Pull-out Strength Values Research Articles

Comparison of the pull-out strengths of three different screws in pedicular screw revisions: a biomechanical study

We investigated the possible effects of three pedicular screws on axial pull-out strength in pedicular revision surgery. Two study groups were formed from calf lumbar vertebrae. Initially, Alici pedicular screws with an outer diameter of 6.5 mm were applied (with or without tapping) to all the pedicles. All the pedicles were subjected to axial pull-out testing to induce pedicular insufficiency. Then, Alici pedicular screws with an outer diameter of 7 mm were applied to the left pedicles. The right pedicles in the two study groups were assigned to receive two different types of pedicular screws with an expandable (enlargeable) end, respectively. Axial pull-out testing was repeated in both groups and the results were compared with the initial pull-out strength values. In the first group, 65% and 64% of the initial pull-out strengths were obtained with 7-mm Alici pedicular screws and with expandable pedicular screws, for the left and right pedicles, respectively. The corresponding pull-out strengths in the other study group were 70% and 68.5% of the initial values, respectively. Tapping of the screw hole entrance resulted in a mean decrease of 13% in the pull-out strength compared to screw applications without tapping. Pedicular screw revisions using a 0.5 mm greater screw in diameter did not provide adequate screw-bone inter-face strength and pedicle filling. Similarly, expandable pedicular screws did not contribute to screw stability.

COMPARATIVE BIOMECHANICS: CERVICAL SPINE FACET JOINT VERSUS LATERAL MASS SCREW INSERTION TECHNIQUE

This study involves a comparative biomechanics of facet joints (FJ) versus lateral mass (LM) screw insertion technique in the human cadaveric lower cervical spine (C3, C4, C5 and C6). The objective of this study is to understand the promising usage of the facet joint insertion technique and to determine the pullout strength of FJ insertion technique for posterior cervical fixation system. A total of 52 disarticulated human vertebrae (C3–C6) were used in this study. DEXA scan was carried out on all specimens before testing. Cortical screws of 3.5 mm and 4.0 mm were used for both FJ and LM techniques, which were subjected to uniaxial load. From the study made so far, the facet joint technique performed well based on the pullout strength values obtained. Having addressed the main concern on screw perforation of lateral mass technique, this facet joint technique not only demonstrated a significantly higher pullout resistance but it is also a relatively low risk surgical procedure.

Influence of Curing Agents on Rubber-to-Textile and Rubber-to-Steel Cord Adhesion

Abstract The results presented in this paper show that the dosage of sulfur greatly influences rubber-to-textile and rubber-to-steel cord adhesion. As far as rubber-to-textile adhesion is concerned, the pull-out strength is reduced when the sulfur level falls below 2 phr, the extent of the reduction depending on the type of fiber and the bonding process. With steel cord the lower limit for sulfur is as high as 3 phr. This is discouraging because it shows that the use of efficient and semi-efficient vulcanization in the manufacture of goods reinforced with fabrics or steel cord is, to say the least, highly problematical. On the other hand, it is often desirable to reduce the proportion of sulfur in order, for instance, to increase resistance to aging and reversion and to reduce compression set and heat build-up. The choice of accelerators also has an important influence on adhesion. A sufficiently long scorch time is required to allow complete wetting of the reinforcing material by the rubber compound. If curing starts before complete wetting of the textile or steel cord has occurred, adhesion cannot be built up. For example, unsatisfactory or no rubber-to-textile and rubber-to-steel cord adhesion is obtained, when ultra-accelerators are used. As the scorch time increases, adhesion improves. Best results are obtained with sulfenamides, but sulfenamides showing increasing scorch time give no improvement in rubber-to-textile bonding. However, DCBS gave much better results for rubber-to-steel cord adhesion than the other sulfenamides and thus appears particularly suitable. Although the results given by the other sulfenamides can be somewhat improved by the addition of a retarder, pull-out strength values do not reach those given by DCBS. Any decrease of scorch time of a compound deteriorates adhesion whether scorch time is reduced by compounding ingredients or by heat history imposed by processing. MBI, used as an antioxidant, which reduces scorch time drastically, causes complete loss of rubber-to-steel cord adhesion and also impairs rubber-to-textile adhesion. Most of the antioxidants, however, have a beneficial effect on mbber-to-steel cord adhesion. For zinc-plated steel cord antioxidants of the amine type give results inferior to those of the phenolic type. To obtain optimal rubber-to-textile and rubber-to-steel cord adhesion the compounder primarily has to consider the efficacy of the bonding agents but in addition he has to take into account the effects which may be exerted by compounding ingredients and processing conditions.