Atypical Idiopathic Inferior Functional Shoulder Instability in a 15-year-old Female: A Case Report and Review of Literature.

Abstract

Introduction: The glenohumeral joint, while offering a high degree of mobility due to its ball-and-socket design, is inherently unstable. Shoulder instability is particularly challenging in pediatric and adolescent populations, where presentations are often atypical and non-traumatic. Functional shoulder instability (FSI), especially when idiopathic and inferior in direction, is exceedingly rare and underrepresented in literature.

Case report: We report a unique case of a 15-year-old female who presented with chronic, atraumatic left shoulder subluxation, persisting over 18 months. The patient experienced pain and limited range of motion but reported no history of injury. Multiple prior consultations yielded temporary relief with analgesics, and no definitive diagnosis was established. Clinical evaluation revealed limited active abduction and external rotation with no signs of ligamentous laxity or neurological involvement. Radiographic assessment demonstrated gross inferior subluxation of the humeral head. Magnetic resonance imaging and computed tomography imaging confirmed intact soft tissue structures with mild joint effusion, anterior glenoid flattening, and a 6% glenoid bone loss. A diagnosis of inferior, non-positional, controllable idiopathic FSI was made, likely due to deltoid atony.

Treatment and outcome: Management included temporary immobilization and physiotherapy using the Watson multidirectional instability protocol focused on scapular motor control retraining. After 10 weeks, the patient showed marked improvement with restoration of overhead abduction and full external rotation. Radiographs confirmed proper joint alignment, and the patient resumed normal activities symptom-free.

Conclusion: This case highlights a rare presentation of inferior idiopathic FSI in an adolescent. Early recognition and structured rehabilitation can lead to excellent outcomes, avoiding unnecessary interventions. Increased awareness of such atypical presentations is essential for prompt diagnosis and effective non-operative management.