The infraspinatus test may not be used to screen for shoulder external rotator strength deficits among patients with shoulder pathology

Background: The infraspinatus test is often used to determine the presence of shoulder external rotator strength deficits. As the accuracy of this test has not been established adequately, the purpose of this study was to determine the accuracy of the infraspinatus test in detecting shoulder external rotator strength deficits. Methods: Sixty-two patients with a unilateral shoulder disorder underwent the infraspinatus test followed by instrumented assessment of shoulder external rotator muscle strength. The infraspinatus test was rated positive or negative based on the presence or absence of a strength deficit on the involved compared with the uninvolved shoulder. The instrumented strength assessment was rated positive or negative based on 4 cutoff thresholds for the presence of a strength deficit on the involved side: ≥10%, ≥15%, ≥20%, or ≥30%. The Sensitivity, specificity, positive and negative likelihood ratio of the infraspinatus test was determined based on each cutoff threshold. Results: Sensitivity ranged from 52.5 to 61.1%, specificity ranged from 72.7 to 90.9%, the positive likelihood ratio ranged from 2.24 to 5.77, while the negative likelihood ratio ranged from 0.52 to 0.59. Conclusions: As considerable external rotator strength deficits may frequently exist among patients with a negative infraspinatus test, this test may not serve a good screening test for external rotator strength deficits. Contrarily, clinicians can be reasonably certain of the presence of an external rotator strength deficit given a positive infraspinatus test.