Percussion test: description and diagnostic accuracy of a new manual test for bone marrow edema of the knee

Background Prompt diagnosis of bone marrow lesion (BML) is difficult but critical for correct treatment. Magnetic resonance imaging is the gold standard, although expensive and time consuming. Simple and reliable clinical test for BML detection is lacking. Aim of the study is to describe a new manual clinical test called Percussion Test (PT) and to statistically determine its diagnostic accuracy in BML, compared to MRI imaging. Methods After evaluation of the inclusion and exclusion criteria, 218 consecutive patients with unilateral knee pain and age comprised between 18 and 80 years old were enrolled in our observational prospective study. Informed consent was obtained for each patient. After medical history collection, PT was performed by a single operator as described. MRI was performed in the affected knee to detect the presence of BML. Coherence in PT and MRI assessment was evaluated in each quadrant of the knee via contingency tables, as sensitivity, specificity, NPV, PPV and diagnostic accuracy were calculated. Results No correlation with a positive PT was demonstrated for the covariables gender (p = 0.156), age (p = 0.272) and BMI (p = 0.639). PT showed a sensitivity ranging from 60.6 (40.6-80.6) to 79.5 (63.0-96.0) and a specificity ranging from 85.7 (80.0-91.5) to 96.0 (93.1-98.9) depending on knee quadrant. Diagnostic accuracy ranged from 81.6 (75.9-86.6) to 89.4 (84.6-93.2), and p-value was < 0.00001 in a chi-squared analysis for all quadrants. Conclusions PT showed sensitivity and specificity values that are comparable with other clinical tests routinely adopted in clinical practice. In the absence of other reliable clinical test, PT has the potential to become a useful bedside tool in the diagnosis and management of BMLs.