Purpose: Hamstring injuries are the most common soft tissue injury in running and kicking sports, such as football, rugby, Australian rules football, and American football. Most hamstring injuries affect the biceps femoris with reported rates reaching 87%. Injuries to the distal musculotendinous junction (DMTJ) of the biceps femoris represent a unique injury subset to the connective tissue scaffold that behaves differently from other hamstring injuries due to its complex multicomponent anatomy and dual innervation. Players often experience relatively rapid symptom resolution yet experience a high recurrence rate. Previous studies showed that the integrity of the connective tissue scaffold is of upmost importance with respect to muscle injury severity and time to return to play (TRP).
Methods and Materials: We designed a study to investigate injury to the biceps femoris DMTJ using a simple reproducible grading system based on the integrity of the connective tissue scaffold and correlated this injury grade with TRP. Using the Australian Football League injury survey from 2014 to 2017, a total of 65 biceps femoris DMTJ injuries were identified from a cohort of 250 hamstring injuries. Cases where TRP had not been documented (20), players who had not truly suffered a DMTJ injury (4), or if magnetic resonance imaging of the hamstring was not available for review (3) were excluded from analysis. The remaining 38 cases were reviewed by three musculoskeletal radiologists. Injuries were graded by consensus using a 3-point classification scheme (grade 1, peritendinous edema and blood-fluid products between muscle fibers without disruption of the connective tissue boundary; grade 2, partial-thickness delamination or tear in any connective tissue component of the musculotendinous junction; and grade 3, complete tear of either the long or short head connective tissue components). The presence of scarring and leg dominance were also noted.
Results: The median TRP for grades 1, 2, and 3 injuries were 25 (range: 6–44), 26 (17–86), and 57 (29–84) days, respectively. There was a significant difference (p value 0.028) in TRP between grade 1 and 2 and grade 3 injuries (Kruskal-Wallis test). A total of 53% of the study cohort had a preexisting focus of scar tissue suggestive of prior injury. There was no significant (p value 0.075) demonstrable association between the presence of a scar and grade of injury (chi-square test). Similarly, there was no statistically significant (p value 0.33) association between the presence of scar tissue and TRP. There was no significant association between leg dominance and injury grade (p value 0.44) or TRP (p value 0.67).
Conclusion: Despite the complex anatomy of the biceps DMTJ, our study shows a correlation between the integrity of the connective tissue scaffold and TRP. Complete failure of the connective tissue scaffold results in longer healing times and hence return to competition.
