An Unusual Cause of Buttock Pain in a Collegiate Football Player: A Septic Sacroiliac Joint

Early recognition of sacroiliac (SI) joint infection can be challenging in young, otherwise healthy individuals presenting with nonspecific buttock or thigh pain. We present the case of a 21-year-old collegiate football player who developed progressive buttock and thigh pain after a minor fall during practice. Initial evaluation suggested sciatic nerve compression, and early MRI revealed only subtle soft tissue edema. Despite conservative treatment and a nerve block, his pain acutely worsened, and he developed fever and chills. Repeat MRI five days later demonstrated a fluid collection consistent with septic sacroiliitis and abscess formation, with additional findings of iliopsoas and gluteal myositis. Blood cultures and CT-guided aspiration confirmed methicillin-sensitive <i>Staphylococcus aureus</i> (MSSA). The patient was treated with intravenous nafcillin for four weeks via peripherally inserted central catheter (PICC) line following a nine-day hospital admission. He made a full recovery and started a slow return to play back into collegiate football three months after admission. This case highlights the diagnostic challenge of septic sacroiliitis in young athletes, the importance of repeat MRI when symptoms progress, and the favorable prognosis when prompt, culture-directed antibiotic therapy is initiated.