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Research Papers

Mechanics and Validation of an in Vivo Device to Apply Torsional Loading to Caudal Vertebrae

[+] Author and Article Information
Robert Rizza

Department of Mechanical Engineering,
Milwaukee School of Engineering,
Milwaukee, WI 53202

XueCheng Liu

Department of Orthopaedic Surgery,
Medical College of Wisconsin,
Milwaukee, WI 53226

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received August 2, 2012; final manuscript received May 20, 2013; accepted manuscript posted May 22, 2013; published online June 12, 2013. Assoc. Editor: James C. Iatridis.

J Biomech Eng 135(8), 081003 (Jun 12, 2013) (7 pages) Paper No: BIO-12-1354; doi: 10.1115/1.4024628 History: Received August 02, 2012; Revised May 20, 2013; Accepted May 22, 2013

Axial loading of vertebral bodies has been shown to modulate growth. Longitudinal growth of the vertebral body is impaired by compressive forces while growth is stimulated by distraction. Investigations of torsional loading on the growth plate in the literature are few. The purposes of this study were two-fold: (1) to develop a torque device to apply torsional loads on caudal vertebrae and (2) investigate numerically and in vivo the feasibility of the application of the torque on the growth plate. A controllable torque device was developed and validated in the laboratory. A finite element study was implemented to examine mechanically the deformation of the growth plate and disk. A rat tail model was used with six 5-week-old male Sprague-Dawley rats. Three rats received a static torsional load, and three rats received no torque and served as sham control rats. A histological study was undertaken to investigate possible morphological changes in the growth plate, disk, and caudal bone. The device successfully applied a controlled torsional load to the caudal vertebrae. The limited study using finite element analysis (FEA) and histology demonstrated that applied torque increased lateral disk height and increased disk width. The study also found that the growth plate height increased, and the width decreased as well as a curved displacement of the growth plate. No significant changes were observed from the in vivo study in the bone. The torsional device does apply controlled torque and is well tolerated by the animal. This study with limited samples appears to result in morphological changes in the growth plate and disk. The use of this device to further investigate changes in the disk and growth plate is feasible.

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Figures

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Fig. 1

(a) A 3D illustration of the torque apparatus in rat tail bones. (b) A cutaway drawing showing the position of the bones and disks relative to the device.

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Fig. 2

(a) A rat is placed in the Broome Restrainer so that its tail is held firmly for installing the Torque device, (b) the implanted torque device, and (c) an X-ray showing implanted device and location of K-wires

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Fig. 6

Variation of displacement (y-direction) in a slice of the growth plate

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Fig. 5

Variation of von Mises stress in the growth plate of one caudal vertebra in the coronal plane

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Fig. 4

Relaxation under an applied torque due to viscoelastic behavior

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Fig. 3

Finite element model of the caudal tail composed of three vertebrae, associated growth plates, and two disks

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Fig. 7

The growth plate in the TG (left) showing wavy curvature in the middle of the growth plate (arrow), while in the SG (right), the growth plate is flat (arrow) (HE, X 10)

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Fig. 8

Alcian blue staining displayed greater numbers of proliferative cartilaginous cells (between the two lines) at 3.5 weeks in the TG (left), while smaller and reduced numbers of these cells (between the two lines) at the same number of weeks in the SG (Alcian blue, X 40)

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