Effect of distal screw number on axial deformation and fragment-specific stability in AO/OTA 2R3 C2.1 distal radius fractures

To investigate the biomechanical influence of distal screw number in palmar plate fixation of unstable intra-articular distal radius fractures with radiodorsal metaphyseal comminution.

Nine matched pairs of cryopreserved human radii were prepared using a standardized AO/OTA 2R3 C2.1 fracture model with a defined radiodorsal metaphyseal defect zone. For each pair, specimens were randomized to palmar fixation using a 2.4-mm variable-angle locking plate with either four or six distal screws. After embedding, constructs were subjected to cyclic axial loading (150 N, 5,000 cycles) simulating early postoperative rehabilitation. Global axial deformation and fragment-specific three-dimensional interfragmentary motion were recorded using an optical motion-tracking system. Statistical analysis was performed using non-parametric tests (p < 0.05).

Two specimens from one donor pair were excluded, leaving 16 radii (8 pairs) for analysis. Bone mineral density and initial construct stiffness did not differ between groups. The six-screw configuration showed significantly lower axial deformation after cyclic loading (p = 0.047) and lower radial fragment-shaft translation at both time points (p = 0.028; p = 0.045). Radial fragment-shaft rotation was lower in the six-screw group at baseline (p = 0.018), but no rotational difference remained after cyclic loading. In the overall cohort, axial deformation decreased after cyclic loading (p = 0.015).

In this unstable intra-articular fracture model with radiodorsal metaphyseal comminution, six distal screws reduced post-cyclic axial deformation and radial fragment-shaft micromotion compared with four screws. The clinical relevance of these findings remains to be determined.