The rotator cuff is a complex group of four muscles and their tendons that surround the shoulder joint, providing stability and allowing for a wide range of motion. These muscles—the supraspinatus, infraspinatus, teres minor, and subscapularis—work together to keep the upper arm bone (humerus) centered within the shallow socket of the shoulder blade. Because shoulder pain can arise from many different structures, specific testing is necessary to determine if the rotator cuff is the source. Assessing an injury involves evaluating symptoms, specialized physical maneuvers, and medical imaging for confirmation.
Recognizing Symptoms and Functional Limitations
A person with a rotator cuff injury often experiences a dull ache that feels deep inside the shoulder. This discomfort frequently worsens at night, especially when lying on the affected side, and can be disruptive to sleep. The pain is often felt not only in the shoulder itself but may also travel down the side of the arm, though it typically does not extend past the elbow.
Functional limitations are a common sign, involving difficulty raising the arm overhead or reaching behind the back, such as when dressing or combing hair. Some individuals report a crackling or popping sensation, known as crepitus, when moving the shoulder. The nature of the pain helps distinguish injury types: an acute tear, often caused by a sudden fall or heavy lift, typically presents with immediate and severe pain and weakness. Conversely, chronic tears or tendinopathy develop gradually, with symptoms worsening slowly over months or years.
Specific Physical Examination Maneuvers
Clinical testing involves specific maneuvers designed to isolate and stress the individual tendons of the four muscles. These tests assess both the strength and the pain response, helping a healthcare professional pinpoint the location and severity of the potential tear. While these examinations are informative, they should be performed gently and interpreted by a clinician, as aggressive attempts can aggravate an existing injury.
The Empty Can Test, also known as Jobe’s test, evaluates the integrity of the supraspinatus tendon, the most frequently injured rotator cuff muscle. This test is performed with the arm lifted to a 90-degree angle in the scapular plane (about 30 to 45 degrees forward from the side). The patient rotates the arm so the thumb points downward, simulating the action of emptying a can. A positive result occurs if the patient experiences pain or weakness when resisting a downward pressure applied by the examiner.
To assess the subscapularis, the largest and strongest of the four muscles, clinicians commonly use the Lift-Off Test. The patient places the back of the hand against the mid-lumbar spine. The patient is then instructed to lift the hand away from the back. An inability to actively lift the hand off the back, or significant weakness when resisting a push toward the back, suggests a tear or dysfunction of the subscapularis tendon.
Testing the posterior muscles, the infraspinatus and teres minor, involves assessing the strength of external rotation. One common method is the External Rotation Lag Sign. The examiner passively moves the patient’s arm into a position of near-maximal external rotation, with the elbow bent to 90 degrees. A positive result occurs if the patient is unable to actively hold that position when the examiner releases the wrist, causing the arm to drift inward.
The Hornblower’s Sign is another test for these muscles. It is performed with the arm abducted to 90 degrees and the elbow bent to 90 degrees, where the patient resists a force attempting to push their hand inward.
Medical Imaging for Definitive Diagnosis
Following the physical examination, medical imaging is used to confirm the diagnosis, determine the exact size of any tear, and exclude other causes of shoulder pain. The first imaging step is usually an X-ray, although it cannot visualize the soft tissues of the rotator cuff. X-rays are useful for identifying bone spurs, arthritis, or fractures that might be contributing to the patient’s symptoms.
For visualizing the soft tissues, an ultrasound is often employed as a first-line diagnostic tool after X-rays. This technology uses sound waves to produce real-time images of the tendons and muscles, allowing the clinician to assess the cuff during movement. Ultrasound is particularly effective for distinguishing between a partial-thickness tear, where the tendon is frayed but not completely separated, and a full-thickness tear, where the tendon has separated from the bone.
The gold standard for comprehensive assessment of the rotator cuff and surrounding structures is the Magnetic Resonance Imaging (MRI) scan. MRI uses radio waves and a strong magnetic field to create detailed images that accurately determine the size, location, and chronicity of tears. This imaging provides a clear picture of the muscle quality and any associated issues, such as fluid accumulation or surrounding structural damage. A complete diagnosis and effective treatment plan rely on combining the information gathered from the patient’s symptoms and physical exam with these precise structural details.