Anatomic Risks with Overpenetration of the Volar Locking Plates' Proximal Holes

Background  Volar locking plate fixation (VLP) is commonly used to treat distal radius fractures (DRF). Risk of dorsal compartment injury with distal screw hole fixation has been studied; however, the risk with proximal screw hole fixation is not well studied. Purpose  The goal of this study was to investigate the risk of dorsal structure injury from the screw holes proximal to the two distal rows. Methods  Nine cadaveric forearms were used. After volar distal radius exposure, a long VLP was applied. Kirschner wires were placed through the most proximal holes into the dorsal compartments. The extensor structures penetrated were noted and tagged with hemoclips. The distance from the dorsal cortex to the structures was measured. Results  The abductor pollicis longus (APL) and extensor pollicis brevis (EPB) muscle bodies were only penetrated; no tendons were penetrated. Proportion of muscle penetration increased with the more proximal screw holes. EPB was more likely to be penetrated distally and APL proximally; both were injured at holes 2 and 3. The extensors were 2 mm from the dorsal cortex of the radius on average; this did not decrease with compression of the forearm. Conclusions  This is the first study to examine the anatomic risk of extensor structure injury with VLP proximal screw hole penetration. No extensor tendons were penetrated by these proximal screw holes; first dorsal compartment muscle bellies may be irritated with overpenetration. Our findings suggest that proximal VLP screws do not need to be downsized if they are not over 2 mm prominent.