Lecture 5 Flashcards
(118 cards)
1
Q
Q: What are the fibrocartilaginous discs between adjacent vertebrae responsible for?
A
A: They act as shock-absorbing cushions
2
Q
Q: What proportion of the height of the spine do healthy intervertebral discs (IVDs) in adults account for?
A
A: Approximately 1/4 of the height of the spine.
3
Q
Q: How do the differences in anterior and posterior disc thickness contribute to the formation of cervical, thoracic, and lumbar curves when a person is standing upright?
A
A: They produce the cervical, thoracic, and lumbar curves.
4
Q
Q: What are some functions of the intervertebral discs (IVDs)?
A
A: They allow for movement between vertebrae, bear weight, and transmit loads from one vertebral body to the next.
5
Q
Q: What are some biomechanical requirements of intervertebral discs (IVDs)?
A
They need to have strength to sustain weight during axial compression, be deformable to accommodate movements, and have strength to resist injury during normal physiological movements.
6
Q
Q: Are there intervertebral discs (IVDs) at the C0/C1 or C1/C2 levels?
A
No, there are no intervertebral discs at the C0/C1 or C1/C2 levels.
7
Q
What type of joint is formed between two vertebrae, and what structures contribute to it?
A
A symphysis joint is formed between two vertebrae, consisting of the vertebral endplates connected by the intervertebral disc (IVD), which includes the annulus fibrosis (AF), nucleus pulposus (NP), and vertebral endplate.
8
Q
What are the three parts that make up the structure of an intervertebral disc (IVD)?
A
The intervertebral disc consists of the annulus fibrosis (AF), nucleus pulposus (NP), and vertebral endplate.
9
Q
How does the water content of the nucleus pulposus (NP) and the fiber orientation of the annulus fibrosis (AF) affect force transmission and resistance to various loads within the intervertebral disc (IVD)?
A
Force transmission and resistance to various types of loads depend on the water content of the nucleus pulposus (NP) and the fiber orientation of the annulus fibrosis (AF).
10
Q
What are proteoglycans, and how do they contribute to the intervertebral disc (IVD)?
A
Proteoglycans are large protein molecules linked to chains of carbohydrates. They have the capability to attract and retain water, similar to a cotton ball. This water-binding capacity allows for and creates the compression-resisting component of IVDs.
11
Q
Describe the role of collagen in the intervertebral disc (IVD).
A
Collagen consists of strands of protein molecules, with the most common types in discs being Type 1 and Type 2. Type 1 collagen withstands tensile stresses and is highly concentrated in the annulus, while Type 2 collagen is more elastic and predominates in the nucleus pulposus. Collagen fibers are embedded in a proteoglycan-water gel within the intervertebral disc.
12
Q
Function of Type 1 collagen
A
Type 1 collagen withstands tensile stresses
13
Q
Where is Type 1 collagen highly concentrated?
A
highly concentrated in the annulus
14
Q
Function of Type 2
A
collagen is more elastic
15
Q
Where is Type 2 collagen highly concentrated?
A
predominates in the nucleus pulposus
16
Q
Where are collagen fibres are embedded?
A
In Proteoglycan-water gel
17
Q
Where is the Nucleus Pulposus located?
A
centrally…& also posteriorly in Lx spine
18
Q
Describe the Nucleus Pulposus.
A
Semi-fluid mucoid material, gelatinous mass, consistency of toothpaste
19
Q
Describe the arrangement of Nucleus Pulposus
A
Hydrophilic proteoglycans with interspersed type 2 collagen; collagen is arranged in a loose irregular meshwork
20
Q
T or F: The Nucleus Pulposus has a high water content ?
A
True 80%
21
Q
Describe the biomechanics of The Nucleus Pulposus.
A
The fluid nature of the NP allows for deformation under pressure, especially compression. The shape is altered but volume is unchanged. When the NP is deformed, it transmits applied pressure in all direction -> water- balloon
22
Q
Do blood vessels or nerves penetrate the NP?
A
No
23
Q
What is the Annulus Fibrosis?
A
The Annulus Fibrosis forms the outer boundary of the intervertebral disc and gradually differentiates from the Nucleus Pulposus.
24
Q
What are the components of the Annulus Fibrosis?
A
It consists of a narrow outer zone of collagenous fibers and a wider inner zone of fibrocartilage.
25
Describe the structure of the Annulus Fibrosis.
It has a high collagen to low proteoglycan ratio and is composed of 15-25 distinct layers called lamellae.
