Finger Dislocation

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Original Editor - Puja Gaikwad

Top Contributors - Puja Gaikwad, Kim Jackson, Anas Mohamed, Shaimaa Eldib, Rucha Gadgil and Wanda van Niekerk  

Introduction

Finger dislocation is a common hand injury that can occur at the proximal interphalangeal (PIP), distal interphalangeal (DIP), or metacarpophalangeal (MCP) joints and can also occur in the dorsal, volar, or lateral planes. With numerous articulated joints connecting multiple small bones, the fingers are mostly at risk of dislocation when exposed to high impact activities and forced overstretching. Such forces are most typically experienced during sports, especially full-contact sports like rugby, basketball, and football. However, progressive, repetitive strain on the joints during daily activities can weaken the joints increasing the possibility of dislocation.

A dislocated finger usually involves excessive forces exerted on the joint above the connective tissue tensile strength. This causes the tissue, often ligaments going into partial or complete tear allowing the bony surfaces of the joint to slide faraway from each other. The remaining connective tissue, tendons, nerves, and blood vessels can get impinged by this movement causing excruciating pain. Depending on the severity of the dislocation the displaced bone can cause damage to the surrounding tissues in addition to damage experienced during its dislocation.

The foremost common joint to be dislocated is the proximal interphalangeal joint (PIPJ) of the middle joint in the finger. When the forces involved are too much and beyond the capacity what the connective tissue and supporting muscles can withstand, one or more small bones of the fingers can displace or ‘pop out’ of their normal position. When this happens, the condition is called a "dislocated finger" and it may affect one or more IP or MCP joints. Forces applied at the time of the injury will depend on the direction of dislocation. Some dislocations may be associated with a fracture or damage to the ligament that supports the sides and front of the joint with the risk of long-term instability.

There are three types of finger dislocation, based on the finger joint involvement. They are as follows:

• Distal interphalangeal (DIP) joint dislocation – occurs in the joints closest to the fingertip.
• Proximal interphalangeal joint dislocation – occurs in the joints in the middle of the finger and It's the most common sports injury, also called "jammed finger".
• Metacarpophalangeal (MCP) joint dislocation –occurs at the base of the finger. These types of joint dislocations are relatively rare, compared to the other two types.

Clinically Relevant Anatomy

Fingers consist of three joints: Metacarpophalangeal (MCP) joints, proximal interphalangeal (PIP) joints, and the distal interphalangeal (DIP) joints. The MCP joint is located between metacarpals and proximal phalanges. The PIP and DIP joints are hinge joints between proximal and middle phalanges and between the middle and distal phalanges respectively. These PIP and DIP joints allow flexion and extension, which helps in grasping, pinching, and clawing or reaching functions. The middle phalanx range of motion available at the PIP joint is 105+/- 5 degrees and accounts for the fingertip flexion during grasping. Flexion and extension of the digit are also possible at the metacarpophalangeal joint; however, the MCP joint performs flexion, extension, adduction, abduction, and circumduction.

The phalangeal joints have stabilizers that provide support during motion. There are static and dynamic joint stabilizers. Static stabilizers involve non-contractile tissue, collateral ligaments, volar plate, dorsal capsule, sagittal bands, ulnar, and radial collateral ligaments, etc. The volar plate is an important stabilizer as it holds up the volar side of the joint capsule and maintains stability and thereby prevents hyperextension of the finger joints. The collateral ligaments provide stabilization against the radial and ulnar deviation of the IP joints. Sagittal bands encircle the metacarpophalangeal joint to keep the extensor tendon centralized and thereby prevent bowstringing. Dynamic stabilizers include extrinsic and intrinsic muscles and tendons. Two major dynamic stabilizers are central slip and lateral bands. The central slip tendon is placed dorsally and provides a PIP joint extension, and the lateral bands provide a DIP joint extension. Lastly, digital arteries and nerves are found in the volar aspect and appear on both ulnar and radial sides of the digits.

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