Nonsurgical Management

The concept of the "box" formed about the head of the proximal phalanx by the volar plate and the accessory and true collateral ligaments of the PIP joint is useful when considering the pathoanatomy of dislocations of this joint. Lateral dislocations may occur after injury to the volar plate and at least one collateral ligament. Both collateral ligaments may also be ruptured.

Biomechanical studies of the constraints about the PIP joint have demonstrated that the collateral ligaments may fail at any point along their course, including an avulsion fracture from the phalanges. The location of ligament failure is dependent on the rate at which the lateral stress is applied. Failure of the proximal portion of the ligament is most common. After reduction and while under digital block anesthesia, the degree of injury to the collateral ligaments may be assessed by the extent to which the joint opens upon the application of lateral stress. Opening over 20 degrees is associated with a 100% chance of complete failure of the collateral ligament, whereas opening less than 20 degrees is associated with only a 53% chance of complete rupture. Although this information is not useful in cases of documented dislocation, it may become useful in those instances in which the patient reports an injury to the PIP joint that he or she has self-reduced.

An intact lateral band will extend the PIP joint, and may mask an injury to the central slip. Therefore, it is important to isolate the central slip when testing for injuries to the extensor mechanism to whatever extent possible. Flexion of the MP joint places the lateral bands at a mechanical disadvantage, allowing preferential assessment ofthe integrity ofthe central tendon insertion. Missed injuries ofthe central slip insertion may result in a boutonniere deformity, which is potentially one of the major pitfalls in the management of injuries to the PIP joint.

Due to the bony architecture of the PIP joint, concentric reduction usually provides sufficient stability to allow for early motion within the limits of reasonable comfort. The arc through which the joint is stable should be assessed at the time of injury to avoid subluxation or redislocation. This is best done when the joint is anesthetized, preferably with a digital block.

Those factors that need to be considered in selecting the optimal position ofjoint immobilization include the volar plate, the collateral ligaments, and the extensor mechanism. In lateral dislocations the volar plate is generally avulsed from the base of the middle phalanx, so splinting in 20 to 30 degrees of flexion would seem prudent to avoid laxity and subsequent hyperextension. Minamikawa et al have demonstrated that the intact PIP joint is most resistant to lateral stress in full extension. This implies that the collateral ligaments are most taut in full extension. Immobilization in slight flexion, therefore, would allow the ligaments to begin healing in a slightly shorter position, possibly avoiding the development of laxity. However, if injury to the extensor mechanism is suspected, the joint should be splinted in full extension to avoid the complication of a boutonniere deformity. Regardless of the position of immobilization, motion should be instituted as early as possible. The common complication of injuries to the PIP joint is stiffness, not laxity. Volar plate and collateral ligament injuries can be mobilized as soon as the patient is comfortable, providing the joint is stable. Central tendon injuries should be protected longer, for about 3 weeks, and then mobilized, protecting the extensor mechanism with a dynamic extension splint.

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