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Biomechanics Exam 1

Lectures 1,2,3

What does the vertebrae articulate with? with each other, with the skull, with the pelvis
What are the levers? vertebrae spinous process
What are the pivots? IVD and facets
What are the passive restraints? ligaments
What are the activations? muscles
What are the functions of the spine? Transfers the weight of the head and trunk to the pelvis, allows sufficient physiologic motions between three body parts, protects the spinal cord
An attempt to combine anatomy and pysiology by applying mechanis and biology What is biomechanics?
The study of forces and their effects What is mechanics?
Which branch of mechanics deals with equilibrium of the bodies at rest or in motion with zero acceleration? statics
What branch of mechanics deals with the study of loads and interacting bodies? dynamics
What branch of dynamics focuses on the geometry of motion? Kinematics
What branch of dynamics deals with the relations between forces? Kinetics
What is the difference between the vertebrae and spine? The vertebral column refers to the osseoligamentous structures with curcatures in the sagittal plance, whereas the spine refers to the musculoskeletal and neurovascular elements
What causes kyphosis curves? Primary curves caused by posterior deviations and wedge shaped bodies
What causes lordotic curves? Anterior deviations and wedge shaped discs
What is the function of the curves of the spine? Increase flexibility and increase shock absorption
How good are ligaments at stabilizing the spine? Restricts motion but also allows motion. Good at stabilizing at the end range only.
What are the mechanical stabilizers of the spine? Neuromuscular control system
What makes up 20-33% of the spine and what are its parts? IVD with nucleus pulposus, annulus fibrosis, and cartilaginous end plate
Greater ratio= ______ Where is the ration the greatest? Mobility; cervicals and lumbars
What makes up the whole disc? Proteoglycans, Water, Collagen
What does the proteoglycan/collagen ration determine? Where is the highest? Amount of water in the disc; greates in nucleus
What type of collagen is found in the annulus? Type I (helicoid fibers) tension resisting tissues
What type of collagen is found in nucleus? Type II copression resisting tissues
How are the concentric bands positioned in the disc? 30 degrees to the disc plane and 120 degrees to adjacent bands
Where does the annulus attach peripherally? centrally? Peripherally to ligamentous sharpey's fibers and centrally to the cartilaginous end plate
What makes up the cartilaginous end plate and what is its function? Hyaline cartilage; separates nucleus and annulus from vertebrae
Where does disc ageing first occur? nucleus
What are the cellular and chemical changes that occur in disc ageing? Cells produce less proteoglycan (less water). Brown pigmentation occurs due to non-reducible collagen cross-links and injury to brittle discs
What happens to discs after 25 YOA? become avascular and receive nutrients and waste exchange through imbibition
How does ageing of the end plates differ from nucleus? Accompanying calcification may compromise nutrition to the nucleus
What differences exist in the ageing of the annulus? Chemical changes are less pronounced; collagen content increases and becomes stiffer
What are the funtional consequences of disc ageing in the nucleus? Nucleus becomes dry, stiff, fibrous, and volume decreases
What are the consequences of disc ageing in the annulus? Annulus becomes weaker (stiffer), takes on more compressive load, but does noit lose disc height
What are some common trends where disc degeneration is seen? More common in men than women. Usually occurs after 20 YOA with the maximum at middle age. Most evident in annulus and end plate.
T/F Ageing and degeneration can be used interchangeably. False. NOT inevitable consequence of ageing
What are some structural changes that can occur from disc degeneration? Inward buckling, Radial bulging, Reduced disc height, Endplate defects, Vertical bulging of endplates into bodies, Radial tears, Circumferential tears, Prolapse
List the three types of anular tears. Concentric clefts, Rim lesions, Radial fissure
What are concentric clefts? Anular tears that occur between adjacent lamellae and represent delamination of anulus. Very common.
What are rim lesions and how common are they? Circumferential avulsions of the periphery with 2X more common anteriorly (typically antero-lateral margin)
What are radial fissures? Radial disruption of the lamellae from the inner anulus to outer lamellae
What is a special case of radial fissure? Disc prolapse which allows escape of nucleus material.
What are some cellular changes that occur in disc degeneration? Cell clustering with concentric rings occuring around some cells, blood vessels and nerves grow toward the center due to loss of hydrostatic pressure,a dn matrix degrading enzymes increase.
What structural changes occur adjacent to the degenerated disc? Z-joints degenerate and osteophytes develop around body margins
What functional changes occur in degeneration? Reduced ROM in bending and increased ROM in rotation.
What are the Kirkaldy-Willis degeneration stages? What stage is chiropractic best in? Normal (0), Dysfunction (1), Unstable (2), Stabilization (3)
Describe the dysfunction stage of degeneration. small degree of joint subluxation with abnormal motion. (most patients in this stage)
Describe the unstable stage of degeneration. Observable and audible catch, sway, or shift with increased motion. Spodylolisthesis on motion.
