Abstract
BACKGROUND: To explore the application of a new three-dimensional computed tomography measurement (maximum-inscribed-sphere method) in female DDH (developmental dysplasia of the hip) patients with gynecoid and anthropoid type pelvis on measuring the bony birth canal before and after unilateral PAO (periacetabular osteotomy). METHODS: A total of 19 female DDH patients of childbearing age were included in this study. The pelvis types were classified as gynecoid (11 patients) and anthropoid (8 patients). The maximum-inscribed-sphere method was applied to measure the bony birth canal. The lateral central edge angle (LCE), the anterior central edge angle (ACE), the Tönnis angle, and the distance between the femoral head and Koher's line were measured. RESULTS: For the gynecoid type, the narrowest part of the bony birth canal before and after the surgery occurred both at the 21st layer of bilateral ischial spines and the 4th sacrum (107.39 mm ± 4.33 mm; 106.27 mm ± 4.76 mm). In anthropoid patients, the narrowest part of the bony birth canal was found at the 21st layer before surgery (105.89 mm ± 6.58 mm), and the 19th layer after surgery (103.48 mm ± 7.36 mm). The most significant narrowing was found at the 8th layer (4.25 mm ± 3.51 mm p < 0.05) in those with gynecoid type pelvis, and at the 9th layer (5.8 mm ± 3.15 mm p < 0.001) in those with anthropoid type pelvis after PAO. There was no statistical significant difference between acetabular dysplasia and bony birth canal in the two type groups before surgery. For the anthropoid type, the increment of LCE angle and the narrowing of bony birth canal from the 13th to 19th layer after PAO was also more significant. As the impact of unilateral PAO on the gynecoid type pelvis was caused by a decreased distance between the femoral head and Kohler's line, resulting in the narrowing of bony birth canal between the 1st and 12th layer. CONCLUSIONS: Unilateral PAO did not affect the narrowest part of the bony birth canal in either pelvis type but caused mild narrowing above the ischial spine, with notable effects in the anthropoid group. In gynecoid pelvis patients, it led to narrowing through changes in the relation between the femoral head and Kohler's line.