Outcome measures

All assessments were conducted using a standardized protocol at all five centers of data collection. Participants underwent a knee examination by a trained clinician under the supervision of physician examiners. The assessment of knee crepitus was performed at baseline, the occurrence of TKR was assessed at 36 months and other outcomes such as self-reported knee pain and physical function, and objective physical function were assessed at baseline and at 24 and 48 months follow-ups.

According to the OAI guidelines, a clinician assessed crepitus by placing the palm of the hand over the patella to detect the presence of a continuous grinding sensation during passive knee flexion-extension movement in the supine position. The test was considered positive for crepitus when a continuous grinding, crackling or crunching sensation during knee extension or flexion was detected. One or two clicks or pops were not considered crepitus, however, it was not necessary for the crepitus to be felt throughout the entire range of motion. The same clinical test has been used in other studies.10, 11

The KL grade is a radiologic grading system for knee OA, which determines the severity of radiographic OA based of the presence and degree of osteophytes, joint-space narrowing (JSN), sclerosis, and deformity affecting the tibiofemoral joint, irrespective of clinical symptoms. KL defines OA in five grades (0 – normal to 4 – severe).16 The OAI used the KL grade only to define tibiofemoral OA, the patellofemoral OA was not evaluated. The occurrence of TKR was evaluated by the OAI radiologists with radiographs at 36 months and coded as “right/left knee, ever have replacement surgery where all or part of joint was replaced”.