[Reliability of the KT-1000 arthrometer (Medmetric) for measuring anterior knee laxity: comparison with Telos in 147 knees]

Abstract

Purpose of the study: The purpose of this study was to compare the reliability and the reproducibility of both the KT-1000 arthrometer (Medmetric) and Telos for measuring anterior knee laxity. The Telos was used as the reference technique.

Material and methods: Criteria for inclusion were preoperative anterior knee laxity, normal contralateral knee, and intra-articular surgery to reconstruct the anterior cruciate ligament. Between January 1st, 2000 and October 31st, 2001, 147 patients were operated on for knee instability using an autograft (BPTB or hamstring tendons). For each patient, comparative measurements were made for both knees preoperatively and postoperatively with an average follow-up of 16 months. Measurements with the KT-1000 apparatus were made with forces of 67 N, 89 N, 134 N and manual maximal force. For the Telos, a force of 250 N was used as recommended by the manufacturer. We also evaluated intraobserver variation between the two devices.

Results: The anterior translation preoperatively as measured by the KT-1000 at 89N was 4.2 +/- 2.4 mm and 6.3 +/- 2.5 mm at maximal manual force. The result for Telos was 3.0 +/- 3.6 mm. The data scatter obtained with Telos was wider than with KT-1000 (p<0.03). The sensitivity of Telos was 72% with 28% false negatives. With KT-1000, sensitivity increased as tensile force increased. Sensitivity was 65% at 89N, 73% at 134N and 92% at maximal manual force. The concordance between the KT1000 and Telos data was low for either preoperative (10%) or postoperative (30%) measurements.

Discussion and conclusion: In this study, the results of sensitivity and reproducibility as well as the minimal scatter of the values demonstrated the reliability of KT-1000 for measuring anterior translation of the knee. We recommend routine use of the KT-1000 device for measuring knee laxity. The low sensitivity and the high rate of false negative observed with Telos raises the question of its use a reference technique.