The “Beer Can Test,” formally known as the Empty Can Test or Jobe’s Test, is a common clinical assessment used by physical therapists and orthopedic specialists to evaluate the integrity of a specific muscle group in the shoulder. This examination helps medical professionals identify potential issues, specifically looking for signs of injury or weakness within the rotator cuff. The test isolates a key structure to determine if a patient’s pain or limited function is related to that area. It is one piece of the diagnostic puzzle when a patient presents with shoulder pain, weakness, or reduced range of motion.
The Target Muscle: The Supraspinatus
The Beer Can Test is designed to place maximal stress on the supraspinatus muscle and its tendon, which is part of the four-muscle rotator cuff group. This muscle originates in the supraspinous fossa on the back of the shoulder blade (scapula). Its tendon travels through a narrow space underneath the acromion before attaching to the upper part of the humerus (arm bone). The supraspinatus is responsible for initiating arm abduction, which is the act of lifting the arm out to the side. It is most active during the first 15 degrees of this movement before the larger deltoid muscle takes over.
The muscle also plays a significant role in stabilizing the shoulder by pulling the head of the humerus inward toward the joint socket. Because the tendon passes through a limited space beneath the acromion, the supraspinatus is particularly vulnerable to injury. Repetitive overhead use, trauma, or degenerative changes can lead to inflammation, tendinopathy, or a tear in this tendon.
How the Test is Performed
The procedure for the Empty Can Test is specific to ensure the supraspinatus is isolated during the assessment. The patient stands or sits while the clinician faces them, positioning the arm in an alignment that maximizes stress on the target tendon. The arm is first raised to 90 degrees of forward elevation in the scapular plane, which is about 30 degrees forward from the side of the body. The patient then rotates the arm fully inward so that the thumb points toward the floor.
This thumb-down position gives the test its informal name, mimicking the action of pouring out a can. This internal rotation is a deliberate maneuver that causes the supraspinatus tendon to become compressed beneath the acromion, isolating it for examination. The clinician stabilizes the shoulder and then applies a downward force to the patient’s forearm. The patient is instructed to resist this downward pressure, causing the supraspinatus to contract forcefully. The clinician often compares this resistance to the patient’s opposite arm to detect any unilateral weakness.
Understanding the Results and Clinical Significance
The Empty Can Test is considered positive if the patient experiences significant pain or noticeable weakness while resisting the clinician’s downward pressure. Pain alone may suggest inflammation of the tendon (supraspinatus tendinopathy) or general shoulder impingement syndrome, typically felt in the subacromial region. The presence of significant weakness is more suggestive of a physical tear in the supraspinatus muscle or tendon. This weakness can range from a partial-thickness tear to a full-thickness rupture and is a more reliable indicator of structural injury than pain alone.
While the test is a valuable screening tool for suspected rotator cuff issues, its diagnostic accuracy is limited when used in isolation. It is most effective when combined with a patient’s medical history and other specific shoulder assessments to form a comprehensive diagnostic picture. A positive result requires further evaluation, often including imaging tests like Magnetic Resonance Imaging (MRI), to confirm the nature and extent of the injury. If a diagnosis confirms a supraspinatus injury, initial management often focuses on non-surgical treatments. This generally includes rest, anti-inflammatory medications to manage pain and swelling, and a structured physical therapy program aimed at restoring range of motion and strengthening the rotator cuff muscles.