Prevention of Unplanned Surgery Due to Delayed Diagnosis of Occult Ipsilateral Femoral Neck Fractures Associated with Femoral Shaft Fractures: A Study of the CT Capsular Sign with Lipohemarthrosis.

BACKGROUND: The purpose of the present study was to investigate the effectiveness of using the computed tomography (CT) capsular sign with lipohemarthrosis of the hip joint as a selective indicator for preoperative magnetic resonance imaging (MRI) of the hip or prophylactic fixation of the ipsilateral femoral neck for the prevention of unplanned surgery due to delayed diagnosis of occult ipsilateral femoral neck fractures in patients with high-energy femoral shaft fractures. METHODS: We evaluated the CT capsular sign with lipohemarthrosis in patients with a high-energy femoral shaft fracture without a preoperative diagnosis of an ipsilateral femoral neck fracture. The CT capsular sign with lipohemarthrosis was considered positive when the side-to-side difference in anterior capsular distension was >1 mm and lipohemarthrosis was seen on soft-tissue-window CT images. A positive CT capsular sign with lipohemarthrosis prompts preoperative hip MRI or prophylactic femoral neck fixation with a reconstruction nail. RESULTS: One hundred and fifty-six consecutive patients were included. Eight patients were preoperatively diagnosed with a displaced or hairline ipsilateral femoral neck fracture, whereas the remaining 148 patients showed no ipsilateral femoral neck fracture on radiographs and bone-window CT images. On soft-tissue-window CT images, 29 (19.6%) of the 148 patients had a positive CT capsular sign with lipohemarthrosis. We performed preoperative MRI for 3 patients; in the remaining 26 patients, prophylactic femoral neck fixation was performed with a reconstruction nail. We identified 5 occult ipsilateral femoral neck fractures among the 29 patients with a positive sign: 2 on preoperative MRI scans, 2 on immediate postoperative radiographs, and 1 on radiographs made 6 weeks postoperatively. In 119 patients with a negative sign, no occult ipsilateral femoral neck fracture was identified. All occult ipsilateral femoral neck fractures healed without further displacement of the femoral neck. Consequently, additional unplanned surgery for delayed diagnosis of occult ipsilateral femoral neck fracture was not required. CONCLUSIONS: The use of the CT capsular sign with lipohemarthrosis as a selective indicator for preoperative hip MRI or prophylactic femoral neck fixation with a reconstruction nail in patients with high-energy femoral shaft fractures is effective for preventing unplanned surgery due to delayed diagnosis of occult ipsilateral femoral neck fractures. LEVEL OF EVIDENCE: Diagnostic Level I. See Instructions for Authors for a complete description of levels of evidence.