European Spine Journal

, Volume 16, Issue 8, pp 1223–1231 | Cite as

Comparison of the effects of bilateral posterior dynamic and rigid fixation devices on the loads in the lumbar spine: a finite element analysis

  • Antonius Rohlmann
  • Nagananda K. Burra
  • Thomas Zander
  • Georg Bergmann
Original Article


A bilateral dynamic stabilization device is assumed to alter favorable the movement and load transmission of a spinal segment without the intention of fusion of that segment. Little is known about the effect of a posterior dynamic fixation device on the mechanical behavior of the lumbar spine. Muscle forces were disregarded in the few biomechanical studies published. The aim of this study was to determine how the spinal loads are affected by a bilateral posterior dynamic implant compared to a rigid fixator which does not claim to maintain mobility. A paired monosegmental posterior dynamic implant was inserted at level L3/L4 in a validated finite element model of the lumbar spine. Both a healthy and a slightly degenerated disc were assumed at implant level. Distraction of the bridged segment was also simulated. For comparison, a monosegmental rigid fixation device as well as the effect of implant stiffness on intersegmental rotation were studied. The model was loaded with the upper body weight and muscle forces to simulate the four loading cases standing, 30° flexion, 20° extension, and 10° axial rotation. Intersegmental rotations, intradiscal pressure and facet joint forces were calculated at implant level and at the adjacent level above the implant. Implant forces were also determined. Compared to an intact spine, a dynamic implant reduces intersegmental rotation at implant level, decreases intradiscal pressure in a healthy disc for extension and standing, and decreases facet joint forces at implant level. With a rigid implant, these effects are more pronounced. With a slightly degenerated disc intersegmental rotation at implant level is mildly increased for extension and axial rotation and intradiscal pressure is strongly reduced for extension. After distraction, intradiscal pressure values are markedly reduced only for the rigid implant. At the adjacent level L2/L3, a posterior implant has only a minor effect on intradiscal pressure. However, it increases facet joint forces at this level for axial rotation and extension. Posterior implants are mostly loaded in compression. Forces in the implant are generally higher in a rigid fixator than in a dynamic implant. Distraction strongly increases both axial and shear forces in the implant. A stiffness of the implant greater than 1,000 N/mm has only a minor effect on intersegmental rotation. The mechanical effects of a dynamic implant are similar to those of a rigid fixation device, except after distraction, when intradiscal pressure is considerably lower for rigid than for dynamic implants. Thus, the results of this study demonstrate that a dynamic implant does not necessarily reduce axial spinal loads compared to an un-instrumented spine.


Lumbar spine Posterior dynamic implant Internal fixation device Finite element method Biomechanics 



The study was financially supported by the Deutsche Forschungsgemeinschaft, Bonn, Germany (Ro 581/17-1) and Synthes GmbH, Oberdorf, Switzerland. Finite element analyses were performed at the Norddeutscher Verbund für Hoch- und Höchstleistungsrechnen (HLRN). The authors thank Dr. J. Weirowski for editorial assistance.


