Summary MCP Dislocations are a dislocation of the metacarpophalangeal joint, usually dorsal, caused by a fall and hyperextension of the MCP joint. Diagnosis can be made clinically and is confirmed by orthogonal radiographs. Treatment is closed reduction unless soft tissue interposition blocks reduction, in which case open reduction is indicated. Epidemiology Incidence rare < 1 per 100,000 annually Anatomic location dorsal dislocations are most common index finger is most commonly involved thumb is second most common digit involved Etiology Pathophysiology mechanism of injury usually a fall on outstretched hand leading to hyperextension of MCP joint login to view 1 more bullet Associated conditions metacarpal and phalanx fractures fractures of the base of proximal phalanx or metacarpal head login to view 1 more bullet Anatomy MCP Joint Osteology a condyloid joint proximal phalanx login to view 2 more bullets metacarpal head login to view 1 more bullet sesamoids embedded in the volar plate attached to flexor pollicis brevis and abductor pollicis brevis in thumb MCP Joint Ligaments proper collateral ligaments are the primary stabilizer of the MCP joint originate from the dorsal aspect of metacarpal head insert on the volar aspect of base of proximal phalanx are tight in flexion accessory collateral ligaments originate volar to the proper collateral ligaments insert on the volar plate are tight in extension volar plate stabilizes the volar aspect of MCP joint comprised of thick fibrocartilaginous portion distally and loose membranous portion proximally login to view 1 more bullet forms volar recess proximally login to view 1 more bullet dorsal capsule a weak stabilizer of the dorsal aspect of MCP joint thin and loose in structure sagittal bands supports the extrinsic tendons originates from the extensor hood attaches volarly with transverse metacarpal ligament Classification Anatomic classification of MCP dislocation Volar Results from hyperextension or hyperflexion injury Dorsal Most commonResults from hyperextension injury Complexity of MCP dislocation Simple (subluxation) No interposition of volar plate and/or sesamoidBase of proximal phalanx remains in contact with the metacarpal head Complex (complete) Interposition of volar plate and/or sesamoidsMetacarpal head becomes entrapped by -displaced natatory ligaments distally -superficial transverse metacarpal ligament proximally Kaplan's lesion (rare) -most common in index finger -metacarpal head buttonholes into palm (volarly) -volar plate is interposed between base of proximal phalanx and metacarpal head Presentation Physical exam deformity seen on inspection depends on type of dislocation dorsal dislocation login to view 6 more bullets volar dislocation login to view 2 more bullets Imaging Radiographs recommended views AP lateral login to view 1 more bullet oblique findings complex dislocation login to view 2 more bullets Diagnosis Radiographic diagnosis confirmed by history, physical exam, and radiographs Treatment Nonoperative closed reduction indications login to view 1 more bullet Operative open reduction indications login to view 1 more bullet Techniques Closed Reduction dorsal dislocation reduction technique login to view 2 more bullets immobilization login to view 1 more bullet volar dislocation reduction technique login to view 1 more bullet immobilization login to view 1 more bullet Open reduction approach dorsal approach login to view 10 more bullets volar approach login to view 11 more bullets soft tissue reduction identify and reduce soft tissue blocking reduction login to view 12 more bullets Complications Joint stiffness due to soft tissue trauma at time of injury or prolonged immobilization Post-traumatic arthritis or osteonecrosis due to repeated attempts at closed reduction, prolonged dislocation, traumatic open reduction Premature physeal closure rare