The Inter-Rater Reliability and Diagnostic Accuracy of Patellar Mobility Tests in Patients with Anterior Knee Pain

Abstract

Background: Patients with patellofemoral pain syndrome (PFPS) often have nonspecific findings on clinical examination. A tight knee and diminished patellar mobility in particular, may contribute to anterior knee pain. Methods: Qualifying patients with anterior knee pain of > 4 weeks were sequentially examined by 2 physicians who used the patellar mobility tests. The tests evaluated for diminished patellar translation superior-inferiorly and medial-laterally, diminished patellar tendon mobility, and absent inferior pole tilt. Each of the 4 tests was scored as 1 (diminished/absent) or 0 (nondiminished/normal), with the sum of the scores determining the patellar mobility scale. Inter-rater reliability and diagnostic accuracy were determined and analyzed. Receiver operating characteristic analysis was used to determine the capacity of the patellar mobility scale to predict PFPS. Results: 98 patients participated in the study. The inter-rater reliability for the 4 individual patellar mobility tests was moderately strong, with diminished medial-lateral patellar mobility demonstrating the strongest reliability (Kappa value [K], 0.59; 95% confidence interval [CI], 0.42−0.72), followed by diminished superior-inferior mobility (K), 0.55; 95% CI, −0.37 to 0.69), inferior pole tilt (K, 0.48; 95% CI, −0.28 to 0.61), and patellar tendon mobility (K, 0.45; 95% CI, −0.27 to 0.56). The diagnostic accuracy of the individual patellar mobility tests in diagnosing PFPS was fair to moderate, with the individual diminished patella tendon mobility test having the highest level of diagnostic accuracy (sensitivity, 49%; specificity, 83%; likelihood ratio [LR] ± 2.8; 95% CI, 1.3−7.3) and also having the highest positive predictive value (0.88). Diminished medial-lateral mobility was second in diagnostic accuracy (sensitivity, 54%; specificity, 69%; LR ± 1.8; 95% CI, 0.9−3.6). Receiver operating characteristic analysis showed only moderate levels of diagnostic capacity (area under the curve, 0.65) because combining all 4 patellar mobility tests to form the patellar mobility scale did not improve the diagnostic accuracy. Conclusion: The clinical importance of diminished patellar and/or patellar tendon mobility findings in the evaluation of patients with anterior knee pain remains unclear. We determined that individual patellar mobility tests had moderate levels of inter-rater reliability, the best agreement found with medial-lateral mobility. The accuracy of the patellar mobility scale for diagnosing PFPS was marginal. As a tool, this cluster of examination techniques may be used by physicians to better understand their patients' conditions and descriptively communicate their findings. However, the patellar mobility scale cannot be used alone for determining the diagnosis of PFPS, as defined in our study. Future studies aim to determine whether post-treatment symptomatic improvements correlate with an improvement on the patellar mobility scale.