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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

Schematic drawings showing four types of expandable screws: (A) 4-slit with 16-mm EEL, (B) 4-slit with 22-mm EEL, (C) 6-slit with 16-mm EEL, and (D) 6-slit with 22-mm EEL.The EEL was defined as the length from the point of diameter change of the internal hole to the screw tip. All of the screws had the same outer diameter of 6 mm, a length of 40 mm from hub to tip, a thread pitch of 2 mm and a thread depth of 0.8 mm. The lengthwise slit length from the screw tip was 27 mm for all screws. All of the expansive screws had an internal hole 3 mm from the screw head, which was connected to a smaller hole (1.5 mm in diameter) that extended to the screw tip.
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pone.0146294.g001: Schematic drawings showing four types of expandable screws: (A) 4-slit with 16-mm EEL, (B) 4-slit with 22-mm EEL, (C) 6-slit with 16-mm EEL, and (D) 6-slit with 22-mm EEL.The EEL was defined as the length from the point of diameter change of the internal hole to the screw tip. All of the screws had the same outer diameter of 6 mm, a length of 40 mm from hub to tip, a thread pitch of 2 mm and a thread depth of 0.8 mm. The lengthwise slit length from the screw tip was 27 mm for all screws. All of the expansive screws had an internal hole 3 mm from the screw head, which was connected to a smaller hole (1.5 mm in diameter) that extended to the screw tip.

Mentions: Five screw designs were employed in the present study: solid screws (control) and four types of expansive screws. All of the screws had the same outer diameter of 6 mm, a length of 40 mm from hub to tip, a thread pitch of 2 mm and a thread depth of 0.8 mm. The lengthwise slit length from the screw tip was 27 mm for all of the screws. All of the expansive screws had an internal hole 3 mm from the screw head, which was connected to a smaller hole (1.5 mm in diameter) that extended to the screw tip (Fig 1). Four types of expansive screws were studied: 4-slit or 6-slit with 16-mm or 22-mm EELs. The EEL was defined as the length from the point of diameter change of the internal hole to the screw tip (Fig 1). The 4-slit and 6-slit screws had 4 or 6 lengthwise slits, respectively, which started from the screw tip to form four or six anterior fins (Fig 2A). For screws with 16-mm or 22-mm EELs, the length from the point of diameter change of the internal hole to the screw tip was 16 mm or 22 mm, respectively. The anterior portion of the screw was split lengthwise by an inner pin to form four or six separated anterior fins. The difference in EEL affects the range of screw expansion following pin insertion. The inner pins were all 3 mm in diameter, and they were 44 mm or 38 mm in length for screws with 16 mm or 22 mm EELs, respectively (Fig 2B and 2C). The insertion pin was inserted into the interior of the screw to open the fins at the tip of the expansive screws. Expansive screws with various design parameters are illustrated in (Fig 1).


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)

Schematic drawings showing four types of expandable screws: (A) 4-slit with 16-mm EEL, (B) 4-slit with 22-mm EEL, (C) 6-slit with 16-mm EEL, and (D) 6-slit with 22-mm EEL.The EEL was defined as the length from the point of diameter change of the internal hole to the screw tip. All of the screws had the same outer diameter of 6 mm, a length of 40 mm from hub to tip, a thread pitch of 2 mm and a thread depth of 0.8 mm. The lengthwise slit length from the screw tip was 27 mm for all screws. All of the expansive screws had an internal hole 3 mm from the screw head, which was connected to a smaller hole (1.5 mm in diameter) that extended to the screw tip.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0146294.g001: Schematic drawings showing four types of expandable screws: (A) 4-slit with 16-mm EEL, (B) 4-slit with 22-mm EEL, (C) 6-slit with 16-mm EEL, and (D) 6-slit with 22-mm EEL.The EEL was defined as the length from the point of diameter change of the internal hole to the screw tip. All of the screws had the same outer diameter of 6 mm, a length of 40 mm from hub to tip, a thread pitch of 2 mm and a thread depth of 0.8 mm. The lengthwise slit length from the screw tip was 27 mm for all screws. All of the expansive screws had an internal hole 3 mm from the screw head, which was connected to a smaller hole (1.5 mm in diameter) that extended to the screw tip.
Mentions: Five screw designs were employed in the present study: solid screws (control) and four types of expansive screws. All of the screws had the same outer diameter of 6 mm, a length of 40 mm from hub to tip, a thread pitch of 2 mm and a thread depth of 0.8 mm. The lengthwise slit length from the screw tip was 27 mm for all of the screws. All of the expansive screws had an internal hole 3 mm from the screw head, which was connected to a smaller hole (1.5 mm in diameter) that extended to the screw tip (Fig 1). Four types of expansive screws were studied: 4-slit or 6-slit with 16-mm or 22-mm EELs. The EEL was defined as the length from the point of diameter change of the internal hole to the screw tip (Fig 1). The 4-slit and 6-slit screws had 4 or 6 lengthwise slits, respectively, which started from the screw tip to form four or six anterior fins (Fig 2A). For screws with 16-mm or 22-mm EELs, the length from the point of diameter change of the internal hole to the screw tip was 16 mm or 22 mm, respectively. The anterior portion of the screw was split lengthwise by an inner pin to form four or six separated anterior fins. The difference in EEL affects the range of screw expansion following pin insertion. The inner pins were all 3 mm in diameter, and they were 44 mm or 38 mm in length for screws with 16 mm or 22 mm EELs, respectively (Fig 2B and 2C). The insertion pin was inserted into the interior of the screw to open the fins at the tip of the expansive screws. Expansive screws with various design parameters are illustrated in (Fig 1).

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