Damage accumulation location under cyclic loading in the lumbar disc shifts from inner annulus lamellae to peripheral annulus with increasing disc degeneration.
It is difficult to study the breakdown of lumbar disc tissue over several years of exposure to bending and lifting by experimental methods. In our earlier published study we have shown how a finite element model of a healthy lumbar motion segment was used to predict the damage accumulation location and number of cyclic to failure under different loading conditions. The aim of the current study was to extend the continuum damage mechanics formulation to the degenerated discs and investigate the initiation and progression of mechanical damage. Healthy disc model was modified to represent degenerative discs (Thompson grade III and IV) by incorporating both geometrical and biochemical changes due to degeneration. Analyses predicted decrease in the number of cycles to failure with increasing severity of disc degeneration. The study showed that the damage initiated at the posterior inner annulus adjacent to the endplates and propagated outwards towards its periphery in healthy and grade III degenerated discs. The damage accumulated preferentially in the posterior region of the annulus. However in grade IV degenerated disc damage initiated at the posterior outer periphery of the annulus and propagated circumferentially. The finite element model predictions were consistent with the infrequent occurrence of rim lesions at early age but a much higher incidence in severely degenerated discs.
Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA.
Muhammad
M
Qasim
Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA; Department of Orthopedic Surgery, 1611 West Harrison Street, Suite 204, Rush University Medical Center, Chicago, IL, USA. Electronic address: Raghu_Natarajan@rush.edu.
Raghu N
RN
Natarajan
Department of Orthopedic Surgery, 1611 West Harrison Street, Suite 204, Rush University Medical Center, Chicago, IL, USA.
Howard S
HS
An
Department of Orthopedic Surgery, 1611 West Harrison Street, Suite 204, Rush University Medical Center, Chicago, IL, USA.
Gunnar B J
GB
Andersson
D001696:Biomechanical Phenomena; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology*; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology*; D007405:Intervertebral Disc Displacement / Q000175:diagnosis*; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008161:Lumbosacral Region / Q000503:physiopathology; D008953:Models, Anatomic; D013314:Stress, Mechanical; D013718:Tensile Strength; D016474:Weight-Bearing
Continuum damage mechanics; Disc degeneration; Fatigue failure; Finite element modeling; Lumbar spine