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Scaphoid Osteochondral Graft for Reconstruction of the Distal Radius: A Computational Method and Case Study
Kathleen M. Kollitz, BS; Jerry I. Huang; Jennifer W. Hsu; Peter R. Cavanagh University of Washington, Seattle, WA
Purpose: To describe a novel computational method for assessing the goodness of fit of an osteochondral graft. A surgical case is presented of a 25 yearold male who sustained a complex, open radiocarpal fracturedislocation with bone loss (Figure 1). The large defect in the lunate facet of the distal radius was reconstructed with the remaining distal pole of the scaphoid, allowing for motionpreserving proximal row carpectomy rather than total wrist fusion (Figure 2). We retrospectively applied our software to five normal wrist CTs to determine the goodness of fit of the graft described. Materials and Methods: CT scans of five wrists were digitally rendered. The capitate facet of the scaphoid was fit to the lunate fossa of the distal radius using custom software based on the iterative closest point (ICP) algorithm. This approach iteratively determines the optimal position of a model surface to minimize the sum of squares of distances from all points on a target surface. The goodness of fit of the two surfaces was reported by calculating the mean residual distance (MRD) between each point on one surface and its nearest neighbor on the other. Results: The MRD for the five subjects was found to be 0.25mm, with 82.898.3% of the articular surfaces within 0.5mm of each other (Table 1, Figure 3). At one year followup, our patient had no pain with wrist flexion 15° and extension 20°. Discussion: We have developed a software algorithm for comparing two articular surfaces to test goodness of fit for a proposed joint reconstruction. Though indications for the articular reconstruction performed in this case study are limited, the software is versatile and may be applied to any boney surface to identify new graft donor sites. The fit assessment renders a richer, threedimensional understanding of the fit of the graft as compared to traditional twodimensional assessments.
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