26
How are the collagen fibers arranged within the Annulus Fibrosis?
All collagen fibers within each lamina run in the same direction, while adjacent laminae have fibers running in the opposite direction, providing strength against bending and torsional loads.
27
What is the significance of the crisscross arrangement of collagen fibers in the Annulus Fibrosis?
It allows the Annulus Fibrosis to withstand high bending and torsional loads.
28
How are the fibers of the Annulus Fibrosis attached?
The fibers of the Annulus Fibrosis are attached to the cartilaginous endplate, with Sharpey’s fibers extending to the vertebral body, providing stronger peripheral attachment.
29
What is the variation in thickness of lamellae within the Annulus Fibrosis?
Lamellae are thicker anteriorly and laterally, while the posterior portion is thinner.
30
How does the Annulus Fibrosis extend fibers and bulge outward?
It can change the angle of the collagen fiber arrangement to extend fibers and bulge outward when under pressure.
31
What is the role of the Vertebral Endplate?
It binds the intervertebral disc to its vertebral bodies.
32
How thick are the upper and lower cartilaginous plates of the Vertebral Endplate?
They are approximately 1mm thick.
33
What function does the Vertebral Endplate serve in nutrient supply to the intervertebral disc?
It permits diffusion and provides the main source of nutrition for the avascular disc.
34
How does the Vertebral Endplate mediate load transfer between the disc and vertebral bodies?
It facilitates load transfer between the intervertebral disc and vertebral body centrum.
35
Describe the coverage of the Vertebral Endplate on the adjacent vertebral body.
Each endplate covers almost the entire surface of the adjacent vertebral body, leaving only a narrow rim of bone, called the ring apophysis, around the perimeter of the vertebral body uncovered by cartilage.
36
What is the mechanical relationship between the Annulus Fibrosis (AF) and Nucleus Pulposus (NP)?
The AF acts as a tight coiled spring, holding the vertebral bodies together against the resistance of the NP, which acts like a ball-bearing made of incompressible gel.
37
How do the vertebral bodies move in relation to the NP?
Movements are guided by facets, and the vertebral bodies roll over the NP, indicated by +θx and -θx, where θ represents angular displacement.
38
What is the blood supply situation for intervertebral discs (IVDs) after approximately 8 years?
IVDs have a blood supply for about 8 years, after which they rely on diffusion for nutrition.
39
How does diffusion play a role in the nutrition of intervertebral discs (IVDs)?
Nutrients are supplied to the IVDs through diffusion via pores in the endplate.
40
How do intermittent changes in posture affect the internal pressure of intervertebral discs (IVDs)?
Intermittent changes in posture cause fluctuations in internal disc pressure, creating a pumping action within the disc.
41
What is the role of water influx and outflux in intervertebral disc (IVD) nutrition?
Water influx transports nutrients into the disc, while outflux flushes out waste products, mimicking the function of the circulatory system.
42
What effect does maintaining a fixed body position over time have on intervertebral disc (IVD) health?
Maintaining a fixed body position over time restricts the pumping action within the disc, potentially leading to negative effects on disc health.
43
What is imbibition in the context of intervertebral discs (IVDs)?
Imbibition refers to the process of absorbing fluid, particularly water, by the gel-like nucleus pulposus.
44
How does imbibition differ from diffusion?
Diffusion is a passive process, while imbibition is an active process involving the absorption of fluid by a solid or gel-like substance (NP), often resulting in swelling.
45
How does movement contribute to imbibition in intervertebral discs (IVDs)?
Movement forces fluids in and out of the discs, similar to squeezing and releasing a sponge, facilitating imbibition.
46
What happens to the water content of the nucleus pulposus (NP) under significant axial force, such as during standing?
Water contained within the NP escapes into the vertebral body through pores when significant axial force is applied to the spine, such as during standing.
47
Describe the change in intervertebral disc (IVD) thickness throughout the day and night.
Static pressure maintains the disc during the day, but by night, the NP contains less water, resulting in a thinner disc. This cumulative thinning can amount to 2 cm in a healthy individual.
48
Why do individuals tend to be taller in the morning than at night?
When laying down, the water-absorbing capacity of the NP draws water back into the nucleus, causing the disc to regain its original thickness. Therefore, individuals are taller in the morning after this process occurs overnight.
49
How does aging affect imbibition and disc health?
With age, the water-absorbing ability of the disc decreases, leading to a loss of height and flexibility in the elderly.
