Distal radius fractures are becoming increasing prevalent in our aging population. Locked volar plating remains the preferred surgical treatment. Prior studies investigating optimal locking plate constructs for fracture stability have predominantly used extra-articular fracture models. Many surgeons have adopted unicortical distal fixation to minimize risk of dorsal cortex penetration and subsequent extensor tendon injury. However, there remains mixed results on the superiority of threaded locking screws versus smooth pegs in construct stability. Theoretically, pegs can provide increased subchondral support with less risk of joint penetration whereas locking screws may achieve stronger bony purchase. This study aimed to determine the biomechanical effect of unicortical distal locking screws and pegs on stability in comminuted, intra-articular distal radius fracture cadavers.

Materials and Methods

We applied volar-locking distal radius plates to 24 cadaveric radiuses. The radiuses were divided into 4 groups based on distal locking fixation: 100% length bicortical screws, 75% length screws, 100% length pegs, and 75% length pegs. Osteotomies simulated AO type 23 C2 dorsally comminuted, intra-articular fractures. We determined each construct's stiffness under physiologic loads (axial compression, dorsal bending, and volar bending) before and after 1,000 cycles of axial conditioning and before axial load to clinical failure (2mm of displacement) and catastrophic failure. We used Analysis of Covariance (ANCOVA) to compare differences of means between groups and Tukey Honest Significant Difference (HSD) test for post-hoc analysis.

Results

There were no significant differences in age, weight, or bone mineral density (BMD) between groups. Stiffness to volar bending and dorsal bending were statistically equivalent between groups before and after cycling loading. Final stiffness under axial load was statistically equivalent for all groups. Force to clinical failure was statistically equivalent between 100% screw length (308N) and 75% screw length (351N) constructs, and equivalent between 100% peg length (127N) and 75% peg length (150N) constructs. Forces to clinical failure were significantly greater for 100% and 75% screw lengths compared to their peg counterparts (p=0.0253 and p=0.0125 respectively). Force to clinical failure was significantly greater for 75% screw lengths than 100% smooth pegs (p=0.005). Force to catastrophic failure was statistically equivalent between all groups.

Conclusions

We recommend the use of 75% length screws or pegs over their bicortical counterparts to prevent dorsal cortex penetration without compromising stability. Surgeons may consider using threaded locking screws over smooth pegs in treating more complex intra-articular distal radius fractures.