Smartphone versus knee ligament arthrometer when size does not matter
Ferretti A, Valeo L, Mazza D, Muliere L, Iorio P, Giovannetti G, Conteduca F, Iorio R. Int Orthop. 2014. [Epub Ahead of Print].
Take Home Message
A mobile phone arthrometer application may be a reliable alternative to the KT-1000 when measuring anterior tibial translation following an anterior cruciate ligament injury.
Clinicians may use a direct measurement of anterior tibial translation (ATT) to assess joint laxity in a knee after an anterior cruciate ligament (ACL) injury or reconstruction. The most common instrument to measure ATT is the KT-1000; however, access to this tool is limited due its size and cost. Clinicians would benefit from a reliable, cost effective method of measuring ATT. Therefore, Andrea and colleagues designed and evaluated a Smartphone application which assesses ATT. A total of 35 patients with a chronic ACL-deficient knee were included in the study. All patients laid supine on a table with their knees flexed on a below-knee support. Two orthopedic doctors with experience operating the KT-1000 assessed each patient. The orthopaedics measured the involved and uninvolved knees 3 times with the KT-1000 and mobile phone arthrometer application in a random sequence. Overall, 420 measurements were performed for both the KT-1000 and the mobile arthrometer application. On average, the involved knee had 14.5 mm and 14.8 mm of ATT according to the KT-1000 and arthrometer application, respectively. Further, the average side-to-side difference of ATT were 8.1 mm and 8.3 mm for the KT-1000 and arthrometer application, respectively. The authors found that the KT-1000 and arthrometer application had good-to-excellent agreement, particularly with the involved knee. 
Ultimately, the current study suggests that the mobile phone arthrometer application may be effective in measuring ATT. While these results may appear exciting on the surface one must be careful with the limitations of the study. Firstly, very few demographic details about the patients were provided. This calls in to question if there were patient characteristics that may influence an examiner’s ability to measure ATT (for example, high body mass index, leg size). Clinicians may find it challenging to get a consistent measurement on patients with a higher body mass index and/or leg size and it is unclear how this would influence the mobile phone arthrometer compared with the KT-1000. Secondly, it is unclear if the examiners ensured a consistent muscle relaxation during the testing procedure. For a Lachman’s test or KT-1000 to be performed effectively, the patient’s muscles must be relaxed. In the current study, patients were tested multiple times with different instruments. This repetition could potentially cause muscle guarding, which would also influence the study’s findings. To control for this issue, future research should look to include biofeedback to promote muscle relaxation during testing. Regardless, the prospect of an accurate and reliable knee arthrometer, which is easily portable, is an exciting concept. Future research should seek to include patients at various stages of the injury/recovery process and body sizes as well as report these details. Furthermore, future research would also benefit from extending the testing sessions to cover multiple days with fewer testing trials per session. Until more research is completed to address these issues, the KT-1000 should remain the gold standard to obtaining an objective ATT measurement. Concurrently, clinicians should be seeking to ensure that as more tools for mobile platforms are created, that we remain vigilant in ensuring that we can use these programs and devices consistently and correctly to promote clinical accuracy.
Questions for Discussion
Do you currently have access to a KT-1000 arthrometer? Do you feel you would utilize a reliable mobile phone arthrometer application in your current daily practice?
Written by: Kyle Harris
Reviewed by:  Jeffrey Driban
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