Impact of Body Mass Index on the Accuracy of Physical Examination and MRI of the Shoulder

Abstract

Background: The physical examination of overweight patients can require specific adaptations. Orthopaedic literature on the impact of body mass index (BMI) on the physical examination of the shoulder is virtually nonexistent. Purpose: To assess whether BMI affects the sensitivity and specificity of common shoulder tests, using arthroscopy as a gold standard. We also examined the effects of BMI on the sensitivity and specificity of magnetic resonance imaging (MRI) of the shoulder for reference. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: We analyzed the data of 116 consecutive patients who underwent shoulder arthroscopy for the treatment of rotator cuff tears, Bankart lesions, and superior labral anterior-posterior (SLAP) lesions. Preoperative BMI, physical examination of the shoulder findings, and MRI findings were extracted. Contingency tables and receiver operating characteristic curves were used to evaluate the sensitivity and specificity of provocative tests of the shoulder and MRI as well as their relationship to BMI. Results: The sensitivity and specificity of the Jobe supraspinatus test were 77.8% and 72.7% in patients with BMI ≤25, 82.6% and 70.6% in those with 25 < BMI ≤ 30, and 81.3% and 55.6% in those with BMI >30, respectively ( P < .001). The apprehension and relocation tests demonstrated higher sensitivity and specificity for the overweight patients (25 < BMI ≤ 30) compared with the other BMI groups, with a sensitivity and specificity of 83.3% and 100% for the apprehension test and a sensitivity and specificity of 75% and 100% for the relocation test, respectively. The O’Brien, Speed, and Ebinger tests for SLAP tears had low accuracy and did not yield statistically significant results. MRI interpretation was found to be influenced by BMI in obese patients, especially when SLAP lesions were assessed. Conclusion: Counterintuitively, tests for shoulder instability had greater specificity in overweight patients and should be encouraged, particularly in obese patients, in whom the specificity of shoulder MRI for the detection of a Bankart lesion is lower. The Jobe test was more sensitive but less specific in overweight patients. These findings may assist care providers in improving the interpretation of the shoulder examination of overweight patients and consequently lead to better treatment-related decisions.