Existing hip joint disease is associated with an increased incidence of hip fracture in adults: A retrospective survey of 9710 individuals from a single center.

Objective: In hip disease patients, pain and movement restrictions might cause changes in bone strength and increase the likelihood of falls, finally leading to hip fracture. The aim of this study was to identify the incidence of, characteristics of and risk factors for hip fracture in patients with existing hip disease. Methods: This was a retrospective cohort study. Patients with existing hip disease treated at both outpatient and inpatient departments of our institute were identified by searching the electronic medical record system and followed retrospectively for the occurrence of hip fracture. Demographic and clinical characteristics, such as age, sex and kind of primary hip disease, were collected from the electronic medical record system. The incidence and timing of hip fracture were estimated, and a Cox regression model was built to identify the independent risk factors for hip fracture in these patients. Results: A total of 9710 eligible patients were included. After a mean follow-up of 3.97 years, hip fractures were identified in 95 patients, for an estimated incidence of hip fracture of 978.37 per 100,000 patients. The femoral neck was involved in 49 fractures (51.58 %), and the femoral trochanter was involved in 45 fractures (47.37 %). Four independent risk factors and one protective factor for hip fracture in patients with hip diseases were identified: age (HR = 1.116, 95 % CI = 1.094-1.138), the presence of osteonecrosis of the femoral head (HR = 2.201, 95 % CI = 1.217-3.980), a lower Harris hip score (HR = 0.966, 95 % CI = 0.949-0.982), a history of previous hip surgery (HR = 2.126, 95 % CI = 1.304-3.466) and the use of walking aids (HR = 0.588, 95 % CI = 0.354-0.975). A scoring system with a total score of 20 points was built, which included all of the above risk factors. The predictive scores for a low risk (estimated incidence of hip fracture ≤30 %), a moderate risk (estimated incidence of hip fracture 31 %-69 %), and a high risk (estimated incidence of hip fracture ≥70 %) of hip fracture were ≤8.5 points, 9.0-13.0 points and ≥13.5 points, respectively. Conclusion: The incidence of hip fracture in the special population of patients with existing hip disease was determined. Elderly patients, patients with a history of hip surgery, patients with osteonecrosis and patients with poor Harris hip scores were at increased risk of hip fracture. In patients with a predictive score greater than 9 points, indicating a moderate to high risk of hip fracture, the use of a walking aid might reduce the risk of hip fracture.