disc

• annulus fibrousus • nucleus propulsus • cartilagenous end plate

• provided weight bearing properties • internal lubrication • provide a matrix for concentration gradients for nutrient exchange

• GAG chains of long polysaccaride molecules that may or may not be sulfated • GAG wrapped around protein core similar to a bottle scrubbing brush

• Keratin sulfate • chondrotin 4-/6- sulfate • hyaluronic acid

• lubrication between collagen 2. fluid transportation for nutrition and waste

nucleus -50-60% proteoglycans -80% collagen which is 80% type II and 0% type I annulus -20% proteglycans -50-60% collagen which is 80% type I

type I- resists tensile forces type II- resist compressive forces

• parallel collagen fibers arranged in 10-12 concentric layers • thickest anterior and laterally • thinnest posterior • fibers run at about 30degrees from the vertical and alternate orientation in each successive layer

outer part of the annulus not covered by the vertebral end plate connected directly to the vertebral body

• Hylanine cartilage on the vertebral body side 2. fibrocartilage on the disc side

• end plate is strongly bound to the disc by extensive collagen attachments • loosely bound to the vertebral body

• at birth there is a rich vascular supply to the disc • weight bearing makes pressure too great in the lumbar spine for vessels to survive • cervical spine can have a direct flood supply until the third decade • only the arteries from the metaphysial arteries penetrate the outer most fibers of the annulus

• pH of GAG rich disc is usually 0.5 lower than surrounding tissues • the osmolarity is higher than the surrounding fluids • the fixed negative charge density facilitated by the ionic solutions creates a swelling pressure that imbibes fluid

glycolosis

• occurs through cartilagenous end plates and blood supply of the vertebral body • smaller nutrients such as oxygen and glucose are moved entirely by diffusion • loading and unloading mover water, but not nutrients • there is a steep concentration gradient from vertebral body to nucleus propulsis

• end plate clarification • proteoglycans become smaller and less effective • calcification can lead to pores in the end plates large enough for proteglycans to pass through • cytokinins or other damaging enzymes can pass into the disc from the enlarged pores

• outer third and into the middle third • pain and degenerative disc can have innervation as much as 2/3 of the the disc or NP, normally the NP has no innervation

• Greater disc height equates to greater segmental ROM 2. loading of the disc increases its stiffness and available ROM

• the end plates are the weakest point under axial loads • with movement the posterior lateral AF absorb the greatest force because they are further from the axis of motion • disc will not prolapse under compression alone and requires some bending in addition to the comprssion

• increases stress on the AF 2. decrease the vertical and horizontal stress on the NP

• rest increases disc height by as much as 10% and fluid volume can increases as much as 20-25% • activity-decreases with in 8 hours or 4 hours carry 40% of body weight

• it transmits vertical forces horizontally and circumferentially • this stretches the AF • as AF recoils energy restores disc form • outer edges of disc bulge and the end plates deflect stress in an axial direction

• sharp’s fibers 2. intervertebral ligaments

• since the annular rings collagen fibers run in alternating direction only have the fibers are availiable to manage the shear forces • therefore only half the AF are stretched during shearing