Accuracy of the Tuning Fork Test for Determination of Presence and Location of Tibial Stress Fractures in a Military Training Population.

Abstract

Stress fractures or bone stress injuries arise from trauma or overuse, often as a result of rapid increase in training. This rapid increase in training occurs frequently as military recruits begin their entry-level training, as many individuals are not accustomed to the level of activity required during boot camp. Tibial stress fractures are the most common bone stress injuries in the military setting. MRI is the gold standard test for identification of stress fractures, but MRI may not be available in field settings. Although limited evidence has suggested that a vibrating tuning fork may be beneficial in determining the presence of a stress fracture, the tuning fork has become a frequent tool used to detect or diagnose stress fractures. Military personnel with suspected unilateral tibial stress fractures were asked to participate in evaluation of tuning forks as a diagnostic tool, in addition to receiving standard diagnostics and treatment. Points of maximal shin tenderness to palpation and vibration, followed by the application of a tuning fork, were evaluated. Each service member also underwent an abbreviated MRI evaluation with a 1.5T magnet consisting of coronal and sagittal STIR (Short Tau Inversion Recovery) and T1 (weighted longitudinal relaxation time) sequences. The results of tuning fork testing were compared to the MRI findings, considering grade 1 changes on MRI to represent a true stress fracture. A two-by-two table was used to determine the performance of tuning fork testing, relative to MRI findings, applying conventional definitions of sensitivity, specificity, positive predictive value, and negative predictive value. Among 63 male active duty members with suspected tibial stress fractures, 39 had MRI-confirmed stress fractures. Tuning fork testing, relative to MRI, demonstrated overall sensitivity of 61.5%, specificity of 25.0%, positive predictive value of 57.1%, and negative predictive value of 28.6%. A sub-analysis restricting to grade 3 and grade 4 MRI findings did not improve the diagnostic performance of tuning forks. The tuning fork is an ineffective tool for diagnosing tibial stress fractures.