Rectus Femoris Injuries in Professional Athletes: MRI Analysis Correlated with Time Interval to Return to Play

Purpose: The rectus femoris is the most commonly injured quadriceps muscle and the second most common site of lower extremity muscle injury. Rectus femoris injuries commonly occur in sports requiring kicking and sprinting, such as Australian Rules Football (Australian Football League [AFL]) and soccer. The integrity of the connective tissue scaffolding (such as the epimysial envelope and central intramuscular tendon rachis) supporting rectus femoris muscle fibers is vital to muscle function and recovery.

Methods and Materials: We designed a study to determine whether a correlation exists between connective tissue injury as graded on magnetic resonance imaging (MRI) and return to play (RTP). A retrospective review of all acute rectus femoris muscle injuries reported to the AFL soft tissue registry between 2013 and 2018 was undertaken. Severity of muscle and connective tissue structural injury was graded (0–3) by three musculoskeletal radiologists by consensus in each case. Definitions are as follows: grade 1, myofibril disruption/detachment with connective tissue intact; grade 2, myofibril disruption/detachment with connective tissue delamination/partial tear; and grade 3, myofibril disruption/detachment with connective tissue defect/full-thickness tear.

Injury location and previous injury (scar) were also recorded. Rehabilitation data were provided by the AFL Research Board (soft tissue registry). Subsequently the correlation between injury grade and RTP was determined.

Results: There were 60 rectus femoris injuries with a complete data set included for analysis. In terms of injury location, 22 of the 60 injuries (37%) involved the central intramuscular tendon rachis (indirect head origin); 32 (53%) involved the epimysial envelope. Of these epimysial injuries, 15 (25%) involved the posterior epimysium, 10 (16.7%) involved the anterior epimysium (direct head origin), and 7 were lateral injuries. Grade 1 injuries were found in 21 of 60 (35%); grade 2 in 24 of 60 (40%), and the remaining 15 cases (25%) had grade 3 tears.

RTP was available in 45 of 60 cases, and injury grade was found to have a direct correlation with RTP (and return to training [RFT]). The median RTP for grade 1, 2, and 3 injuries was 14 days (range: 7–29 days); 28 days (range: 14–82 days), and 41 days (20–82 days), respectively (p < 0.001). RFT was utilized in the 15 out-of-season injury cases and also proved statistically significant (p = 0.005).

Conclusion: This study demonstrates a direct correlation between connective tissue injury severity and the RTP/RFT interval. An MRI grading system based on connective tissue integrity has the potential to guide appropriate and safe rehabilitation for acute rectus femoris injuries in elite athletes participating in kicking and sprinting sports.