Rotator Cuff Tear

01Pathophysiology

The rotator cuff is a group of four muscles and their tendons that stabilize the glenohumeral joint: the supraspinatus, infraspinatus, teres minor, and subscapularis (often remembered by the mnemonic SITS). Each muscle has a distinct action. The supraspinatus initiates abduction (the first 15 degrees), the infraspinatus and teres minor perform external rotation, and the subscapularis handles internal rotation. Of these four, the supraspinatus is the most commonly torn, and it is the tendon that exam vignettes test most frequently.

The reason the supraspinatus is so vulnerable lies in its anatomy. Its tendon passes through the narrow subacromial space, sandwiched between the humeral head below and the acromion and coracoacromial ligament above. With repetitive overhead movements, the tendon is repeatedly compressed against the undersurface of the acromion, a process known as subacromial impingement. Over years, this mechanical irritation leads to tendinopathy, microtearing, and eventual macroscopic rupture.

A second contributing factor is the tendon's blood supply. The supraspinatus tendon has a "critical zone" of relative hypovascularity located approximately 1 cm proximal to its insertion on the greater tuberosity of the humerus. This watershed area receives poor perfusion, which impairs the tendon's ability to heal from repetitive microtrauma. This is why degenerative tears tend to occur at this exact location.

In younger patients, the mechanism is typically traumatic: a fall on an outstretched hand (FOOSH) or a sudden forceful abduction or deceleration injury (as in throwing athletes). These tears are usually acute, full-thickness, and involve otherwise healthy tendon tissue. In contrast, older patients develop tears gradually through the degenerative process described above, often presenting with insidious onset of weakness and pain.

The connection between pathophysiology and symptoms is direct. Because the supraspinatus initiates abduction, a full-thickness tear causes inability to maintain the arm in abduction (the drop arm sign). Pain occurs in the subacromial space during the mid-arc of abduction (60 to 120 degrees), because this is the range where the torn or inflamed tendon is maximally compressed under the acromion, producing the classic painful arc. Night pain results from the dependent position of the arm compressing the inflamed subacromial structures against the acromion while lying down.

02Classification and Clinical Manifestation

The distinction between acute traumatic and chronic degenerative tears is high-yield for exam purposes. A vignette describing a 25-year-old baseball pitcher with sudden shoulder pain and weakness after a forceful throw points to an acute traumatic tear requiring early surgical consultation. A vignette describing a 60-year-old with months of progressive shoulder pain and weakness during overhead reaching points to a chronic degenerative tear, where conservative management is tried first.

03Diagnostic Workup

The workup begins with a thorough physical examination. When a patient presents with shoulder pain and weakness, the examiner should test each rotator cuff muscle individually. The empty can test (Jobe test) is performed by having the patient abduct the arms to 90 degrees in the scapular plane (about 30 degrees forward of the coronal plane) with the thumbs pointing downward, then resist downward pressure. Pain or weakness indicates supraspinatus pathology. The drop arm test asks the patient to slowly lower the arm from full abduction; inability to control the descent (the arm drops suddenly) strongly suggests a full-thickness supraspinatus tear and is one of the most tested physical exam findings.

For imaging, the best initial test is a plain radiograph. While X-rays cannot directly visualize soft tissue tears, they are essential to rule out fractures, glenohumeral dislocation, and osteoarthritis. In chronic, large rotator cuff tears, the X-ray may reveal superior migration of the humeral head, because the torn supraspinatus no longer holds the humeral head down against the pull of the deltoid. This finding, when described in a vignette, is a strong clue pointing toward an advanced rotator cuff tear.

The most accurate test is MRI. It is ordered after the X-ray when a rotator cuff tear is clinically suspected. MRI provides detailed information about the tear type, the number of tendons involved, the degree of tendon retraction, and the presence of fatty infiltration of the muscle belly (a sign of chronicity that predicts poorer surgical outcomes). If the standard MRI is inconclusive, particularly for small partial-thickness tears on the articular side, MR arthrography with intra-articular gadolinium can increase diagnostic sensitivity.

