Quantifying Rates of Fracture Repair

Background: After skeletal injury, there is a highly regulated physiologic process culminating in repair of the broken bone. Easily quantifying the rate at which fractures are healing with a high degree of fidelity is not currently possible. Clinical trials using xray endpoints require high numbers of patients because of the inherent difficulty in quantifying fracture repair using radiographs. While numerous agents over several decades of study have shown positive effects on fracture healing in preclinical studies, none are currently in clinical use.This reflects our inability to quantify this process sufficiently to demonstrate clinical efficacy in humans.

Methods: A novel loading frame was developed to apply load to the dorsal surface of the radius after fracture. This load frame was constructed to fit within the bore of an ultra high resolution micro-ct scanner (XtremeCT, Scanco, Switzerland) with resolution of 80 microns which is approved for use in human subjects. By scanning subjects pre- and post- loading in the frame, a known load can be applied and the resultant displacement measured. This displacement can be used to calculate stiffness and strain across the healing fracture.

Results: The force:pressure relationship of the loading frame was calibrated using a materials testing machine and found to be 0.20891 N/mmHg. To test our design, cadaveric wrists with simulated distal radius fractures of varying severity were scanned pre and post load. Displacement ranged from 0.178-0.514mm in the distal radius with an applied pressure of 100 mmHg, which correlated to 23.32N of force, ± 0.19N.

Conclusions: This novel loading system can allow for accurate and precise quantification of fracture healing in human distal radius fractures. Accurate quantification of stiffness of healing fractures can be used to demonstrate efficacy of pharmacologic agents designed to accelerate fracture repair during clinical trials.