Pedicle Screw Theory

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Pedicle screws are widely used for the treatment of spinal instability using spine fusion technique. Screw loosening is one of the major problems faced by the surgeon which leads to delay in recovery of the patient. The present study tries to understand the factor and interaction effect of density, insertion depth and insertion angle on pullpull out strength and insertion torque of the pedicle screw. A pull out study was carried out on rigid polyurethane foam blocks representing osteoporotic to normal bone densities according to the ASTM-1839 standard. The study according to ASTM-1839 standard. From the study, it was found that density contributes highest towards pull out strength and insertion torque. The interaction effect is significant…show more content…
However,, these instruments these instruments are not immune to failures have failures such as screw loosening or screw breakage. The incidence of screw loosening occurs between 0.6% and 11% [6–8] and screw breakage due to stress concentration has ranged between 2.6% and 60% [7,10,11] causing fusions to become instable, causing instability of fixations and other serious post-operation complications which may require subsequent surgery. Pedicle screw Lloosening of the pedicle screw is widely seen, especially in patients with osteoporosis [11]. Hence, surgeons need a thorough understanding of the holding and stability mechanisms of pedicle screws [12]. Currently, osteoporosis is not a contraindication for fusion surgery but it is challenging for surgeons due to potential complications such as screw back-out, migration or loosening which may compromise the surgical outcome [13,14]. These complications may lead to nonunion making surgical revision necessary. According to a recent study, there was 9% revision cases in 643 adult spinal deformity surgeries of this 40% were related to nonunion [15]. Some methods attempted to reduce the risk of screw failure is to use bone cement augmentation [16–18] and expandable screw [19–21].…show more content…
These studies have been carried out on individual effect of the factor. In During these studies, the interaction effects weare not quantified. A detailed study on the effect of the factors and their interaction effect will help in better understanding ofn the holding power of the pedicle screws, particularly in low- density bones. The present study attempts to study this using an experimental pull out study of the pedicle screw in synthetic cancellous bone models. The assumptions made for the current study are: complex geometry of pedicle and vertebra are not taken into account and a uniform block was assumed to represent the spinal structure. It was assumed that complex geometry is not going to play a role in pull out study but might influence the loading pattern physiologically. Pedicle region which contributes 60 % to the holding power [12,27] was not considered since osteoporosis mostly affects the vertebral body. Contribution of pedicle was assumed to be uniform in all bone types. The results of such a study can be used in developing a better predictive modeling to estimate for estimating the pedicle screw holding power of pedicle screw. This will help to improve in better pre- surgical planning resulting in reduced operation time and early patient recovery. In this context, the

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