11/13

Question 1

Articular cartilage

Answer 1

Hyaline cartilage

Aggrecans are the proteoglycans , water decreases as move from surface to the deep zone

Type II collagen is 50% of the dry weight

Young person: keratan sulfate is low, Chondroitin 4-sulfate is main chondroitin sulfate

Old person: keratan sulfate increases, Chindroitin 6-sulfate is predominant chondroitin sulfate

Integrans: convert mechanical stimuli to intracellular signals that affect gene expression

Question 2

Synovial Fluid

Answer 2

Generated by synovium

Provides via diffusion: articular nutrition, lubrication, removal of debris

Question 3

Articular Pathologies

Answer 3

Inflammatory conditions: opaque, higher WBC count, neutrophils, positive for crystals like gout

Non inflammatory: normal transparency, due to osteoarthritis with specks of cartilage floating around, normal monocytes, no bacterial or crystal cultures

Septic: opaque, more volume, high WBC count with neutrophils, positive for bacterial culture

Question 4

Meniscus

Answer 4

Collagen is 60-70% dry weight, mainly Type I

Elastin

Fibrochondrocytes

Fibrocartilage

Circumferential Fibers: withstand hoop stresses and prevent protrusion (along with horn attachment) out of knee

Radial Fibers: hold circumferential Fibers in place

Surface: random orientation, resist shear forces, and hold in water

Horn attachments: anchor points to keep meniscus in knee joint

Viscoelastic behavior: shock absorber

Question 5

Functions of meniscus

Answer 5

1. Load bearing: transmit more Hahn half load in extension and 85% in flexion, partial meniscectomy results in much higher contact stress, axial load transmitted to circumferential which is stronger than radial shear strength
2. Shock absorption: biphasic with water phase and solid phase with GAGs/collagen, not as permeable and stiff as articular cartilage
3. Joint stability: superiority concave and inferiorly flat so conform to both bones, posterior horn of medial meniscus is a secondary stabilizer to anterior directed force, some varus/valgus stability

Medial meniscus at risk in ACL deficient knees

4. Proprioception: mechanoreceptors in horns, feedback extremes of motion, may contribute to functional stability of knee
5. Lubrication: aids in articular cartilage nutrition, promotes viscous hydrodynamic action for fluid-film lubrication

Question 6

Meniscus Blood Supply

Answer 6

100% vascular at birth then normal at 10

Perimeniscal Capillary Plexus on the outer portion of each (MM has slightly more), anterior/posterior horns have enhanced blood supply while avascular at popliteal hiatus

Vessels radiate inward from periphery, inner 2/3 gets nutrients by diffusion only

Majority of meniscus is avascular

Vascularity has direct relevance in treatment of meniscal tears-

1. Red-red Zone: outer portion, heals
2. Red-white Zone: middle portion, should heal but needs enhancement techniques
3. White-white Zone: theoretically does not heal

Question 7

Nucleus pulposis

Answer 7

Gelatinous material, predominately proteoglycans

Chondrocyte like

Resistant to compression, interaction with water

Effects of aging: Cell conc. decreases, water content decreases, proteoglycans change, more dense and stiff

Anulus Fibrosis aging: inner portion increases in size, regeneration of fibrocartilage, outer lamellar become stiff

Question 8

Ligaments

Answer 8

Built in laxity, good with tension, bad with compression, like a rope not a bar

Primarily type I collagen

Forces are anisotropic and ligaments crimp over each other

Crimp: nonlinear portion of stress test where ligaments straighten out

Direct attachment: 4 zones of increasing density and calcification

Indirect attachment: merge in periosteal layer, not as strong

Sprain- tendons and muscles have strains
Grade I: pain and no instability, not appreciably stretched, no laxity

Grade II: some torn fibers, minimal instability, increased laxity but endpoint on physical exam

Grade III: completely ruptured, may be from dislocation, increased joint laxity without an endpoint

Question 9

Tendons

Answer 9

Type I collagen primarily, some type III

Specialized direct insertions zones:
Tendon
Fibrocartilage
Mineralized fibrocartilage
Bone

Two types of tendons:
1. Pull in a straight line are enclosed by paratenon, Achilles, LCT that’s continuous with tendon

2. Tendons that bend or flex (hand) are enclosed by a tendon sheath, acts like pulley, motion assisted by synovial fluid made by epitenon