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