Study Notes on Scapular Motion and Joint Mechanics

The role of upward rotators in scapula motion and control.
Gravity's influence on downward rotators.
- Upward rotation of the scapula pulls it into upward rotation for increased motion.
- Gravity facilitates downward rotation when in an upright position, causing upward rotators to eccentrically lengthen to control the motion.
- In a lying position (e.g., making a snow angel), gravity does not affect scapular motion. Upward rotators must work against gravity only during upward movements.

Upward Rotators:
- These muscles contract during upward rotation and must control downward rotation eccentrically.
Downward Rotators:
- Typically not active in standing but are engaged when gravity's pull is neutralized (e.g., lying down).

Upward Rotation:
- In anatomical position to glenoid fossa pointing toward the ceiling.
Downward Rotation:
- From upward rotation back to anatomical position. The scapula can rotate past anatomical position with specific movements (e.g., arm behind the back).

For instance, in a lat pull down exercise:
- Downward rotators work against gravity when pulling against resistance.
- Important muscles include rhomboids, levator scapulae, and pectoralis minor.

Scapular Tilt:
- Occurs when the scapula's bottom edge moves away from the rib cage during hyperextension.
- The top of the scapula may rise over the ribcage during this motion.
Scapular Winging:
- Noted when the medial border lifts off the rib cage; often relates to the serratus anterior's inability to maintain position due to weakness or dysfunction.

The shoulder girdle's greater need for ligaments due to shallow joint structure.
- Muscles and ligaments maintain the arm's attachment to the body, which is crucial due to the shoulder joint's shallowness.

The proximal head of the humerus (larger) fits into the giblet fossa (smaller):
- Includes greater tubercle, lesser tubercle, bicipital groove, and surgical neck (weakest part).
Rotator Cuff Muscles:
- Attach at tubercles, stability in glenohumeral joint; include:
- Greater Tubercle:
  - Supraspinatus: initiates shoulder abduction.
  - Infraspinatus: responsible for external rotation.
  - Teres Minor: external rotation.
- Lesser Tubercle:
  - Subscapularis: responsible for internal rotation.

The joint capsule's structure allows for the necessary movement of the joint.
The capsule tightens under load and follows prescribing rules of arthrokinematics.
In flat motions, a loose joint capsule allows increased mobility necessary for function but can lead to conditions like frozen shoulder (adhesive capsulitis).

Bursa (small sacs) fill with synovial fluid to reduce friction during movement, especially in high-friction areas.
When a bursa is inflamed, it can result in pain (bursitis).