Plaster of Paris as an osteoconductive material for interbody vertebral fusion in mature sheep

Study Design. In adult female sheep, histologic and biomechanical criteria were used to determine whether the osteoconductive performance of plaster o f paris would promote the incorporation of the tubular titanium mesh implan ts used for interbody vertebral fusions. Objectives. To compare the osteogenicity of plaster of paris with that of a utogenous iliac crest bone and bone marrow 6 months after they were loaded into tubular titanium mesh cages and implanted as L3-L5 bridges after L4 co rpectomies. Summary of Background Data. One of the aims of surgery for vertebral pathol ogy is to stabilize the spine by interbody fusions, The morbidity associate d with the use of iliac crest autograft bone for fusion grafts prompted tri als using plaster of paris as an osteoconductive substrate. Methods. The total volume of bone that invested the L3-L5 mesh cages after 6 months was quantitated by computed tomography scans. All specimens subseq uently were cut into fusion mass segments for biomechanical testing in flex ion, extension, compression, and torsion, and then embedded in plastic for sectioning and histomorphometry to determine the trabecular bone volume wit hin the titanium mesh. Results. In each experimental model, implants of plaster of paris were the osteoconductive equal of autogenous iliac crest bone/marrow preparations. T he volumes of bone formed around and within the titanium mesh were identica l, and the tissues were biomechanically in distinguishable. A partial mecha nism was determined by modifying the system for midshaft femoral defects. Conclusions. In the sheep, a tubular titanium mesh backed with plaster of p aris forms an osteoconductive conduit to achieve a biomechanically stable i nterbody lumbar vertebral fusion.