Multiinstitutional epidemiological study regarding osteoarthritis of the hip in Japan

Background. Osteoarthritis (OA) of the hip is a major disease that affects the healthy lifespan of a population. It is necessary to fully understand the patients' conditions before a systematic treatment can be applied. However, a nationwide epidemiological study regarding hip OA has not yet been conducted in Japan. The present study examined the current status of patients with hip OA, including the disease etiology. Methods. This is a multiinstitutional study of new patients presenting with hip OA at the orthopedic outpatient clinics of 15 institutions in five geographical areas of Japan. The collected data from each patient included the sex, age, treatment history for developmental dysplasia of the hip (DDH), the clinical score of the hip joints based on the Japanese Orthopaedic Association (JOA) scoring system, and the pelvic inclination according to anteroposterior radiographs. In addition, the etiology was determined from the following 17 options: primary OA, acetabular dysplasia, intragluteal dislocation, osteonecrosis, trauma, Perthes disease, slipped capital femoral epiphysis, infection, rheumatoid arthritis, ankylosing spondylitis, neuroarthropathy, endocrine diseases, metabolic diseases, hereditary bone diseases, synovial chondromatosis, generalized OA, and others. Results. There were a substantially larger number of female patients than male patients. This difference regarding sex was present in each generation. The mean age of the patients was 58 +/- 14 years. The peak age at presentation was approximately 50 years. Most patients had no history of therapy for DDH. The older patients had lower gait and activities of daily living scores. The etiology was assessed to be acetabular dysplasia in most of the patients. A lower frequency of elderly patients demonstrated acetabular dysplasia. The patients who had a pelvic posterior inclination increased with increasing age. Conclusions. The patients with hip OA in Japan were unique in regard to age distribution, sexual heterogeneity, and disease etiology.