This study evaluates the reliability and validity of a single ultrasound measurement of the lateral condyle-capsule distance (LCCD) in the temporomandibular joint (TMJ) as a cost-effective alternative to more complex methods. By adopting a longitudinal test–retest design, researchers assessed intraobserver consistency using 72 TMJ ultrasound analyses. A single examiner performed the initial LCCD measurement, and one week later, repeated three measurements to calculate the average. Intraclass correlation coefficients (ICC) and Bland–Altman plots were applied to assess reliability and validity, comparing the initial measurement to the mean of the subsequent measurements. Results demonstrated strong intraobserver reliability with an ICC of 0.981 (95% CI: 0.969–0.988), highlighting a high level of consistency. The mean difference between ultrasound measurements was minimal, at 0.019 mm (95% CI: 0.0005–0.0383), with a standard deviation of 0.080 mm, indicating excellent validity. The 95% Limits of Agreement (LoA) ranged from −0.138 to 0.177, with a mean relative error of only 0.009 mm.
These findings suggest that trained examiners can achieve highly reliable and valid LCCD measurements in the TMJ using a single ultrasound measurement. This approach may be beneficial in clinical practice, reducing time and resource requirements while maintaining accuracy. The study supports the feasibility of this simpler measurement technique as a reliable alternative in assessing TMJ conditions. Additionally, the risk of measurement bias is low since the mean of three LCCD values was used as a reference for validity, rather than relying solely on one measurement.
