1^st MP Joint Dislocation

• rare
• Frank dislocation of the first MTP joint is almost always dorsal in direction.

1st MP Dislocation Classification / Treatment 

• Type I – These dislocations occur with disruption of the sesamoid-plantar plate complex through the relatively weak proximal attachments of the plate to the metatarsal neck.  There is no injury to the intersesamoid ligament, and the space between the sesamoids is not widened when viewed on the plain AP radiograph.  The sesamoids come to lie between the joint surfaces just dorsal to the metatarsal head, which can be visualized on a lateral radiograph.  This complex injury pattern is not reducible by closed means because the plantar plate is interposed into the MTP joint.  Open reduction is required through a transverse plantar incision or dorsal incision to remove the interposed plantar plate.
• Type II – These injuries involve a disruption of the sesamoid complex and are subclassified into IIA and IIB.  IIA dislocations show disruption of the intersesamoid ligament with widening of the space and dislocation of the metatarsal head through this space.(response 4)  IIB injuries produce a transverse fracture through one or both sesamoids.  The proximal fracture fragment remains in its normal relationship to the adjacent sesamoid held in place by strong intersesamoid ligament.  Frequently, the distal sesamoid fragment becomes a loose body within the joint and may require removal.

References:

Jahss MH:  Traumatic dislocations of the first metatarsophalangeal joint.  Foot Ankle 1980;1:15-21

Schenck RC Jr, Heckman JD:  Fractures and dislocations of the forefoot:  Operative and nonoperative treatment.  JAAOS 1995;3:70-8.