The gothic arch: a reliable measurement for developmental dysplasia of the hip.

The "Gothic Arch" is a radio-graphic finding on AP pelvis x-rays postulated to be predictive of hip osteoarthritis. The purpose of this study was to determine the reliability of measurement of the Gothic Arch in patients with no known hip pathology and patients with unilateral developmental dysplasia of the hip (DDH). After obtaining IRB approval, nine skeletally mature patients (18 hips) with no known hip pathology were selected to serve as the control group. The AP pelvis x-rays at skeletal maturity of eight patients (16 hips) with unilateral DDH treated with closed reduction and casting comprised the comparison group. A digitizing program was designed to measure the Gothic Arch based on landmarks identified by the user. Two pediatric orthopaedic surgeons and two orthopaedic residents completed the program on two separate occasions. Intra-and interobserver reliability were determined using intraclass cor-relation coefficients (ICC) for continuous variables. Both the unilateral DDH group and the control group demonstrated excellent inter- and intraobserver reliability (ICC >0.70) for base, height, area, and orientation of the Gothic Arch, but poor reliability (ICC <0.40) for medial and lateral sharpness. The Gothic Arch can be reliably measured on AP pelvis x-rays of patients with normal and dysplastic hips. III, Diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.