TECHNIQUE TO ASSESS THE RIGIDITY OF CALLUS BONE DURING EXTERNAL FIXATION OF DISTAL RADIAL FRACTURES

Abstract

Distal radial fractures account for 17% of all fractures treated, with peaks in the bimodal distribution corresponding to young and senior patients. External fixation is one of the best techniques to allow quick patient recovery and is necessary for complex fractures, such as that of the distal radius. However, the safe removal time for these frames remains unclear. A conservative approach commonly leaves the external fixator in place for six weeks, which may be unnecessarily prolonged and lead to increased complications. The aim of this work is to develop a technique to quantify, objectively, a safe removal time for these frames. Studies have been conducted on external fixation of tibial fractures, however there are differences that do not allow transfer of these studies to the external fixation of distal radial fractures. These differences include configuration of the fixation frame, bone and fracture geometries, and the application and transfer of the load to the bone. In this work, the dynamic transfer of the load between the fractured bone and the fixator is investigated. An instrumented grip and a measuring device have been developed to monitor the axial force and displacement when the patient applies a load. Using measurements collected by the instrument and data specifying the frame geometry, a finite element model is used to calculate the load carried by the fixator and by the bone, and the rigidity of the new callus is determined. Plotting the rigidity on semi-logarithmic scale the healing rate can be established. This technique has been successfully verified in a laboratory simplified structure representative of bone fracture. The rigidity of several intra-gap materials has been estimated experimentally using the technique, and the results compared to the real value of the material. These measurements do not interfere in any way with the patient treatment and they can be collected from the first day after the operation. The technique has been tested on 14 volunteer patients and the increase in callus rigidity can be detected by measurements during treatment using the technique described. A randomised prospective study has been initiated to validate this technique and investigate the healing process. A positive outcome would enable the rigidity of the new callus bone and the healing rate to be monitored during clinical assessment. Any healing delay or non-union could be promptly detected, improving the quality of the treatment.