Macnab proposes the so-called Hip-Spine Syndrome when discussing lumbar spinal deformities that sometimes affects the progression of osteoarthritis of hip joint. This study examines the relationship between lumbar kyphotic deformity and the progression of osteoarthritis of the hip joint. <Method and result> Total hip arthroplasty was performed on 51 patients for a year in our department. Patients were divided into two categories: Category 1: Patients with secondary osteoarthritis of hip joint (SOA: 37 joints) based on acetabular dysplasia, and Category 2: Patients with primary osteoarthritis (POA: 14 joints). Both sacral tilting angle and lumbar lordosis angle decreased in POA group in comparison with SOA group. <Discussion/ Conclusion> Lumbar degenerative kyphosis could cause posterior pelvic tilting, resulting in promotion of osteoarthritis of hip joint. Such a mechanism is probably due to: 1) the decrease of the front covering of the femoral head and/or, 2) increase in the stress applied to hip joint.
