The Relationship Between Fracture Area and Standing Pelvic Sagittal Inclination in Patients With Subchondral Fracture of the Femoral Head.

BACKGROUND: Some subchondral fractures of the femoral head follow a course of rapid destructive arthrosis (RDA) of the hip. It has also been suggested that there is an association between standing posterior pelvic tilt and the development of RDA. This study aimed to examine the relationship between fracture area and standing pelvic sagittal inclination in subchondral fractures of the femoral head. METHODS: This study included 27 patients with subchondral fractures of the femoral head. The fracture area (nine axial sections) and fracture width were observed on MRI. Patients with fractures of the anterior one-third of the femoral head were classified into the anterior (A) group, and patients with fractures not extending into the anterior area were designated the non-anterior (NA) group. The supine and standing center edge (CE) angles and standing sacral slope (SS) were measured on radiographs of the hip, and supine SS was measured on CT or MRI. RESULTS: There were 17 fractures in group A and 10 in group NA. In group A, standing SS - supine SS (ΔSS: -8.6°, range: -15.4° to -2.6°) and standing CE - supine CE (ΔCE: -7.1°, range: -18.6° to -2.1°) were significantly more negative than in group NA (-4.1°, range: -6.7° to -1.1°, p<0.01; and -2.8°, range: -6.3° to -0.1°, p=0.01). In group A, 11 patients had progression of collapse, and 13 patients underwent total hip arthroplasty. In group NA, there were no cases of progressive collapse, and joint preservation was possible in five patients. In patients with posterior pelvic tilt more than 8° in the supine to standing position, the fracture area was located anteriorly in all cases. CONCLUSION: With subchondral fractures of the femoral head, there is a relationship between standing pelvic sagittal inclination posteriorly and fracture area, and this affects prognosis. Patients with fractures in the anterior superior portion of the femoral head have a poor prognosis.