Tissue Mechanics- Fibrocartilage, Disc, and Menisci

what are the roles of fibrocartilage within joints, and how does it contribute to joint function

• increase joint congruency

• assist with joint lubrication

• protect edges of joint

• act as a shock absorber

• act as load bearers (transmit loads)

describe the structure and functions of the meniscus in the knee joint

acts as a buffer, dampens impact like shock absorber, increases stability, distrubtes load and protects AC and bony surfaces

how does the meniscus distribute load and protect articular cartilage in the knee

helps distribute the load over a larger area

explain the difference between the “red” and “white” zones of the meniscus and their significance for injury healing

Red- vascular, made up of about 80% type I collagen, cells are spindle shaped and are more “fibroblast-like”

White- avascular, made up of 70% collagen 60% being type II and 40% being type I, contains a greater portion of PGs, cells are more chondrocyte-like

what is the structural composition of the meniscus, and how does it differ from articular cartilage

1. articular surface composed of fine collagen fibrils

2. collagen bundles are large, rope like and principally arranged circumferentially around the semilunar meniscus

3. innermost area has randomly arranged fibers with more PGs, weeping occurs here from squeezing 2nd later

describe how the meniscus structure affects its response to tensile and compressive loads

hoop stress- the collagen are circumferentially arranged so as tensile loads are resisted, stiffer in the circumferential direction as opposed to the radial direction

how do injuries to the meniscus typically affect knee mechanics, and what are common types of meniscal tears

when the meniscus tears, the remaining fibers can maintain the mechanical functionality

radial tie fibers transfer stresses to the remaining intact circumferential collagen fibers, a tear needs to rach about 90% of the meniscus width before tibial contact stresses increases

discuss the pros and cons of surgical versus non-surgical treatment options for meniscal injuries

Surgery will increase the incidence of premature OA secondary to shifting load on to AC

describe the basic structure and function of the TMJ disc

avascular and aneural, intermediate band has high concentration of aggrecan

passive- the superior and inferior lamina

active- direct attachment to the lateral pterygoid

how the the TMJ disc function during relaxed versus forceful jaw movements

relaxed- lateral pterygoid is relaxed, passive elastic properties of the superior lamina applies a posterior tractive force to maintain the disc within the mandibular fossa correctly

forceful- the elastic properties of the lamina primarily maintain control of the disc while the suprahyoids and inferior fibers of the lateral pterygoid muscle translate the condyle and disc forward

what are the viscoelastic properties of the TMJ disc and how do they compare to tendons or ligaments

hysteresis, creep, and stress relaxation all very similar to tendon/ligament. reaches equilibrium in about 5 minutes

explain the common treatments for TMJ disc injuries and their potential outcomes

medication

splints: like night gaurds

PT: strengthening of the lateral pterygoid

surgery: does not really do anything because it does not restore the function of the joint

describe the structure and composition of the IVD and its two main components

nucleus pulposus: centrally located 88-90% water, the remainder is PGs and collagen typeII

annulus fibrosis: outer portion of disc, water content is about 78%, collagen is 60% type II and 40% type I arranged in layered bands. Type I is most abduntant in the outer layer

what role does the nucleus pulposus play in load distribution within the IVD

distributing compressive loads evenly throughout the disc by generating hydrostatic pressure due to its high water content

explain the importance of the annulus fibrosus and how its composition varies acorss regions

type 1 fibers more abundant at outer layer, type II more abundant at inner layer, within the bands the fibers are 30 to the vertebra and 120 to the adjacent layers to help it respond to every direction

what is the function of the endplate in the IVD, and how does it contribute to disc nutrition

found at the top and bottom of the IVD, creates an area of diffusion which provides nutrition to the inner layers of the disk including the nucleus, stabilizer of spinal motion significantly reduces the shearing force that would be present at the movement segment

describe the viscoelastic properties of the IVD and how they contribute to daily changes in disc height

Creep- is the reason for disk height loss and can lead to reduced nutrient diffusion

Quick hysteresis response, which allows for fluid recovery

how does aging affect the composition and function of the IVD

water content of the nucleus and the annulus can decrease by 70%, loss of water is attributed to loss of PGs especially aggrecan

what is disc herniation, and how does it impact spinal mechanics and stability

nucleus pulposus leaks into fibrosis annulus

cracks in endplates can lead to herniation into the vertebral bodies

what are common treatments for DDD, and what are the potential outcomes of each

medication

exercise: low reps, no load, and repeated often or with resistance exercise, cyclic loading seems to be the key

intradiscal electrothermal therapy- prove placed into the disc and burn the tissue that is damaged

chymopapaon injections- injected directly into disc to dissolve part of the disk

discectomy: partial or full removal of disc

disk replacement: helps restore normal spinal height

how does exercise benefit individuals with DDD, and what are some effective exercise guidelines

adds strength to surronding musculature

low reps, no load, and repeated often, or with resistance exercise

compare to the effectiveness and risks of discectomy versus disc replacements in treating DDD

discectomy- leads to more shear force and more DDD, destabilizes the spine

replacement- restores the normal spinal height, can mitigate the advancement of DDD

what are schmorl’s nodes, and how are they related to spinal degeneration

fracture of the endplates and nucleus pulposus begins to leak leading to DJD

discuss how cyclic loading affects the nutrition and health of the IVD

allows weeping to occur to force fluid in and out, carrying nutrients in the fluid to supply the disc

repeated controlled, pain-free movements