Anterior tibial translation and device-specific reliability of the KNEELAX3 arthrometer in healthy women.

Abstract

Instrumented arthrometers are widely used to quantify anterior knee laxity in the diagnosis and follow-up of anterior cruciate ligament (ACL) injuries. The KNEELAX3 enables computerized measurement of anterior tibial translation (ATT); however, device-specific normative data and reproducibility in healthy women have not been fully established. This study aimed to determine reference ATT values in healthy Japanese women and to evaluate the reliability of KNEELAX3 measurements. Sixty healthy Japanese women (mean age 27.1 ± 3.6 years) with no history of knee pathology were included. The ATT was measured at 132 N with the knee in 20° of flexion. Three experienced examiners performed the measurements. Examiner A conducted repeated measurements on separate days to assess intra-rater reliability, and all three examiners measured on the same day to assess inter-rater reliability. Reliability was evaluated using intraclass correlation coefficients (ICC). Bland-Altman analysis was performed to assess systematic error and calculate the minimal detectable change at the 95% confidence level (MDC₉₅). Mean ATT was 5.5 ± 1.8 mm on the right and 6.4 ± 1.8 mm on the left, indicating a small side-to-side difference in these healthy individuals. Intra-rater reliability was moderate to good (ICC 0.75-0.88), and inter-rater reliability was moderate to good (ICC 0.76-0.87). The ICC for side-to-side differences was lower (0.44-0.56), indicating limited reliability compared with absolute ATT measurements. No proportional bias was detected in any analysis. However, fixed bias was observed between one examiner and the others in the right knee. The MDC₉₅ for absolute ATT ranged from 1.84 to 2.58 mm, and 2 mm for side-to-side differences, suggesting that smaller differences may fall within measurement variability. KNEELAX3 demonstrated clinically moderate to good reliability for measuring ATT in healthy women. Side-to-side differences showed limited reliability and should be interpreted with caution, particularly when small. Differences approaching 2-3 mm may exceed measurement variability; however, interpretation should be device-specific and integrated with clinical findings. Standardized measurement techniques are important to minimize examiner-dependent variability.