Influence of an additional locking screw on fracture reduction after volar fixed-angle plating-introduction of the "protection screw" in an extra-articular distal radius fracture model.

Background: Though, volar fixed-angle plating has become increasingly popular to treat distal radius fractures no studies are available comparing the mechanical properties of different screw configurations to fix the plate to the shaft. The aim of the present study was to evaluate the effect of an additional locking screw directly proximal to the fracture site and to assess if such a screw might be protective against secondary loss of reduction after volar fixed-angle plating.

Methods: Ten Sawbones radii were used to simulate an extra-articular distal radius fracture model (AO/OTA 23-A3). In the first group (n = 5), volar fixed-angle plates (Aptus Radius 2.5, Medartis, Switzerland) were fixed to the radius shaft with a single nonlocking cortex screw in the oval hole and with two locking screws in the holes proximal to the long hole (LLNx); in the second group, the plates were fixed identically as in the first group, but an additional locking screw was inserted into the plate-hole distal to the oval hole, proximal to the fracture site (LLNL). After embedding, specimens were tested with a servohydaulic material testing machine under cyclic axial loading with 800 N for 2,000 cycles. Axial stiffness, elastic axial deformation (elastic dorsal tilt angle), and plastic deformation (plastic dorsal tilt angle) were recorded.

Results: After 2,000 cycles, stiffness was 761.6 (+/-59.5) N/mm in group LLNx and 628.9 (+/-37.6) N/mm in group LLNL without significant difference. Elastic deformation and elastic tilt angle were 1.05 (+/-0.08) mm and 3.9 (+/-0.3) degree in group LLNx. In group LLNL, elastic deformation and elastic tilt angle were 1.27 (+/-0.08) mm and 4.7 (+/-0.3) degree, respectively. Plastic deformation and plastic tilt angle were significantly higher in group LLNx (p < 0.001). After 2,000 cycles, dorsal tilt angle was 1.9 (+/-0.3) degree in group LLNx and 0.7 (+/-1.0) in group LLNL.

Conclusion: This study showed the mechanical superiority of volar fixed-angle plates with a "protection screw" in an extra-articular fracture model. Further clinical investigation is needed to verify the results.