Smartphone versus knee ligament arthrometer when size does not matter

Purpose

The use of available mechanical methods to measure anterior tibial translation (ATT) in anterior cruciate ligament (ACL)-deficient knees are limited by size and costs. This study evaluated the performance of a portable device based on a downloadable electronic smartphone application to measure ATT in ACL-deficient knees.

Methods

A specific smartphone application (SmartJoint) was developed for this purpose. Two independent observers nonsequentially measured the amount of ATT during execution of a maximum manual Lachman test in 35 patients with an ACL-deficient knee using KT 1000 and SmartJoint on both involved and uninvolved knees. As each examiner performed the test three times on each knee, a total of 840 measurements were collected. Statistical analysis compared intertest, interobserver and intra-observer reliability using the interclass correlation coefficient (ICC). An ICC > 0.75 indicates excellent reproducibility among measurements.

Results

Mean amount of ATT on uninvolved knees was 6.1 mm [standard deviation (SD?=?2)] with the KT 1000 and 6.4 mm (SD?=?2) with SmartJoint. Mean side-to-side difference was 8.1 mm. (SD?=?4) with KT 1000 and 8.3 mm (SD?=?3) with SmartJoint. Intertest reliability between the two methods yielded an ICC 0.797 [95 % confidence interval (CI) 0.717–0.857] for the uninvolved knee and of 0.987 (CI 0.981–0.991) for the involved knee. Interobserver ICC for SmartJoint and KT 1000 was 0.957 (CI 0.927–0.976) for the uninvolved knee and 0.992 (CI 0.986–0.996) for the involved knee and 0.973 (CI 0.954–0.985) for the uninvolved knee and 0.989 (CI 0.981–0.994) for involved knee, respectively.

Conclusion

The performance of SmartJoint is comparable and highly correlated with measurements obtained from KT 1000. SmartJoint may provide a truly portable, noninvasive, accurate, reliable, inexpensive and widely accessible method to characterize ATT in ACL-deficient knee