Diagnostic Performance of Clinical Examination for Detecting Knee Effusion: Impact of Obesity and Periarticular Adiposity.

introductionKnee joint effusion is generally readily detected on clinical examination. However, the clinical examination may be negative despite ultrasonographic confirmation of an effusion. The aim of our study was to assess the diagnostic performance of clinical examination compared with that of ultrasonography for detecting knee effusion, identify factors associated with failure to detect an ultrasonographically confirmed effusion on clinical examination, and evaluate patients' perception of knee swelling and the factors influencing this perception. METHODOLOGY: A cross-sectional study was conducted in 200 patients (400 knees). Ultrasonography was considered the reference standard. Sensitivity, specificity, predictive values, diagnostic accuracy, and likelihood ratios were calculated. Factors associated with the outcomes of interest were analyzed using logistic regression based on generalized estimating equations (GEEs) to account for the correlation between the two knees of the same patient.

resultsUltrasonographic evidence of knee effusion was present in 223 knees. Clinical examination had a sensitivity of 31.8%, a specificity of 95.5%, a positive predictive value of 89.9%, a negative predictive value of 52.6%, a diagnostic accuracy of 60.0%, a positive likelihood ratio of 7.04, and a negative likelihood ratio of 0.71. Sensitivity increased with ultrasonographic grade, from 29.6% for grade 1 to 33.8% for grade 2 and 40.9% for grade 3. In multivariable analysis, overweight, obesity, and local periarticular fat were associated with failure to detect effusion on clinical examination. Patients' perception of swelling had a sensitivity of 50.2%, a specificity of 69.5%, a positive likelihood ratio of 1.65, and a negative likelihood ratio of 0.72. Failure to perceive an effusion was associated with older age, educational level, and less severe pain, whereas in the absence of effusion, greater pain intensity was associated with more frequent perception of swelling.

conclusionsClinical examination had low sensitivity despite high specificity. The risk of non-detection was particularly high in patients with overweight or obesity and in those with greater periarticular fat, situations in which ultrasonography may be useful. Patients' perception of swelling did not consistently correspond to the presence of an effusion and appeared to be strongly influenced by the visual analog scale for pain.