 subjects with biceps femoris injuries displayed a significant decrease in BFLH volume (p < 0.01), often accompanied by an increase in BFSH volume. Two of these subjects also presented with fatty infiltration within the previously injured BFLH.
Conclusion: The results of this study provide evidence of long-term musculotendon remodeling following a hamstring strain injury. Additionally, many athletes are likely returning to sport with residual atrophy of the BFLH and/or hypertrophy of the BFSH. It is possible that long-term changes in musculotendon structure following injury alters contraction mechanics during functional movement, such as running and may contribute to reinjury risk.