REPOSITIONING BONE FRAGMENTS USING REGISTRATION OF PAIRED-POINTS AND ASSISTED-CONSTRAINTS IN VIRTUAL BONE REDUCTION SURGERY

When repositioning fractured bones in orthopedic surgery, correctness and accuracy are vital to allow the bone to regain the function and facial aesthetics of native uninjured bone. Various improvements to repositioning techniques have been proposed using points, curves, and surfaces to find correspondence between the fracture fragments. The aim of this study was to investigate the appropriate registration constraints for fractured bone reduction. One paired-point and three assisted-constraints registration methods were tested based on contralateral, landmark, and fracture line markers. The fractured proximal femur of a patient was used to compare the performance of these registration methods. Semi-automatic repositioning based on a singular value decomposition algorithm was performed to solve the problem of matching the data from two fragments. The repositioning results show that the proposed registration methods have great promise in assisting the user in defining the paired points, which is often difficult due to visibility limitations on images of fractured bone. Each of the proposed approaches was shown to yield different benefits. In terms of repositioning correctness, the use of contralateral constraints produced the smallest RMS error (1.853 mm). The contralateral template method yielded the lowest fragment deviation error, but was not significantly superior to the other approaches. Fracture line-based constraints may potentially enable the relocation of fragments closest to pre-injured conditions.