Bone-bonding ability of bioactive bone cement under mechanical stress

Bioactive bone cement (BABC) is able to bond to bone through a Ca-P rich la yer. It was evaluated so far in a rat tibial model, where no mechanical str esses are supposed to take place, The objective is to investigate the behav ior of BABC in the environment of posterolateral spinal fixation model, in which the bone cement interface is exposed to continuous mechanical stress. Japanese white rabbits were used. Fixation of L5-L6 segment was done by wi ring the spinous and transverse processes of L5 and L6 vertebrae. Then BABC was applied over the transverse processes and the intertransverse process membrane on both sides. Polymethylmethacrylate (PMMA) bone cement was used similarly in the control group. Animals were sacrificed after 1 day, 4, 8, and 16 weeks postoperatively. Bone cement interface was examined using Giem sa surface staining and SEM, and affinity index was measured. Biomechanical testing was done nondestructively in right and left torsion. BABC bonded t o bone directly with no intervening soft tissue at 4, 8, and 16 weeks, whil e soft tissue was consistently seen between PR PMMA bone cement and bone. B ABC-spine constructs were stiffer than PMMA-spine constructs at all time in tervals. BABC bonded directly to bone under mechanical stress and afforded stiffer fixation than PMMA bone cement. (C) 1999 John Wiley & Sons, Inc.