Rapidly progressive protrusio acetabuli in patients with rheumatoid arthritis.

Current literature suggests protrusio acetabuli in patients with rheumatoid arthritis progresses at a gradual rate of 2-3 mm per year. This report presents five patients with rheumatoid arthritis (RA) who experienced rapidly progressive protrusio. The period of rapid clinical progression averaged 40 days. During progression, medial protrusio increased an average of 7.5 mm, superior protrusio advanced 6.9 mm, femoral head width decreased 2.7 mm and center-edge angle increased 20.7 degrees. Axial protrusio occurred along an axis 137 degrees from vertical. A key clinical feature was an absence of significant hip symptoms before a marked increase in symptoms over a period of days to several weeks, resulting in a significant decrease in the patient's ambulatory capacity. Osteopenia was a consistent preexisting radiographic feature. The findings underscore the existence of rapidly progressive protrusio in the natural history of RA and its importance in the differential diagnosis of hip pain in patients with RA. Early recognition is important to minimize the potential complications of delayed surgical treatment.