Coxa Vara of Unknown Etiology: A Unique Case Report.

Introduction: Coxa vara is a rare pediatric hip disorder characterized by a reduced femoral neck shaft angle (NSA) (<120°), resulting in limb length discrepancy, gait abnormalities, and hip dysfunction. While developmental coxa vara has characteristic radiological features, atypical presentations with unknown etiologies are infrequently reported. Case Report: A 7-year-old boy with left hip pain presented without any history of trauma or systemic illness. Radiographs and computed tomography imaging revealed coxa vara with a transcervical femoral neck fracture with a mixed predominantly sclerotic lesion in the femoral neck. A closed-wedge valgus osteotomy was performed with internal fixation using a locking plate and screws placed proximal to the physis. Intraoperative biopsy ruled out tumor or infection. Although initial outcomes were favorable, recurrence of coxa vara and femoral neck fracture occurred after 1 year and 9 months. Revision surgery involved medial open-wedge osteotomy with bone grafting and fixation using a pediatric dynamic hip screw, with the lag screw crossing the physis for stability. At the 8th-year follow-up, the patient was pain-free, with minimal limb shortening and good functional mobility. X-rays showed solid radiographic union, disappearance of the previously noted sclerotic lesion in the left femoral neck, and maintenance of the NSA. Discussion: This case involves coxa vara with atypical radiographic features, complicating its classification as developmental or acquired. Initial fixation that preserved the physis resulted in recurrence. Subsequent fixation crossing the physis, along with correction of the Hilgenreiner epiphyseal (HE) angle, effectively prevented recurrence. At 8-year follow-up, the patient demonstrated a good clinical and radiological outcome. Conclusion: The HE angle is a critical prognostic factor in predicting the recurrence of coxa vara. Surgical stability should take precedence over physeal preservation.