PREDICTION OF BONE-GRAFT STRENGTH USING DUAL-ENERGY RADIOGRAPHIC ABSORPTIOMETRY

Study design. A biomechanical study of anterior iliac crest bone was done to investigate a relationship between the compressive strength of tricortical iliac crest grafts and bone mineral density (BMD) of the iliac crest measured by dual-energy x-ray absorptiometry (DEXA). Objectives. This study investigated the potential usefulness of DEXA for measuring BMD of the iliac crest and documented bone graft strength predictability by BMD measurements. Summary of Background Data. The corticocancellous iliac bone is frequently used as an interbody graft for anterior spine fusion. The decreased compressive strength of bone graft may lead to collapse, pseudarthrosis and recurrence of symptoms, particularly in the osteoporotic patient. The DEXA accurately determines BMD of the spine and the hip, but no previous studies are available on the pelvis. Methods. The BMDs were measured on the intact pelvis of the elderly and the corresponding tricortical grafts, using DEXA. The strut and Smith-Robinson type grafts were placed under axial loading using Material Testing System. Load to failure and compressive strength were obtained and statistically correlated to BMDs. Results. There was a high correlation between the BMDs of the intact pelvis and each graft (R = 0.8, P < 0.001). The ultimate load to failure and compressive stress were linearly correlated to the BMD of the intact pelvis (R = 0.82, P < 0.001, R = 0.78, P < 0.001, respectively) as well as to the BMD of the graft (R = 0.77, P < 0.001, R = 0.75, P < 0.001, respectively). Conclusions. These results suggest that the biomechanical strength of the iliac bone graft is very dependent on its BMD, and DEXA has a potential clinical value in predicting iliac bone graft strength for cervical spine fusion.