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| T/F Compression causes herniation. | FALSE! |
| Farfan produced herniation with 15 degrees of bending. What was significant about this study that makes it invalid? | There were no posterior elements! (Pedicles, lamina, etc.) Because you can't get 15 degrees of bending without removing those! |
| T/F In Roaf''s studies bulge is always on the concave side. | TRUE |
| T/F Denucleation decreased bulging is Roaf's studies. | FALSE!! Denucleation INCREASED bulging! |
| Define SHEAR stress: | The intensity of force parallel to the surface on which it acts |
| T/F A straight shear across a disc is a common injury. | FALSE! Failure forced must be too high for this to occur!! VERY RARE!! |
| Define TORSION: | A type of load applied by a COUPLE of forses about the long axis of a structure. |
| What is the other name for torsional loading? | TORQUE |
| What kind of stresses are caused by torsional loading? | Shear, compression and tension |
| At what angle is shear stress applied to a structure under torsional loading? | 90 degrees |
| Is shear stress during torsional loading higher at the CENTER or the PERIPHERY? | PERIPHERY |
| How is COMPRESSION distributed during torsional loading? | 45 degress to the axis in the OPPOSITE direction of the applied force |
| How is TENSION distributed during torsional loading? | 45 degress to the axis in the same direction as the applied force |
| T/F A normal disc can handle torsion better than a degenerated disc. | FALSE! Normal discs had a 25% higher failure rate with torque! |
| T/F Large discs have a larger torsional strength. | TRUE |
| What is the average faulure anlgle for torsional strain? | 15 degrees |
| T/F The first experimental disc "prolapse" was performed by Adams and Hutton and was featured in Spine magazine. | TRUE |
| In the experiment by Adams and Hutton, the spine was hyperflexed and laterally bent and then a sudden compressive force was applied. What side of the spine was the prolapse observed? | CONVEX |
| Adams and Hutton found a pattern to failures. What discs, degeneration grade, and in what age group were discs most likely to fail under their methods? | L4 and L5, Grade 2 degeneration, 40-49 YOA |
| T/F Most herniation/prolapse patients present with a precipitating traumatic event. | FALSE! Most do NOT had a hx of traumatic event |
| When Adams and Hutton altered their experiment by varying loads at 40 loads/minute, what happened? | 6 or 49 prolapsed, 35 end plate failures/vert. collapse |
| What did Adams and Hutton's 40 loads/minute variation prove? | That repetition is probably NOT a mechanism for gradual prolapse |
| Define VISCOELASTICITY: | The physical properties of a structure that document its time-dependent behavior |
| Define CREEP: | A viscoelactic material defoms WITH TIME when it is subjected to a CONSTANT load. |
| T/F Zararian's studies on COMPRESSION CREEP showed that normal discs creep more slowly than degenerated discs - reach maximum deformation after a longer period of time. | TRUE |
| T/F As a disc degenerates, it loses its capacity to attenuate shocks and to distribute load uniformly over the entire endplate. | TRUE |
| Define Hysteresis: | A phenomenon associated with energy loss exhibited by viscoelactic materials when they are subjected to loading and unloading cycles |
| Which has a greater hysteresis: higher or lower load? | HIGHER |
| At the same load, which would have the smallest hysteresis: a very young disc or a middle-aged disc? | Middle-aged disc (doesn't absorb shock as well) |
| Upon a second loading, is there an increase or decrease in hysteresis? | DECREASE! There is less shock protection with repetitive loads!! |
| In epidemiological studies on HYSTERESIS by Kelsey and Hardy, who had an increase incidence because of repetitive axial loading? | Motor vehicle drivers - especially truck drivers |
| Define FATIGUE: | The process of the growth of cracks in structures subjected to repetitive load cycles with loads LESS than failure load. |
| T/F Repetitive load cycles less than failure load will NEVER cause a structure to fail. | FALSE! What a fatigue crack reaches a certain sive the stress in the rest of the structure becomes so high that the structure fails |
| Although Brown's fatigue experiments were performed IN VITRO and during sleep the body can repair and regenerate, his experiments may still be clinically significant. Why? | Because the repair and regeneration of IVDs is thought to be low and because IVDs are avascular after 25YOA |