50
What nerve innervates the superficial/outer fibers of the annulus fibrosis in the intervertebral disc (IVD)?
The sinuvertebral nerve, originating from the dorsal root ganglion, innervates the superficial/outer fibers of the annulus fibrosis.
51
Do nerve fibers extend beyond the superficial fibers of the annulus fibrosis into the nucleus pulposus (NP)?
No, nerve fibers do not extend beyond the superficial fibers of the annulus fibrosis into the nucleus pulposus (NP).
52
What is the innervation pattern of the nucleus pulposus (NP) within the intervertebral disc (IVD)?
The NP lacks nerve endings, as nerve fibers do not extend beyond the superficial fibers of the annulus fibrosis
53
How are axial compressive forces distributed between the nucleus and annulus of the intervertebral disc (IVD)?
Axial compressive forces are primarily borne by the nucleus, accounting for 75%, while the annulus bears 25%.
54
What maintains a baseline level of tension in the center of the nucleus pulposus (NP) even when the disc is unloaded?
The water-absorbing capacity of the NP causes the disc to swell within its casing, maintaining a baseline level of tension known as the "preloaded state."
55
What does the preloaded state provide for the spine?
The preloaded state provides stability, readiness to absorb and distribute forces, and resistance to forces.
56
How does aging affect the preloaded state of the intervertebral disc (IVD)?
With age, the disc loses its preloaded state
57
What causes the protrusion of the nucleus pulposus (NP) when a motion segment is cut vertically?
The NP protrudes due to the pressure it is under, indicating the presence of intrinsic pressure or "pre-stress."
58
What is the measurement of intrinsic pressure in the unloaded lumbar disc?
The intradiscal pressure in the lumbar NP is approximately 10 N/cm2 in the unloaded state.
59
What contributes to the intrinsic pressure or "pre-stress" in the intervertebral disc (IVD)?
The intrinsic pressure results from forces exerted by the longitudinal ligaments and the ligamentum flavum.
60
Describe the hydrostatic function of the intervertebral disc (IVD) during loading of the spine.
During spine loading, the NP acts hydrostatically, allowing for a uniform distribution of pressure throughout the disc. This enables the entire disc to serve as a cushion between vertebral bodies, storing energy and distributing loads.
During spine loading, the NP acts hydrostatically, allowing for a uniform distribution of pressure throughout the disc. This enables the entire disc to serve as a cushion between vertebral bodies, storing energy and distributing loads.
61
Name the Loads on the IVD
Tip ** Come share the load
* Compression * Tension
* Shear
* Torsion
* Combined loads
62
What are the intervertebral discs (IVDs) responsible for carrying in addition to facet joints?
.
The IVDs are responsible for carrying all the compressive loads that the trunk is subjected to.
63
How do compressive loads on the intervertebral discs (IVDs) vary between standing, sitting, and bending?
In standing, forces on the IVDs exceed the weight of the trunk. In sitting, the forces on the IVDs are more than three times the weight of the trunk. Bending increases compressive forces significantly due to the contraction of back muscles.
64
What happens to hydrostatic pressure within the nucleus pulposus (NP) during compressive loading?
Hydrostatic pressure develops within the NP during compressive loading, dispersing forces towards the endplates and annulus. This mechanism slows the rate at which applied loads are transmitted to adjacent vertebrae, providing shock-absorbing abilities to the disc.
65
How does the viscoelastic matrix of the NP distribute forces within the intervertebral disc (IVD)?
The viscoelastic matrix of the NP distributes forces smoothly to the annulus and endplates, causing the disc to bulge laterally.
66
Describe the sequence of force transmission within a healthy intervertebral disc (IVD) under axial compressive loads.
Axial compressive loads are transmitted from the endplate of the superior vertebra to the NP, raising internal pressures. The rise in nucleus pressure exerts forces radially onto the annulus. Tensile stress in the annulus prevents nucleus expansion, and increased nuclear pressure then exerts forces onto the vertebral endplates.
67
What is the typical response of the intervertebral disc (IVD) to increasing loads?
The IVD provides little resistance at low loads but becomes stiffer as the load is increased, offering more stability at higher loads.
68
How does strain rate affect the mechanical behavior of the viscoelastic intervertebral disc (IVD)?
Generally, the quicker an IVD is compressed or rotated, the stiffer it becomes.
69
How can asymmetric compressive loading affect the nucleus pulposus (NP) within the intervertebral disc (IVD)?