  1. 1.
    Chou WY, Hsu CJ, Chang WN, Wong CY (2002) Adjacent segment degeneration after lumbar spinal posterolateral fusion with instrumentation in elderly patients. Arch Orthop Trauma Surg 122:39–43PubMedGoogle Scholar
  2. 2.
    Eberlein R, Holzapfel GA, Schulze-Bauer CAJ (2000) An anisotropic model for annulus tissue and enhanced finite element analysis of intact lumbar disc bodies. Comp Meth Biomech Biomed Eng 4:209–229CrossRefGoogle Scholar
  3. 3.
    Eberlein R, Holzapfel GA, Schulze-Bauer CAJ (2002) Assessment of a spinal implant by means of advanced FE modeling of intact human intervertebral discs. In: Fifth World Congress on computational mechanics. Vienna University of Technology, Vienna, Austria, pp 1–14Google Scholar
  4. 4.
    Gardner A, Pande KC (2002) Graf ligamentoplasty: a 7-year follow-up. Eur Spine J 11(Suppl 2):S157–S163PubMedGoogle Scholar
  5. 5.
    Graf H (1992) Lumbar stability: surgical treatment without fusion. Rachis 412:123–137Google Scholar
  6. 6.
    Grob D, Benini A, Junge A, Mannion AF (2005) Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patient-oriented outcome in 50 cases after an average of 2 years. Spine 30:324–331PubMedCrossRefGoogle Scholar
  7. 7.
    Heuer F, Schmidt H, Klezl Z, Claes L, Wilke HJ (2006) Stepwise reduction of functional spinal structures increase range of motion and change lordosis angle. J Biomech  10.1016/j.jbiomech.2006.1001.1007 (in press)
  8. 8.
    Kanayama M, Hashimoto T, Shigenobu K (2005) Rationale, biomechanics, and surgical indications for Graf ligamentoplasty. Orthop Clin North Am 36:373–377PubMedCrossRefGoogle Scholar
  9. 9.
    Kumar MN, Baklanov A, Chopin D (2001) Correlation between sagittal plane changes and adjacent segment degeneration following lumbar spine fusion. Eur Spine J 10:314–319PubMedCrossRefGoogle Scholar
  10. 10.
    Lee CK (1988) Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 13:375–377PubMedCrossRefGoogle Scholar
  11. 11.
    Mochida J, Toh E, Suzuki K, Chiba M, Arima T (1997) An innovative method using the Leeds–Keio artificial ligament in the unstable spine. Orthopedics 20:17–23PubMedGoogle Scholar
  12. 12.
    Mulholland RC, Sengupta DK (2002) Rationale, principles and experimental evaluation of the concept of soft stabilization. Eur Spine J 11 (Suppl 2):S198–S205PubMedGoogle Scholar
  13. 13.
    Niosi CA, Zhu QA, Wilson DC, Keynan O, Wilson DR, Oxland TR (2006) Biomechanical characterization of the three-dimensional kinematic behaviour of the Dynesys dynamic stabilization system: an in vitro study. Eur Spine J 15:913–922PubMedCrossRefGoogle Scholar
  14. 14.
    Nockels RP (2005) Dynamic stabilization in the surgical management of painful lumbar spinal disorders. Spine 30:S68–72PubMedCrossRefGoogle Scholar
  15. 15.
    Nolte LP, Panjabi MM, Oxland TR (1990) Biomechanical properties of lumbar spinal ligaments. In: Heimke G, Soltesz U, Lee AJC (eds) Clinical implant materials, advances in biomaterials, vol 9. Elsevier, Heidelberg, pp 663–668Google Scholar
  16. 16.
    Patwardhan AG, Havey RM, Meade KP, Lee B, Dunlap B (1999) A follower load increases the load-carrying capacity of the lumbar spine in compression. Spine 24:1003–1009PubMedCrossRefGoogle Scholar
  17. 17.
    Putzier M, Schneider SV, Funk J, Perka C (2004) Application of a dynamic pedicle screw system (DYNESYS) for lumbar segmental degenerations—comparison of clinical and radiological results for different indications. Z Orthop Ihre Grenzgeb 142:166–173PubMedCrossRefGoogle Scholar
  18. 18.
    Rahm MD, Hall BB (1996) Adjacent-segment degeneration after lumbar fusion with instrumentation: a retrospective study. J Spinal Disord 9:392–400PubMedCrossRefGoogle Scholar
  19. 19.
    Rohlmann A, Bauer L, Zander T, Bergmann G, Wilke HJ (2006) Determination of trunk muscle forces for flexion and extension by using a validated finite element model of the lumbar spine and measured in vivo data. J Biomech 39:981–989PubMedCrossRefGoogle Scholar
  20. 20.
    Rohlmann A, Bergmann G, Graichen F (1997) Loads on an internal spinal fixation device during walking. J Biomech 30:41–47PubMedCrossRefGoogle Scholar
  21. 21.
    Rohlmann A, Bergmann G, Graichen F (1999) Loads on internal spinal fixators measured in different body positions. Eur Spine J 8:354–359PubMedCrossRefGoogle Scholar
  22. 22.
