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Questions and Answers
What is the primary function of interstitial fluid pressurization in joints?
What is the primary function of interstitial fluid pressurization in joints?
Which lubrication method primarily uses a bearing surface created by a fluid film?
Which lubrication method primarily uses a bearing surface created by a fluid film?
What occurs during mixed lubrication in joint surfaces?
What occurs during mixed lubrication in joint surfaces?
What happens to the friction coefficient when interstitial pressurization is high?
What happens to the friction coefficient when interstitial pressurization is high?
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Which type of wear involves direct contact between bearing surfaces without lubrication?
Which type of wear involves direct contact between bearing surfaces without lubrication?
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What is the main consequence of prolonged immobilization of hyaline cartilage?
What is the main consequence of prolonged immobilization of hyaline cartilage?
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What is the primary purpose of articular cartilage?
What is the primary purpose of articular cartilage?
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How does cyclic loading and unloading benefit cartilage?
How does cyclic loading and unloading benefit cartilage?
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Which zone of articular cartilage contains the highest concentration of proteoglycans?
Which zone of articular cartilage contains the highest concentration of proteoglycans?
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What occurs when cartilage is loaded in tension?
What occurs when cartilage is loaded in tension?
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Which of the following best describes the role of fluid flow in hyaline cartilage?
Which of the following best describes the role of fluid flow in hyaline cartilage?
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What characterizes the Surface Tangent Layer of articular cartilage?
What characterizes the Surface Tangent Layer of articular cartilage?
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What happens to proteoglycans during loading of the articular cartilage?
What happens to proteoglycans during loading of the articular cartilage?
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What is the main purpose of microfracture surgery on cartilage?
What is the main purpose of microfracture surgery on cartilage?
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What effect does rapid loading have on cartilage stiffness?
What effect does rapid loading have on cartilage stiffness?
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What effect does high compressive loading have on cartilage?
What effect does high compressive loading have on cartilage?
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Which outcome is associated with loss of cartilage thickness?
Which outcome is associated with loss of cartilage thickness?
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During unloading, which of the following occurs in articular cartilage?
During unloading, which of the following occurs in articular cartilage?
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What characteristic of hyaline cartilage impedes its ability to repair itself?
What characteristic of hyaline cartilage impedes its ability to repair itself?
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What is the primary type of collagen found in articular cartilage?
What is the primary type of collagen found in articular cartilage?
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The radial orientation of collagen fibers in the Deep Layer of articular cartilage contributes mainly to:
The radial orientation of collagen fibers in the Deep Layer of articular cartilage contributes mainly to:
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What is a characteristic feature of hydrophilic proteoglycans in articular cartilage?
What is a characteristic feature of hydrophilic proteoglycans in articular cartilage?
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What determines the ability of the Surface Tangent Layer to decrease friction between joint surfaces?
What determines the ability of the Surface Tangent Layer to decrease friction between joint surfaces?
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What is primarily responsible for fatigue wear in bearing materials?
What is primarily responsible for fatigue wear in bearing materials?
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Which of the following effects can result from the disruption of the collagen-PG matrix in cartilage?
Which of the following effects can result from the disruption of the collagen-PG matrix in cartilage?
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What factors relate to the progression of cartilage failure?
What factors relate to the progression of cartilage failure?
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Which property is decreased as cartilage failure progresses?
Which property is decreased as cartilage failure progresses?
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Study Notes
Articular Cartilage
- Articular cartilage is a thin layer covering the ends of bones where they meet to form joints.
- It is primarily composed of water (70-85%), type II collagen (10-30%), and proteoglycans (8-10%).
- The high water content makes it resilient and smooth.
- Proteoglycans are essential for the cartilage's ability to absorb and distribute loads.
- Collagen fibers provide tensile strength to the material.
Structure and Zones
- Articular cartilage is composed of four zones:
- Zone I (Surface layer): The outermost layer oriented parallel to the joint surface, with high collagen content for load distribution and shear resistance. Low proteoglycan content.
- Zone II (Transitional stratum): Contains randomly oriented collagen fibers, which permits deformations. Higher proteoglycan content compared to Zone I, and more water.
- Zone III (Radiate stratum): Collagen fibers are oriented perpendicular to the surface with the highest proteoglycan content.
- Zone IV (Calcified cartilage): The deepest layer, grading into the subchondral bone, with collagen fibers oriented vertically or radially to the joint surface. Tidemark is the boundary between Zone IV and the subchondral bone; it does not allow water to pass.
Function
- Distributes loads across the joints to reduce stress on bone.
- Reduces friction between joint surfaces.
- Supports smooth joint movement. Cartilage is smoother than glass on glass.
- Proteoglycans (PGs) have negative charges, and resist expansion (due to water) by the tensile restraint provided by collagen.
Cartilage Loading
- Under compression, fluid flows out of the cartilage through pores in Zone I. This causes PGs to become less saturated and collagen to become compressed, making cartilage stiffer.
- During unloading, fluid flows back into the cartilage.
- Tensile stress on the cartilage leads to deformation and eventually break down, which is why excessive tensile loading can damage the cartilage. Cyclic loading and unloading are better for cartilage.
Cartilage Injury and Repair
- Cartilage injuries typically do not heal on their own due to lack of blood vessels and nerves.
- Microfracture surgery can help by stimulating blood vessel growth into the area to bring nutrients to the injured site.
- New cartilage is fragile and requires specific rehabilitation limitations (partial weight bearing for up to 5 weeks, running after at least 12 weeks).
Cartilage Damage and Wear
- Wear or damage (degeneration) occurs due to mechanical actions (e.g., overuse, impact loading).
- Interfacial wear occurs when cartilage bears directly against cartilage without a fluid film.
- Wear can weaken the collagen-proteoglycan matrix, and reduce a joint's load-bearing and lubricating abilities.
- These changes can lead to increased permeability and decreased cartilage stiffness.
- Increased magnitude and frequency of loading stresses worsens damage and wear.
Cartilage Physiology
- Hyaline cartilage lacks blood vessels and nerves; nourishment occurs through fluid flow during loading/unloading cycles.
- Cartilage is designed to withstand compressive forces, but not tensile stress. Tensile stress is damaging.
- Cartilage does not adapt readily to changes in stress, so poor loading can cause wear or damage.
Immobilization
- Prolonged immobilization can lead to cartilage degeneration.
- Reduced motion results in reduced fluid flow and nutrition, leading to thinning, softening, or fissuring of the cartilage. Loss of cartilage thickness leads to pressure point necrosis.
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Description
This quiz covers the structure and composition of articular cartilage, including its importance in joint function. Explore the four distinct zones of cartilage and the roles of water, collagen, and proteoglycans in maintaining its properties. Test your understanding of the material and its implications in biomechanics.