Overview of humerus, scap, and wrist muscles***

Muscles and Motion of the Upper Limb

Humerus and Scapula Functions

  • Humerus: Principal bone in the upper arm.
  • Scapula: Provides attachment points for various muscles and allows motion of the shoulder joint.
      - Key Actions: Rotation, protraction, retraction, elevation, and depression of the scapula.

Scapulothoracic Movements

  • Basic motion types:
      - Protraction: Moving the scapulae away from the spine (bone moves forward).
      - Retraction: Moving the scapulae towards the spine (bone moves backward).
      - Elevation: Lifting the shoulder blades upwards (shrugging).
      - Depression: Lowering the shoulder blades downwards.

Scapular Depression and Transfer from Wheelchair

  • When transitioning from a seated position to standing (e.g., from a wheelchair), individuals often:
      - Press down on elbows to lift the trunk.
      - This motion requires scapular depression, which utilizes gravity and muscle contraction to stabilize and lift.

Muscle Contributions to Scapula Motion

  • Major muscles affecting scapula movements:
      - Pectoralis Major: Acts as a depressor.
      - Lower Trapezius: Assists in scapular depression.
      - Levator Scapulae: Functions as an elevator.
      - Rhomboids: Responsible for scapular retraction.
      - Serratus Anterior: Plays a role in protraction.

Shoulder Girdle and Degrees of Freedom

  • The shoulder girdle is uniquely connected to the trunk by the sternoclavicular joint (SC joint):
      - Essentially the only solid bony connection to the trunk.
  • Degrees of Freedom: Three degrees, allowing for motion in all planes.

Scapulohumeral Rhythm

  • Defined as the relationship between humeral elevation and scapular rotation:
      - The humerus moves twice as much as the scapula (2:1 ratio).
      - Specifically, for every 120 degrees of shoulder elevation, there is typically 60 degrees of scapular upward rotation leading to a total of approximately 180 degrees of overhead lifting motion.

Muscle Actions for Internal and External Rotation

  • Internal Rotators:
      - Subscapularis: A rotator cuff muscle that assists with internal rotation.
      - Teres Major: Another significant internal rotator.
  • External Rotators:
      - Infraspinatus: A rotator cuff muscle primarily responsible for external rotation.
      - Teres Minor: Works alongside infraspinatus for external rotation.

Shoulder Blade Movement during Exercises

  • Retractors (to pull shoulder blades together):
      - Rhomboids: Primary retractors.
      - Middle Trapezius: Also aids in retraction.
      - Upper Trapezius: Contributes, but less so than the others.
  • Understanding how muscles pull on the scapula and the humerus is critical for proper exercise and rehabilitation techniques.

Differentiating between Muscular Roles

  • Important to distinguish which muscles move the humerus versus those that move the scapula to understand their functional contributions:
      - Approximately five key muscles for scapular motion and shoulder movements (including variations of trapezius and rhomboids).

Elbow and Forearm Dynamics

  • Elbow Flexors:
      - Biceps Brachii: Strong elbow flexor; dual role at the shoulder as a weak flexor but a strong supinator when contracted.
      - Brachialis: A monoarticular muscle, strictly acts on the elbow without influence on the shoulder or forearm rotation.
      - Brachioradialis: Assists in flexing the elbow; acts to return the forearm to a neutral position from either supination or pronation.

  • Triceps Brachii (elbow extensor):
      - Composed of three heads:
        - Long Head: Crosses the shoulder joint; can assist in shoulder abduction.
        - Medial and Lateral Heads: Biarticular, work strictly at the elbow.
      - Inserts on the olecranon of the ulna, allowing elbow extension.

Pronation and Supination Mechanism

  • Proninators:
      - Pronator Teres: Two-headed muscle affecting pronation at the radioulnar joint; assists in flexing the elbow.
      - Pronator Quadratus: Located distally, acting exclusively on the radioulnar joint.

  • Supinators:
      - Biceps Brachii: Major supinator of the forearm; its action is facilitated by its insertion on the radial tuberosity.
      - Supinator Muscle: Specifically designed for supination, working from the lateral side of the forearm.

Common Injuries and Conditions

  • Tennis Elbow (Lateral Epicondylitis): Inflammation of lateral extensors often occurs due to overuse; common in racquet sports.

  • Medial Epicondylitis: Often resulting from overflexing motions in sports like baseball pitching;

  • Carpal Tunnel Syndrome: Involves compression of the median nerve within the carpal tunnel (formed by carpal bones and ligaments). Symptoms include numbness and pain in areas innervated by the median nerve.

Anatomy of the Wrist and Hand

  • Wrist Joints: Composed of carpal bones, metacarpals, and phalanges mirroring foot anatomy structure:
      - Proximal Row of Carpal Bones: Scaphoid, Lunate, Triquetrum, Pisiform.
      - Distal Row of Carpal Bones: Trapezium, Trapezoid, Capitate, Hamate.

  • Common Injuries: Include overuse syndromes like tendinitis or fractures related to wrist movements and repetitive activities.

  • Nerve Considerations: Important nerves in wrist innervation include:
      - Median Nerve: Enters through the carpal tunnel; affected during carpal tunnel syndrome.
      - Ulnar Nerve: Not passing through the carpal tunnel, providing sensation on the ulnar side of the hand.