Sunday, February 07, 1999
Treatments of vertebral body fractures include analgesics, bed rest and external bracing. Despite these treatments, progressive kyphosis, prolonged pain and disability may still occur.
One possible solution may be the fortification or augmentation of the vertebral bodies with a biodegradable calcium phosphate (Ca-P) bone substitute, said Jeffrey M. Spivak, MD, director, Hospital for Joint Diseases Spine Center, New York, who presented scientific paper 45 Thursday. A study by Dr. Spivak and colleagues compared an injected Ca-P bone substitute with injected polymethylmethacrylate bone cement (PMMA) for augmentation of osteoporotic vertebral bodies and vertebral bodies following com-pression fracture.
"Percutaneous vertebroplasty by injection of PMMA into vertebral bodies has been described for this application and has achieved good enhancement of vertebral body strength and relief of pain," Dr. Spivak said. "However, there are several intraoperative and long-term potential complications with this technique, including thermal damage to the neural elements dur-ing polymerization of the PMMA and negative effects on bone remodeling.
"One solution to these problems may involve the use of biodegradable alternatives to PMMA. Ideally, these biodegradable materials would increase the strength of the vertebral body, degrade when the fracture repair is completed and be replaced by new bone growth."
Dr. Spivak said that recently, new biodegradable Ca-P bone substitute materials have been developed. Like PMMA, these materials can be mixed into an injectable paste. One of these pastes hardens and cures at physiologic temperature and pH and in an aqueous environment to reach a final maximum compressive strength in about four hours.
Unlike PMMA, the paste remains workable for several hours at room temperature, and the solidification proceeds endothermically. Most importantly, Dr. Spivak said, this material is similar to bone in chemical composition and crystalline size, and is biocompatible and bioresorbable. In previous in vivo studies, Ca-P bone substitute materials have been shown to be biocompatible. The histologic response to these materials has shown no significant inflammatory response and no foreign-body giant cell reaction. During remodeling, the Ca-P material is progressively replaced by normal bone tissue.
Forty fresh osteoporotic thoracolumbar vertebrae were used for two separate parts of this study: Injection into osteoporotic vertebrae and injection into post-frac-tured vertebrae. Before and after injection, the specimens were radiographed in the lateral projection to determine changes in vertebral body height and then loaded to failure in anterior bending.
The results showed both the fracture strength and stiffness of Ca-P bone substitute and PMMA cement groups were similar and significantly stronger than intact control group. This indicates that the use of Ca-P bone substitute to strengthen osteoporotic vertebral bodies and stabilize compression fractures might provide an alternative to the use of PMMA cement.
In addition to Dr. Spivak, co-authors of the study, all at the Musculoskeletal Research Center of the department of orthopaedic surgery, Hospital for Joint Diseases, are Bo Bai, research associate; Frederick J. Kummer, PhD, associate director; and Laith M. Jazrawi, MD, research resident.