Rapidly progressive idiopathic arthritis of the hip: incidence and risk factors in a controlled cohort study of 1471 patients after intra-articular corticosteroid injection

Objective Rapidly progressive idiopathic arthritis of the hip (RPIA) is defined by progressive joint space narrowing of > 2 mm or > 50% within 1 year. Our aims were to assess (a) the occurrence of RPIA after intra-articular steroid injection, and (b) possible risk factors for RPIA including: patient age, BMI, joint space narrowing, anesthetic and steroid selections, bone mineral density, and pain reduction after injection. Materials and methods A retrospective search of our imaging database identified 1471 patients who had undergone fluoroscopically guided hip injection of triamcinolone acetonide (Kenalog) and anesthetic within a 10-year period. Patient data, including hip DXA results and patient-reported pain scores, were recorded. Pre-injection and follow-up radiographs were assessed for joint space narrowing, femoral head deformity, and markers of osteoarthritis. Osteoarthritis was graded by Croft score. Associations between patient characteristics and outcome variables were analyzed. Results One hundred six of 1471 injected subjects (7.2%) met the criteria for RPIA. A control group of 161 subjects was randomly selected from subjects who underwent hip injections without developing RPIA. Compared to controls, patients with RPIA were older, had narrower hip joint spaces, and higher Croft scores before injection (p < 0.05). Patients who developed RPIA did not differ from controls in sex, BMI, hip DXA T-score, anesthetic and steroid injectates, or pain improvement after injection. Conclusion We found that approximately 7% of patients undergoing steroid hip injection developed RPIA. More advanced patient age, greater joint space narrowing, and more severe osteoarthritis are risk factors for the development of RPIA after intra-articular steroid injection.