Purpose of the study: The goal of this study was to compare KT-1000 and Telos measurements after anterior cruciate ligament reconstruction (ACLR).
Material and method: Forty eight patients with asymptomatic ACLR (4 failures with positive pivot shift and 12 knees with positive (+) Lachman test) were assessed (mean 2.5 years after surgery) by the same examiner by means of: 1) Lachman radiographic with Telos at 150 N, 2) MEDmetric KT-1000 at 69 N, 89 N and maxi-manuel (MM). The examiner tested more than 200 patients each year. Measurements were performed for KT-1000 according to the manufacturers' recommendations and for Telos according to Staübli. Only side to side differences in millimeters are reported. Reproducibility of KT-1000 measurements were also evaluated: interobserver reproducibility was assessed by 16 examiners on a healthy patient, and the experienced examiner tested 20 times a healthy patient.
Results: An Interobserver error of 4 mm range (+/- 2 mm related to 0) was observed by 12 to 44 p. 100 of the examiners, respectively at 69 N to MM. An intraobserver error of 4 mm range (+/- 2 mm related to 0) was observed in 10 p. 100 at MM and in 20 p. 100 at 89 N. Mean side to side laxity with KT-1000 was 0.93 mm +/- 1.1 [-1 to 5] at 69 N, 1.3 mm +/- 1.6 [-2 to 6] at 89 N, and 1.41 +/- 1.8 [-2 to 6] at MM. With Telos the mean side to side laxity was 3.95 mm +/- 3.84 [0 to 15]. Significant differences (p = 0.0001) were found between measurements obtained by the two methods. No statistical correlation could be detected between values observed by Telos and KT-1000 (R < 0.1). If we consider a 3 mm side to side difference 23 knees (48 p. 100) had abnormal anterior laxity with Telos and with KT-1000 only 3 (6.2 p. 100) at 89 N and 6 (12.5 p. 100) at MM (1 (2 p. 100) at 69 N). With a 5 mm side to side difference, 12 knees (25 p. 100) had abnormal anterior laxity with Telos and with KT-1000 only 1 (2 p. 100) at 89 N and 1 (2 p. 100) at MM (0 at 69 N). Only Telos measurements were correlated to positive pivot shift (p = 0.007) and positive Lachman test (p = 0.01).
Conclusion: Interobserver reproducibility of KT-1000 measurements was low, but improved for intraobserver agreement. However, even for a unique KT-1000 experienced examiner, reliability of KT-1000 was poor when comparing Telos and KT-1000 predicitive value to diagnose ACLR failure. Telos results were much more pejorative but the only ones corelated with ACLR failures. We recommand Telos instead of KT-1000 to assess laxity after ACLR.