Kt-2000 Test
Nhyiraba Valentin
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We assessed the reliability of the KT-2000 knee arthrometer at 67, 89, 134, and 178 N and at manual maximum forces on 30 college students who were free from present or previous knee injuries. Two examiners tested all subjects on two occasions. Anterior laxity (P < 0.0001) and side-to-side difference (P < 0.05) significantly increased as force increased. There was a significant difference (P < 0.0001) between testers for anterior laxity but not for side-to-side difference. We used intraclass correlation coefficients to estimate relative reliability. Anterior laxity intraclass correlation coefficients (2,1) between testers ranged from 0.81 to 0.86 and within tester correlations ranged from 0.92 to 0.95. Intraclass correlation coefficients for between testers for side-to-side differences ranged from 0.38 to 0.58 and within tester correlations ranged from 0.53 to 0.64. Subject-to-subject variability needs to be taken into account when interpreting intraclass correlation coefficient values. Our absolute reliability estimates (95% confidence intervals) were small, indicating little variability. Our data demonstrate the KT-2000 arthrometer to be reliable. Researchers should present both relative and absolute reliability estimates, although we believe absolute estimates are of greater clinical value. Side-to-side differences are better discriminators than individual absolute values. We recommend that a < 3 mm side-to-side difference be used to indicate stable knees.
There is acceptable intra-rater but poor inter-rater reliability with all tested arthrometers. Measures of knee laxity are comparable between Rolimeter, KLT and KT-1000 but higher for KiRA. Clinically, the present study shows that repeated arthrometry measurements should always be performed by the same investigators.
The aims of this study were (i) to assess the equivalence of measurements, the intra- and inter-rater reliability as well as the device-specific standard errors of measurements (SEM) of four different arthrometers in healthy knees, and (ii) to compare the results of these arthrometers in four different raters with different experience levels (advanced raters vs. beginners) in terms of anterior tibial translation (ATT) and side-to-side differences (SSD).
The study was approved by the ethical committee of the Medical University of Innsbruck (EK Nr: 1256/2020) and conducted according to the Declaration of Helsinki. All participants agreed and signed the informed consent.
KiRA, a triaxonal accelerometer for rotational and translational laxity evaluation, can be used to perform both an instrumented Lachman and Pivot Shift test [19]. For ATT measurements, the arthrometer relies on a standard Lachman test. The device is placed at the distal lower leg of the patient and fixed with an elastic strap in contact with a shin guard in order to optimize the stability of the sensor (Fig. 1: KiRA).
A total of four examiners performed the study protocol. Examiners 1 and 2 were experienced orthopedic surgeons (advanced), with more than 5 years of experience preforming manual knee examination, while examiners 3 and 4 were students (beginner) in their final year of medical school. Both advanced users were experienced in the use of one of the four arthrometers (Examiner 1: KLT, Examiner 2: KiRA). The beginners, by contrast, were familiar with the execution of the clinical Lachman Test but had no experience in the use of arthrometers. For this reason, prior to the study, all examiners were instructed in the proper use of all arthrometers according to the respective user manuals, and given ample opportunity to familiarize with the handling of the devices.
In accordance with the recommendations by Koo and Li, ICCs were interpreted as poor when below 0.50, as moderate when between 0.50 and 0.75, as good when between 0.75 and 0.90 and as excellent when above 0.90[14].
All reliability statistics reflecting the agreement of ATT and SSD measures obtained by pairs of advanced and beginner raters with all four arthrometer as well as corresponding measurement values are shown in Table 1.
The main finding of the present study was that intra-rater reliability of arthrometer measurements is acceptable with Rolimeter, KLT and KT-1000, whereas inter-rater reliability is generally poor with all tested devices. Standard errors of measurements (SEM), absolute anterior tibial translation (ATT) as well as side-to-side differences (SSD) in ATT are comparable between Rolimeter, KLT and KT-1000 but higher for KiRA.
While the joint statistical analyses of ATT and SSD values suggest that intra-rater reliability is acceptable with three (Rolimeter, KLT, KT1000) out of the four arthrometers tested, measures of inter-rater reliability clearly showed that results obtained by different examiners are not readily comparable. For SSD, equivalent test results were found with the Rolimeter (between both advanced and beginner raters) and KLT (between beginners only). Considering also the ICCs, which mostly showed poor agreement, particularly of SSD ratings, our data warrant caution in comparing results obtained by different examiners. Several factors may explain the low ICCs and conflicting results between raters. In addition to statistical reasons (ICCs relate the between-subject to the within-subject variance, with the former being typically small, particularly for SSD measures in healthy subjects), inconsistent positioning of patient and device might lead to strongly deviating measurements. Moreover, measures of ATT may also be affected by differences in the forces applied during the execution of the Lachman test, which is why only the usage of SSD values is recommended in clinical routine.
