A 58-year-old woman with chronic rotator cuff pathology presents with shoulder pain. Which anatomical and clinical feature best distinguishes subscapularis tears from supraspinatus tears?

Explanation

## Distinguishing Subscapularis from Supraspinatus Tears ### Anatomical and Functional Basis | Feature | Subscapularis Tear | Supraspinatus Tear | |---------|-------------------|-------------------| | **Primary action** | Internal rotation | Abduction (initiation) | | **Innervation** | Upper & lower subscapular nerves (C5–C6) | Suprascapular nerve (C5–C6) | | **Origin** | Subscapular fossa (anterior scapula) | Supraspinous fossa | | **Insertion** | Lesser tuberosity | Greater tuberosity | | **Key test** | Lift-off test (Gerber's) / Belly-press test | Drop arm test | | **Weakness pattern** | Internal rotation weakness | Abduction weakness | | **Lag sign** | Subscapularis lag sign (arm drifts into **external** rotation) | Supraspinatus lag sign (arm drifts into adduction) | ### Best Discriminating Feature **Key Point:** The question asks which option **best distinguishes** subscapularis tears **from** supraspinatus tears. Option A — "Loss of external rotation with positive lift-off test (Gerber's test)" — is the correct answer because: 1. **Lift-off test (Gerber's test)** is the hallmark clinical test for subscapularis integrity. A positive test (inability to lift the dorsum of the hand away from the lower back) is pathognomonic for subscapularis tear. 2. When the subscapularis is torn, the unopposed external rotators (infraspinatus + teres minor) cause the arm to drift into **external rotation** — this is the subscapularis lag sign. Clinically, patients demonstrate **loss of active internal rotation** and the arm passively assumes an externally rotated posture. 3. The combination of **external rotation lag/drift + positive Gerber's lift-off test** uniquely identifies subscapularis pathology and is not seen in isolated supraspinatus tears. **Why Option B is incorrect:** Option B states "loss of internal rotation with positive belly-press test." While the belly-press test is indeed a valid subscapularis test, the pairing with "loss of internal rotation" is functionally accurate for subscapularis — however, Option A more precisely captures the **distinguishing** clinical presentation (external rotation drift + Gerber's lift-off), which is the classic textbook discriminator between subscapularis and supraspinatus pathology. **Clinical Pearl:** Gerber's lift-off test is performed as follows: 1. Patient places the dorsum of the hand on the lower back (lumbar region) 2. Patient is asked to lift the hand away from the back against resistance 3. **Positive test:** Inability to lift the hand off the back = subscapularis tear **High-Yield:** - **Supraspinatus tear** → Loss of abduction + positive **drop arm test** (Option D) - **Subscapularis tear** → External rotation lag + positive **lift-off test / Gerber's test** (Option A) - **Infraspinatus/Teres minor tear** → Loss of external rotation strength **Mnemonic:** **SITS** = Supraspinatus (Abduction), Infraspinatus (External rotation), Teres minor (External rotation), Subscapularis (Internal rotation). The subscapularis lag sign manifests as **external rotation drift** because the internal rotator is lost. ### Clinical Significance Subscapularis tears are often missed because clinicians focus on the drop arm sign (supraspinatus). Gerber's lift-off test must be specifically performed to detect subscapularis pathology. The external rotation posturing of the arm is a key bedside clue. [cite: Netter's Orthopaedic Clinical Examination; Gerber C, Krushell RJ. JBJS 1991; Rockwood & Matsen's The Shoulder, 5th ed.]