Hand Joints

Introduction

Introduction to the Joints of the Hand

The hand is a complex arrangement of 19 bones linked by a series of synovial joints that provide the mobility and stability necessary for power grip, precision pinch, and fine manipulation. These joints are grouped into intercarpal joints (between the carpal bones), carpometacarpal (CMC) joints (between the distal carpal row and the metacarpals), metacarpophalangeal (MCP) joints (between metacarpal heads and proximal phalanges), and interphalangeal (IP) joints (between the phalanges). Each joint type is structurally adapted to its function, from the highly mobile saddle joint of the thumb to the stable hinge joints of the fingers.

The stability of the hand joints relies on a system of collateral ligaments, palmar (volar) plates, and the extensor hood mechanism. The precise arrangement of these structures allows for the coordinated movements required for dexterity, while also being susceptible to traumatic injuries, degenerative arthritis, and inflammatory conditions.

Study

1. Intercarpal Joints and the Midcarpal Joint

The intercarpal joints are plane synovial articulations between adjacent carpal bones within the proximal row (scaphoid, lunate, triquetrum) and within the distal row (trapezium, trapezoid, capitate, hamate). They are reinforced by strong palmar and dorsal intercarpal ligaments, and interosseous ligaments (e.g., scapholunate, lunotriquetral) that bind the bones together and maintain carpal alignment.

The midcarpal joint is a functional articulation between the proximal and distal carpal rows (excluding the pisiform, which forms a separate joint with the triquetrum). It has an S‑shaped joint cavity and contributes to wrist flexion, extension, radial and ulnar deviation. This joint is particularly important in the dart‑thrower’s motion (radial extension to ulnar flexion).

2. Carpometacarpal (CMC) Joints

The first CMC joint (thumb) is a saddle (sellar) joint between the trapezium and the base of the first metacarpal. It allows flexion, extension, abduction, adduction, opposition, and retroposition. A loose but strong capsule and several ligaments stabilise it, most notably the anterior (palmar) oblique ligament (beak ligament), which is the primary restraint to dorsal subluxation.

The CMC joints of the index, middle, ring, and little fingers are plane synovial joints that permit only a small amount of gliding. The fifth CMC joint is the most mobile of these, allowing a degree of opposition (cupping the palm). These joints are reinforced by palmar and dorsal CMC ligaments and interosseous ligaments.

3. Metacarpophalangeal (MCP) Joints

The MCP joints are condyloid synovial joints between the rounded heads of the metacarpals and the shallow concave bases of the proximal phalanges. They allow flexion, extension, abduction, adduction, and limited circumduction. Stability is provided by proper collateral ligaments (taut in flexion), accessory collateral ligaments (taut in extension), and a fibrocartilaginous palmar (volar) plate that prevents hyperextension. The deep transverse metacarpal ligament connects the palmar plates of the second to fifth MCP joints, maintaining the transverse metacarpal arch.

The thumb MCP joint is similar but more hinge‑like, with a sesamoid bone embedded in the palmar plate, and its ulnar collateral ligament is commonly injured (gamekeeper’s thumb).

4. Interphalangeal (IP) Joints

The proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints are pure hinge (ginglymus) joints, allowing only flexion and extension. Their structure mirrors the MCP joints: strong proper and accessory collateral ligaments, a thick palmar plate, and a dorsal capsule reinforced by the extensor hood. The PIP joint is particularly prone to hyperextension injuries and the development of boutonnière and swan‑neck deformities when the extensor mechanism is disrupted.

5. Ligaments and Stabilisers of the Hand Joints

The palmar plates are thick fibrocartilaginous structures on the palmar aspect of the MCP and IP joints, firmly attached to the proximal phalanx and loosely to the metacarpal or more proximal phalanx, functioning as a checkrein to hyperextension. The collateral ligaments arise from the dorsal aspect of the head of the proximal bone and pass obliquely to the palmar aspect of the base of the distal bone; they are slack in extension and taut in flexion, which is why the fingers should be immobilised in flexion to prevent ligament shortening.

The extensor hood mechanism (dorsal digital expansion) integrates the tendons of the extensor digitorum, lumbricals, and interossei, controlling the intricate balance of flexion and extension at the MCP and IP joints.

6. Blood Supply

The joints of the hand are supplied by branches of the superficial and deep palmar arches, the palmar metacarpal arteries, and the proper palmar digital arteries. The dorsal metacarpal arteries also supply the dorsal aspect of the joints.

7. Nerve Supply

According to Hilton’s law, the nerves crossing the joints supply them. The MCP and IP joints receive articular branches from the median nerve (radial three and a half digits) and the ulnar nerve (medial one and a half digits). The radial nerve contributes via the posterior interosseous nerve to the dorsal wrist and some intercarpal joints, but its role in finger joints is minimal.

8. Clinical Considerations

Thumb CMC osteoarthritis: Very common, especially in postmenopausal women, presenting with basal thumb pain, weakness, and a squared deformity of the thumb base. The anterior oblique ligament degenerates, leading to dorsal subluxation.

Gamekeeper’s thumb (skier’s thumb): Acute or chronic injury to the ulnar collateral ligament of the thumb MCP joint due to forced abduction and hyperextension. A Stener lesion occurs when the adductor aponeurosis becomes interposed between the torn ligament and its insertion, preventing healing.

Bennett fracture: An intra‑articular fracture‑dislocation of the base of the first metacarpal, with a small volar ulnar fragment held in place by the anterior oblique ligament, while the shaft dislocates dorsally.

Rolando fracture: A comminuted intra‑articular fracture of the base of the first metacarpal (Y‑ or T‑shaped), with a worse prognosis.

Boxer’s knuckle: Injury to the sagittal bands of the extensor hood at the MCP joint, causing extensor tendon subluxation.

Boutonnière deformity: Disruption of the central slip of the extensor tendon at the PIP joint leads to flexion of the PIP and hyperextension of the DIP.

Swan‑neck deformity: Laxity or rupture of the palmar plate of the PIP joint or imbalance of the extensor mechanism leads to hyperextension of the PIP and flexion of the DIP.

MCP joint dislocation: Typically dorsal, often requiring open reduction due to interposition of the palmar plate or sesamoid bones.

Summary

Summary of Hand Joints

The hand joints comprise intercarpal, CMC, MCP, and IP articulations. The thumb CMC is a saddle joint allowing opposition; the MCP joints are condyloid, enabling flexion, extension, abduction, and adduction; the IP joints are hinge joints for pure flexion and extension. The palmar plates and collateral ligaments provide stability. Common pathologies include thumb CMC osteoarthritis, ulnar collateral ligament injuries (gamekeeper’s thumb), Bennett and Rolando fractures, and digital deformities (boutonnière, swan‑neck). A thorough understanding of these joints is essential for diagnosing hand injuries and deformities.