The Jobe’s Empty Can Test is a common orthopedic evaluation tool designed to assess the integrity of the shoulder joint, specifically focusing on the muscles of the rotator cuff. Clinicians use this maneuver to help identify the source of shoulder pain and weakness, particularly when a patient has difficulty with overhead movements. The test targets a single, small muscle and its tendon, making it a staple in the initial clinical assessment of potential rotator cuff injuries.
The Targeted Muscle and Test Mechanics
The Jobe’s Empty Can Test is designed to isolate the supraspinatus muscle, one of the four muscles that comprise the rotator cuff. Located in the top part of the shoulder blade, the supraspinatus plays a primary role in initiating the movement of raising the arm away from the body (abduction). Although the deltoid muscle provides the majority of lifting power, the supraspinatus is responsible for the first 15 to 20 degrees of motion and stabilizing the shoulder joint.
The test’s biomechanical rationale relies on placing the supraspinatus in a position of maximum stress. The “empty can” position involves elevating the arm to 90 degrees of abduction within the scapular plane (about 30 degrees forward from the side). The arm is then maximally internally rotated, turning the thumb downward as if pouring liquid out of a can. This rotation forces the supraspinatus tendon beneath the acromion bone, which can reproduce pain or demonstrate weakness if the tendon is inflamed, impinged, or torn.
Step-by-Step Procedure for the Test
The procedure begins with the patient sitting or standing comfortably. The clinician positions the affected arm by raising it to about 90 degrees of elevation in the scapular plane. The arm is then moved into the characteristic “empty can” position by fully rotating it inward so the thumb points toward the floor. This combination of abduction and internal rotation is necessary to properly stress the targeted structure.
Once the arm is positioned, the examiner places one hand on the patient’s forearm or elbow. The patient is instructed to actively hold the arm steady against a downward pressure applied by the clinician. The examiner gradually applies force downward, and the patient resists this pressure. The test is typically performed bilaterally, testing the unaffected shoulder first to establish a baseline for strength.
Interpreting Results and Test Limitations
A positive result is indicated by the patient experiencing sudden pain or a distinct inability to resist the applied downward pressure, showing noticeable weakness compared to the unaffected side. Pain during resistance suggests supraspinatus tendinopathy (irritation or inflammation) or subacromial impingement. Significant weakness, especially without severe pain, often suggests a complete or partial tear in the supraspinatus tendon.
The test is not a definitive diagnostic tool and has inherent limitations due to its variable diagnostic accuracy. Studies on reliability show a wide range: sensitivity (the ability to correctly identify a tear) ranges from 54% to 96%, and specificity (the ability to correctly rule out a tear) ranges from 30% to 68%. Because of these varied results, a positive test is typically used to raise suspicion for supraspinatus pathology, but it requires confirmation. Clinicians routinely use the Jobe’s test as one component of a comprehensive physical examination, often combining it with other specialized shoulder tests and imaging studies like an MRI for a precise diagnosis.