While adequate inter- and intra-rater reliability is important in the field of science and research, in daily practice, it is particularly a low rate of false positivefalse-positive measurements that is of primary importance. The rates of false positives have previously been documented for the KT-1000 and Rolimeter and ranged between 2- and 5% [2, 9, 17]. However, no respective data have been published for KLT and KiRA. In the present investigation, the rate of false positive measurements was low for the Rolimeter (0%), KT-1000 (2.1%) and KLT (3.1%) but substantially higher for KiRA (34.4%). In beginners, measurements with an SSD greater than 3 mm were more frequently recorded (24.0%) as in more experienced raters (10.4%). The reasons for the differences in the reliability of measures obtained with KiRA and the other devices are speculative and discussed in the limitations section.
Christan Fink receives royalties from Karl Storz and consultancies from Karl Storz and Medacta, but declares of having no conflict of interest with the present study. All other authors declare that they have no conflict of interest.
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Knee ligament arthrometer testing is considered experimental, investigational, or unproven for evaluating ligament laxity in the knee or for other indications because the peer-reviewed medical literature does not support the clinical value of this testing and the effectiveness of this approach has not been established.
There are a number of commercially available knee arthrometers. These devices provide computerized measurements of knee laxity. Knee ligament arthrometer testing can not replace the need for a physical examination and/or magnetic resonance imaging (MRI).
Spindler et al (2004) performed a evidence-based systematic review of randomized controlled trials assessing patellar tendon versus hamstring tendon autografts. Objective and subjective outcome measures included surgical technique, rehabilitation, instrumented laxity, isokinetic strength, patello-femoral pain, return to pre-injury activity, as well as Tegner, Lysholm, Cincinnati, and International Knee Documentation Committee-1991 scores. Slight increased laxity on arthrometer testing was observed in the hamstring population in 3 of 7 studies. Pain with kneeling was greater for the patellar tendon population in 4 of 4 studies. Only 1 of 9 studies reported increased anterior knee pain in the patellar tendon group. Frequency of additional surgery seemed to be related to the fixation method and not graft type. No study showed a significant difference in graft failure between patellar tendon and hamstring tendon autografts. Objective differences (e.g., range of motion, isokinetic strength, arthrometer testing) were not detected between groups in the majority of studies, suggesting that their sensitivity to detect clinical outcomes may be limited.
Papannagari et al (2006) stated that recent follow-up studies have reported a high incidence of joint degeneration in patients with anterior cruciate ligament (ACL) reconstruction. Abnormal kinematics after ACL reconstruction have been thought to contribute to the degeneration. These investigators hypothesized that ACL reconstruction, which was designed to restore anterior knee laxity under anterior tibial loads, does not reproduce knee kinematics under in-vivo physiological loading conditions. In a controlled laboratory study, these researchers examined both knees of 7 patients with complete unilateral rupture of the ACL with magnetic resonance image, and constructed 3D models from these images. The ACL of the injured knee was arthroscopically reconstructed using a bone-patellar tendon-bone autograft. Three months after surgery, the kinematics of the intact contralateral and reconstructed knees were measured using a dual-orthogonal fluoroscopic system while the subjects performed a single-legged weight-bearing lunge. The anterior laxity of both knees was measured using a KT-1000 arthrometer. The anterior laxity of the reconstructed knee as measured with the arthrometer was similar to that of the intact contralateral knee. However, under weight-bearing conditions, there was a statistically significant increase in anterior translation of the reconstructed knee compared with the intact knee at full extension (approximately 2.9 mm) and 15 degrees (approximately 2.2 mm) of flexion. Furthermore, there was a mean increase in external tibial rotation of the ACL-reconstructed knee beyond 30 degrees of flexion (approximately 2 degrees at 30 degrees of flexion), although no statistical significance was detected. The authors concluded that the data showed that although anterior laxity was restored during KT-1000 arthrometer testing, ACL reconstruction did not restore normal knee kinematics under weight-bearing loading conditions.
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