EVALUATING THE RELIABILITY OF VASTUS MEDIALIS THICKNESS MEASUREMENT USING B-MODE ULTRASOUND: A ONE-WEEK INTERVAL STUDY

Background The vastus medialis (VM) muscle is essential for patellofemoral joint stability, and its dysfunction is linked to multiple knee disorders. Ultrasound (US) offers a practical method for VM assessment. The reliability of longitudinal-plane thickness measurements by novice examiners remains unclear. Material and methods 18 healthy adults (mean age 23.5±1.25 years) underwent three VM thickness measurement sessions: two on the same day and one after one week. Measurements at rest (R) and during maximal voluntary isometric contraction (MVIC) were obtained using a standardized protocol. Intra-class correlation coefficients (ICCs), standard error of measurement (SEM), and smallest detectable difference (SDD) were calculated to assess intra-rater reliability. Results Single-session measurements achieved excellent reliability (ICC≥0.93) for both R and MVIC, with greater precision from averaging multiple registrations. One-week interval measurements showed moderate-to-good reliability (ICC 0.52-0.87), improving with repeated measurements. Mean VM thickness increased from 27.1±3.9 mm (R) to 32.4±4.6 mm (MVIC). Conclusions Longitudinal US measurement of VM thickness is highly reliable within a single session, especially when multiple images are averaged. Consistent landmarks, standardized procedures, and examiner training can enhance long-term measurement reliability in clinical and research settings.