Atraumatic Subcapital Femoral Neck Fracture as the Initial Presentation of Osteonecrosis of the Femoral Head: A Case‐Based Systematic Review

OBJECTIVE: Atraumatic subcapital femoral neck fracture associated with osteonecrosis of the femoral head (ONFH) is rare and may be difficult to recognize before surgery, while the available evidence regarding its diagnosis and management remains limited. We therefore aimed to describe an atypical presentation of ONFH as an atraumatic subcapital femoral neck fracture and to synthesize the available evidence on its diagnostic features, treatment patterns, and outcomes through a systematic review. METHODS: A CARE-compliant case report was combined with a PRISMA 2020-guided systematic review registered in PROSPERO. MEDLINE, Embase, Cochrane CENTRAL, and Scopus were searched from inception to February 28, 2026, for reports of atraumatic subcapital or transcervical femoral neck fractures associated with ONFH. Two reviewers independently screened studies, extracted data, and assessed methodological quality using the appropriate Joanna Briggs Institute critical appraisal checklists. Findings were synthesized descriptively because of substantial clinical heterogeneity and the absence of comparative studies. RESULTS: Eighteen studies involving 50 patients (58 fractured hips) were included. Magnetic resonance imaging (MRI) was reported in 38 of 50 patients (76%). Reported primary-treatment failures occurred in 3 of 8 internally fixed hips and 1 of 41 hips treated with arthroplasty; however, these uncontrolled descriptive findings do not permit comparative or causal inference. CONCLUSIONS: ONFH should be considered in atraumatic femoral neck fractures with atypical radiographic features. The available evidence is insufficient to determine the comparative effectiveness of arthroplasty and internal fixation, and treatment decisions should therefore remain individualized.