    Rohlmann A, Claes L, Bergmann G, Graichen F, Neef P, Wilke H-J (2001) Comparison of intradiscal pressures and spinal fixator loads for different body positions and exercises. Ergonomics 44:781–794CrossRefGoogle Scholar
  23. 23.
    Rohlmann A, Graichen F, Weber U, Bergmann G (2000) 2000 Volvo Award winner in biomechanical studies: monitoring in vivo implant loads with a telemeterized internal spinal fixation device. Spine 25:2981–2986PubMedCrossRefGoogle Scholar
  24. 24.
    Rohlmann A, Neller S, Claes L, Bergmann G, Wilke H-J (2001) Influence of a follower load on intradiscal pressure and intersegmental rotation of the lumbar spine. Spine 26:E557–E561PubMedCrossRefGoogle Scholar
  25. 25.
    Rohlmann A, Zander T, Bergmann G (2005) Effect of total disc replacement with ProDisc on the biomechanical behavior of the lumbar spine. Spine 30:738–743PubMedCrossRefGoogle Scholar
  26. 26.
    Rohlmann A, Zander T, Schmidt H, Wilke H-J, Bergmann G (2006) Analysis of the influence of disc degeneration on the mechanical behaviour of a lumbar motion segment using the finite element method. J Biomech 39:2484–2490PubMedCrossRefGoogle Scholar
  27. 27.
    Rohlmann A, Zilch H, Bergmann G, Kölbel R (1980) Material properties of femoral cancellous bone in axial loading. Part I: Time independent properties. Arch Orthop Trauma Surg 97:95–102PubMedCrossRefGoogle Scholar
  28. 28.
    Schmoelz W, Huber JF, Nydegger T, Claes L, Wilke HJ (2003) Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment. J Spinal Disord Tech 16:418–423PubMedGoogle Scholar
  29. 29.
    Schmoelz W, Huber JF, Nydegger T, Claes L, Wilke HJ (2006) Influence of a dynamic stabilisation system on load bearing of a bridged disc: an in vitro study of intradiscal pressure. Eur Spine J 15:1–10CrossRefGoogle Scholar
  30. 30.
    Seitsalo S, Schlenzka D, Poussa M, Osterman K (1997) Disc degeneration in young patients with isthmic spondylolisthesis treated operatively or conservatively: a long-term follow-up. Eur Spine J 6:393–397PubMedCrossRefGoogle Scholar
  31. 31.
    Sengupta DK (2004) Dynamic stabilization devices in the treatment of low back pain. Orthop Clin North Am 35:43–56PubMedCrossRefGoogle Scholar
  32. 32.
    Sharma M, Langrana NA, Rodriguez J (1995) Role of ligaments and facets in lumbar spinal stability. Spine 20:887–900PubMedCrossRefGoogle Scholar
  33. 33.
    Shirazi-Adl A, Ahmed AM, Shrivastava SC (1986) Mechanical response of a lumbar motion segment in axial torque alone and combined with compression. Spine 11:914–927PubMedCrossRefGoogle Scholar
  34. 34.
    Stoll TM, Dubois G, Schwarzenbach O (2002) The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system. Eur Spine J 11 Suppl 2:S170–178Google Scholar
  35. 35.
    Ueno K, Liu YK (1987) A three-dimensional nonlinear finite element model of lumbar intervertebral joint in torsion. J Biomech Eng 109:200–209PubMedCrossRefGoogle Scholar
  36. 36.
    Wilke H, Neef P, Hinz B, Seidel H, Claes L (2001) Intradiscal pressure together with anthropometric data—a data set for the validation of models. Clin Biomech 16:S111–126CrossRefGoogle Scholar
  37. 37.
    Wilke HJ, Neef P, Caimi M, Hoogland T, Claes LE (1999) New in vivo measurements of pressures in the intervertebral disc in daily life. Spine 24:755–762PubMedCrossRefGoogle Scholar
  38. 38.
    Wilke HJ, Rohlmann A, Neller S, Graichen F, Claes L, Bergmann G (2003) ISSLS prize winner: a novel approach to determine trunk muscle forces during flexion and extension: a comparison of data from an in vitro experiment and in vivo measurements. Spine 28:2585–2593PubMedCrossRefGoogle Scholar
  39. 39.
    Zander T, Rohlmann A, Calisse J, Bergmann G (2001) Estimation of muscle forces in the lumbar spine during upper-body inclination. Clin Biomech 16:S73–S80CrossRefGoogle Scholar
  40. 40.
    Zander T, Rohlmann A, Klöckner C, Bergmann G (2002) Comparison of the mechanical behavior of the lumbar spine following mono- and bisegmental stabilization. Clin Biomech 17:439–445CrossRefGoogle Scholar
  41. 41.
    Zander T, Rohlmann A, Klöckner C, Bergmann G (2002) Influence of bone graft characteristics on mechanical behaviour of the spine. J Biomech 35:491–497PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Antonius Rohlmann
    • 1
  • Nagananda K. Burra
    • 1
  • Thomas Zander
    • 1
  • Georg Bergmann
    • 1
  1. 1.Biomechanics Laboratory, Orthopaedic HospitalCharité—Universitätsmedizin BerlinBerlinGermany

Personalised recommendations