Bone substitute first or screws first? A biomechanical comparison of two operative techniques for tibial-head depression fractures.

BACKGROUND: The aim of this study was to investigate a drillable and injectable bone substitute (calcium phosphate cement) and the operative technique enabled by the drillable option in a new biomechanical fracture model for tibial depression fractures in synthetic bones.
MATERIALS AND METHODS: Lateral depression fractures of the tibial plateau (AO 41-B2, Schatzker III) were created in a biomechanical fracture model in three different synthetic bones (Sawbone 3401, Synbone 1110/1116). Reproducible fractures were generated employing Synbone 1110, which exhibited a comparable strength to human osteoporotic bones and was used for the further experiments. After reduction of the fractures, the stabilization was performed with two different operative techniques. In group 1, first an osteosynthesis with four screws was performed and then the metaphyseal defect was filled up with calcium phosphate cement (Norian drillable). In group 2, initially the filling up with Norian drillable was done enabling a complete filling of the defect, followed by placing of the screws. Displacement under cyclic loading with 250 N for 3,000 cycles, stiffness, and maximum load in load-to-failure tests were determined.
RESULTS: A comparison of the two operative techniques of stabilization showed a distinctly lower displacement and higher stiffness for group 2 when the defect was filled up first. For the maximum load, no significant differences could be demonstrated.
CONCLUSIONS: A complete filling of the defect by first applying the calcium phosphate cement significantly reduces the secondary loss of reduction of the depression fracture fragment under cyclic loading with a clinically relevant partial weight bearing. The beneficial effects of drillable calcium phosphate cement may also be transferable to defects other than tibial-head depression fractures.