To examine the diagnostic accuracy of hip internal rotation, hip flexion, and knee flexion measurements for the presence of osteophytosis and joint space narrowing (JSN) in early symptomatic osteoarthritis (OA).
The baseline data for 598 participants of the Cohort Hip & Cohort Knee study were used. Participants underwent a standardized physical and radiographic examination. The active range of motion (ROM) was assessed using a goniometer. The ROM cutoff with the highest discriminative ability for radiographic features of OA was defined by maximizing the sum of the sensitivity and specificity. Several diagnostic measures were calculated to establish the diagnostic accuracy of ROM measurements for the presence of radiographic features.
In patients with hip symptoms, hip internal rotation <24° and flexion <114° were found to be the cutoffs with the highest discriminative ability to distinguish between patients with and without radiographic features. In patients with knee symptoms, knee flexion <132° was the cutoff with the highest discriminative ability. The American College of Rheumatology (ACR) criterion of hip internal rotation <15° increased the probability of the presence of osteophytosis or JSN from 25% to 58%. The diagnostic accuracy of hip and knee flexion measurements was low.
To reduce the number of patients that are not identified by the ACR criterion of hip internal rotation <15°, it is recommended to change the cutoff to internal rotation <24° in patients with early symptomatic OA. Individual hip and knee flexion measurements seem to be of little diagnostic value in early symptomatic OA.