summary Base of Thumb metacarpal fractures can be extra-articular fractures, Bennett fractures (partial intra-articular), or Rolando fractures (complete intra-articular). Diagnosis can be made by orthogonal radiographs of the thumb. Treatment ranges from splint immobilization for certain extra-articular fractures to surgical fixation for displaced Bennett or Rolando fractures. Epidemiology Incidence 80% of thumb fractures involve the metacarpal base the most common pattern is extraarticular epibasal fracture Etiology Pathophysiology mechanism of injury most Bennett and Rolando are fractures caused by axial force applied to the thumb in flexion pathoanatomy imperfect reductions and above forces lead to increased joint contact pressures and subsequent predisposition to early arthritis excessive angulation may lead to MCP joint hyperextension deformity Anatomy Osteology CMC joint is a saddle-shaped joint composed of the trapezium and the base of the thumb (1st) metacarpal flexion-extension motion abduction-adduction motion Muscles three muscles provide deforming forces at the base of the thumb abductor pollicis longus (PIN) proximal, dorsal, and radial force on the shaft fragment extensor pollicis longus (PIN) proximal, dorsal, and radial force on the shaft fragment adductor pollicis (Ulnar n.) supination and adduction force on the shaft fragment Ligament volar beak ligament spans the tuberosity of the trapezium to the volar edge of the 1st metacarpal keeps trapezium connected to the volar-ulnar base fragment dorsoradial ligament spans the dorsoradial tubercle of the trapezium to the dorsal base of the 1st metacarpal Biomechanics very limited axial rotation average flexion-extension of 53 degrees average abduction-adduction of 42 degrees Classification Classification of fractures of the first metacarpal Extra-articular oblique Oblique fracture line not involving the articular surface Extra-articular transverse Pure transverse fracture line not involving the articular surface Intra-articular Bennett Intra-articular fracture with a palmar ulnar fragment Intra-articular Rolando Y or T shaped complete intra-articular fracture Intra-articular comminuted Severely comminuted complete intra-articular fracture Presentation Symptoms acute pain at the base of thumb with Physical exam inspection swelling and ecchymosis tenderness to palpation at CMC joint motion pain with range of motion Imaging Radiographs recommended views true AP of thumb (Robert's View) arm in full pronation with dorsum of thumb on cassette true lateral of thumb hand pronated 30 degrees and beam angled 15 degrees distally oblique optional imaging traction view may be obtained to better understand the fracture pattern in Rolando and severely comminuted fractures findings bennett fractures a small fragment of 1st metacarpal base articulating with trapezium rolando fractures Y sign represents a splitting of the 1st metacarpal base into volar and dorsal fragments criteria dictating treatment extra-articular fracture <30 degrees angulation Bennett's fracture <1mm articular step-off Rolando comminution dictates operative strategy sensitivity and specificity a 30-degree pronated view provides the best view CT indications complex fracture patterns for assessment of fracture fragment detail Diagnosis Radiographic diagnosis confirmed by history, physical exam, and radiographs Treatment Nonoperative closed reduction and thumb spica casting indications extra-articular fractures with <30 degrees of angulation following closed reduction Bennett fractures with <1mm displacement modalities a reduction is achieved with longitudinal traction, palmar abduction, and pronation thumb spica casting indications fractures greater than 3 weeks old that will no motion at fracture site should be treated allowance of step-off and casting Operative closed reduction and percutaneous k-wire fixation indications extra-articular fractures with >30 degrees of angulation following closed reduction inability to maintain reduction <30 degrees with thumb spica Rolando fracture <1mm displacement small fracture fragments that are not amenable to screw fixation open reduction internal fixation indications >1mm of displacement in Bennett, Rolando, and severely comminuted fractures with large fracture fragments amenable to fixation distraction and external fixation indications Rolando fracture with >1mm displacement and major soft tissue injury severely comminuted fractures with major soft tissue injury or impacted articular fragments Bennett, Rolando, or severely comminuted fractures with fragments too small for ORIF Techniques Closed reduction and percutaneous k-wire fixation instrumentation a transverse extra-articular fracture can be treated with transarticular k-wire fixation oblique extra-articular fractures can be treated with intermetacarpal k-wire fixation complication specific to this treatment loss of reduction Open reduction internal fixation approach volar approach of Gedda and Moberg soft tissue thenar muscles are reflected volarly and a longitudinal capsulotomy is made bone work fracture is clamped in a volar-dorsal plane instrumentation fracture provisionally reduced with k-wire and fixed with screws or T-plate depending on fracture pattern complication specific to this treatment injury to the superficial branch of the radial nerve wound healing complications if significant edema is present outcomes adequacy of anatomic reduction predicts development of radiographic arthritis but does not predict symptomatic arthritis Distraction and external fixation instrumentation two 3mm are placed in the dorsoradial aspect of the distal shaft of the metacarpal two 3mm are placed in the dorsoradial aspect of the radius pins may be placed into the second metacarpal shaft to control deforming forces complications specific to this treatment pin site infection Complications Posttraumatic arthirtis incidence the exact incidence is unclear risk factors highly comminuted intra-articular fracture major step off multiple small fragments Malunion Prognosis Malreductions may lead to early short-term stiffness or instability and long-term radiographic arthritis Prognostic variables favorable acute intervention extra-articular fracture negative Bennett fracture Rolando fracture severely comminute fracture delayed intervention