Asymmetric compressive loading can cause the NP to migrate in a direction opposite to the compression. During flexion of the lumbar spine, the NP migrates posteriorly, while during extension, it migrates anteriorly.
70
What is the role of the nucleus pulposus (NP) migration in self-stabilization of the intervertebral disc (IVD)?
The NP exerts force in the opposite direction of migration, contributing to self-stabilization of the disc, particularly during asymmetric loading.
71
How does NP migration behavior differ between asymptomatic and symptomatic/degenerative intervertebral discs (IVDs)?
While NP migration behaves predictably in asymptomatic discs, a variable pattern of migration occurs in individuals with symptomatic and/or degenerative IVDs.
72
What types of motions produce tensile stresses in parts of the annulus fibrosis (AF) of the intervertebral disc (IVD)?
Tensile stresses are produced in parts of the AF during normal motions of flexion, extension, lateral bending, and axial rotation.
73
Is tensile force on the entire disc common in daily living?
No, tensile force on the entire disc, as would occur with distraction, is not common in daily living.
74
How does distraction of the functional spinal unit (FSU) affect the annular fibers of the intervertebral disc (IVD)?
During distraction of the FSU, the disc height increases, and all annular fibers are lengthened and tensed, regardless of their orientation.
75
Which parts of the annulus fibrosis (AF) are tensed during flexion, extension, lateral flexion, and axial rotation?
During flexion, the posterior annulus is tensed; during extension, the anterior fibers are tensed; during lateral flexion, the convex side is tensed; and during axial rotation, fibers are tensed 45 degrees to the disc plane.
76
What happens to the intervertebral disc (IVD) during compressive loads?
The disc bulges during compression and contracts in tension.
77
What type of stresses do shear forces cause in the intervertebral disc (IVD)?
Shear forces cause stresses parallel to the endplate, resulting in a type of sliding movement (translation) of one body upon the other.
78
How do collagen fibers of the annulus fibrosis respond to shear forces?
The collagen fibers of the annulus that run in the direction of the translation are strained, while the others are compressed.
79
When is the intervertebral disc (IVD) subjected to shear stresses?
The disc is subjected to shear stresses during torsional loading.
80
In what loading condition is the stiffness of the spine greatest?
The stiffness of the spine is greatest during compression; however, large values are also seen during shear loading.
81
What is laterolisthesis indicative of regarding the intervertebral disc (IVD)?
The presence of laterolisthesis indicates severe disruption of the restraining mechanisms of the annulus. This disruption often does not manifest radiologically until severe plastic deformation of the annulus has occurred, usually over many years.
82
What type of stresses does axial rotation of the trunk inflict on the functional spinal unit (FSU)?
Axial rotation of the trunk inflicts torsional stresses on the FSU.
83
How do the collagen fibers of the annulus fibrosis respond to torsional stresses?
Only collagen fibers inclined in the direction of movement undergo tensile strain due to the alternating direction of the fibers.
84
How does the annulus fibrosis resist axial rotation movements?
The annulus resists axial rotation movements with only half of its collagen fibers, while the other half remain slack.
85
What is the significance of the alternation of the direction of fibers in the annulus fibrosis?
The alternation of the direction of fibers in the annulus is integral to the disc's capacity to resist twisting movements.
86
What happens to internal pressure within the intervertebral disc (IVD) during torsional movements?
Maximum tension forces within the internal layers of the annulus fibrosis lead to strong compressive force on the nucleus pulposus, increasing internal pressure proportionally to the degree of rotation.
87
How can bending loads be conceptualized in terms of their effects on the intervertebral disc (IVD)?
Bending loads can be thought of as a combination of tensile and compressive loads on the intervertebral disc (IVD).
88
What is a significant risk factor in disc herniation according to epidemiological studies?
Combined loads have been found to be a significant risk factor in disc herniation.
89
Describe the mechanism of disc prolapse based on experiments.
The mechanism of disc prolapse involves a sudden application of compressive force with the spine in a flexion and lateral bending posture.
90
How does loading speed affect the stiffness of intervertebral disc (IVD) tissues?
At faster loading speeds, the disc tissues become stiffer, while at slower loading speeds, the disc is more flexible.
91
What is creep in the context of intervertebral disc (IVD) viscoelasticity?
Creep is a viscoelastic property in which deformation of the structure continues when a sustained load is applied.
92
How does disc degeneration affect creep behavior?
