Abstract
This paper proposes an optimum design of the pedicle screw with respect to bone density and variables of the screw design. First, pedicle screws are designed and manufactured with design variables including the core diameter and conical angle that affect the pullout force of the pedicle screw. Variables of bone density are also classified into two groups, namely grade 10 (0.16 g/cc) with osteoporotic bone density and grade 20 (0.32 g/cc) with normal bone density. The effect of each parameter on the pullout force and relationship between the pullout force and screw designs are investigated. Furthermore, bone damage after fixation failure or insertion in the patient body is considered separately from the pullout strength. Therefore, cross sectional images of the artificial bone are observed to analyze the degree of damage after the pullout test of the pedicle screw by using micro-CT (computed tomography). The region and degree of bone damage are quantitatively analyzed. The effects of the core diameter and conical angle of the pedicle screw on the pulling force, bone damage, and fracture behavior are analyzed via the aforementioned experiments and analysis. An optimal pedicle screw design is suggested based on the experimental results.
Highlights
IntroductionProblems including bending, fracture, loosening, detachment, and movement of pedicle screws from the bone have been constantly raised due to the insufficient fixation strength of the interface between the screw and bone
An advent of pedicle screws for spinal and chiropractic treatments were 1950s by Boucher [1].problems including bending, fracture, loosening, detachment, and movement of pedicle screws from the bone have been constantly raised due to the insufficient fixation strength of the interface between the screw and bone
The pullout force of the screw designed in the study was compared with those in previous studies as shown in Figure 8, and the results indicate that it exhibited a significant improvement
Summary
Problems including bending, fracture, loosening, detachment, and movement of pedicle screws from the bone have been constantly raised due to the insufficient fixation strength of the interface between the screw and bone. This is because the selection of pedicle screw design and surgical method fail to consider the bone density of various patients. The fixation failure leads to decreases in the stress and fracture load capacity as well as stress shielding This causes the micro bone fracture of vertebra due to decreases in bone mineral density [7,8,10]
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