The “Bunny Tail” Lesion: An MRI Pattern of Proximal Biceps Femoris Tendon Injury With Rapid Return to Play in Elite Soccer Players—a Retrospective Observational Case Series

Background: Hamstring injuries are the leading cause of time lost in professional soccer. Among these, tendon-related lesions of the biceps femoris (BF) are associated with longer recovery and higher reinjury risk. Emerging magnetic resonance imaging (MRI) findings suggest the existence of morphological subtypes with different prognostic implications. Purpose: To describe an MRI pattern of proximal BF tendon injury-the "Bunny Tail lesion"-and report its management and outcomes in elite soccer players. Study Design: Case series; Level of evidence, 4. Methods: Over 2 competitive seasons (July 2023-June 2024), all acute hamstring injuries in a Serie A club were prospectively recorded and retrospectively reviewed. Players were eligible if MRI showed focal peritendinous edema at the distal tip of the proximal tendon of the BF long head, with increased intratendinous signal and preserved tendon continuity. Three musculoskeletal radiologists independently classified lesions using the British Athletics Muscle Injury Classification (BAMIC). Interobserver agreement was assessed with Fleiss κ. Rehabilitation followed a structured, football-specific program with standardized return-to-training and return-to-play (RTP) criteria. Results: Eight professional players met inclusion criteria. All lesions showed a well-circumscribed ovoid peritendinous edema surrounding the distal extremity of the proximal BF tendon, with preserved structural continuity. Lesions were variably categorized as BAMIC 2b to 2c, with one graded 3c by a single radiologist. Interobserver agreement for combined grade and tissue classification was very low [Fleiss κ close to 0]. All athletes were managed conservatively and returned to training after 14.6 ± 3.0 days and to play after 26 ± 6 days. No reinjuries occurred during a mean follow-up of 395 ± 202 days. Conclusion: This small series describes a consistent MRI pattern of proximal BF tendon injury characterized by focal ovoid peritendinous edema at the distal tendon tip, preserved continuity, and relatively rapid RTP despite predominantly tendinous BAMIC classification. This pattern may represent a less severe variant within the spectrum of proximal BF tendon injuries.