Topic Overview

Clinical Anatomy of Scapular Muscles

1. Deltoid

• Axillary nerve injury (fracture of surgical neck of humerus, inferior dislocation of shoulder):

  • Paralysis of deltoid.

  • Loss of abduction beyond 15°.

  • Flattening of shoulder contour.

  • Loss of skin sensation over regimental badge area.

• Safe IM injection site → middle of deltoid belly (avoid axillary nerve & posterior circumflex humeral vessels).

2. Supraspinatus

• Rotator cuff syndrome (painful arc syndrome):

  • Most commonly torn tendon in rotator cuff injuries.

  • Pain during abduction (60°–120°).

• Calcific tendinitis → calcium deposition in tendon → painful abduction.

• Suprascapular nerve entrapment → weakness of initiation of abduction.

3. Infraspinatus

• Injury to suprascapular nerve (at spinoglenoid notch):

  • Isolates infraspinatus.

  • Weakness of lateral rotation of arm.

• Tear of tendon → difficulty in external rotation.

4. Teres Minor

• Axillary nerve palsy:

  • Paralysis of teres minor + deltoid.

  • Loss of abduction and external rotation.

• Selectively tested by resisted external rotation in adduction.

5. Teres Major

• Not part of rotator cuff (does not stabilize joint).

• Forms posterior axillary fold (with latissimus dorsi) → palpable landmark in axilla.

• Lower subscapular nerve injury → weakness of adduction and medial rotation.

6. Subscapularis

• Part of rotator cuff (anterior stabilizer).

• Tendon tear → increases risk of anterior dislocation of humeral head.

• Weakness of medial rotation and adduction.

• Tested clinically by lift-off test (patient lifts hand off back → if weak → subscapularis lesion).

7. Rotator Cuff as a Group

• Function → stabilize humeral head in glenoid cavity during movement.

• Rotator cuff tear (SITS muscles):

  • Common in elderly & athletes.

  • Leads to painful abduction, weakness of rotation, instability of shoulder joint.

• Sites of entrapment & nerve involvement:

  • Suprascapular nerve → supraspinatus, infraspinatus weakness.

  • Axillary nerve → deltoid, teres minor paralysis.

• Clinical tests:

  • Empty can test → supraspinatus tendon integrity.

  • External rotation test → infraspinatus/teres minor.

  • Lift-off test → subscapularis.