Reliability, validity and minimal detectable change of the quadriceps angle assessment in patients with knee osteoarthritis

Knee osteoarthritis (OA) is a multifaceted degenerative disease characterized by knee alignment alterations that impact the amplitude of the quadriceps angle (Q-angle). Q-angle is a diagnostic measure of knee alignment, and an indicator of the load distribution of patellofemoral and tibiofemoral joints. However, accurate assessment of this parameter necessitates the implementation of standardized and reliable measures to ensure methodological reproducibility. Thus, this study aimed to examine the concurrent validity, reliability, and minimal detectable change (MDC) of the Q-angle in patients with knee osteoarthritis (OA). The intra-rater and inter-rater reliabilities of each goniometric measurement were determined with the use of intraclass correlations (ICCs). The correlations between goniometric (clinical) and radiography (gold standard) measurements of Q-angle were assessed for concurrent validity. The intra-rater reliabilities of goniometric assessments in the supine and standing positions of the Q-angle were 0.90 and 0.96, respectively. The standard error of measurement (SEM) and minimal detectable change (MDC95) were 1.18 and 3.27 degrees for supine assessment and 0.87 and 2.40 degrees for standing assessment, respectively. The inter-rater reliabilities of goniometric assessments of the supine and standing position of the Q-angle were 0.86 and 0.92, respectively. SEM and MDC95 values were 1.59 and 4.39 degrees for supine assessment and 1.19 and 3.28 degrees for standing assessment, respectively. The radiographic measure showed a strong correlation with supine goniometric assessment (p