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Biomechanical comparison of pedicle screws versus spinous process screws in C2 vertebra: A cadaveric study.

Liu GY, Mao L, Xu RM, Ma WH - Indian J Orthop (2014)

Bottom Line: Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients.The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = -0.862, P = 0.403).Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, Ningbo 6 Hospital, 315040, Ningbo, ZheJiang, People's Republic of China.

ABSTRACT

Background: Biomechanical studies have shown C2 pedicle screw to be the most robust in insertional torque and pullout strength. However, C2 pedicle screw placement is still technically challenging. Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients. The purpose of this study was to compare the pullout strength of spinous process screws with pedicle screws in the C2.

Materials and methods: Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to -20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig as used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods. The pedicle screws were inserted in usual manner as in previous biomechanical studies. The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane. Each vertebrae was held in a customs jig, which was attached to material testing machine (Material Testing System Inc., Changchun, China). A coupling device that fit around the head of the screw was used to pull out each screw at a loading rate of 2 mm/min. The uniaxial load to failure was recorded in Newton'st dependent test (for paired samples) was used to test for significance.

Results: The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = -0.862, P = 0.403). In all but three instances (38%), the spinous process pullout values exceeded the values for the pedicle screws. The working distances for the spinous process screws was little shorter than pedicle screws in each C2 specimen.

Conclusion: Spinous process screws provide comparable pullout strength to pedicle screws of the C2. Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.

No MeSH data available.


Related in: MedlinePlus

Computed tomography scan showing placement of C2 spinous process screw (left) and pedicle screw (right)
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Figure 2: Computed tomography scan showing placement of C2 spinous process screw (left) and pedicle screw (right)

Mentions: Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to −20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig was used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods.91011 The pedicle screws were inserted in usual manner as in previous biomechanical studies910111213 The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane [Figure 1]. Screws were placed in such a manner so that the first thread penetrated the far cortex. All spinous process screws insertion was performed without breeching the inner cortex of lamina under direct visualization. After each hole was drilled and tapped according to the manufacturer's specifications, 4.0 mm cortical screw (Vertex Fixation System, Sofamor Danek, Memphis, TN, USA) was inserted into the spinous process on one side, and pedicle screw was inserted on the other. The type of screw was randomized at each vertebrae, either left or right [Figure 2]. To grasp the screws with a coupling device, it was necessary to leave all of the screws approximately 4-6 mm outside. The screw length was defined as the actual working screw length.


Biomechanical comparison of pedicle screws versus spinous process screws in C2 vertebra: A cadaveric study.

Liu GY, Mao L, Xu RM, Ma WH - Indian J Orthop (2014)

Computed tomography scan showing placement of C2 spinous process screw (left) and pedicle screw (right)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4232822&req=5

Figure 2: Computed tomography scan showing placement of C2 spinous process screw (left) and pedicle screw (right)
Mentions: Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to −20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig was used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods.91011 The pedicle screws were inserted in usual manner as in previous biomechanical studies910111213 The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane [Figure 1]. Screws were placed in such a manner so that the first thread penetrated the far cortex. All spinous process screws insertion was performed without breeching the inner cortex of lamina under direct visualization. After each hole was drilled and tapped according to the manufacturer's specifications, 4.0 mm cortical screw (Vertex Fixation System, Sofamor Danek, Memphis, TN, USA) was inserted into the spinous process on one side, and pedicle screw was inserted on the other. The type of screw was randomized at each vertebrae, either left or right [Figure 2]. To grasp the screws with a coupling device, it was necessary to leave all of the screws approximately 4-6 mm outside. The screw length was defined as the actual working screw length.

Bottom Line: Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients.The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = -0.862, P = 0.403).Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, Ningbo 6 Hospital, 315040, Ningbo, ZheJiang, People's Republic of China.

ABSTRACT

Background: Biomechanical studies have shown C2 pedicle screw to be the most robust in insertional torque and pullout strength. However, C2 pedicle screw placement is still technically challenging. Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients. The purpose of this study was to compare the pullout strength of spinous process screws with pedicle screws in the C2.

Materials and methods: Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to -20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig as used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods. The pedicle screws were inserted in usual manner as in previous biomechanical studies. The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane. Each vertebrae was held in a customs jig, which was attached to material testing machine (Material Testing System Inc., Changchun, China). A coupling device that fit around the head of the screw was used to pull out each screw at a loading rate of 2 mm/min. The uniaxial load to failure was recorded in Newton'st dependent test (for paired samples) was used to test for significance.

Results: The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = -0.862, P = 0.403). In all but three instances (38%), the spinous process pullout values exceeded the values for the pedicle screws. The working distances for the spinous process screws was little shorter than pedicle screws in each C2 specimen.

Conclusion: Spinous process screws provide comparable pullout strength to pedicle screws of the C2. Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.

No MeSH data available.


Related in: MedlinePlus