One of the purported advantages of volar plating for distal radius fractures has been the ability to allow patients to perform early postoperative motion. Evaluation of the strength and stiffness of volar plates, through biomechanical simulation of the forces across the wrist, tests this hypothesis. Recent biomechanical investigations have shown that multiple plating systems appear strong enough to withstand physiologic force. [11
The most comprehensive study of distal radius volar plate biomechanics to date compared the failure properties and stiffness of ten volar plates, [11
] which included three of the four plate systems used in this study. The majority of the biomechanical testing was performed using a wedge osteotomy model, with a small comparison group of eight segmental resection. This study showed that stainless steel plates were stiffer than titanium plates, and that in the segmental resection model, distal fixation failure was common. All plates in all groups failed with plate bending.
Willis et al. have published the only study to date comparing the behavior of volar plates using a sawbones model. [28
] In this study, four volar plates were compared to the Synthes π dorsal plate system. Two of the volar plates were locking plates (Hand Innovations DVR, and Synthes volar locking plate), but only the DVR used distal locking technology. This study showed that the Synthes π plate was significantly stiffer than the volar plates in a wedge compression radius fracture model, and that the DVR and volar locking plates were more stiff than the nonlocking volar plates.
In our study, the use of a sawbones model to test volar plates in a gap resection construct is novel. Synthetic sawbones felt to simulate real bone most closely were chosen to standardize the biomechanical protocol; sawbones also offer a cost-efficient model for implant trials. Quantitative analysis of the angle of deformation confirmed that the DVR plate had a significantly lower degree of bending at failure than the Synthes, Wright, and Avanta plates. Of the four plates tested, the DVR plate had a significantly higher peak load at failure but did not differ in stiffness when compared to the other three plates. In clinical applications, these data would suggest that the DVR can tolerate higher sustained force through the wrist before failing. However, the stiffness data are likely more clinically relevant since the measured forces replicate physiologic loading more accurately. The similarities in stiffness across the four plate systems support the idea that since all four plates performed similarly during gradually increasing load, with the same degree of displacement, all provide sufficient fixation to tolerate physiologic forces during healing. Compared to Koh’s study, only one of the plate types showed any distal fixation failure, specifically tine pullout in the Avanta plate.
To validate the sawbones model, a small cadaver study was also performed. Cadaver specimens were not standardized by densitometry, age, sex, or size. Cadaver construct behavior was compared to synthetic bone and showed the same mode of failure and comparable peak loads to failure. This cadaver model, as a control measure, supports the use of sawbones for future use in biomechanical studies.
There were several limitations in this study. A different number of distal fixation points were used with each plating system, as all possible distal fixation holes were filled. While this reproduces the actual clinical scenario, the difference in screw number is a weakness of nonexact comparison. The comparative cadaver study was small and thus not amenable to statistical analysis or comparison of the plate constructs, and the specimens were not standardized.
This study evaluated four volar plates in peak load to failure with constant compression and fatigue preloading, as well as for stiffness of the implants. Our results showed a significantly higher peak loading force required to deform the DVR plating system with sustained compressive force and after physiologic force application. However, there were minimal differences in stiffness between the DVR, Lo-Con VLS, Synthes stainless, and the Avanta tine plates. There was no proximal fixation failure in any of the plates, and only two of the Avanta plates showed distal fixation failure. These results indicate that all of these plates can withstand physiologic loading to allow early wrist range of motion after surgery for distal radius fractures.