Hip-Spine Syndrome: The Coronal Alignment of the Lumbar Spine and Pelvis in Patients with Ankylosed Hips

INTRODUCTION: Fixed abduction and/or adduction deformities of the hip joint may cause pelvic obliquity with subsequent development of secondary lumbar scoliosis. However, the relationships between the magnitude of a fixed angle (either abduction or adduction) of the hip and the direction of pelvic tilt and lumbar scoliosis remain unclear. The purpose of this study was to investigate the coronal alignment of the lumbar spine and pelvis in patients with ankylosed hips. METHODS: A total of 56 patients were analyzed, including 17 males and 39 females, with an average age of 65 years (range: 45 to 80 years). Regarding the coronal spinopelvic alignment, the following parameters were measured: the degree of lumbar scoliosis (LS; Cobb angle), pelvic obliquity (PO), and ankylosed hip angle (AHA). The PO and AHA were defined as the angle between the inter-teardrop line and a horizontal line, respectively, and the long axis of the femur on the side of the ankylosed hip. For each parameter, correlations between the parameters were evaluated using a regression analysis. A P value of <0.05 was considered significant. RESULTS: Positive linear correlations were observed between the AHA and direction of the PO angles (r = 0.831, p<0.01), the AHA and direction of the LS angles (r = 0.770, p<0.01), and the directions of the PO and LS angles (r = 0.832, p<0.01). CONCLUSIONS: This study provides evidence to suggest that, in patients with ankylosed hips, the abduction position is positively correlated with the downward PO and the convexity of the LS toward the AH side. In contrast, the adduction position is positively correlated with these results on the opposite side.