A Possible Protective Effect of the 'Cam Deformity' on Femoral Neck Fracture: The Relationship between Hip Morphology and the Types of Hip Fracture.

We retrospectively evaluated the cases of 169 hip fracture patients, their previous fractures, and the contralateral hip joint's morphology. A history of contralateral hip fracture was present in 23 patients (Contra group). The other patients had a unilateral hip fracture: a trochanteric fracture (Troch group, n=73) or a femoral neck fracture (Neck group, n=73). In the Troch and Neck groups, we used anteroposterior and cross-table axialview radiographs of the contralateral hip to evaluate the proximal femur's anatomy. In the Contra group, the concordance rate between the first and second types of hip fracture was 65.2%, and the second hip fracture's morphology indicated that the trochanteric fracture had a cam deformity in terms of the femoral head-neck ratio. The average alpha angle and femoral head-neck offset in the Troch group were significantly larger than those in the Neck group. In the Neck group, pistol-grip deformities of Arbeitsgemeinschaft für Osteosynthesefragen types B1 (subcapital), B2 (transcervical), and B3 (displaced) were observed in 42.1%, 75%, and 6% of cases, respectively. There was a smaller alpha angle and a larger femoral head-neck offset in the contralateral hip of femoral neck fractures; thus, the "cam deformity" may protect against femoral neck fractures.