## Most Common Rotator Cuff Tear: Supraspinatus **Key Point:** The supraspinatus is the most frequently torn rotator cuff muscle, accounting for approximately 50–70% of all rotator cuff tears. ### Anatomical Basis **High-Yield:** The supraspinatus is vulnerable because: - It lies in the supraspinous fossa, a relatively narrow space - It passes under the acromion and coracoacromial ligament, creating a narrow subacromial space - It is subject to chronic impingement during overhead activities - The critical zone (an area of relatively poor blood supply near its insertion on the greater tuberosity) is prone to degenerative changes ### Frequency of Rotator Cuff Tears by Muscle | Muscle | Frequency (%) | Mechanism | | --- | --- | --- | | Supraspinatus | 50–70 | Impingement, degenerative, trauma | | Infraspinatus | 20–30 | Often associated with supraspinatus tears | | Subscapularis | 10–15 | Less common; often from anterior dislocation | | Teres minor | <5 | Rare; usually with massive tears | ### Clinical Correlation **Clinical Pearl:** Supraspinatus tears present with: - Loss of active abduction ("drop arm" sign) - Weakness in the first 15–20° of abduction - Positive "empty can" test (Jobe's test) - Chronic shoulder pain, especially at night **Mnemonic:** **SITS** = Supraspinatus, Infraspinatus, Teres minor, Subscapularis. The first letter (S) is the most common tear. ### Why Supraspinatus? The supraspinatus occupies the smallest space relative to its workload and is compressed between the humeral head below and the acromion above, making it susceptible to both acute traumatic tears and chronic degenerative tears from repetitive overhead activities or age-related degeneration. [cite:Gray's Anatomy 42e Ch 7]
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