Anatomy and Movements of the Upper Limb

Scapular Landmarks and Movements

The scapula is a flat, triangular bone with several critical landmarks that facilitate muscle attachment and joint stability. The glenoid cavity is a shallow depression that serves as the articulation site for the humerus. Surrounding this area are three fossae (depressions) that house the rotator cuff muscles:

1. Supraspinous fossa (located posteriorly).
2. Infraspinous fossa (located posteriorly).
3. Subscapular fossa (located anteriorly).

The spine of the scapula acts as a ridge separating the two posterior fossae, while the acromion and coracoid processes serve as major muscle attachment points.

Because the scapula is not a fixed bone but moves against the posterior rib cage, it undergoes several distinct movements:

• Protraction: Moving the scapula laterally and anteriorly (e.g., punching forward).
• Retraction: Moving the scapula medially toward the spine (e.g., pulling shoulders back).
• Elevation: Moving the scapula superiorly (e.g., shrugging).
• Depression: Moving the scapula inferiorly.

The Humerus and the Glenohumeral Joint

The humerus is the long bone of the upper arm. Its proximal end articulates with the scapula at the glenohumeral joint. Because the glenoid cavity is quite shallow, this ball-and-socket joint offers an exceptional range of motion but is inherently unstable.

Humerus Landmarks

The humerus features several landmarks essential for movement and clinical importance:

• Anatomical Neck vs. Surgical Neck: The anatomical neck is located at the epiphyseal plate, separating the head from the shaft (diaphysis). Distal to this is the surgical neck, a narrower region that is a common site for fractures.
• Epicondyles: The medial epicondyle is the attachment site for most anterior forearm flexors, while the lateral epicondyle serves the posterior forearm extensors.
• Distal Articulations: The distal end of the humerus features the capitulum (which articulates with the radius) and the trochlea (which articulates with the ulna).
• Olecranon Fossa: A deep depression on the posterior side that accommodates the ulna during elbow extension.

Movements of the Upper Arm

The glenohumeral joint allows for a wide variety of movements:

• Flexion and Extension: Moving the arm forward and backward.
• Abduction and Adduction: Moving the arm away from or toward the midline of the body.
• Internal and External Rotation: Turning the humerus toward or away from the body's midline.

The Forearm: Radius and Ulna

The forearm consists of two bones: the radius and the ulna. To remember their positions, remember that the radius is on the thumb side and the ulna is on the pinkie side.

Forearm Landmarks

The two bones are connected by the interosseous membrane, which helps facilitate rotation.

• The Ulna: Features a radial notch, which is a smooth surface where it articulates with the radius. The ulna aligns with the medial epicondyle and the trochlea of the humerus.
• The Radius: Aligns with the lateral epicondyle and the capitulum.

Pronation and Supination

One of the most unique movements of the forearm is the rotation of the radius around the ulna at the radioulnar joints.

• Supination: The palm faces anteriorly (anatomical position).
• Pronation: The palm faces posteriorly.

Mnemonic Tip: To remember which bone is which, remember: "Rad Cap, Lad" — the Radius aligns with the Capitulum, and the uLna aligns with the meDial epicondyle/trochlea.

The Wrist and Hand

Distal to the forearm are the carpals (8 bones), metacarpals (5 bones), and phalanges (14 bones).

The radiocarpal joint (the wrist) is a condyloid joint that allows for flexion, extension, abduction, and adduction. The joints of the fingers include the metacarpophalangeal joints (knuckles) and the interphalangeal joints (proximal and distal).

The first digit of the hand is the thumb, correctly known as the pollex. When studying the carpals, a common mnemonic for the proximal and distal rows is: "Some Lovers Try Positions That They Can’t Handle".