Leveraging In Vivo Motion Assessment: Investigating the Impact of Fixation and Fracture Pattern on Healing

/ABSTRACT We seek to understand how variations in surgical fixation and weightbearing for distal femur fractures impact the mechanical environment and influence healing. The concept of mechanotransduction, where physical forces on the macroscale are converted into biochemical signals that guide cellular responses, is relevant to the healing of all human fractures. Distal femur fractures treated with locked plate fixation are an excellent model for study given a relatively high rate (up to 32%) of healing complications and a range of fixation strategies that produce different motion profiles at the fracture site. Although the clinical importance of mechanotransduction in fracture healing—in particular the strain across a fracture site—has been qualitatively demonstrated, there is a lack of quantitative clinical data, the specific mechanisms are not fully characterized, and progress to improve related clinical outcomes has been stagnant. This lack of quantitative clinical data limits our ability to design surgical techniques, implants, and rehabilitation protocols to optimize healing. Currently, a major obstacle in the field is a lack of clinically applicable, validated tools with which to assess interfragmentary strain or motion. To overcome this, we aim to employ three novel, noninvasive, and complementary methods of quantifying clinical fracture site motion. Methods 1 and 2: Weightbearing CT (WBCT) and biplane fluoroscopy will quantify in vivo fracture site motion for research subjects in the early postoperative period following open reduction and internal fixation (ORIF) of a distal femur fracture. Method 3: Computational modeling will quantify in vivo fracture site motion for a larger cohort of patients following distal femur fracture fixation, inclusive of those having undergone WBCT and biplane fluoroscopy. WBCT and biplane fluoroscopy provide direct in vivo assessment, while computational modeling offers an indirect, scalable method of estimating fracture site motion. In the smaller cohort, the proposed research leverages these complimentary methods of assessing fracture site motion to define in vivo motion profiles for common fixation strategies as well as to demonstrate how this motion changes during early fracture healing via serial WBCT imaging. The scalability of computational modeling will be leveraged to quantify the association of fracture site motion with fracture healing. These methods support future translational research involving heretofore untestable hypotheses, including research into optimal fixation strategies and rehabilitation protocols, and provide the ability to contextualize mechanotransduction in the setting of other factors relevant to fracture healing. Exploring quantification of clinical interfragmentary strain itself, the work will allow us to explore the relative feasibility and marginal benefit of this assessment. This translational study opens multiple avenues of mechanistic and clinical investigation with the potential for early and long-term clinical impact by decreasing the incidence of delayed union and nonunion of fractures, and potentially allowing more rapid rehabilitation. Finally, quantification of mechanotransduction on the macroscale will provide an avenue for multiscale translational research. Project Number: 1I01RX005057-01A2 | Fiscal Year: 2026 | NIH Institute/Center: Veterans Affairs (VA) | Principal Investigator: William Lack | Institution: VA PUGET SOUND HEALTHCARE SYSTEM, SEATTLE, WA | Activity Code: I01 | Study Section: Musculoskeletal Health & Function[RRD2] View on NIH RePORTER: https://reporter.nih.gov/project-details/11115927