MP Joint Injuries
The MP joint allows flexion, extension, abduction, adduction, and a limited amount of circumduction. Stability is conferred by the snug box-like sling of collaterals and volar plate. The collaterals are tight in flexion, loose in extension due to the eccentric configuration of the metacarpal heads. The volar plates are thick fibrocartilaginous condensations of joint capsule, firmly attached distally, loosely attached proximally. They are held together by the deep transverse metacarpal ligament.
Lateral MP Dislocations (Collateral Ligament Injuries)
Often missed. Diagnosed by pain in response to lateral stress applied with the MPs flexed (when extended, lateral stress will not typically hurt, because little stress is actually applied to the collaterals in this position). A bony fleck may be avulsed off the base of the proximal phalanx.
Treatment – Acute
Splinting the MP at 50o flexion for 3 weeks.
If more than 2 to 3 mm of displacement of an avulsion, or if the fragment includes 20% of the base of the proximal phalanx, open reduction and internal fixation of the ligament with a bone suture anchor, or of the fragment with tension banding.
Treatment – Chronic
Corticosteroid injection, immobilization in 50o flexion for 3 weeks, then buddy taping and motion.
Dorsal MP Dislocations
These can be divided into ï¿½simpleï¿½ and ï¿½complexï¿½ based on the pathoanatomy and the subsequent ability or inability to reduce them closed. ï¿½The two can usually be distinguished fairly easily by clinical and radiographic examination, and the surgeon should not have to resort to multiple unsuccessful attempts at closed reduction to conclude that he or she is contending with an irreducible dislocation.ï¿½
Simple Dorsal MP Dislocations (Subluxations)
These look more dramatic than complex; the proximal phalanx is sitting at a 60-90o angle, but still articulating with the metacarpal.
Be careful not to convert a simple into a complex during the reduction!
Closed reduction – make sure the wrist is flexed to take the tension off the flexor tendons. Hyperextend the proximal phalanx to 90o, then push down on the joint as you bring it into flexion, so as to not entrap the volar plate. Once reduced, immediate active motion with buddy taping.
Complex Dorsal MP Dislocations (Irreducible)
The volar plate is typically the impediment to reduction.
There are 3 clues to the recognition of the complex dislocation:
1. The position of the proximal phalanx – usually sits dorsally, but almost parallel to the metacarpal, not at a 60-90o angle.
2. The skin in the palm of the hand – puckering of the palmar skin or a dimple.
3. Radiographs – presence of a sesamoid within a widened joint space is pathognomonic.
It is justified to give it one try at closed reduction.
Open reduction is best done through a volar approach, unless there is a large dorsal osteochondral fracture of the metacarpal head, in which a dorsal approach is used.
Once reduced (either open or closed) they are typically stable, and no immobilization is necessary -early motion with buddy taping.