RELIABILITY OF KT1000 ARTHROMETRY FOR MEASURING ANTERIOR KNEE LAXITY: COMPARATIVE ANALYSIS WITH TELOS IN 147 PATIENTS.

Abstract

Purpose: The purpose of this study was to compare the reliability and reproducibility of anterior knee laxity measurements made with the KT1000 arthrometere (Medmetric) and radiographically with Telos. The Telos measurement was taken as the standard system.

Material and methods: Inclusion criteria were preoperative anterior laxity differential less than 10 mm, a healthy contralateral knee, and intra-articular surgery. Between January 2001 and December 20001, 147 patients underwent surgery for free graft repair of anterior laxity. Both measurement methods, KT1000 and Telos were used to measure both knees before surgery and at mean 16 months postsurgery. KT1000 measurements were taken at 67N, 89N, 134N and maximum manual force. Telos was measured at 150 N as recommended by the manufacturer. A differential laxity measured at more than 3 mm was considered pathological for KT1000 and greater than 5 mm for Telos. We also determined the intrao-bserver reproducibility (experimented operators) with both methods on the 147 healthy knees considering the measurements taken preoperatively and postoperatively.

Results: Mean preoperative differential laxity was 4.2±2.4 with KT1000 at 89N and 6.3±3.1 mm at maximal manual force. It was 7.7±3.4 mm with Telos. The mean postoperative differential laxity with KT1000 was 2.1±2.2 mm at 89N and 2.6±2.5 mm at maximal manual force. With Telos it was 3±3.6 mm. The Telos values showed a wider distribution than the KT1000 values (p< 0.03). The sensitivity with Telos was 72% with 28% false negatives. With KT1000, the sensitivity improved with greater traction. It was 65% at 89N, 73% at 134N and 92% at maximal manual force. For the healthy knee, the anterior laxity measurements taken by an experimented operator were reproducible with KT1000, p=0.04, kappa = 7.8.

Discussion: The sensitivity and reproducibility results as well as the narrow distribution of the values show that KT1000 is a reliable method for the measurement of anterior knee laxity. Its use can be recommended in routine practice due to the good benefit-cost ratio. The low sensitivity is a drawback of the Telos method due to the high percentage of false negatives. Its use in routine practice should be revisited.