M01.03.037 Proximal Interphalangeal Joint

The proximal interphalangeal joint (PIPJ) is a crucial structure in the hand, enabling fine motor control and flexibility. It connects the proximal and middle phalanx of each finger, except for the thumb. This article explores the PIPJ’s anatomy, movements, neurovascular supply, and clinical correlations.

Overview

• Location: Between the proximal and middle phalanx in all fingers except the thumb.
• Type of Joint: Synovial hinge joint.
• Functions: Permits flexion and extension, contributing to fine motor control.

Anatomical Structure

Articulating Surfaces

• Head of the Proximal Phalanx: Curved condylar processes that form a shallow groove.
• The base of the Middle Phalanx: Concave sections forming a raised ridge that fits securely into the groove of the proximal phalanx, providing intraarticular stability.

Joint Capsule

• A fibrous capsule surrounds the PIPJ, lined with synovial membrane and filled with synovial fluid.

Ligaments

The joint capsule is reinforced by various ligaments:

• Proper and Accessory Collateral Ligaments: Located on the radial and ulnar aspects of the joint, preventing excessive adduction and abduction.
• Volar Plate: A fibrocartilaginous structure that prevents excessive hyperextension. It forms a “U” shape across the joint, attached to the head of the proximal phalanx via checkrein ligaments and inserting distally onto the middle phalanx.

Table: Key Ligaments and Functions

Movements

Flexion

• The PIPJ flexes to 100-110°.
• Primary Flexor: Flexor digitorum superficialis.
• Secondary Flexor: Flexor digitorum profundus (primarily acts on the distal interphalangeal joint).

Extension

• Extension is achieved by:
  • Extensor Digitorum
  • Lumbricals
  • Interossei Muscles
  • Extensor Indicis (assists the index finger)

Table: Muscle Actions for Movements

Clinical Relevance

Boutonnière Deformity

• Cause: Injury to the central slip tendon (extension mechanism).
• Result: The PIPJ cannot extend, while the distal interphalangeal joint (DIPJ) is hyperextended.
• Treatment: Early intervention is necessary to prevent permanent deformity. Splintage or surgery may be required.

Proximal Interphalangeal Joint Dislocation

• Cause: Trauma, often from hyperextension.
• The most Common Direction is dorsal dislocation.
• Associated Injury: Volar plate damage.
• Treatment: Joint reduction, splinting, and possibly surgery if the joint remains unstable.

Neurovascular Supply

Blood Supply

• The palmar digital arteries supply the arterial blood to the PIPJ.

Innervation

• Sensory Innervation: Provided by the palmar digital nerves, branches of the median and ulnar nerves.

Points to Remember

• The PIPJ is a hinge joint allowing flexion and extension.
• It is stabilized by ligaments, including the collateral and volar plate ligaments.
• The central slip tendon is crucial for PIPJ extension; injury leads to Boutonnière deformity.
• The PIPJ can be dislocated, commonly in a dorsal direction, due to trauma.
• Understanding the anatomy and functions of the PIPJ is essential for diagnosing and treating hand injuries.

Summary Table: Key Features of the Proximal Interphalangeal Joint