title: A description of spinal fatigue strength.
abstract: Understanding fatigue failure of the spine is important to establish dynamic loading limits for occupational health and safety. In this study experimental data were combined with published data to develop a description of the predictive parameters for spinal fatigue failure. 41 lumbar functional spinal units (FSUs) from cadaveric spines (age 49.0 ± 11.9 yr) where cyclically loaded. Three different levels of sinusoidal axial compression (0-3 kN, 0-2kN or 1-3kN) were applied for 300,000 cycles. Further, published data consisted of 70 thoracic and lumbar FSUs loaded in axial compression for 5000 cycles. Cyclic forces ranged from lower peaks (Fmin) of 0.7-1kN to upper peaks (Fmax) of 1.2-7.1 kN. Based on Wöhler analysis, a fatigue model was developed accounting for three parameters: I) specimen-specific scaling based on the endplate area, II) specimen-specific strength dependency on age or bone mineral density, III) load-specific correction factors based on Fmax and Fmin. The most predictive model was achieved for a combination of Fmax, endplate area and bone mineral density; this model explained 61% of variation (p<0.001). A model including Fmax, endplate area and age explained only 28% of variation (p<0.001). Inclusion of a load-specific correction factor did not significantly improve model prediction of fatigue failure. This analysis presents the basis for the prediction of specimen-specific fatigue failure of the lumbar spine, provided the endplate area and bone mineral density can be derived.
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Germany. Electronic address: g.huber@tuhh.de.
authors.forename: Gerd
authors.initials: G
authors.lastname: Huber
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Nagel
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, UK.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Skrzypiec
authors.affiliation: Dept. of Legal Medicine, University Medical Centre Hamburg-Eppendorf, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Klein
authors.affiliation: Dept. of Legal Medicine, University Medical Centre Hamburg-Eppendorf, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Germany.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Morlock
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D015519:Bone Density; D006801:Humans; D008159:Lumbar Vertebrae / Q000473:pathology* / Q000503:physiopathology; D008161:Lumbosacral Region / Q000473:pathology; D008875:Middle Aged; D011312:Pressure; D016474:Weight-Bearing
keywords: Fatigue; Functional spinal unit; In vitro; S-N-curve; Wöhler