Posterior Acetabular Wall Fracture Mimicking a Subcapital Femoral Neck Fracture on Plain Radiographs: A Diagnostic Pitfall and the Role of Intraoperative Fluoroscopy: A Case Report.

INTRODUCTION: Radiographic interpretation of femoral neck fractures may be complicated by projectional anatomy. A fracture of the posterior acetabular wall can project over the femoral head-neck junction on anteroposterior pelvis radiographs and mimic a subcapital femoral neck fracture. While the literature extensively addresses occult (false-negative) hip fractures, false-positive interpretations, where acetabular fracture pathology is misidentified as a femoral neck fracture, are rarely reported. To the best of our knowledge, reports describing this specific false-positive diagnostic pitfall are uncommon in the literature. CASE REPORT: An 85-year-old Caucasian woman presented with left hip pain and difficulty ambulating following a twist and short fall mechanism of injury. Radiographs were initially interpreted as demonstrating a subcapital femoral neck fracture, and the patient was scheduled for operative fixation with cannulated screws. Intraoperative fluoroscopic images suggested the irregularity was more consistent with a posterior acetabular wall fracture rather than a fracture of the femoral neck. Surgery was aborted. Subsequent computed tomography confirmed a non-displaced fracture of the posterior wall of the acetabulum. She was managed non-operatively with protected weight bearing and physical therapy. At 2-week follow-up, she was ambulating with a cane and walker and reported satisfactory functional recovery. CONCLUSION: A posterior acetabular wall fracture may mimic a subcapital femoral neck fracture on plain radiographs. Recognition of this pitfall is important to avoid unnecessary operative intervention. When radiographic findings are inconsistent with intraoperative fluoroscopic findings, surgeons should abort the planned procedure and obtain confirmatory imaging before proceeding.