Distal radius fracture fixation using volar plate: A comparative study evaluating the biomechanical behavior of uni and bicortical distal screws

Comparative Biomechanical Study of Fragment-Specific Plates and Headless Screws for Radial Styloid and Lunate Facet Fixation in Distal Radius Fracture Evaluated in a Synthetic Composite

PURPOSE

To evaluate the compressive stiffness (ability to resist compression under an applied load) of fragment-specific plate and headless screw fixation for radial styloid and volar lunate facet fractures in a synthetic composite distal radius.

METHODS

A simulated radial styloid fracture (AO type B1.1) and simulated volar lunate facet fracture (AO type B3.3) were created in synthetic composite distal radii and fixed with a fragment-specific plate (FSP) using a radial styloid or lunate facet plate or with two- or three-headless screws (2HS, 3HS), creating 6 fixation models: B1.1/FSP, B1.1/2HS, B1.1/3HS, B3.3/FSP, B3.3/2HS, and B3.3/3HS. Compressive stiffness of fixation constructs under initial static load, cyclic load, and final static load was investigated. Nonaxial loadings, including shearing and rotation, were not evaluated.

RESULTS

Regarding AO type B1.1, the mean stiffness of the B1.1/FSP construct was not significantly different from the intact radius, and the mean stiffness was greatest in the B1.1/3HS and lowest in the B1.1/2HS construct. For AO type B3.3, the mean stiffness of the B3.3/3HS construct was not significantly different from the intact radius, and the mean stiffness of the B3.3/FSP and B3.3/2HS construct was greatest and lowest, respectively. Minimal differences in stiffness between initial and final static loads confirmed that there was no evidence of failure implant under cyclic compressive loads.

CONCLUSIONS

Fragment-specific plates and two- or three-headless screw fixation maintained mechanical stability through compressive cyclic loading for radial styloid and volar lunate facet fractures. The FSPs and three-headless screws fixations provided superior stiffness over the two-headless screws fixation. There was no articular fracture failure in all fixation constructs with initial static compression, cyclic loading, and final compression.

CLINICAL RELEVANCE

Fragment-specific plates and headless screws can both be considered as adequate fixation for radial styloid and volar lunate facet fractures.

Practical Method to Evaluate the Stiffness of Fractured Radius

Distal radius fractures (DRFs) are one of the most common fractures of the upper extremity system. To evaluate the performance of DRF treatments, the construct (i.e., a DRF fixed by an implant) was compressed at the distal radius in the axial direction to evaluate the compressive stiffness. In previous studies, various constructs of both cadaveric and synthetic radii have been proposed for biomechanical testing for DRF. Unfortunately, high deviations of the measured stiffness have been reported across the literature, which may relate to the inconsistency of applied mechanical actions (i.e., the tested radii may under various combinations including compression, bending, and shear). In the present study, a biomechanical apparatus and an experimental procedure were proposed for the biomechanical testing of radii under pure compression. After the biomechanical tests of synthetic radii, it was found that the standard deviation of stiffness was significantly lower than that in previous studies. Thus, the biomechanical apparatus and the experimental procedure were proven to be a practical method for the evaluation of radii stiffness.