Biomechanical Assessment of Hydroxyapetite Vertebroplasty in Cadaveric Compression Fractures

Derek A. Taggard, MD
Patrick W Hitchon, MD
Thomas N. Rogge, MS
Vijay K Goel, PhD
John S. Drake, BSE (Iowa City, IA)

Multiple strategies exist for the management of thoracolumbar burst fractures. Particularly in the osteoporotic and elderly, minimally invasive techniques for stabilization are desirable. A biologially inert substance that produces an exothermic reaction, polymethylmethacrylate (PMMA) has been used to enhance structural support during spinal stabilization as well as for percutaneous vertebroplasty. Carbonated hydroxyapatite cement (HAC) is an osteoconductive, biocompatible cement that may be an alternative to PMMA. Fresh, unconstrained cadaveric thoracolumbar spines were tested for motion in 6 degrees of freedom before and after production of a T11 burst fracture. Unilateral, transpedicular vertebroplasty was performed randomly with either PMMA or HAC. The material was allowed to cure and the spines were again load tested. A final load test followed fatiguing with 5000 cycles of flexion and extension. Motion in the intact state was similar for the two groups. Burst fractures in the HAC group resulted in 30% more motion than the spines receiving PMMA. Initial results suggest both materials resulted in moderate restabilization as compared to the intact state. As compared to the fractured state, vertebroplasty with HAC resulted in better motion reduction in flexion but not in lateral bending or axial rotation. After fatiguing the spines, both groups produced motion values similar to the fractured state. Compared to the cemented state, HAC maintained stability better than PMMA. Thus, HAC appears to have a satisfactory early stabilizing effect, particularly in flexion, as compared to PMMA. Retained motion in other planes may be clinically addressed with application of external orthosis.