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A Biomechanical Comparison of Expansive Pedicle Screws for Severe Osteoporosis: The Effects of Screw Design and Cement Augmentation.

Tai CL, Tsai TT, Lai PL, Chen YL, Liu MY, Chen LH - PLoS ONE (2015)

Bottom Line: For screws without cement augmentation, solid screws exhibited the lowest pullout strength compared to the four expansive groups (p < 0.01).No significant differences in pullout strength were observed between the expansive screws with different designs (p > 0.05).Taken together, our results show that pedicle screws combined with cement augmentation may greatly increase screw fixation regardless of screws with or without expansion.

View Article: PubMed Central - PubMed

Affiliation: Graduate Institute of Medical Mechatronics, Department of Mechanical Engineering, Chang Gung University, Kweishan, Taoyuan, Taiwan.

ABSTRACT
Expansive pedicle screws significantly improve fixation strength in osteoporotic spines. However, the previous literature does not adequately address the effects of the number of lengthwise slits and the extent of screw expansion on the strength of the bone/screw interface when expansive screws are used with or without cement augmentation. Herein, four designs for expansive pedicle screws with different numbers of lengthwise slits and different screw expansion levels were evaluated. Synthetic bones simulating severe osteoporosis were used to provide a comparative platform for each screw design. The prepared specimens were then tested for axial pullout failure. Regardless of screw design, screws with cement augmentation demonstrated significantly higher pullout strength than pedicle screws without cement augmentation (p < 0.001). For screws without cement augmentation, solid screws exhibited the lowest pullout strength compared to the four expansive groups (p < 0.01). No significant differences in pullout strength were observed between the expansive screws with different designs (p > 0.05). Taken together, our results show that pedicle screws combined with cement augmentation may greatly increase screw fixation regardless of screws with or without expansion. An increase in both the number of slits and the extent of screw expansion had little impact on the screw-anchoring strength. Cement augmentation is the most influential factor for improving screw pullout strength.

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Related in: MedlinePlus

Photographs showing various cemented screws after the pullout tests. Left to right: solid, 4-slit with 16-mm EEL, 4-slit with 22-mm EEL, 6-slit with 16-mm EEL, and 6-slit with 22-mm EEL.A larger expansion range was observed for screws with 22-mm EELs compared with screws with 16-mm EELs and that cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Regardless of the number of slits (4 or 6), the cement/bone composite structure was distributed closer to the screw head for screws with a larger expansion range (22-mm EELs).
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pone.0146294.g005: Photographs showing various cemented screws after the pullout tests. Left to right: solid, 4-slit with 16-mm EEL, 4-slit with 22-mm EEL, 6-slit with 16-mm EEL, and 6-slit with 22-mm EEL.A larger expansion range was observed for screws with 22-mm EELs compared with screws with 16-mm EELs and that cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Regardless of the number of slits (4 or 6), the cement/bone composite structure was distributed closer to the screw head for screws with a larger expansion range (22-mm EELs).

Mentions: The average diameters at the screw tip after screw expansion for 4-slit screws with 16- and 22-mm effective expansion lengths (EELs) were 10.61 ± 0.54 mm and 13.02 ± 0.46 mm (p < 0.001), respectively. For 6-slit screws with 16- and 22-mm EELs, the average diameters were 11.07 ± 0.67 mm and 13.24 ± 0.28 mm (p < 0.001), respectively. Expansive screws with 16- and 22-mm EELs after expansion are shown in Fig 4. The results revealed that screws with longer EELs achieved larger expansion ranges, whereas no significant difference in expansion range was observed between 4-slit and 6-slit designs with the same EEL (p > 0.05). The physical examination of various screws with cement augmentation after pullout tests is shown in Fig 5. Observations of the failed specimens after pullout tests also revealed that a larger expansion range was observed for screws with 22-mm EELs compared to screws with 16-mm EELs. Furthermore, cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Regardless of the number of slits (4 or 6), the cement/bone composite structure was distributed closer to the screw head for screws with a larger expansion range (22-mm EELs). A typical force-displacement curve and the mean maximum pullout strength for various screws with and without cement augmentation are shown in Figs 6 and 7, respectively. Regardless of the screw design (4 or 6 slits and EELs of 16 or 22 mm, or a solid screw), screws with cement augmentation exhibited significantly higher pullout strengths than did pedicle screws without cement augmentation (p < 0.001). However, no significant difference in pullout strength was observed among the five cemented groups (p > 0.05). Additionally, in the cementless group, solid screws showed the lowest pullout strength compared to the four expansive groups (p < 0.01), whereas no significant difference was observed among the four expansive groups (p > 0.05). Furthermore, for a given screw fixation technique (cemented or cementless), no significant difference in pullout strength was observed among expansive screws with different numbers of slits or degrees of screw expansion (p > 0.05). The difference in both the number of slits and expansive extent had little impact on screw-anchoring strength. Cement augmentation was the most influential factor improving screw pullout strength.


