Evidence of Negative Effects of Defect Size and OlderPatient Age by Quantitative CT-Based 3D Image Analysisin Ultraporous Beta-Tricalcium Phosphate GraftedExtremity Bone Defects at One Year

Synthetic bone graft materials are commonly used to fill defects after curettage of benign bone lesions. Ultraporousbeta tricalcium phosphate (TCP) is a popular synthetic compound used in this situation. Prior clinical studies based on plain X-rayanalysis suggest incorporation of TCP is incomplete, even when combined with bone marrow (BMA).Purpose.Thepurposewastoanalyze volumetric CT-based changes in defects grafted with TCP with/without BMA in a completed prospective RCT to objectivelydetermine (1) relationship between size and age versus TCP incorporation and (2) whether there is an advantage to addition of BMA.Methods. Twenty-one patients with CT scans at≥1 year follow-up available for digital analysis (TCP=10, TCP w/BMA =11) form thestudy population. CT image stacks were evaluated by creating volumetric masks using MIMICS imaging software for total defect,graft remaining, and graft incorporated volumes graft incorporation endpoints.Results. Overall, there was significant (p=0.0029)negative correlation (r2= 0.38) between defect size and ratio of incorporated bone to defect size. This relationship remained strong(r2= 0.56) particularly for defects>20 cc but not for smaller defects. Bone width was also a significantly related factor (r2=0.94), with less graft incorporation in larger bone sites, in part likely due to the linear relationship between defect size and bonewidth. Relationship with age was complex and closely tied to defect volume. For larger defect volumes, younger patients weremore successful at graft incorporation. Although age itself was not an independently significant factor, as defect volume increased,advanced age more negatively impacted new bone formation.Conclusions. Larger size defect and affected bone and advancing ageappear to be important negative factors in synthetic graft incorporation. Results showed no advantage to addition of BMA to TCP.