Upper extremity anatomy
Functional anatomy of the upper extremity
Shoulder region
Movement of the shoulder requires the glenohumeral joint (shoulder joint) and the scapular complex (shoulder girdle) to move together in a pattern called scapulohumeral rhythm. The shoulder region is composed of three primary bones: the humerus, scapula, and clavicle. The humerus and scapula form the glenohumeral joint, and the scapula and clavicle together make up the shoulder girdle. The clavicle articulates with the scapula at the acromioclavicular joint and with the sternum at the sternoclavicular joint.
Primary movements of the shoulder
- Shoulder flexion/extension
- Shoulder external rotation/internal rotation
- Shoulder abduction/adduction
- Scapular elevation/depression
- Scapular upward rotation/downward rotation
- Upward rotation accompanies arm elevation, as in overhead reaching, and is produced by the upper and lower trapezius and the serratus anterior working together as a force couple
- Scapular abduction/adduction
- Scapular muscle actions: the upper trapezius and levator scapulae elevate the scapula (with the scapula fixed, both also bend the neck to the same side, and the upper trapezius extends it), the middle trapezius and rhomboids retract it, the serratus anterior protracts it and helps rotate it upward, and the pectoralis minor pulls it downward and forward against the chest wall
The glenohumeral joint articulates the humeral head into a concave glenoid fossa. The ligaments that aid in stability are the superior, middle, and inferior glenohumeral ligaments.
- The superior glenohumeral ligaments prevent excessive external rotation and inferior translation.
- The middle glenohumeral ligament prevents excessive external rotation and anterior translation.
- The inferior glenohumeral ligament prevents anterior-inferior dislocation, the anterior portion external rotation, and the posterior portion internal rotation.
The glenohumeral joint has other important anatomical features:
- Labrum - a fibrocartilaginous rim around the glenoid fossa that deepens the socket and improves glenohumeral stability
- Bursae - act as fluid-filled sacs that provide cushioning and friction reduction between tendons, joints, muscles, and bone
- Long head of biceps tendon - originates at the supraglenoid tubercle/superior labrum, courses over the humeral head, and helps depress and stabilize the humeral head anteriorly
The four rotator cuff muscles (SITS) also cross the glenohumeral joint and work together to compress the humeral head into the glenoid fossa while producing their individual actions:
- Supraspinatus - initiates abduction and helps depress the humeral head
- Infraspinatus and teres minor - produce external rotation
- Subscapularis - produces internal rotation
The sternoclavicular joint articulates with the sternum and the clavicle via a fibrocartilage. This articulation is the only bony connection between the axial skeleton and the upper limb.
The acromioclavicular joint connects the scapula to the clavicle, allowing motion of the shoulder, stabilization and movement of the scapula, and stability to the shoulder girdle.
The acromioclavicular joint is stabilized by the acromioclavicular ligament and the coracoclavicular ligament (made up of the conoid and trapezoid ligaments). This joint lies within a small capsule that provides additional support and protection.
The scapulothoracic joint is a non-synovial, physiological joint formed by the interface between the scapula and the thoracic wall, supported by surrounding muscles and bursae rather than a true bony articulation. Its motion works together with the sternoclavicular and acromioclavicular joints, since scapular movement on the thorax requires motion at those joints, and together they produce full shoulder motion.
Elbow region
The elbow region consists of connections of bony structures between the distal humerus and the proximal radius and ulna. Three joints comprise the elbow: humeroulnar, humeroradial, and proximal radioulnar. The humeroulnar and humeroradial joints produce elbow flexion and extension. The proximal radioulnar joint works with the distal radioulnar joint to produce forearm supination and pronation; the distal radioulnar joint belongs to the forearm/wrist region rather than the elbow itself.
