Healthy knee KT1000 measurements of anterior tibial translation have significant variation

Purpose The most commonly used arthrometer for measuring and reporting anterior tibial translation after anterior cruciate ligament reconstruction is the KT1000. Reports on its consistency and reproducibility vary in the literature, but it remains the "gold standard". The purpose of this study was to assess agreement of KT1000 measurements in a daily clinical setting. Methods A retrospective analysis of anterior knee translation in the healthy knee of 770 patients over a 17-year time period was performed. In this cohort, a total of 24 investigators performed 1890 measurement sets at 89 Newtons (N), 134N and at maximum manual force (MMax) level. To assess the inter- and intra-observer agreement, the intraclass-correlation coefficient (ICC) was calculated. The "investigator effect" was a difference between two examiners in the same patient and the "device effect'' a difference within one examiner in the same patient. Minimally important difference (MID) was calculated as 0.5 of the standard deviation. Results Thirteen investigators were female, performing 1099 measurements and 11 were male, performing 791 measurements. ICC ranged between 0.558 and 0.644. At the MMax level, male investigators had a higher mm reading than female investigators (p < 0.001). Increased experience did not correlate with a higher ICC. MID ranged between 0.85 and 1.65 mm. Conclusion This study investigated the KT1000 arthrometer in a clinical setting with a large number of investigators. This device delivers moderate agreement of results. Both the device and investigator effect are present. The MMax level has shown the lowest agreement and a dependency on the investigator gender.