DISLOCATION OF PROXIMAL INTERPHALANGEAL JOINT
The proximal interphalangeal joint is basically a hinge joint supported by the architecture of the bone and by strong collateral ligaments on either side, which are, in turn, reinforced by a strong volar ligament or plate. The dorsal capsule of the proximal interphalangeal joint is strengthened by the central slip of the extensor tendon and by the insertions of the lateral bands of the extensor tendon hood. Ligament injuries of the proximal interphalangeal joint, the most common injuries of the hand, include simple sprains of the collateral ligament or the volar plate (most common), complete dislocations, and the most severe injuries-fracture-dislocations.
Any injury to the proximal interphalangeal joint can significantly affect motion and function of the finger and hand as the lesser fingers typically work in concert together and dysfunction of one finger hinders the remaining fingers. During the diagnostic evaluation, the examiner must palpate specific areas for tenderness and assess the stability of the joint both actively, as the patient flexes the finger, and, passively, as the examiner moves the finger.
The most common dislocation of the proximal inter-phalangeal joint, the dorsal dislocation, is often called the coach’s finger. Frequently occurring in athletic events, the dorsal dislocation is usually reduced by trainers or coaches shortly after injury. The uncommon volar dislocation of the proximal interphalangeal joint is a more serious injury because it disrupts the central slip of the extensor mechanism. Unless properly treated by splinting with the joint in extension, volar dislocation can result in a disabling boutonnière deformity. Rotational dislocations are rare. A unique aspect of this type of dislocation is the appearance of the phalanges on the lateral radiograph: the proximal phalanx is seen in an oblique plane and the middle phalanx in a true lateral plane.
Treatment Of Dorsal And Rotational Dislocations
Although closed reduction usually produces a satisfactory result, open reduction is occasionally required to restore the phalanges to their anatomic positions. If there is evidence of instability after reduction, simple dorsal and rotational dislocations of the proximal inter-phalangeal joint can be treated with splinting for 3 weeks; if the joint is stable, early active motion with buddy taping is prescribed for 4 to 6 weeks.
Fracture-dislocations are the most severe and disabling injuries of the proximal interphalangeal joint. In addition to dislocation, a fracture disrupts the volar surface of the middle phalanx, resulting in both dorsal and volar instability. These injuries are often missed because the dislocation reduces spontaneously and patients do not come to medical attention and/or the fracture of the volar lip of the middle phalanx appears quite insignificant on the radiograph to a non-hand specialist and restricted motion is not instituted, with subsequent resultant subluxation and joint degeneration.
Some fracture-dislocations can be treated with closed reduction of the dislocation and use of an extension block splint. The splint allows full flexion of the finger and a range of extension that maintains the reduction and stability of the proximal interphalangeal joint. This method of treatment requires close radiographic follow-up. As healing increases the stability on the volar side, the amount of extension can be gradually increased until the joint remains stable in full extension.
Fracture-dislocation with a large fragment from the volar lip requires open reduction with Kirschner wire or screw fixation. Late reconstruction of this injury involves either arthrodesis, volar plate interposition arthroplasty, or prosthetic arthroplasty.
In all injuries of the proximal interphalangeal joint, the patient should be informed that the joint will remain enlarged for a long time, possibly many years, and that some loss of motion is quite common.
Treatment Of Volar Dislocations
In the more severe volar dislocation, the proximal inter-phalangeal joint must be splinted in extension for 4 to 6 weeks to avoid creating a boutonnière deformity. A rare injury of the proximal interphalangeal joint, fracture of the dorsal lip of the middle phalanx results in an avulsion of the central slip of the extensor mechanism. This injury must be treated with open reduction and, if necessary, pin or screw fixation of the fracture fragment. Failure to recognize this injury and restore the attachment of the central slip to the middle phalanx leads to a boutonnière deformity, with chronic pain and instability. If boutonnière deformity develops, arthrodesis of the proximal inter-phalangeal joint is often the only salvage procedure possible.