Effects of Plate-Bone Contact on Bridge Plate Fracture Fixation Biomechanics: Computational, Experimental, and Analytical Modeling.

Bridge plating is commonly used for internal fixation of comminuted fractures. The inner working length between screws has been established as a key parameter controlling postoperative biomechanical stability. However, plate-bone contact may affect these biomechanics in complex ways, and the offset between the plate and bone is variable across surgeries. The objective of this study was to examine the effects of construct and loading parameters on interfragmentary motion and maximum plate stress of bridge plating constructs. Finite element models were developed with variations in inner working length, plate-bone offset, fracture gap size, and loading type and magnitudes. Experiments with synthetic bones were conducted in parallel to support model credibility. Analytical models were also developed based on beam bending and torsion of the plate, assuming rigidity outside the inner working length. Finite element and experimental results of axial and torsional loading scenarios without plate-bone contact confirmed linear relationships between inner working length and interfragmentary motion. Analytical predictions of interfragmentary motion showed very good agreement with the finite element simulations in these scenarios. Conversely, in cases with plate-bone contact, a shorter effective working length was formed, and results were dependent on additional variables such as fracture gap. The study shows how the mechanics of bridge plating can be understood and predicted based on beam theory up to the point of plate-bone contact, and how interfragmentary motions and maximum plate stresses are influenced by the interaction of surgical variables in the presence of plate-bone contact.