Primary movements of the elbow
- Elbow flexion/extension
- Forearm supination/pronation
Other elbow structures
- Capsule - a thin structure that surrounds the anterior and posterior components of the joint
- Bursae - fluid-filled sacs that cushion and reduce friction at the elbow joint
Ligaments of the elbow
- Ulnar collateral ligament
- Triangular ligament with anterior, posterior, and oblique (transverse) bands that reinforces the medial humeroulnar joint against valgus stress
- Radial collateral ligament
- Fan-shaped ligament that runs from the lateral epicondyle to the annular ligament, to support the humeroradial joint laterally
- Annular ligament
- Cone-shaped ligament that envelopes the radial head and attaches to the anterior and posterior margins of the radial notch of the ulna; protects the radial head
- Quadrate ligament
- Extends from the radial notch on the ulna surface to the neck of the radius; reinforces the inferior portion of the joint capsule
Wrist and hand region
The wrist and hand region is composed of the distal radius, the distal ulna, the carpals, the metacarpals, and the phalanges. There are six joints of the wrist and hand: radiocarpal joint, midcarpal joint, carpometacarpal joint (CMC), metacarpophalangeal joint (MCP), proximal interphalangeal joint (PIP), and distal interphalangeal joint (DIP). The radiocarpal and midcarpal joints together produce the wrist motions: flexion and extension, and radial and ulnar deviation (the wrist’s abduction and adduction).
Primary movements of the wrist and hand
- Wrist flexion/extension
- Wrist radial deviation/ulnar deviation
- Finger flexion/extension
- Finger abduction/adduction
- Intrinsic finger movement
Other wrist and hand structures
- Capsule of wrist and hand - provide support to internal structures
- Volar plate - present on the palmar aspect of the MCP, PIP, and DIP to protect joints
- Palmar aponeurosis - sheet of fibrous tissue in the palm that protects underlying tendons and nerves.
- Extensor hood - fibrous connection on the dorsum of the finger that aids in extension of the PIP and DIP
- Nerves - radial, median, and ulnar are the primary nerves of innervation for the wrist and hand
Ligaments of the wrist
- Dorsal radiocarpal
- Limits flexion, pronation
- Radiate
- Radiates from the head of the capitate to the surrounding carpals; stabilizes the midcarpal joint
- Radial collateral ligament
- Limits ulnar deviation
- Ulnar collateral ligament
- Limits radial deviation
- Palmar ulnocarpal
- Limits extension and supination
- Palmar radiocarpal
- Limits wrist extension and supination
- Distal radioulnar ligament
- Composed of the anterior and posterior radioulnar ligaments to provide strength to the capsule
Ligaments of fingers
- Collateral ligaments
- Run along each side of the MCP, PIP, and DIP joints, from the head (condyle) of the proximal bone to the base of the next phalanx, blending with the volar plate
- All fibers tighten during flexion, but only volar fibers tighten during extension
- Accessory
- Oriented from the condylar head to the volar plate
- Transverse
- Provide stability linking the MCP joints and reinforcing the anterior capsule
Upper extremity range of motion normals
| Joint | Motion | Normal range |
|---|---|---|
| Shoulder | Flexion | 160-180° |
| Shoulder | Extension | 50-60° |
| Shoulder | Abduction | 170-180° |
| Shoulder | Adduction | 50-75° |
| Shoulder | External rotation | 80-90° |
| Shoulder | Internal rotation | 60-100° |
| Elbow | Flexion | 140-150° |
| Elbow | Extension | 0-10° |
| Forearm | Supination | 90° |
| Forearm | Pronation | 80-90° |
| Wrist | Flexion | 80-90° |
| Wrist | Extension | 70-90° |
| Wrist | Radial deviation | 15° |
| Wrist | Ulnar deviation | 30-45° |
| MCP | Flexion | 85-90° |
| MCP | Extension | 30-45° |
| PIP | Flexion | 100-115° |
| PIP | Extension | 0° |
| DIP | Flexion | 80-90° |
| DIP | Extension | 20° |
| 1st CMC | Flexion | 45-50° |
| 1st CMC | Abduction | 60-70° |
| 1st CMC | Adduction | 30° |
| 1st MCP | Flexion | 50-55° |
| 1st MCP | Extension | 0° |
| 1st IP | Flexion | 85-90° |
| 1st IP | Extension | 0-5° |
This anatomical foundation sets up the special tests and clinical conditions covered in the chapters that follow, including comparing clinical presentation and interventions for the upper extremity.