Dinner fork deformity | Radiology Signs

Answer:

The dinner fork deformity is the profile of the wrist after a Colles fracture: a distal radial fracture with dorsal angulation and dorsal displacement of the distal fragment, radial shortening and often an associated ulnar styloid fracture, which gives the forearm and hand the silhouette of an upturned dinner fork. It follows a fall on the outstretched hand and is the commonest fracture of the upper limb in older adults, where it is a fragility fracture that should prompt osteoporosis assessment. The radiographic report should quantify the parameters that determine management, because they predict function: dorsal tilt, with the normal volar tilt of about 11 degrees, radial inclination, normally about 22 degrees, radial height, normally 11 to 12 mm, ulnar variance, and the presence and size of any intra-articular step or gap, with more than 2 mm of articular incongruity generally accepted as an indication for reduction and fixation. Distinguish it from the Smith fracture, the volarly angulated reverse Colles that produces a garden spade deformity, the Barton fracture, an intra-articular rim fracture with carpal subluxation, and the chauffeur fracture of the radial styloid. Associated injuries to seek are scaphoid fracture, scapholunate dissociation, distal radioulnar joint instability and, clinically, acute median nerve compression.

Why is it called so?

The dorsally angulated distal fragment raises the hand into a curve that reproduces the profile of a dinner fork lying on its back.

Pathophysiology

A fall onto the extended, pronated wrist transmits axial load through the carpus to the distal radius. The volar cortex fails in tension and the dorsal cortex, which bears the compressive load, comminutes and impacts. Loss of dorsal cortical support allows the distal fragment to tilt and displace dorsally, and impaction shortens the radius, so radial height and inclination fall and ulnar variance becomes positive. In osteoporotic bone the metaphyseal trabeculae collapse readily, which is why the injury occurs after low-energy falls and why dorsal comminution frequently makes the reduction unstable, favouring loss of position after closed manipulation and cast immobilisation.

Alternative names: Colles deformity; silver fork deformity

Other associated named signs: Garden spade deformity of the Smith fracture and the Terry Thomas sign of scapholunate dissociation