Distal radius fracture osteosynthesis by volar locking plate: influence of epiphyseal screw positioning on risk of loss of reduction

Ulnar variance is an important radiological parameter for good functional outcome after distal radius fracture osteosynthesis. Secondary loss of reduction due to radial shortening is a common complication after volar locking plate fixation. Some authors recommend beginning by placing the most ulnar epiphyseal screw, ensuring that it is positioned as close as possible to the distal radioulnar and radiocarpal joints. The hypothesis of our study was that the positioning of the ulnar epiphyseal screw relative to the distal radioulnar and radiocarpal joints influences the maintenance of reduction during follow-up.

190 distal radius fractures were treated with volar locking plate fixation and divided into two cohorts: cohort A with <2 mm and cohort B with ≥2 mm loss of ulnar variance. Minimum follow-up was 45 days. The positioning of the most ulnar epiphyseal screw was evaluated using a single variable, the ulno-distal index. Means were compared using t-tests and proportions using chi-squared tests. The alpha risk was set at 5%. The intra- and inter-observer reliability of the ulno-distal index measurement were assessed.

Mean ulno-distal index was significantly lower in cohort A at 11.28 mm, compared to 13.33 mm in cohort B; p < 0.0001. Ulno-distal index <12 mm was a significant protective factor: p < 0.0001 and relative risk 0.558. No other intrinsic or extrinsic factors of secondary loss of reduction significantly influenced the risk of ulnar variance alteration.

The study confirmed the hypothesis that, in distal radius fracture treated with volar locking plate fixation, the closer the ulnar epiphyseal screw to the distal radioulnar joint and radiocarpal joint, the lower the risk of ulnar variance alteration.