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.

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.

Types Of Dislocation

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.

Also, there are three types of finger dislocations classified by the displacement of the bones as follows:

• Dorsal dislocation: The phalanx near to the fingertip is displaced toward the back of the hand.
• Volar dislocation: The phalanx close to the fingertip is displaced toward the palm of the hand.
• Lateral dislocation: The phalanx proximal to the tip of the finger is displaced to the side.

• DIP Joint Dislocation

DIP joint dislocations classically present with a deformity at the fingertip. Dorsal, lateral, and volar DIP joint dislocations are all possible sites.  Dorsal DIP joint dislocations occur most often and are related to fractures and skin injuries. They're not always related to flexor tendon avulsions but can have an interposed volar plate causing a non-reducible dislocation. Volar DIP joint dislocations are similar to dorsal PIP joint dislocations and both are associated with extensor tendon injuries. The lateral DIP joint is more likely to have post-reduction instability compared to volar or dorsal dislocations. Isolated DIP joint dislocation without related injuries like soft tissue or fractures is rare and is commonly managed with closed reduction and splinting in the emergency departments.

• PIP Joint Dislocation

PIP joint dislocations are very common dislocation due to sporting activities and are also known as “coach’s finger.” The classical signs and symptoms of PIP joint dislocation is a deformity, reduced range of motion, and pain. PIP joint dislocations can be classified into dorsal, volar, and lateral dislocations. Dorsal dislocations are common; however, volar dislocation correlates with an increased rate of complications and often difficult reductions.

Dorsal PIP joint dislocation occurs most commonly at the middle finger and is associated with volar plate, collateral ligament, and dorsal joint capsule injuries. Dorsal dislocation results from longitudinal compression and hyperextension commonly occur by a ball hitting the tip of the finger. Swan neck deformity occurs mostly in dorsal dislocations and results from volar plate injury. Trapping of the volar plate inside the joint can occur, causing malalignment and oblique rotation resulting under challenging reductions.

Volar dislocation of the PIP joint may result with and without rotation of the intermediate phalanx.  It is rare but can occur in combination with injury to the central slip of the extensor tendon. If left Untreated, after PIP joint dislocation rupture of the central slip is often associated with pseudo-boutonniere PIP flexion contracture). Pseudo-boutonniere is a chronic PIP flexion with the absence of a DIP extension.

Lateral PIP dislocation may occur and involves the disruption of the collateral ligaments. The patient presents with joint instability and the widening of the joint space seen on x-ray. Finally, rotary volar dislocations can occur when the phalanx displaces and rotates around one of the collateral ligaments, allowing the proximal phalanx to wedge itself between the lateral band and extensor tendon. In the classic lateral radiographic finding, it has been known as the “Chinese finger-trap.”

• Metacarpophalangeal Joint Dislocation

Hyperextension or high-energy axial loads at the metacarpophalangeal joint may result in dislocation. MCP joint dislocation infrequently occurs due to the protection against hyperextension by the volar plate and radial and ulnar deviation by the collateral ligaments. The foremost common MCP joint dislocation occurs in the index finger. Dislocation of the MCP joint of the middle finger happens when it's subjected to ulnar stress while in hyperextension. The common MCP joints usually dislocate dorsally. The clinical presentation of MCP joint dislocation is with the IP joint in flexion and MCP joint in extension. A nonreducible dislocation with dimpling on the volar surface shows volar plate interposition.

Causes

Finger dislocation is caused by a "jamming" force applied to the end of the finger, or the finger could also be forced into hyperextended. Either of these situations or a combination of both may result in a dislocation. The possible causes of a dislocated finger can include:

• Sports injuries: They are common causes of dislocated fingers. According to a research review, around half of all sports-related hand injuries affect the fingers. Sports with the highest incidence of hand injuries include football, cricket, netball, gymnastics, basketball, lacrosse, and wrestling, etc. are at higher risk of finger dislocation due to the increased exposure to jarring and overstretch forces. Especially sports played with a ball, can lead to the high impact of the IP joints in the fingertips and overstretch forces to the MCP joints when catching. Fingers can also get accidentally trapped in clothing or equipment during tackles or experience jarring impacts from collisions or falls or even seen in martial arts.
• Fall: Finger dislocation is the result of excessive force applied to the joints of the fingers. It can happen to those trying to hold back themselves during an awkward fall onto an outstretched finger. The impact from the fall can push fingers beyond their normal range of motion and out of their joints and thereby causing dislocation.
• Accidents: Rarely dislocations can occur during a violent incident or during a road accident.
• Genetics: Some people are born with weak ligaments. Ligaments are tissues that connect bones at the joint and give structural support.
• Health conditions: People with health conditions that weaken joints and ligaments could also be at greater risk of dislocations.

In all incidences, the key factor is that the excessive force applied to the joint, very commonly seen in hyperextension but can also be involved with a lateral force.