Biomechanical analysis of dual versus lateral locked plating in elderly bicondylar tibial plateau fractures: Does medial comminution matter?

OBJECTIVE: To assess dual plating versus lateral locked plate fixation of bicondylar tibial plateau fractures in an elderly cadaveric model with and without medial bone loss PARTICIPANTS: 10 pairs of elderly (range 78-93 years of age) fresh frozen tibias. INTERVENTION: Bicondylar tibial plateau fractures were created reproducing AO/OTA 41 C1 (without medial bone loss) and C2 fractures (with medial bone loss). Cadavers were randomized to 4 different groups. Groups 1 and 2 were 41 C1 fractures and fixated with either dual or lateral plating, respectively. Groups 3 and 4 were fixated in a similar fashion with medial metaphyseal bone loss (41 C2 fracture) with dual plating Group 3 and lateral plating group 4. Lateral plating consisted of a 3.5 mm 5-hole lateral plate (ALPS, ZimmerBiomet) with 6 bicortical locking screws proximally and two diaphyseal screws. Dual plating groups underwent lateral plating and additional 3.5 mm 5-hole posteromedial 1/3 tubular plate (ZimmerBiomet) placed at the apex of the fracture with two shaft screws and one unicortical screw proximally. Specimens were tested in a Mechanical Testing System (MTS) machine loading both condyles. OUTCOME MEASUREMENTS: Specimens were loaded to 300 N and coronal alignment obtained. Specimens were then cycled from 100 N to 700 N for 5000 cycles at 2 Hz. Average axial displacement, maximal displacement, average force and coronal alignment after 5000 cycles were recorded. Lastly, force to failure was recorded at 100 N/sec. RESULTS: Mean axial displacement was 4.21 mm ranging from 3.12 mm in group 1 to 5.92 mm in group 4 (P = 0.51). Failure force averaged 3340 N ranging from 4342 N in group 1 to 2433 N in group 4 (P = 0.36). Maximal displacement ranged from 3.69 mm in group 1 to 7.37 mm in group 4 (P = 0.21). Change in coronal alignment ranged from 0.98° in group 1 to 1.97° in group 4 (P = 0.45). No statistically significant difference was noted between all four groups for all data points. CONCLUSION: The results of this study demonstrate that a lateral locked plate may offer an alternative means of fixation in AO/OTA 41 C1 and C2 fractures.

Hybrid screw fixation for femoral neck fractures: Does it prevent mechanical failure?

INTRODUCTION: Traditionally, femoral neck fracture fixation has been performed using three partially threaded cancellous screws. However, fracture collapse with femoral neck shortening, and varus deformation frequently occurs due to posterior medial comminution and lack of calcar support. We hypothesize replacing the inferior neck/calcar screw with a fully threaded, length stable, screw will provide improved biomechanical stability, decrease femoral neck shortening and varus collapse. METHODS: Ten matched cadaveric pairs (20 femurs) were randomly assigned to two screw fixation groups. Group 1 (Hybrid) utilized one fully threaded calcar screw & two partially threaded superior screws. Group 2 (PT) utilized all partially threaded screws. Specimens underwent standardized femoral neck osteotomies, 45° from the horizontal, with 5 mm posteromedial wedge removed to simulate posteromedial comminution. Screws were placed using fluoroscopic guidance. Specimens were biomechanically tested using two loading sequences: 1) Axial load applied up to 700 N, followed by cyclic loading at 2 Hz with loads of 700 to 1,400 N for 10,000 cycles. 2) All surviving constructs were cyclically loaded to failure in stepwise incremental manner with max load of 4,000 N. Paired t-tests used to compare stiffness, cycles to failure, and max load to failure (defined as 15 mm load actuator displacement). RESULTS: Construct stiffness was 2848 ± 344 N/mm in PT vs. 2767 ± 665 for Hybrid (P = 0.628). Load to failure demonstrated, hybrid superiority with max cycles to failure (3797 ± 400 cycles) vs. (2981 ± 856 cycles in PT) (p = 0.010), and max load prior to failure (3290 ± 196 N) vs. (2891 ± 421 N in PT) (p = 0.010). No significant difference in bone mineral density was noted in any of the specimens. CONCLUSIONS: Our study is the first to assess the biomechanical effects of hybrid fixation for femoral neck fractures. Hybrid screw configuration resulted in significantly stronger constructs, with higher axial load and increased cycles prior to failure. The advantageous mechanical properties demonstrated using a fully threaded inferior calcar screw provides a length stable construct which may prevent the common complication of excessive femoral neck shortening, varus collapse and poor functional outcome.