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Biomechanics
Evaluating New Materials for Fixation
Target Condition: Fractured or osteoporotic vertebrae.
Traditional Approach: Injection of methacrylate bone cement.
New Approach: Biodegradable calcium phosphate cement.
Progress: The material's mechanical efficiency for this application has been demonstrated.
Investigator Dr. Fred Kummer
New techniques for improving the fixation of joint prostheses and implants are continually being tested in Dr. Kummer’s Mechanical Testing Laboratory. These have included the use of bioactive coatings, defect filling materials and cements.
Of particular interest are calcium phosphate (CaP) materials that serve to stabilize an implant or fracture during the crucial healing stage and then gradually degrade biologically, leaving no inorganic residue, and are replaced by normal bone. These materials have been studied for their utility as implant coatings and grouting materials to improve the fixation of devices for treating hip fractures and spinal deformities and to expedite repair of fractured spinal vertebrae.
One study focused on biodegradable calcium phosphate cement for prophylactic augmentation of osteoporotic vertebrae and treatment of vertebral compression fractures. The conventional treatment involves injection of polymethylmethacrylate bone cement (PMMA) to enhance vertebral body strength and relieve pain. There are intraoperative and long-term problems with PMMA, however, including thermal damage to the neural elements during polymerization and negative effects on bone remodeling.
X-rays confirm the effectiveness and mechanical integrity of an experimental bone cement. Shown here are lateral (top) and axial (bottom) views of a fractured vertebra before and after augmentation with a calcium phosphate bone-substitute material. Arrows show where the vertebral height has been restored as a result of this new treatment.
The new cement, like PMMA, can be mixed into an injectable paste. Unlike polymerizing PMMA, however, CaP cement is essentially nonheat-producing. It is biocompatible and is progressively resorbed over time and replaced by normal bone tissue during remodeling. What remained to was to determine whether a biodegradable CaP cement has sufficient mechanical integrity to strengthen osteoporotic vertebral bodies and stabilize vertebral compression fractures. PMMA injected vertebral bodies were used for comparison.
The study demonstrated that injection of biodegradable CaP cement into an osteoporotic vertebral body can significantly increase its fracture strength and stiffness. Moreover, the injection of this cement into a vertebral compression fracture can partially restore vertebral height and prevent further vertebral collapse while avoiding the potential problems associated with the use of PMMA cement.
Evaluating New Materials for Fixation
Target Condition: Fractured or osteoporotic vertebrae.
Traditional Approach: Injection of methacrylate bone cement.
New Approach: Biodegradable calcium phosphate cement.
Progress: The material's mechanical efficiency for this application has been demonstrated.
Investigator Dr. Fred Kummer
New techniques for improving the fixation of joint prostheses and implants are continually being tested in Dr. Kummer’s Mechanical Testing Laboratory. These have included the use of bioactive coatings, defect filling materials and cements.
Of particular interest are calcium phosphate (CaP) materials that serve to stabilize an implant or fracture during the crucial healing stage and then gradually degrade biologically, leaving no inorganic residue, and are replaced by normal bone. These materials have been studied for their utility as implant coatings and grouting materials to improve the fixation of devices for treating hip fractures and spinal deformities and to expedite repair of fractured spinal vertebrae.
One study focused on biodegradable calcium phosphate cement for prophylactic augmentation of osteoporotic vertebrae and treatment of vertebral compression fractures. The conventional treatment involves injection of polymethylmethacrylate bone cement (PMMA) to enhance vertebral body strength and relieve pain. There are intraoperative and long-term problems with PMMA, however, including thermal damage to the neural elements during polymerization and negative effects on bone remodeling.
X-rays confirm the effectiveness and mechanical integrity of an experimental bone cement. Shown here are lateral (top) and axial (bottom) views of a fractured vertebra before and after augmentation with a calcium phosphate bone-substitute material. Arrows show where the vertebral height has been restored as a result of this new treatment.
The new cement, like PMMA, can be mixed into an injectable paste. Unlike polymerizing PMMA, however, CaP cement is essentially nonheat-producing. It is biocompatible and is progressively resorbed over time and replaced by normal bone tissue during remodeling. What remained to was to determine whether a biodegradable CaP cement has sufficient mechanical integrity to strengthen osteoporotic vertebral bodies and stabilize vertebral compression fractures. PMMA injected vertebral bodies were used for comparison.
The study demonstrated that injection of biodegradable CaP cement into an osteoporotic vertebral body can significantly increase its fracture strength and stiffness. Moreover, the injection of this cement into a vertebral compression fracture can partially restore vertebral height and prevent further vertebral collapse while avoiding the potential problems associated with the use of PMMA cement.