A Biomechanical Comparison of Expansive Pedicle Screws for Severe Osteoporosis: The Effects of Screw Design and Cement Augmentation.

Tai CL, Tsai TT, Lai PL, Chen YL, Liu MY, Chen LH - PLoS ONE (2015)

Photographs showing various cemented screws after the pullout tests. Left to right: solid, 4-slit with 16-mm EEL, 4-slit with 22-mm EEL, 6-slit with 16-mm EEL, and 6-slit with 22-mm EEL.A larger expansion range was observed for screws with 22-mm EELs compared with screws with 16-mm EELs and that cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Regardless of the number of slits (4 or 6), the cement/bone composite structure was distributed closer to the screw head for screws with a larger expansion range (22-mm EELs).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4697834&req=5

pone.0146294.g005: Photographs showing various cemented screws after the pullout tests. Left to right: solid, 4-slit with 16-mm EEL, 4-slit with 22-mm EEL, 6-slit with 16-mm EEL, and 6-slit with 22-mm EEL.A larger expansion range was observed for screws with 22-mm EELs compared with screws with 16-mm EELs and that cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Regardless of the number of slits (4 or 6), the cement/bone composite structure was distributed closer to the screw head for screws with a larger expansion range (22-mm EELs).
Mentions: The average diameters at the screw tip after screw expansion for 4-slit screws with 16- and 22-mm effective expansion lengths (EELs) were 10.61 ± 0.54 mm and 13.02 ± 0.46 mm (p < 0.001), respectively. For 6-slit screws with 16- and 22-mm EELs, the average diameters were 11.07 ± 0.67 mm and 13.24 ± 0.28 mm (p < 0.001), respectively. Expansive screws with 16- and 22-mm EELs after expansion are shown in Fig 4. The results revealed that screws with longer EELs achieved larger expansion ranges, whereas no significant difference in expansion range was observed between 4-slit and 6-slit designs with the same EEL (p > 0.05). The physical examination of various screws with cement augmentation after pullout tests is shown in Fig 5. Observations of the failed specimens after pullout tests also revealed that a larger expansion range was observed for screws with 22-mm EELs compared to screws with 16-mm EELs. Furthermore, cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Regardless of the number of slits (4 or 6), the cement/bone composite structure was distributed closer to the screw head for screws with a larger expansion range (22-mm EELs). A typical force-displacement curve and the mean maximum pullout strength for various screws with and without cement augmentation are shown in Figs 6 and 7, respectively. Regardless of the screw design (4 or 6 slits and EELs of 16 or 22 mm, or a solid screw), screws with cement augmentation exhibited significantly higher pullout strengths than did pedicle screws without cement augmentation (p < 0.001). However, no significant difference in pullout strength was observed among the five cemented groups (p > 0.05). Additionally, in the cementless group, solid screws showed the lowest pullout strength compared to the four expansive groups (p < 0.01), whereas no significant difference was observed among the four expansive groups (p > 0.05). Furthermore, for a given screw fixation technique (cemented or cementless), no significant difference in pullout strength was observed among expansive screws with different numbers of slits or degrees of screw expansion (p > 0.05). The difference in both the number of slits and expansive extent had little impact on screw-anchoring strength. Cement augmentation was the most influential factor improving screw pullout strength.

Bottom Line: For screws without cement augmentation, solid screws exhibited the lowest pullout strength compared to the four expansive groups (p < 0.01).No significant differences in pullout strength were observed between the expansive screws with different designs (p > 0.05).Taken together, our results show that pedicle screws combined with cement augmentation may greatly increase screw fixation regardless of screws with or without expansion.

View Article: PubMed Central - PubMed

Affiliation: Graduate Institute of Medical Mechatronics, Department of Mechanical Engineering, Chang Gung University, Kweishan, Taoyuan, Taiwan.

ABSTRACT
Expansive pedicle screws significantly improve fixation strength in osteoporotic spines. However, the previous literature does not adequately address the effects of the number of lengthwise slits and the extent of screw expansion on the strength of the bone/screw interface when expansive screws are used with or without cement augmentation. Herein, four designs for expansive pedicle screws with different numbers of lengthwise slits and different screw expansion levels were evaluated. Synthetic bones simulating severe osteoporosis were used to provide a comparative platform for each screw design. The prepared specimens were then tested for axial pullout failure. Regardless of screw design, screws with cement augmentation demonstrated significantly higher pullout strength than pedicle screws without cement augmentation (p < 0.001). For screws without cement augmentation, solid screws exhibited the lowest pullout strength compared to the four expansive groups (p < 0.01). No significant differences in pullout strength were observed between the expansive screws with different designs (p > 0.05). Taken together, our results show that pedicle screws combined with cement augmentation may greatly increase screw fixation regardless of screws with or without expansion. An increase in both the number of slits and the extent of screw expansion had little impact on the screw-anchoring strength. Cement augmentation is the most influential factor for improving screw pullout strength.

Show MeSH
Related in: MedlinePlus