Dislocation and fracture-dislocation of the proximal interphalangeal joint

Dislocations of the proximal interphalangeal (PIP) joint are classified according to AO/OTA as 70E2.2–5[5], where 2–5 indicates which finger is injured.

PIP joint dislocations involving a fracture of the proximal phalangeal head are classified according to AO/OTA as 78.2–5.1.3B[5], where 2–5 indicates which finger is injured. The associated fractures are usually coronal fractures of the phalangeal head.

$Dislocation of the proximal interphalangeal joint and fracture-dislocations of the proximal interphalangeal joint - proximal phalanx of the hand$

While dislocations and ligament injuries are common in the hand, they are most common at the PIP joint.

The spectrum of these lesions ranges from minor ligamentous stretching (sprains) to complete disruptions of the ligaments.

Palmar and dorsal dislocations of the proximal interphalangeal joint

Dislocations of the PIP joint are classified by the direction of displacement of the middle phalanx. They can be palmar, dorsal, lateral, or lateral rotatory.

Lateral and lateral-rotatory dislocations of the proximal interphalangeal joint

Mechanism of the injury

Typically, these injuries occur as a result of lateral deviation and rotation, with the PIP joint in semi-flexion. This happens during sporting activities, or while catching a finger in rotatory machines, such as drills, etc.

Lateral deviation and rotation as the mechanism of injury for dislocations of the proximal interphalangeal joint

The collateral ligament usually tears at one of two locations:

At its attachment to the proximal phalanx
At its attachment to the volar plate and middle phalanx

Often, these injuries are accompanied by a partial lesion of the volar plate.

Collateral ligament tear at its attachment to the proximal phalanx and a collateral ligament tear at attachment to the volar plate and middle phalanx

Deforming forces

Boutonnière deformity

When the central slip is detached, the lateral bands are palmarly displaced and pull the distal interphalangeal (DIP) joint into hyperextension.

The flexor digitorum superficialis (FDS) pulls proximally on the middle phalanx, forcing the PIP joint into flexion.

Boutonnière deformity showing the detached slip and palmarly displaced lateral bands pulled the distal interphalangeal joint into hyperextension

Swan-neck type deformity

If the middle phalanx is palmarly dislocated at the PIP joint by the energy of the trauma, the flexor digitorum profundus (FDP) pulls the DIP joint into flexion.

Coronal fractures are rare, occur in the coronal plane, and are associated with palmar or dorsal dislocations.

If the PIP joint is dislocated dorsally, a coronal dorsal fracture is present. If the PIP joint is dislocated palmarly, a coronal palmar fracture is associated.

Typically, these fractures result from sports injuries due to axial loading associated with hyperflexion or hyperextension.

$Dorsal and palmar coronal fracture-dislocations of the proximal interphalangeal joint$