Introduction

The wrist joint, also known as the carpometacarpal (CMC) joint and radiocarpal joint, is a complex articulation that plays a crucial role in the function of the hand. This joint allows for flexion, extension, abduction, adduction, and circumduction of the wrist and enables the intricate movements necessary for gripping and manipulating objects. This comprehensive course will delve into the anatomical structures, biomechanics, physiology, pathophysiology, clinical assessment, and treatment strategies associated with the wrist joint.

Anatomy of the Wrist Joint

Bones

The wrist joint is a synovial articulation that links several bones, namely:

• The radius and ulna of the forearm (proximal row)
• Eight carpal bones (distal row)
• The five metacarpal bones (middle row)

Articular Surfaces and Joint Spaces

The articular surfaces of these bones create multiple joint spaces:

1. Radiocarpal joint space, between the radial head and scaphoid, lunate, triquetral, and pisiform bones.
2. Midcarpal joint space, between the scaphoid, lunate, and triquetrum, on one side, and the hamate, capitate, and trapezium, trapezoid, and pisiform bones, on the other.
3. Intercarpal joint spaces, between the carpal bones themselves.
4. Carpometacarpal joint spaces, between each of the carpal bones and their corresponding metacarpal bone.

Articular Capsule and Ligaments

The wrist joint is enclosed by a synovial capsule that provides stability and lubrication. Several ligaments reinforce the joint, including:

• Dorsal radiocarpal ligament
• Palmar radiocarpal ligament
• Scapho-lunate ligament
• Long radiolunate ligament
• Triangular fibrocartilage complex (TFCC)
• Radial collateral (ulnar collateral) ligaments
• Interosseous ligaments

Synovium and Articular Cartilage

The synovium lines the articular capsule and secretes synovial fluid, providing lubrication for smooth movement. The articular cartilage covers the articular surfaces of the bones and allows for low-friction articulation.

Biomechanics and Physiology of the Wrist Joint

Articular Mechanism

The wrist joint exhibits a complex articular mechanism, allowing for multiple degrees of freedom. The radial head's movement within the radiocarpal joint space and the intercalated segment instability (ISI) between the scaphoid and lunate bones facilitate flexion, extension, abduction, adduction, and circumduction.

Muscles and Tendons Involved in Wrist Motion

Several muscles and their associated tendons influence wrist motion. Some important ones include:

• Extensor carpi radialis longus (ECRL) and brevis (ECRB), responsible for extension and radial deviation
• Flexor carpi radialis (FCR), flexion and radial deviation
• Pronator teres, pronation
• Supinator, supination
• Wrist extensors (extensor carpi ulnaris, extensor digitorum, and extensor carpi radialis longus) and wrist flexors (flexor carpi radialis, palmaris longus, and flexor carpi ulnaris), responsible for extension and flexion, respectively

Blood Supply and Nerve Innervation

The blood supply to the wrist joint is provided by branches of the radial, ulnar, and anterior interosseous arteries. The principal nerve supply comes from the posterior interosseous, anterior interosseous, and median nerves.

Pathophysiology of the Wrist Joint

Common Injuries and Conditions

Several injuries and conditions can affect the wrist joint, including:

• Strains and sprains
• Fractures of the carpal bones or metacarpals
• Instability (scapholunate dissociation)
• Arthritis (osteoarthritis, rheumatoid arthritis, psoriatic arthritis)
• Tenosynovitis and tendon ruptures
• Ganglion cysts

Diagnosis and Imaging Modalities

Clinical assessment involves a detailed history, physical examination, and imaging modalities such as X-rays, MRI, or CT scans. The choice of imaging modality depends on the suspected pathology and clinical presentation.

Treatment Strategies for Wrist Injuries and Conditions

Conservative Management

Conservative management options for wrist injuries include:

• Rest and immobilization (cast, splint, or brace)
• Ice, compression, and elevation
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Physical therapy exercises to improve strength and range of motion

Surgical Interventions

Several surgical interventions may be necessary for more severe or refractory wrist conditions, such as:

• Arthroscopy
• Open reduction and internal fixation (ORIF)
• Joint fusion (arthrodesis)
• Total joint replacement (TJR)
• Tendon repair or reconstruction