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Biomechanical evaluation of cervical intervertebral plug stabilization in an ovine model
Boel A Fransson1, Qingan Zhu, Rodney S Bagley
1Department of Veterinary Clinical Sciences, Washington State University, Pullman, WA 99164-7460, USA. bfransso@vetmed.wsu.edu
Objective:
(1) To determine the biomechanical stability of cervical spinal segment C5-C6 after ventral slot (VS) decompression and distraction-stabilization by a modified polymethylmethacrylate (PMMA) intervertebral plug technique (IVP) in an ovine model. (2) To determine if the distraction of the disk space is maintained after VS-IVP, and the frequency of bony intervertebral union.
Study Design:
Experimental in vivo study in an ovine model with an in vitro control study.
Animals:
Adult (>2 years age), intact sheep (n=18).
Methods:
Ten sheep had VS/IVP surgery of C5-6 with computed tomography (CT) images obtained immediately before and after surgery, as well as 8 (n=10) and 24 (n=5) weeks postoperatively. Cervical spines harvested 8 weeks (8-week group; n=5) and 24 weeks (24-week group; n=5) after surgery had three-dimensional (3D) flexibility tests in flexion-extension, axial rotation, and lateral bending. Image data was analyzed qualitatively and quantitatively in 3D. Eight ovine cervical spines served as controls and had biomechanical testing in intact condition (n=5) and after in vitro VS/IVP (n=5).
Results:
Significantly decreased range of motion (ROM) was noted in all loading modes when comparing in vitro operated spines and the 24-week group to intact spines. The 8-week group was not significantly different from the intact group, except in lateral bending. Quantitative CT analysis of treatment groups showed progressive disk space collapse and ventral implant migration. Intervertebral bony union did not occur.
Conclusion:
Biomechanical stability was obtained immediately after VS/IVP surgery, but ROM at 8 weeks was not different from intact spines. However, at 24 weeks, the operated level had regained stability similar to the immediate postoperative level. Distraction of the disk space was not maintained and bony union did not occur in this ovine model of VS/IVP.
Clinical Relevance:
In clinical situations requiring constant increased stability of cervical segments for an extended time, more rigid stabilization techniques are required.
