Injuries to accessory head of rectus femoris in professional football players: anatomical description, imaging findings, and clinical implications

BACKGROUND: The quadriceps femoris muscle compartment comprises four muscles, including the bi-articular rectus femoris, which is particularly prone to strain in kicking athletes. Anatomical variations such as accessory heads occur frequently but are seldom identified clinically. This retrospective case series describes injuries involving a previously undescribed accessory rectus femoris head in professional footballers. MATERIALS AND METHODS: We retrospectively reviewed a series of cases in professional footballers from 2022–2024 with acute anterior thigh injuries. Inclusion criteria required MRI evidence of a supernumerary rectus femoris muscle belly injury. MRI scans were reviewed to characterize the injury, and return-to-play times were recorded. One cadaver was dissected to confirm the accessory muscle anatomy in the thigh. RESULTS: Seven footballers met the inclusion criteria. MRI revealed an accessory anterolateral rectus femoris muscle belly with distinct proximal and distal aponeuroses, separate from the main rectus femoris. All injuries occurred at the myotendinous junction of the accessory head. Median return-to-play was 8 weeks. Cadaveric dissection confirmed an accessory muscle head arising from the anterior inferior iliac region and merging with the quadriceps tendon, corroborating the MRI findings. CONCLUSIONS: Recognizing anatomical variants is clinically important, as their characterization may explain atypical injury patterns and influence prognosis and clinical management. Identification of an accessory rectus femoris head on imaging can improve diagnostic accuracy, prevent misdiagnosis of injury severity and inform targeted rehabilitation strategies, thereby improving return-to-play outcomes.