Surgical Approach to a Rare Forearm Morel-Lavallée Lesion: Diagnostic and Management Challenges in the Upper Extremity.

Morel-Lavallée lesions (MLLs) are closed soft-tissue degloving injuries most often reported in the pelvis and lower extremity after high-energy shear trauma. Upper extremity (UE) involvement is exceedingly rare and frequently misdiagnosed as cellulitis or abscess. We report a 49-year-old Black male with a history of psychiatric disorders and intravenous drug use (IVDU) who presented to the Hospital of Central Connecticut's Emergency Department (ED) with a swollen, erythematous, and painful right forearm one week after blunt trauma. Contrast-enhanced computed tomography (CT) was inconclusive, but ultrasonography demonstrated a 20-cm unencapsulated suprafascial fluid collection. Magnetic resonance imaging was not obtained, given the emergent presentation requiring urgent intervention. Empiric intravenous vancomycin and piperacillin-tazobactam were initiated, and within 12 hours, spontaneous drainage confirmed infection and prompted urgent incision, drainage, and wide debridement, which established the definitive diagnosis. Intraoperative findings revealed a shearing-induced hematoma with overlying necrotic tissue, and pathology was consistent with an infected MLL. Given the large defect, marginal wound bed viability, and the patient's refusal of split-thickness skin grafting (STSG) due to concerns about donor-site morbidity, a dermal allograft skin substitute was used to provide immediate coverage without graft harvest. The substitute integrated successfully, and longitudinal follow-up demonstrated progressive epithelialization with durable closure. This case expands the limited literature on UE MLLs by illustrating how delayed history, atypical anatomy, and equivocal imaging can obscure diagnosis and delay definitive care. Forearm MLLs may closely mimic cellulitis or abscess, underscoring the importance of maintaining diagnostic suspicion for closed degloving injuries in patients presenting with post-traumatic UE swelling. Once infection and necrosis are evident, timely surgical intervention is essential to achieve source control and preserve soft-tissue viability. Management should be individualized based on lesion characteristics and patient-specific risk factors. In this case, use of a dermal allograft provided durable closure in a high-risk patient who declined STSG, demonstrating a viable reconstructive alternative. Early recognition and tailored operative strategy are critical to reducing morbidity in anatomically uncommon presentations such as the forearm.