Upper Limb Osteology and Joints: An Anatomical Overview

Stability here is provided by the acromioclavicular ligament and the powerful coracoclavicular ligament. The coracoclavicular ligament is specifically composed of two parts:

• Trapezoid ligament
• Conoid ligament

Clinical Note: AC Joint Separation Often caused by falling directly onto the shoulder, an acromioclavicular joint separation is graded based on the severity of the ligamentous injury and the degree of displacement between the clavicle and the acromion.

The Shoulder (Glenohumeral) Joint

The "true" shoulder joint is the glenohumeral joint, a ball-and-socket articulation. It consists of the head of the humerus articulating with the glenoid cavity of the scapula, which is supported by the glenoid lip (labrum).

This joint is highly mobile but inherently unstable, relying on several structures for support:

• Ligaments: Coracohumeral, glenohumeral, and the transverse ligament of the humerus.
• Muscles (Rotator Cuff): The supraspinatus, infraspinatus, and teres minor provide essential dynamic stability.

The range of motion is extensive, including flexion/extension (transverse axis), abduction/adduction (sagittal axis), and medial/lateral rotation (vertical axis).

Exam Tip: Shoulder Dislocation Approximately 90% of shoulder dislocations are "anterior," meaning the humeral head is displaced to the front of the body. These injuries carry a risk of damaging the brachial plexus.

The Elbow and Forearm

The elbow is a complex, compound joint involving three bones: the humerus, the radius, and the ulna. These bones form three distinct articulations within a single common capsule:

1. Humeroulnar joint: A uniaxial hinge joint formed by the trochlea of the humerus and the trochlear notch of the ulna.
2. Humeroradial joint: A spheroid joint formed by the capitulum of the humerus and the head of the radius.
3. Proximal radioulnar joint: A pivot joint formed by the articular circumference of the radius and the radial notch of the ulna.

Stability in the elbow is maintained by the ulnar collateral ligament, the radial collateral ligament, and the annular ligament, which encircles the head of the radius.

The Hand and Wrist

The skeletal structure of the hand is organized into three groups: the carpals (wrist), metacarpals (palm), and phalanges (fingers).

Carpal Anatomy

The carpal bones are arranged in two rows:

• Proximal row: Scaphoid, lunate, triquetrum, and pisiform.
• Distal row: Trapezium, trapezoid, capitate, and hamate.

The wrist contains several specialized plane joints:

• Midcarpal joint: Located between the proximal and distal rows.
• Intercarpal joints: Located between individual bones within the rows.
• Specific articulations: Such as the pisohamate and pisometacarpal joints.

The Carpal Tunnel

The structural integrity of the wrist is vital for protecting neurovascular structures. The carpal tunnel is a critical passageway formed by the carpal bones and the transverse carpal ligament (flexor retinaculum). It houses the median nerve and several tendons.

Clinical Note: Carpal Tunnel Syndrome Compression of the median nerve within this narrow space can lead to carpal tunnel syndrome, affecting sensation and motor function in the hand.