Describe the stabilization stage of degeneration. LBP decreasing severity, stiffness and reduced movement, degenerative scoliosis, loss of disc height, small foramina, osteophytes
T/F Disc prolapse and herniation can be used interchangeably. True
T/F Prolapse is particularly common in men and lumbars. True
T/F Prolapse is an end-stage degeneration. False
What are the three types of prolapse? Protrusion, Extrusion, Sequestration
T/F Protrusion represents disc bulging. True
What type of prolapse occurs when it is no longer attached to the nucleus? Sequestration
What type of prolapse can be refered to as incomplete prolapse? Extrusion
T/F No deformation occurs in elasticity. True
What is viscoelasticity? Property of of a material to return to its original form following the removal of the deforming load with some degree of stickiness
What type of loading rate occurs with physiologic loads? traumatic? Slow rate with physiologuc loads, Fast rate with traumatic loads
What does a slow load curve represent? More flexible, more deformation
What does a fast load curve represent? More resistance, less deformation
What is the difference between compression and tension? Compression is the normal force that tends to push together material fibers whereas tension tends to elongate (pull apart) fibers.
What was the result of the Virgin study on compression and herniation. No herniation of the nucleus pulposus even with a longitudinal incision at the posterolateral annulus (most common site)
How was the Brown, Hanson, & Yorra study different from the Virgin study? They used compressed functional spinal units and although no herniation occured, vertebral endplates were fractured.
T/F The Farfan study concluded that degenerative discs were weaker in compression that non-degenerated. False. they were stronger
What is the most common site of herniation? Posterolateral
According to the Brown. Hanson, & Yorra study, where is the most tensile strength? Least? Most strength and anterior and posterior ends. Least strength at nucleus and lateral ends.
According to Galante, what angles have the greatest tensile strength? 30 degrees to the disc plane with 3X more strength than horizontally
What is stiffness? A measure of resistance offered to external loads by a structure as it deforms.
What does anistropic refer to? The mechanical properties of the disc vary with different spatial orientations. (same force applied with differences in distance moved)
How does stiffness relate to compression and tension? Less stiffness in tension than in compression.
According to Galante, what angle represents the greatest stiffness? 15 degrees to disc plane
When did herniation occur in Farfan's study? Why was this not significant? 15 degrees of bending. Posterior elements of the vertebrae were removed which is not likely in humans.
T/F Bulge is always on the concave side of the disc. True
T/F Denucleation decrease disc bulging. False
What is shear stress? The intensity of force parallel to the surface on which it acts.
Wat is a relatively rare cause of anular tears? Shear stress
What is torsion? A type of load applied by a couple of forces about the long axis of a structure.
Where does torsion loading produce shear stress? highest? lowest? 90 degrees to the axis of torsion with the highest at the periphery and lowest at the center
Where does torsion cause compression stress? 45 degrees to the axis of torsion in the direction opposite the applied force
Where does torsion produce tension stress? 45 degrees to the axis of torsion in the direction of the applied force.
What resulted from Farfan's study on torsion as the major causing load of herniation? 25% higher torsion in a normal disc than degenerated, larger disc produces a higher torsional strength, average herniation at 15 degrees (not likely)
What did Adams & Hutton study represent? Herniation occurred when a sudden compressive force applied in hyperflexion and lateral bending.
Why was the Adam & Hutton study flawed? Most herniation/prolapse patients do not present with a precipitating traumatic event 9sudden compressive force).
Where did prolapse occur in the Adam & Hutton study? convex side
What is creep? A viscoelastic material deforms with time when it is subjected to a constant suddenly applied load. (shock absorption)
What is the difference in creep of a normal and degenerated disc? Normal discs creep more slowly. Degenerated discs are less viscoelastic and creep more quickly.
What is hysteresis? A phenomenom associated with energy loss exhibited by viscoelastic materials when they are subjected to loading and unloading cycles.
How does hystereis vary with load? Higher load = Greater hysteresis
How does hysteresis vary with age of the disc? Large hysteresis = very young disc, Smallest hysteresis = middle aged disc
How does hysteresis vary with repetition? Second loading = decreased hysteresis
What is fatigue? The process of the growth of cracks in structures subjected to repetitive load cycles with loads less than failure load.
What is fatigue failure? When a fatigue crack reaches a certain size, the stress in the rest of the structure becomes so high that the structure fails.
Why was Brown's study on fatigue failure insignificant? Represented signs of failure after 200 cycles and complete failure after 1000 cycles, however done in vitro when in reality repair/regeneration occur.
What is the take home message for disc herniation? Compression WITH flexion/extension/letral bending WITH torsion and structural changes over time will cause herniation.
Created by: jtnguyen