Bennetts Fracture

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Definition

-  Intra-articular fracture dislocation of base of 1st metacarpal

-  Oblique intra-articular metacarpal fracture of ulnar side of base (palmar beak fragment)

-  Dislocation at the carpometacarpal joint

 

Features

-  Most common thumb fracture

-  Ulnar fragment of thumb metacarpal destabilises thumb

-  Metacarpal displaced proximal, radially & dorsally by Abductor Pollicis Longus (APL)

-  Also rotated in supination by APL

-  Failure to appropriately Mx leads to loss of function + unstable & arthritic joint

-  +/- weak pinch & opposition

 

Mechanism

-  Axial blow to partially flexed metacarpal ie: fist injury, bike falls

 

 

Associated S/S

-  Thumb pain + swelling

-  Carpometacarpal joint instability

-  Weak pinch + opposition

 

Complications

-  Open fracture

 

DDx

-  Rolando fracture

-  3 part fracture = Bennetts + lage dorsal fragment

-  Worse prognosis, uncommon

 

 

Ix

-  Hand Exam

-  X-Ray

-  Oblique fracture w triangular fragment at ulnar base of metacarpal

-  Note size of volar lip fragment & degree of shaft displacement

-  +/- CT-Hand

 

 

Mx

-  Reduction

-  Longitudinal traction on thumb

-  Abduction & extension of metacarpal

-  Thumb Spica cast 4-6 weeks

-  Re-X-ray

-  Thermoplastic splint + protected mobilisation

-  K-wire

-  If <3mm displacement, beak fragment <50% joint surface

-  Secure 1st metacarpal to trapezium or 2nd metacarpal

-  Thumb Spica cast 4-6 weeks

-  ORIF

-  If >3mm displacement

-  2.5cm incision over radial base of thumb metacarpal

-  Dorsal sensory branch of radial nerve protected

-  EPB & APL retracted

-  Radial artery protected

-  Thumb retraction

-  Secure w K-wire

-  +/- cortical lag screw OR T or L plates OR Condylar plate

 

 

 

References

 

Wheeless Textbook of Orthopaedics: www.wheelessonline.com/ortho/bennetts_fracture_dislocation

Pic (X-Ray): www.med.wayne.edu/diagradiology/tf/ms/MS18.html

Pic (Mechanism): handbook.muh.ie/trauma/Limb-Upper/Hand_Finger_Injuries.htm

Pic (Rolando): radiographics.rsna.org/content/20/3/819/F31.large.jpg