What causes a silver fork deformity on the lateral wrist radiograph?
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Answer:
A silver fork or dinner fork deformity is the profile of the wrist when the distal radial fragment is displaced and angulated dorsally, producing a dorsal prominence at the fracture with the hand deviated volarly beyond it, so the forearm and hand in profile resemble the curve of a fork. It is the clinical and radiographic signature of a Colles fracture, an extra-articular distal radial fracture with dorsal angulation, typically from a fall onto the outstretched hand in an older patient with osteoporosis, and frequently accompanied by an ulnar styloid fracture. Assessment is by the three standard measurements: radial height, normally 11-13 mm; radial inclination, normally 22-23 degrees; and volar tilt, normally 10-11 degrees volar, which becomes dorsal tilt in a Colles fracture. Loss of these parameters guides the decision between cast immobilisation and fixation. The mirror image is the Smith fracture, with volar angulation, which produces the garden spade deformity.
Why is it called so?
The dorsally angulated wrist seen from the side traces the curve of the back of a dinner fork.
Pathophysiology
A fall onto the outstretched, dorsiflexed hand transmits an axial load through the carpus to the distal radius. The volar cortex fails in tension while the dorsal cortex is compressed and comminuted, so the distal fragment tilts and translates dorsally, hinging on the intact volar periosteum. Because it also impacts proximally, radial height is lost and the radial styloid no longer projects distal to the ulna, reducing radial inclination. The resulting dorsal step at the fracture with the hand carried volarly is what the profile records. Osteoporotic metaphyseal bone comminutes readily, which is why the deformity is often marked and unstable in the elderly.
Alternative names: Dinner fork deformity, Colles deformity
Other associated named signs: Garden spade deformity of the Smith fracture, the Barton and reverse Barton fractures, the chauffeur fracture, and the pronator quadratus fat pad sign
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