summary Thumb CMC Dislocations are rare injuries that occur due to axial force on a flexed thumb. Diagnosis is clinical and can be confirmed by orthogonal radiographs. Treatment is closed reduction and immobilization with unstable injuries requiring surgical stabilization. Epidemiology Incidence makes up <1% of hand injuries Anatomic location Mostly dorsal dislocations Volar dislocations are rare Etiology Pathophysiology mechanism axial force on a flexed thumb (more common) dorsal force applied in 1st web space (e.g. handlebar driven into a motorcyclist’s thumb on impact) (less common) pathoanatomy dorsoradial ligament is torn anterior oblique ligament is stripped/peeled off the 1st metacarpal base but remains continuous Anatomy Dorsal side ligaments are the primary stabilizers to dorsal/dorsoradial forces 16 total ligaments that stabilize the TMC joint superficial anterior oblique does NOT stabilize joint in flexion does NOT prevent dorsal subluxation provides for laxity of TMCJ to allow pronation during opposition forms “voluminous pouch” to accommodate metacarpal translation deep anterior oblique (beak) ligament pivot for TMCJ for pronation of thumb dorsoradial ligament stabilizer (“check rein”) to radial subluxation becomes taut with radial/dorsoradial subluxation before other ligaments if all other ligaments but this one are cut, CMC still remains reduced lax in stage IV arthritis posterior oblique ligament ulnar collateral ligament intermetacarpal ligament dorsal intermetacarpal dorsal trapeziotrapeziod volar trapeziotrapeziod dorso trapezio-II metacarpal volar trapezio-II metacarpal trapezio-III metacarpal transverse carpal ligament trapeziocapitate volar scaphotrapezial radial scaphotrapezial 7 main stabilizers of TMCJ – SAOL, dAOL, DRL, POL, UCL, IML and DIML 9 stabilizers of trapezium – DTT, VTT, DT-II MC, VT-II MC, T-III MC, VST, RST, trapeziocapitate and transverse carpal 4 key ligamentous restraints of the thumb anterior oblique ligament remains attached to volar fragment in Bennett/Rolando fracture posterior oblique ligament intermetacarpal ligament dorsoradial ligament Presentation History collide onto fixed object/axial force on a flexed thumb dorsal force applied to 1st web space e.g. handlebar driven into a motorcyclist’s thumb on impact) Symptoms pain over thenar eminence Physical exam swelling, bruising over thenar eminence unable to form a fist Imaging Radiographs recommended views PA lateral optional views roberts used to evaluate for base of thumb fractures findings joint space widening dorsoradial shift of metacarpal MRI indications persistent/recurrent instability after reduction guide to ligamentous reconstruction Diagnosis Radiographic diagnosis confirmed by history, physical exam, and radiographs Treatment Nonoperative closed reduction and immobilization in extension and pronation indications stable on reduction (implying the AOL is intact) Operative closed reduction and temporary pinning reconstruction of the dorsal capsuloligamentous complex with tendon autograft + temporary pinning recommended treatment indications grossly unstable joint (AOL possibly torn as well) results better abduction and pinch strength than closed reduction and pinning Complications Anterior osteophyte often visible Low incidence of recurrent dislocation