Intradiscal pressure in the degenerated porcine intervertebral disc

Summary

Measuring intradiscal pressure is one way of mechanically assessing the discs degenerative state. In this study, the load-bearing capacity of degenerated and their adjacent lumbar intervertebral discs was evaluated using two different injury models. Seventeen adolescent pigs were divided into two groups, an annulus injury group and an endplate injury group. The annulus injury group was subjected to a stab incision in the L3-L4 disc, whereas the endplate injury group received a cranial endplate perforation of the L4 vertebral body. Both groups were biomechanically evaluated three months later using a miniaturized servohydraulic testing machine across L2-L4 and with two pressure needles inserted into the nucleus pulposus of the L2-L3 and L3-L4 discs. Linear relationships between the intradiscal pressure and the applied load were determined within the load range studied. When comparing the ratio of the injured to the adjacent disc pressure, the endplate injury was lower (mean value 0.31) than the annulus injury (mean value 0.51). The pressures in the discs adjacent to the degenerated level were found to be slightly higher. This increase can be expected due to a redistribution in mobility demands in segments adjacent to those with increased stiffness, i.e. degenerated intervertebral discs.

Keywords

Degeneration - injury model - intradiscal pressure - porcine lumbar spine

• References

• 1 Nachemson A. The load on lumbar disks in different positions of the body. Clin Orthop 1965; 107-122.
• 2 Berkson M. Mechanical properties of the human lumbar spine. Flexibilites, intradiscal pressures, posterior element influences. Proc Inst Med Chgo 1977; 31: 138-143.
• 3 Hansson Hansson, Holm S. Clinical implications of vibration-induced changes in the lumbar spine. Orthop Clin North Am 1991; 22: 247-253.
• 4 Steffen T, Baramki H, Rubin R. et al. Lumbar intradiscal pressure measured in the anterior and posterolateral annular regions during asymmetrical loading. Clin Biomech 1998; 13: 495-505.
• 5 Sato K, Kikuchi S, Yonezawa T. In vivo intradiscal pressure measurment in healthy individuals and in patients with ongoing back problems. Spine 1999; 24: 2468-2474.
• 6 Brinkmann Brinkmann, Grootenboer H. Change of disc height, radial disc bulge, and intradiscal pressure from discectomy. Spine 1991; 6: 641-646.
• 7 Adams MA, Freeman BJC, Morrison HP. et al. Mechanical initiation of intervertebral disc degeneration. Spine 2000; 25: 1625-1636.
• 8 Adams M, McMillan DW, Green T. et al. Sustained loading generates stress concentrations in lumbar intervertebral discs. Spine 1996; 21: 434-443.
• 9 Kaigle AM, Holm SH, Hansson TH. Kinematic behavior of the porcine lumbar spine - a chronic lesion model. Spine 1997; 22: 2796-2806.
• 10 Latham JM, Pearcy MJ, Costi JJ. et al. Mechanical consequences of annular tears and subsequent intervertebral disc degeneration. Clin Biomech 1994; 9: 211-219.
• 11 Karlsson L, Lundin O, Ekstrom L. et al. Injuries in adolescent spine exposed to compressive loads: an experimental cadaveric study. J Spinal Dis 1998; 11: 501-507.
• 12 Keller T, Holm S, Hansson T. et al. The dependence of intervertebral disc mechanical properties on physiologic conditions. Spine 1990; 15: 751-761.
• 13 Eck J, Humphreys C, Lim T-H. et al. Biomech- anical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine 2002; 27: 2431-2434.
• 14 Yingling V, Callaghan J, McGill S. The porcine cervical spine as a model of the human lumbar spine: an anatomical, geometric, and functional comparison. J Spinal Dis 1999; 12: 415-423.
• 15 Holm S, Holm AK, Ekstrom L. et al. Experimental disc degeneration due to endplate injury. J Spinal Disor Tech 2004; 17: 64-71.
• 16 Kurowski Kurowski, Kubo A. The relationship of degeneration of the intervertebral disc to mechanical loading conditions on lumbar vertebrae. Spine 1986; 11: 726-731.
• 17 Holm Holm, Urban J. The intervertebral disc: factors contributing to its nutrition andmatrix turnover. In: Joint Loading - Biology and Health of Articular Structures. ed. Helminen HJ, Kiviranta I, Saamanen A-M, Tammi M, Paukkonen K, Jurvelin J. Bristol: John Wright and Sons Ltd.; 1987. pp. 187-226.
• 18 Kaigle A, Ekstrom L, Holm S. et al. In vivo dynamic stiffness of the lumbar spine exposed to cyclic loading: influence of load and degeneration. J Spinal Dis 1998; 11: 65-70.
• 19 Ekstrom L, Holm S, Holm AK. et al. In vivo porcine intradiscal pressure as a function of external loading. J Spinal Disord Tech 2004; 17: 312-316.
• 20 McNally McNally, Adams M. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine 1992; 17: 66-73.
• 21 Acaroglu E, Iatridis J, Setton L. et al. Degeneration and aging affect the tensile behaviour of human lumbar annulus fibrosus. Spine 1995; 20: 2690-2701.
• 22 Tsai K-H, Lin R-M, Chang G-L. Rate-related fatigue injury of vertebral disc under axial cyclic loading in a porcine body-disc-body unit. Clin Biomechanics 1998; 13: 32-39.
• 23 Kulak R, Schultz A, Belytschko T. et al. Biomech- anical characteristics of vertebral motion segments and intervertebral discs. Orthop Clin North Am 1975; 6: 121-133.
• 24 McNally McNally, Arridge G. An analytical model of intervertebral disc mechanics. J Biomechanics 1995; 28: 53-68.
• 25 Ishihara H, Tsuji H, Hirano Netal. Biorheological responses of the intact and nucleotomized inter- vertebral discs to compressive, tensile, and vibratory stresses. Clin Biomech 1993; 8: 250-254.
• 26 Koeller W, Muehlhaus S, Meier W. et al. Biomech- anical properties of human intervertebral discs subjected to axial dynamic compression- influence of age and degeneration. J Biomech 1986; 19: 807-816.
• 27 Gardner-Morse MG, Stokes IA. Physiological axial compressive preloads increase motion segment stiffness, linearity and hysteresis in all six degree of freedom for small displacement about the neutral posture. J Orthop Res 2003; 21: 547-552.
• 28 Osti OL, Vernon-Roberts B, Fraser RD. Anulus tears and intervertebral disc degeneration. An experimental study using an animal model. Spine 1990; 15: 762-767.
• 29 Kaigle A, Holm S, Hansson T. Experimental instability in the lumbar spine. Spine 1995; 20: 421-430.
• 30 Kaapa E. Collagens, proteoglycans, and neural structures in a porcine model of intervertebral disc degeneration. Dissertation. Oulu, Finland: 1993
• 31 Hult E, Ekstrom L, Holm S. et al. Hyomex: aminiture universal testing machine for in vivo biomechanical studies. JMed Eng Technol 1994; 18: 169-172.