Diagnostic performance of self-reported knee crepitus using a Knee injury and Osteoarthritis Outcome Score item.

Objective: To assess the diagnostic performance of a single Knee injury and Osteoarthritis Outcome Score (KOOS) item in evaluating the presence of knee crepitus.

Design: All 184 participants aged 18-40 years with a symptomatic knee, 9-36 months following anterior cruciate ligament reconstruction (ACLR) who were prospectively enrolled in a post-traumatic knee osteoarthritis trial (ACTRN12620001164987) were included. Participants completed the KOOS and underwent physical examination for knee crepitus at baseline. Self-reported knee crepitus (index test) of the ACLR knee was defined as a response of "often" or "always" on item S2 of the KOOS-Symptom subscale (KOOS-S2: Do you feel grinding, hear clicking or any other type of noise when your knee moves?). The presence of knee crepitus on physical examination (reference standard) was defined as continuous grinding, crunching or crackling during three consecutive squats with the investigator's palm placed lightly over the patella. Sensitivity, specificity, positive (LR+) and negative likelihood ratios (LR-), and positive (PPV) and negative predictive values (NPV), with 95% confidence intervals (CI), were calculated.

Results: On physical examination, 113 (62%) participants had knee crepitus, and 71 (39%) met the criteria for self-reported knee crepitus. KOOS-S2 demonstrated a specificity of 73% (95%CI 61%-83%), sensitivity of 47% (95%CI 37%-57%), LR+ of 1.75 (95%CI 1.14-2.70), LR- of 0.72 (95%CI 0.58-0.91), PPV of 74% (95%CI 64%-81%), and NPV of 46% (95%CI 41%-52%).

Conclusion: KOOS-S2 may be a useful method to rule in the presence of knee crepitus on physical examination in individuals post-ACLR; however, it is inadequate for ruling out this clinical sign.