2025 ISAKOS Biennial Congress Paper
Digital Glide Test: A New Measurement Technique To Quantify Patellar Translation
Miho J. Tanaka, MD, PhD, Boston, MA UNITED STATES
Nikitha Crasta, MBBS, Cambridge, MA UNITED STATES
Maria Virginia Velasquez-Hammerle, MD, Boston, MA UNITED STATES
Kyle K Grover, BS, New Hartford, NY UNITED STATES
Massachusetts General Hospital, Harvard Medical School, Boston, MA, UNITED STATES
FDA Status Not Applicable
Summary
The digital glide test was performed to assess patellar translation and was found to differentiate between knees with and without patellar instability with high accuracy.
Abstract
In the diagnosis of patellar instability, dynamic assessment is critical in evaluating patellar translation. Despite the advent of sensitive imaging modalities such as MRI, surgeons still rely on physical examinations such as the glide test to quantify patellar translation; however, this technique is subjective and can have limited reliability. Therefore, the purpose of this study was to evaluate the utility of the digital glide test in evaluating patellar translation during the assessment of patellar instability.
Patients with symptomatic patellar instability were included in this study and compared to knees without patellar instability. Using digital video held 12 inches above the knees, the patellar glide test was performed to assess for lateral patellar translation. Images were captured in unloaded and loaded positions, and patellar translation was quantified as percentage of patellar width. Descriptive statistics were used to describe lateral translation and were compared between symptomatic and asymptomatic knees. For each measurement of translation, receiver operating characteristic (ROC) curve analysis was performed, with area under the curve (AUC) >0.7 indicating good diagnostic ability of the test. Youden’s J statistic was calculated to determine the optimal cutoff values to distinguish between asymptomatic vs symptomatic knees.
83 knees from 51 patients were included in this study, of which 43 knees had patellar instability and the remainder had no symptoms of instability. When comparing stable and unstable knees, lateral patellar translation was greater in the symptomatic group (28.8+/-11.4% vs 15.2+/-4.5%, p<0.001). ROC curve analysis demonstrated that patellar translation >24% detected the presence of patellar instability with AUC 0.82 (95% CI 0.73, 0.92). 24% translation was found to identify patellar instability with sensitivity 62.8%, specificity 100%, PPV 100%, and NPV 69.2%.
The digital glide test was found to differentiate between knees with and without patellar instability with high accuracy. In this study, knees with >24% translation (ie, greater than approximately one quadrant of the patella) were found to be unstable. As dynamic assessment of patellar translation is critical during evaluation of patellofemoral disorders, utilization of digital measurement techniques during physical examination may have a future role in the diagnosis and management of patellar instability.