Augmentation of anterior vertebral body screw fixation by an injectable, biodegradable calcium phosphate bone substitute.
METHODS
A biomechanical study to evaluate the effects of a biodegradable calcium phosphate (Ca-P) bone substitute on the fixation strength and bending rigidity of vertebral body screws.


OBJECTIVE
To determine if an injectable, biodegradable Ca-P bone substitute provides significant augmentation of anterior vertebral screw fixation in the osteoporotic spine.


BACKGROUND
Polymethylmethacrylate (PMMA) augmented screws have been used clinically; however, there is concern about thermal damage to the neural elements during polymerization of the PMMA as well as its negative effects on bone remodeling. Injectable, biodegradable Ca-P bone substitutes have shown enhanced fixation of pedicle screws.


METHODS
Sixteen fresh cadaveric thoracolumbar vertebrae were randomly divided into two groups: control (no augmentation) (n = 8) and Ca-P bone substitute augmentation (n = 8) groups. Bone-screw fixation rigidity in bending was determined initially and after 10(5) cycles, followed by pullout testing of the screw to failure to determine pullout strength and stiffness.


RESULTS
The bone-screw bending rigidity for the Ca-P bone substitute group was significantly greater than the control group, initially (58%) and after cyclic loading (125%). The pullout strength for Ca-P bone substitute group (1848 +/- 166 N) was significantly greater than the control group (665 +/- 92 N) (P < 0.01). Stiffness in pullout for the Ca-P bone substitute groups (399 +/- 69 N/mm) was significantly higher than the control group (210 +/- 51 N/mm) (P < 0.01).


CONCLUSIONS
This study demonstrated that augmentation of anterior vertebral body screw fixation with a biodegradable Ca-P bone substitute is a potential alternative to the use of PMMA cement.
Bai
B
B
Musculoskeletal Research Center, Department of Orthopaedic Surgery, Hospital for Joint Diseases Orthopaedic Institute, New New York, New York 10003, USA.
Kummer
F J
FJ
Spivak
J
J
D020341:Absorbable Implants; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D001863:Bone Screws; D018786:Bone Substitutes / Q000008:administration & dosage*; D002102:Cadaver; D002130:Calcium Phosphates / Q000008:administration & dosage*; D006801:Humans; D016014:Linear Models; D010024:Osteoporosis / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical
D001672:Biocompatible Materials; D018786:Bone Substitutes; D002130:Calcium Phosphates