Dislocation of a joint occurs when traumatic forces cause complete loss of continuity between the joint’s two articulating surfaces. Subluxation, on the other hand, occurs when the loss of continuity between the joints is only partial. A dislocation may or may not involve a fracture.  Dislocations of the finger joints involve either an interphalangeal (IP) joint or a metacarpophalangeal (MCP) joint.
Reduction of a finger dislocation is indicated if the joint space is partially or completely disrupted, with or without an open wound.
In the presence of the following conditions, early consultation with a hand surgeon is warranted to determine whether management should be primarily surgical, without attempted reduction:
Digital neurovascular compromise
Open joint dislocation
Ligamentous or volar plate rupture
Joint instability 
The fingers (index through small fingers) are composed of three bones each and are all associated with a single metacarpal. Thus, there are three joints in each finger, all of which have significant motion and require stabilization to prevent subluxation and dislocation. This is accomplished with a combination of bony restraints, ligaments, and other static soft-tissue stabilizers, and the dynamic action of muscles. For more information about the relevant anatomy, see Hand Anatomy and Metacarpophalangeal and Interphalangeal Ligament Anatomy.
Each IP or MCP joint has two collateral ligaments and a volar fibrocartilaginous plate. Joint support is facilitated by these structures, as well as by the surrounding tendons. Overall, the IP joints are much more secure than the MCP joints because of the IP joints’ bicondylar arrangement and the fact that the collateral ligaments are tight throughout the entire range of motion. The MCP joints, on the other hand, are condyloid joints with additional lateral motion; their collateral ligaments are most taut during flexion only. Dislocation of a digit dorsally necessitates failure of the volar plate. On the other hand, lateral dislocation violates at least one of the collateral ligaments and produces a partial or complete tear in the volar plate.
Forces responsible for inducing a dislocation may include hyperextension, hyperflexion, ulnar or radial stress (typically, lateral dislocations), axial load, or injury caused by direct pressure or crushing.
Types of dislocations
Dislocations of the distal IP (DIP) joint of the second through fifth digits are relatively uncommon because of the stability afforded by the DIP joint’s flexor and extensor tendinous attachments.  Of the DIP joint dislocations that do occur, most are dorsal and are in combination with an open fracture.
Dislocations of the proximal IP (PIP) joint of the second through fifth digits are the most common dislocations within the hand; dorsal dislocations occur most frequently. [6, 7, 8] If the PIP joint was reduced prior to medical evaluation, the dislocation must be identified as volar, dorsal, or lateral because if the resultant splinting is incorrect, it can result in the development of a boutonniere deformity.
Dorsal PIP joint dislocations are typically due to a sports-related high-speed force to the distal finger, which, in turn, causes axial stress and hyperextension.  Lateral PIP joint dislocations are due to a blow in the radial or ulnar direction; ulnarly directed dislocations are more common than radially directed dislocations. Lateral PIP dislocations are often reduced in the field. Volar PIP joint dislocations are extremely uncommon.  They occur when a longitudinal blow to a moderately flexed middle phalanx causes disruption of a collateral ligament and partial avulsion of the volar plate. They are nearly always accompanied by an injury to the central slip of the extensor tendons.
Dislocations of the MCP joint of the second through fifth digits are relatively uncommon because of the MCP joint’s ligamentous anatomy and location at the base of the fingers.  They occur primarily from ulnarly and dorsally directed trauma while the MCP is fully extended. Such forces break the volar plate, joint capsule, and at least part of one of the collateral ligaments. They are usually dorsal, and the second and fifth digits are more commonly affected because of their lesser protection from neighboring digits.
Dislocations of the thumb IP joint are rare because of the significant stability of the IP joint. Thumb IP joint dislocations are usually dorsal and usually occur in association with a fracture. They may be associated with a rupture of the flexor pollicis longus. Dislocations of the thumb MCP joint are primarily dorsal and caused by hyperextension forces.