Two-dimensional Morphological Characteristics of the Distal Radius on Axial Magnetic Resonance Image and the Effects on Distal Screw Length.

BACKGROUND: Detection of dorsal cortical penetration of distal locking screws is difficult owing to the irregular shape of the dorsal surface of the distal radius. This study was designed to analyze two-dimensional morphological characteristics of the distal radius on axial magnetic resonance image, and to suggest a guideline for evaluation of screw length in distal radius fractures on the fluoroscopic or plain X-ray true lateral image.

METHODS: Anteroposterior length and lateral width of the distal radius, distance between the highest and the lowest point of the dorsal cortex (deceptive length), and widths of the first to second (hazard zone) and the third to fifth extensor compartments (safe zone) at the Lister tubercle level were measured on 104 axial magnetic resonance images by two hand surgeons.

RESULTS: The mean length and width of the distal radius at the Lister tubercle level were 22.96 mm and 30.42 mm, respectively. The mean hazard zone and safe zone widths were 8.72 mm and 19.43 mm, respectively. The mean deceptive length was 4.07 mm and the deceptive length did not have a relationship with height, sex, and age of subjects.

CONCLUSIONS: We suggest that 4 mm be used as a reference value for the evaluation screw length at the safe zone. If the vertical distance between a distal screw tip and the peak of the Lister tubercle is lesser than 4 mm on a fluoroscopic or plain X-ray true lateral image, dorsal cortical penetration should be suspected. When dorsal cortical penetration at the hazard zone is suspected, both oblique or pro-supination views should be checked.