M01.03.036 Metacarpophalangeal Joint

The Metacarpophalangeal (MCP) joint plays a crucial role in hand function by connecting the metacarpal bones to the proximal phalanges of each digit. This article delves into the anatomy of the MCP joint, including its articulating surfaces, ligaments, movements, and clinical correlations.

Overview of the Metacarpophalangeal Joint

The MCP joint is a synovial, condyloid joint located in the hand. It allows for a wide range of movements, making it essential for hand dexterity.

Key Points to Remember:

• MCP Joint Function: Connects the metacarpal head and the base of the proximal phalanx of each digit.
• Number of Joints: Five MCP joints in each hand, one for each digit.
• Joint Type: Condyloid synovial joint.

Anatomical Structure of the MCP Joint

1. Articulating Surfaces

The MCP joint consists of the following:

• Metacarpal Head: Large, convex articulating surface.
• The base of Proximal Phalanx: Smaller, concave articulating surface.

Both surfaces are lined with hyaline cartilage to facilitate smooth movement.

2. Joint Capsule

The MCP joint is surrounded by a fibrous capsule that:

• Attaches close to the margins of the articulating surfaces.
• Thicker medially and laterally, where it is reinforced by the collateral ligaments.

3. Ligaments

Several ligaments reinforce the MCP joint:

• Collateral Ligaments: Located on the medial and lateral aspects of the joint.
• Palmar Ligament: A fibrocartilaginous thickening on the anterior side, blending with collateral ligaments.
• Deep Transverse Metacarpal Ligaments: Link the palmar ligaments of digits 2–5, enhancing stability.
• Extensor Tendons: Fibers from the extensor muscles (e.g., extensor digitorum) reinforce the posterior side.

Table 1: Ligaments of the MCP Joint

Movements at the MCP Joint

1. Thumb Movements

• Flexion: Flexor pollicis brevis and longus.
• Extension: Extensor pollicis brevis and longus.
• Adduction: Adductor pollicis.
• Abduction: Abductor pollicis longus and brevis.
• Axial Rotation: Simultaneous contraction of flexor pollicis brevis and abductor pollicis brevis.

2. Digits 2-5 Movements

• Flexion: Flexor digitorum superficialis, flexor digitorum profundus, lumbricals.
• Extension: Extensor digitorum, extensor indicis, extensor digiti minimi.
• Adduction: Palmar interossei muscles.
• Abduction: Dorsal interossei muscles, abductor digiti minimi (5th digit).

Table 2: Muscles Involved in MCP Joint Movements

Stability and Mobility

The MCP joint’s stability is ensured by:

• Collateral Ligaments: Limit hyperflexion and hyperextension.
• Palmar Ligament: Prevents hyperextension.
• Deep Transverse Metacarpal Ligament: Provides stability during gripping.

Blood Supply and Innervation

1. Blood Supply

The MCP joint is supplied by branches from the radial and ulnar arteries:

• Princeps pollicis artery: Supplies the thumb.
• Radialis indicis artery: Supplies the index finger.
• Common palmar digital arteries: Supply the rest of the digits.

2. Innervation

• Posterior Interosseous Nerve: From the radial nerve.
• Deep Terminal Branches of the Ulnar Nerve.
• Palmar Branches of the Median Nerve.

Clinical Relevance: Skier’s Thumb

Skier’s Thumb

• Cause: Injury to the ulnar collateral ligament (UCL) of the first MCP joint, commonly seen in skiers.
• Mechanism: Forcible abduction of the thumb, often from falling on an outstretched arm while holding a ski pole.
• Diagnosis:
  • Physical Exam: Assess joint laxity during abduction.
  • Ultrasound: Evaluate the integrity of the ulnar collateral ligament.
• Treatment: Severe cases may require surgical repair for ligament rupture or avulsion fractures.