The assessment of shoulder integrity relies on specific physical examination tests performed by clinicians. These maneuvers help pinpoint the source of pain or weakness within the shoulder joint. The shoulder’s range of motion is stabilized by the rotator cuff, a group of four muscles and their tendons. A thorough physical exam uses specialized techniques to test the strength and function of this muscle group to determine if symptoms are caused by inflammation, tendon injury, or a muscle tear.
The Original Jobe Test Technique
The terms “Jobe Test” and “Empty Can Test” describe the same maneuver used to assess the integrity of the supraspinatus tendon. This test isolates the supraspinatus muscle, which initiates arm movement away from the body.
The patient’s arm is moved into 90 degrees of abduction and 30 degrees of forward flexion (the scapular plane). The arm is then maximally internally rotated so the thumb points toward the floor, mimicking the motion of emptying a can. This characteristic position is what gives the test its popular name.
The examiner applies downward resistance to the forearm or wrist, and the patient resists this force. The internal rotation brings the supraspinatus tendon further under the acromion bone, increasing mechanical tension and potential impingement. This positioning attempts to isolate the supraspinatus muscle while minimizing the contribution of the deltoid muscle.
Interpreting the Test Results
A positive result is noted when the patient experiences pain, muscle weakness, or both, while resisting the downward pressure. Clinicians must differentiate between these two responses, as each suggests a different underlying pathology within the supraspinatus unit. Results are typically compared to the patient’s unaffected arm to establish a baseline.
Pain during the maneuver, without significant weakness, often suggests tendinopathy or subacromial impingement syndrome. This pain is usually localized to the subacromial region, indicating the tendon is irritated or compressed as it passes beneath the acromion bone.
Marked weakness is considered a more significant sign, suggesting a partial or full-thickness tear of the supraspinatus tendon. The test’s accuracy in detecting a torn tendon is greatest when weakness is the main indicator. When weakness is the criterion for a positive result, the Empty Can Test has an accuracy of approximately 70% in detecting a full-thickness tear.
The Full Can Modification and Clinical Application
The “Full Can” modification was developed as an alternative to address the pain provocation inherent in the Empty Can position. The Full Can Test uses the same 90 degrees of abduction and 30 degrees of forward flexion, but the arm is held in external rotation, with the thumb pointing upward.
The biomechanical rationale is that external rotation moves the supraspinatus tendon away from potentially impinging structures under the acromion. The original Empty Can position was often painful, potentially leading to inaccurate results due to pain inhibiting muscle strength. By reducing pain, the Full Can modification allows for a cleaner assessment of true muscle strength.
Research suggests the Full Can Test is less pain-provoking than the Empty Can Test. The diagnostic accuracy for detecting a supraspinatus tear based on muscle weakness is comparable between the two methods. When weakness is the indicator, the Full Can Test has a slightly higher reported accuracy, around 75%.
Many clinicians prefer the Full Can modification today because it offers similar diagnostic utility for detecting a tear while being more tolerable for the patient. The subtle difference in arm rotation—thumb down (Empty Can) versus thumb up (Full Can)—represents a refinement aimed at improving patient comfort and strength assessment reliability.