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 leads to avulsion of the volar plate from metacarpal neck Associated conditions metacarpal and phalanx fractures fractures of the base of proximal phalanx or metacarpal head seen in up to 50% Anatomy MCP Joint Osteology a condyloid joint proximal phalanx contains shallow and concave surface congruent with metacarpal head metacarpal head is cam shaped 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 allows for hyperextension of MCP joint forms volar recess proximally allows for flexion of proximal phalanx 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 simple hyperextension of proximal phalanx on metacarpal head flexion of PIP joint complex bayonet positioning of proximal phalanx (dorsal to metacarpal shaft) skin dimpling in proximal palmar crease volar dislocation extensor lag present dorsal skin depression found proximal to base of proximal phalanx Imaging Radiographs recommended views AP lateral best view to see dislocation oblique findings complex dislocation joint space widening may indicate interposition of volar plate entrapment of sesamoid in MCP joint is diagnostic of complex dislocation Diagnosis Radiographic diagnosis confirmed by history, physical exam, and radiographs Treatment Nonoperative closed reduction indications simple dislocations Operative open reduction indications complex dislocations/delayed presentation Techniques Closed Reduction dorsal dislocation reduction technique apply direct pressure over dorsal aspect of proximal phalanx with the wrist in flexion to take tension off the intrinsic and extrinsic flexors avoid longitudinal traction during closed reduction as it may pull volar plate into joint and convert to irreducible immobilization early ROM and dorsal blocking splint following successful reduction volar dislocation reduction technique apply direct pressure over volar aspect of proximal phalanx with MCP in flexion immobilization immobilize in 30° of flexion for 2 weeks, then active ROM in dorsal blocking splint Open reduction approach dorsal approach approach midline incision soft tissue split extensor tendon and joint capsule longitudinally in thumb, develop interval between EPL and EPB may be able to push volar plate out with freer elevator usually need to split volar plate to remove from joint pros decreased risk of injury to neurovascular bundle easier to address metacarpal head fractures volar approach approach oblique incision important to incise skin only to avoid injury to neurovascular bundle soft tissue release A1 pulley to expose volar plate push volar plate and surrounding ligaments/tendons out with freer elevator pros provides better access to volar plate and surrounding ligaments/tendons cons risk of injury to neurovascular bundle difficult to address osteochondral fractures soft tissue reduction identify and reduce soft tissue blocking reduction dorsal dislocations in thumb FPL tendon displaces ulnarly to create a noose with radially displaced intrinsics index finger flexor tendon displaces ulnarly and lumbrical displaces radially which tighten around metacarpal neck in small finger flexor tendons and lumbrical displace radially and the abductor digiti minimi and flexor digiti minimi ulnarly volar dislocations interposition of dorsal capsule in joint avulsion and entrapment of distal insertion of volar plate or collateral ligament distal and volar displacement of tendinous juncture connecting 4th and 5th EDC tendons in small finger entrapment of 1st dorsal interossei in thumb 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