Methicillin-Resistant Staphylococcus aureus Sternoclavicular Joint Septic Arthritis With Contiguous Sternomanubrial Osteomyelitis in a Patient With Diabetes Mellitus: A Case Report

Sternoclavicular joint (SCJ) septic arthritis with contiguous sternomanubrial osteomyelitis is rare but potentially life-threatening because of its proximity to the mediastinum and great vessels.This report describes a middle-aged man with diabetes mellitus and prior right lower-extremity osteomyelitis requiring below-knee amputation (BKA) who presented with left anterior chest pain and swelling near the sternoclavicular joint, accompanied by shoulder and neck pain and dysphagia.Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated left sternoclavicular joint septic arthritis with osteomyelitis involving the medial clavicle, manubrium, and adjacent first rib, associated chest wall abscess with extension toward the anterior mediastinum.Although blood cultures obtained during the index hospitalization were negative, methicillin-resistant Staphylococcus aureus (MRSA) was isolated from the resected intraoperative bone specimen.The patient underwent surgical debridement and sternoclavicular joint resection with pectoralis major muscle flap coverage, followed by prolonged anti-MRSA antimicrobial therapy.During rehabilitation, an acute febrile episode was empirically managed with escalated broadspectrum coverage.Following completion of parenteral therapy, the patient demonstrated complete shortterm clinical recovery, surgical site improvement, and declining inflammatory markers.However, persistent mild inflammatory marker elevations highlight the need for continued surveillance, as short-term clinical improvement cannot be equated with confirmed long-term infection eradication.Early recognition and appropriate imaging are critical to identify extensive local disease.This case underscores the importance of considering sternoclavicular joint infection in patients with localized chest pain and swelling, particularly those with diabetes or recent bloodstream infection, even without fever or marked leukocytosis.