Traumatic Serratus Anterior Muscle Tear Presenting as Isolated Posterior Shoulder Pain in a Professional Volleyball Athlete: A Case Report.

Serratus anterior muscle injuries are rare, most commonly reported in rowing and overhead throwing athletes. These injuries typically present with anterolateral chest wall pain and a palpable mass. Atypical presentations may lead to diagnostic challenges, particularly when symptoms mimic shoulder pathology. We report the case of a 26-year-old male professional volleyball player who presented with acute-onset posterior shoulder pain following a serving motion. The pain persisted for two weeks and was exacerbated by overhead movements, particularly during spiking. Physical examination revealed localized posterior shoulder pain with mild limitation of external rotation, while rotator cuff testing was normal. Initial clinical suspicion included posterosuperior labral injury or posterior internal impingement. Point-of-care ultrasonography of the shoulder showed no significant abnormalities, and magnetic resonance imaging (MRI) was subsequently requested, which revealed a traumatic partial-thickness tear of the serratus anterior muscle, with a fluid-filled gap measuring approximately 13 mm and associated edema extending posteriorly beneath the rhomboid musculature. No intra-articular or rotator cuff pathology was identified. This case illustrates a rare serratus anterior injury in a volleyball athlete, a mechanism seldom reported in the literature. Unlike typical presentations, the patient had isolated posterior shoulder pain resulting from posterior tracking of edema, mimicking intra-articular pathology and representing a potential diagnostic pitfall. MRI was key to establishing the diagnosis and excluding other causes, and the patient was successfully managed with a conservative, structured rehabilitation protocol. Serratus anterior muscle tear should be considered in the differential diagnosis of posterior shoulder pain in overhead athletes, particularly when clinical findings do not support intra-articular pathology. Early recognition and appropriate imaging are essential to avoid misdiagnosis and ensure optimal management.