Park et al. reported that the combination of painful arc sign, drop-arm sign, and infraspinatus muscle test yields what approximate post-test probability for ruling in a full-thickness rotator cuff tear?

• A. 75%
• B. 91%
• C. 60%
• D. 80%

Answer: (B)

When you add multiple positive clinical tests that all point to the same pathology, your confidence in that diagnosis increases substantially. In this scenario, the painful arc sign, the drop-arm sign, and the infraspinatus muscle test each relate to the rotator cuff, and when all three come back positive, they reinforce the same underlying problem: a full-thickness rotator cuff tear.

The combined result pushes the probability that a full-thickness tear is present to about 91%. In other words, after seeing all three positive findings, roughly nine out of ten of these patients truly have the tear. The reason this is so convincing is that each test contributes information that increases the odds, and together they dramatically raise the likelihood beyond what any single test would provide.