04Management and Treatment

Management follows a logical decision tree that exam questions frequently test. The first decision point is whether the tear is partial or full-thickness, and the second is the patient's age and functional demand.

For partial-thickness tears and chronic degenerative full-thickness tears in older, low-demand patients, the next best step is conservative management. This includes oral NSAIDs for pain control (with gastroprotection if risk factors are present), activity modification (avoiding overhead movements), and a structured physical therapy program. Physical therapy is the cornerstone of conservative management and should target rotator cuff strengthening, periscapular muscle conditioning, and posterior capsule stretching. If pain prevents the patient from participating in physical therapy, a subacromial corticosteroid injection can be offered to reduce inflammation and facilitate rehabilitation. However, repeated steroid injections (more than 3 per year) should be avoided, as they can weaken the tendon and promote further tearing.

For full-thickness tears in young, active patients, or for acute traumatic tears, the next best step is surgical referral for arthroscopic repair. Early repair (within 3 to 6 weeks) is preferred in acute traumatic tears because delayed intervention allows the torn tendon to retract and the muscle to undergo fatty infiltration, both of which reduce the likelihood of a successful repair. Post-operatively, the arm is immobilized in a sling for 4 to 6 weeks, followed by a progressive rehabilitation protocol lasting 4 to 6 months.

Contraindications and special considerations: Corticosteroid injections should be used cautiously in patients with diabetes (they can acutely worsen glycemic control). NSAIDs should be avoided or used with caution in patients with chronic kidney disease, peptic ulcer disease, or cardiovascular risk. In patients who have failed conservative therapy and have an irreparable tear (commonly seen in chronic, retracted tears with advanced fatty infiltration), alternative surgical options such as tendon transfer or reverse total shoulder arthroplasty should be considered.

05Differential Diagnosis and Distractors

The single most tested differential on exams is adhesive capsulitis vs. rotator cuff tear. The critical distinguishing feature is passive range of motion. In a rotator cuff tear, the patient cannot actively raise the arm, but the examiner can passively move it through the full range. In adhesive capsulitis, both active and passive motion are restricted. When a vignette describes a patient whose shoulder "cannot be moved by the examiner," think adhesive capsulitis first.

06Traps and High-Yield Pearls

The most common way students miss rotator cuff tear questions is by confusing it with subacromial impingement syndrome. Both conditions cause shoulder pain with overhead activity and share positive impingement signs (Neer and Hawkins). The critical separator is weakness on strength testing. If the vignette states that the patient has pain but full strength, the answer is impingement. If the vignette includes weakness in abduction or external rotation, think rotator cuff tear.

A second frequent trap involves the drop arm test. Students sometimes associate any shoulder pain with a positive drop arm test, but this finding is characteristic of a full-thickness tear only. Partial tears and impingement will not produce a truly positive drop arm sign.

Another tested concept is the imaging sequence. Students may jump directly to MRI, but the best initial test remains a plain radiograph. The exam tests whether you know to order the X-ray first (to exclude fracture, dislocation, or arthritis) before moving to MRI for soft tissue evaluation. Selecting MRI as the first step, without an X-ray, is a common wrong answer.

Finally, watch for the vignette describing an older patient with a chronic full-thickness tear who is managing well with physical therapy. The exam may tempt you to select surgical repair, but in an elderly, low-demand patient with acceptable function, continued conservative management is correct. Surgery is reserved for young or active patients, acute traumatic tears, and those who have failed a proper trial of conservative therapy lasting at least 6 to 12 weeks.

The core competency being tested across rotator cuff tear questions is your ability to (1) distinguish a tear from impingement using strength testing, (2) differentiate it from adhesive capsulitis using passive range of motion, (3) order the correct imaging sequence, and (4) match the treatment plan to the patient's age, activity level, and tear characteristics.