Degenerated discs creep faster and reach final deformation sooner than healthy discs, making the disc less viscoelastic.
93
What is the significance of the duration and amplitude of loads on intervertebral disc (IVD) viscoelastic properties?
The duration and amplitude of loads are important factors because the disc exhibits time-dependent viscoelastic properties.
94
How do short duration-high amplitude loads affect the intervertebral disc (IVD)?
Short duration-high amplitude loads can cause irreparable structural damage to the IVD when stress higher than the ultimate failure stress is generated at a given point.
95
What is the mechanism of failure for long duration-low amplitude loads on the intervertebral disc (IVD)?
Long duration-low amplitude loads lead to fatigue failure, where a tear develops at a point with stress much less than the ultimate stress, eventually resulting in complete disc failure.
96
What is hysteresis in the context of intervertebral disc (IVD) mechanics?
Hysteresis is the loss of energy when the disc is subjected to repetitive cycles of loading and unloading, representing the absorption or dissipation of energy by the distorted structure of the IVD.
97
How does hysteresis change with the magnitude of load applied to the intervertebral disc (IVD)?
The larger the load, the greater the hysteresis.
98
How does hysteresis affect the protective capacity of the intervertebral disc (IVD) against repetitive loads?
When the load is applied a second time, hysteresis decreases, indicating less capacity to absorb shock energy (load). This implies that the discs are less protected against repetitive loads.
99
How does hysteresis change with age, and what are the implications for the elderly?
The shock-absorbing property of hysteresis decreases with time, making the elderly more susceptible to trauma from external forces.
100
What types of materials exhibit hysteresis?
Viscoelastic materials exhibit hysteresis, which is a measure of the loss of energy when a structure is subjected to repetitive load and unload cycles.
101
Provide an example illustrating the protective mechanism of hysteresis in the intervertebral disc (IVD).
Hysteresis can be thought of as a protective mechanism where shock energy is absorbed by the discs when a person jumps up and down, traveling from the feet to the head.
102
What factors influence hysteresis in the intervertebral disc (IVD)?
Hysteresis depends on the load applied, spinal level, and degree of degeneration. It is also decreased when the same disc is loaded a second time, reaching a steady state after a few cycles.
103
What happens to intervertebral discs (IVDs) over time in degenerative disc disease (DDD)?
Over time, IVDs begin to dehydrate and lose height.
104
How does loss of water content in degenerative disc disease affect the nucleus pulposus (NP) hydrostatic pressure?
Loss of water content leads to conversion of fibrocartilage and a decrease in NP hydrostatic pressure.
105
What is endplate occlusion in the context of degenerative disc disease?
Endplate occlusion refers to the reduction in the ability of the endplates to allow nutrient transport into the intervertebral disc.
106
How do injury and aging affect the shock-absorbing capability of intervertebral discs (IVDs) in degenerative disc disease?
Injury and aging irreversibly reduce the water-absorption capacity of the discs, leading to a decrease in shock-absorbing capability.
What is the typical reduction in fluid content of
107
What is the typical reduction in fluid content of a geriatric intervertebral disc (IVD) due to degenerative disc disease?
A typical geriatric disc has a fluid content reduced by approximately 35%.
108
What are the initial changes observed in the annulus fibrosis (AF) during degenerative disc disease?
The first changes occur in the AF, characterized by small circumferential separations between the annular lamellae, leading to delamination.
109
What is a rim tear in the context of annular tears?
A rim tear is a horizontal tearing of the very outer annular fibers of the disc near their attachments into the endplates.
110
What is a circumferential or concentric tear?
A circumferential or concentric tear is a tear that occurs between and within the lamellae of the annulus fibrosis.
111
What is a radial tear?
A radial tear is a horizontal tear that originates from the central region of the nucleus pulposus and extends outward towards the peripheral edges of the disc
112
What are the two main types of disc herniations based on containment within the annular wall?
Contained herniations: These are within the annular wall and can be further categorized into bulge and protrusion.
113
What is a bulge in the context of disc herniations?
A bulge is a contained herniation within the annular wall.
114
What is a protrusion in the context of disc herniations?
A protrusion is also a contained herniation within the annular wall.
115
What are the two main types of disc herniations based on being outside the annular wall?
Non-contained herniations: These are outside the annular wall and can be further categorized into extrusion and sequestration.
116
What is an extrusion in the context of disc herniations?
An extrusion is a non-contained herniation outside the annular wall.
117
How are you able to see annular tears?
MRI
118
