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.
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.
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.
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.
The collateral ligament usually tears at one of two locations:
Often, these injuries are accompanied by a partial lesion of the volar plate.
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.
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.
Lateral view x-ray of a fracture-dislocation