Virtual Simulation for Interactive Visualization of 3D Fracture Fixation Biomechanics

Abstract

Introduction: In the surgical fixation of fractures, proper biomechanical stability is key in preventing clinical complications including poor fracture healing, residual deformity, loss of fixation, or implant failure. Stability is largely influenced by treatment decisions made by the surgeon. The interplay of surgeon-controlled variables and their effect on the three-dimensional (3D) biomechanics of a fracture fixation construct are often not intuitive, and current training methods do not facilitate a deep understanding of these interactions.

Methods: A simulation software interface, FracSim, was developed. FracSim is built on a large precomputed library of finite element simulations. The software allows a surgeon to make adjustments to a virtual fracture fixation construct/weight-bearing plan and immediately visualize how these changes affect 3D biomechanics, including implant stress and fracture gap strain, important for clinical success. Twenty-one orthopaedic residents completed an instructor-led educational session with FracSim focused on bridge plating. Subjects completed pretests and posttests of knowledge of biomechanical concepts and a questionnaire.

Results: Subjects scored a mean of 5.6/10 on the pretest of biomechanical knowledge. Senior residents scored better than junior residents (P = 0.04). After the educational session with FracSim, residents improved their test scores to a mean of 8.0/10, with a significant improvement (P < 0.001). Questionnaire scores indicated that subjects believed that FracSim had realistic implants, constructs, and motions and that training with FracSim was purposeful, desirable, efficient, fun, and useful for enhancing the understanding of fracture fixation biomechanics.

Discussion: This new type of simulation software enables interactive visualization of 3D fracture fixation biomechanics. Limitations of this study include lack of a control group undergoing traditional education and lack of a delayed posttest to assess retention. FracSim may provide an effective and engaging way to promote a deeper understanding of biomechanical concepts in the orthopaedic learner.

Figure 1.

Key features of FracSim software interface for interactive visualization of fracture fixation biomechanics (also see Supplemental Video). First (top), the surgeon specifies a fracture fixation construct (in this case for bridge plating) by selecting from drop-down menus: fracture gap size (blue labels), plate length and screw configuration (green), implant and screw material (yellow), and loading mode (orange). Finite element simulations were precomputed for every possible combination of these variables. In the main window, the simulation of postoperative biomechanics is quickly displayed on a rotatable/zoomable 3D construct. The surgeon can animate loading of the construct by dragging a slider bar. Stresses on implants and bone strains are plotted with separate color maps, and the transparencies of bone and implant can be controlled for easier inspection. A representation of the deformable fracture gap is also displayed. Maximum clinically important stress and strain values are provided and can be located with markers. The Quad View tab (not shown) allows simultaneous viewing, with 3D manipulation, of up to four saved constructs. The Charts tab allows plotting of key variables for comparison including maximum implant stress, maximum screw stress, fracture gap axial strain, and fracture gap shear strain.

Figure 2.

Educational concepts demonstrated with FracSim during session with orthopaedic residents, for both compression/bending and torsional loading. Example fracture fixation constructs are shown, along with corresponding fracture gap representations (right side). During the educational session, dynamic loading of the constructs was visualized along with inspection with different views. In the figure above, for torsion loading, superimposed black circles indicate fixation screw locations.

Figure 3.

Scores on knowledge test, before and after instructional session using FracSim software. The test had a maximum of 10 points and focused on knowledge of bridge plating fracture fixation biomechanics. * indicates significance by unpaired t-test. ** indicates significance by paired t-tests, comparing the post-test and corresponding pre-test scores. Eight junior residents and 13 senior residents completed the testing. Means +/− 1 std. dev. are shown.