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App quantifies tibial translation of ACL injured patients during pivot shift testing
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TORONTO — Researchers at the University of Pittsburgh created an iPad app that can be used to determine pivot shift grade according to the tibial translation measured in patients with ACL deficiency, according to a study presented at The International Society Arthroscopy, Knee Surgery & Orthopaedic Sports Medicine Congress.
“The standardized pivot shift test improved clinical measurement accuracy,” presenter Volker Musahl, MD, of University of Pittsburgh, said. “The quantitative pivot shift application can detect tibial translation due to pivot shift and, compared to previous technologies, the pivot application is noninvasive, standardized and quantitative. A clinical examination can and should be standardized.”
A standardized test
To quantify tibial translation in patients using an app, Musahl and the co-researchers first developed and tested a standardized pivot shift test. Twelve orthopedic surgeons from different centers visited the researchers’ institution and each performed their preferred pivot shift test technique, according to Musahl. They formulated a standardized pivot shift test based on previous literature and the translation and acceleration of each surgeon’s technique. The results of the standardized test showed less variability of translation and improved accuracy, according to Musahl.
A pivot shift test in the training room is shown. Stickers are visible on the knee and are tracked by the iPad app.
Images: Musahk V
The researchers also created a simple image analysis to track the lateral knee, but they felt motion artifacts and time-intense post-hoc limited the technique, they wrote in their abstract.
“We had previously developed a simple image analysis which is based on quantifying translation of the lateral knee with markers on the lateral epicondyle, Gerdy’s tubercle and fibular head,” Musahl said. “The video is recorded and then reported image by image into the software and markers then get recorded image by image and can produce a translation code. This is labor-intensive and costs a lot to test.”
A screen shot of the pivot shift iPad app is pictured. In the upper left corner is the raw video. Second from the top is the filtered video. In the lower left is the marker center track. On the main screen is the translation (y axis) over time (x axis). The curve shows approximately 5.2-mm translation occurring at 1.5 seconds, depicting a “high-grade” pivot shift.
iPad app
Musahl and colleagues designed an iPad (Apple; Cupertino, Calif.) app through a Pittsburgh software company (Truefit; Cranberry, Pa.) that records video, checks marker motion and calculates translation codes. They tested the software on 34 consecutive patients who underwent anatomic ACL reconstruction for complete ruptures and were participants in the Prospective International Validation of Outcome Technology (PIVOT) study, a collaborative effort with surgeons from the Rizzoli Institute in Bologna, Italy; Kobe University in Kobe, Japan; Sahlgrenska University in Goteborg, Sweden; and their own institution.
The patients were examined under anesthesia, and investigators noted patients’ tibial translation during the pivot shift testing in their operative and nonoperative knees. The researchers found no pivot shift in 10 knees and too much leg movement, which caused false readings of a reduction, in four knees. In 20 patients with pivot shift in both knees, 10 patients had grade 1 pivot shift with an average anterior translation of 2.7 mm compared to 3.6 mm in patients with grade 2 pivot shift, which was a statistically significant difference, Musahl said. The researchers measured the contralateral knee as grade 0 in every patient on the iPad app.
“The quantitative pivot shift analysis could be used to define clinical grading of ACL injury and in the future, assess ACL graft function” Musahl said. – by Renee Blisard Buddle
Reference:
Hoshino Y. Knee Surg Sports Traumatol Arthrosc. 2013; doi: 10.1007/s00167-013-2396-0.
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Disclosure: Musahl has no relevant financial disclosures.