disc vascular bone Flashcards
What percentage of people have a lumbarization or a scaralization of the lumbar spine?
about 10%
What is the primary bone cells?
- Osteocyte- entombed cell making up 90-95% of bone cells and are probably responsible for transduction of mechanical energy
- osteoblast- express PTH for production of bone
- osteoclast- bone remover
What is the ECM of bone?
composed predominantly of collagens, non-collagenous glycoproteins, hyaluronan and proteoglycans
Describe the boney architecture of the vertebral body
a. the center is made of soft trabecular bone
b. the outer layers forms an epiphyseal ring of cortical bone
Why is the body of the vertebrae soft?
the body is not a compact boney structure but is soft and highly vascularized
When is bone loss visible on x-ray?
when it is at least 40%
What is the vertebral end plate?
a. layer of cartilage about 1 mm thick on the top and bottom of the the vertebral body
b. encircled by the epiphyseal ring
c. covers the entire nucleus proposus, but not the entire annulus
What are the parts of the arch of the lumbar vertebrae?
- pedicles
- transverse process
- superior articular process
- lamina
- inferior articular process
- spinous process
What are the pedicles?
a. boney processes extending from the body posteriorly
b. lever arms for the posterior musculature to the vertebral bodies
c. roof/floor of the foramina
What is the lamina?
- concentric rings around nucleus propulsus
- anternating orientation of fibers with each layer
- compossed primarily of type 1 collagen fibers oriented in a oblique angle
Which articular process is more anterior?
the superior articular process sits over the junction of the pedicle and lamina where as the inferior articular process comes off the lamina
Where is the mamilary process located?
On the back of the superior articulating process
Where is the accessory process of the lumbar vertebrae located?
posterior aspect of the TP near its base
Describe the spinous process
thick, broad, and somewhat quadrilateral; it projects backward and ends in a rough, uneven border, thickest below where it is occasionally notched
What is the pars interarticularis?
the region between the superior and inferior articulating processes in the lamina
How does the vascular system impact function of the vertebrae?
The body of the vertebrae’s load bearing capacity is greatly enhanced by large volume of blood and presence of blood in the intratrabecular spaces
corking the body
What are the primary vessels serving vertebral body?
- aorta
- Two lumbar arteries
- Periosteal
- anastomosis with with anterior spinal artery
- anterior spinal artery
- nutrient artery
What are the primary vessels serving the disc?
- Metaphyseal and nutrient arteries of the body extend into the end plate that allow for diffusion of nutrients into the disc
- The vertebral body has its greatest density to end plate at the center of the body
- Slight blood supply at the periphery from the metaphyseal arteries
What unique properties do the vessels of the vertebral bodies have?
They are valveless and therefore there is no separation between veins and arteries
How does the valveless vasculature of the vertebral body impact the body and disc?
- Blood flow is dependent on compression and decompression to move the fluid through
- Inflammation can easily spread due to stasis in the system and impact the end plates due to its poor capacity for metabolic activity
What is “corking” of the vertebral body?
during flexion the the PLL will compression the nutrient foramen limiting blood flow out of the body and there by increasing its loading capacity
What makes up the lumbar nucleus propulsus?
primarily composed of proteoglycans and type II collagen
How does the NP move?
- in a healthy disc it doesn’t move at all
- It accumulates in the area of least resistance or it moves like a ball of gas under pressure following the path of least resistance
- It does not move with increase disc pressures
What is the function of the NP?
absorb compression and prevention of excessive movement while allowing continued movement
What makes up cellular content of the annulus fibrosis?
primarily type I collagen which provides high tensile strength
How are the fibers of the annulus arranged?
1.12-15 layers of fibers known as lamella
2.alternating fiber orientation between layers
progress towards an almost horizontal orientation in the central rings
How does the the lumbar screw home mechanism work?
the fibers assume a more vertical orientation and become more taut creating a compression of the disc
Why does rotation increase risk of disc shearing?
The annular fibers become more vertically oriented and are therefore less able to resist shearing forces
How long does it take a disc to heal?
half life of collage is 300-500 days
HOw long does it take for pain to start to decrease with disc herniations?
- GAG must be reabosrbed to decrease mechanic pressure
- Younger people will have more GAG than older people
- half life is 1.7 to 7 days
What factors contribute to degeneration of the the disc?
- shearing of the disc
- loss of the nucleus increases nonphysiologic compressive forces on the annulus
- end plate rupture decrease nutritional exchange
How does the nucleus facilitate annular function?
- the nucleus is not compressible, but it is deformable
2. so when the nucleus is loaded it expands radially tensioning the annular fibers
How doe the annular fibers of the disc resist shearing?
- the fibers having an alternating oblique orientation
- fibers oriented parallel to the force vector are either tensioned or slackened based on their orientation
- fibers oreinted perpendicular to the force vector are tension (i.e. during flexion the anterior and posterior fibers are lengthened
How does the disc permit motion and transfer force from one vertebrae to another?
- the annular fibers are responsible for transfering weight from one vertebrae to the next
- the nucleus assists the annular fibers by expanding radially with loading and tensioning the annular fibers for improved transfer of force and load from one body to the next
What are the different disc injuries?
- protusion- penetration of the nucleus through some of the annular fibers
- herniation- penetration of the nuclear material far enough through the annular fibers so that pressure is applied to PLL
- prolapse- nucleus passes through the annular fibers and mechanically impacts the PLL
How will the location of a prolapse effect standing posture?
- lateral prolapse they will lean away to pull the roots off of it
- central prolapse they will stand up right
- medial prolapse they will lean towards the same side
How come an L5 prolapse will not hit the L5 nerve root?
- The L5 root sleeve is actually located behind the L4 vertebral body and a result the disc could likely miss the L5 root and hit the S1 root
- Like wise findings in the L5 distribution might be a L4 disc issue and segmental mobility is the only way to differentiate
Protrusion of the disc typically occurs in which direction?
posterior or lateral because these areas are furtherest from the IAR
What clinical findings might you expect with a disc protrusion?
- Pain is difficult to reproduce because the injury is contained within the annulus
- initially there could be a feeling of nausea and sweating
- dull ache
- possible referred symptoms with segmental facilitation
- potential muscle guarding secondary to gamma motro response with type IV receptor stimulation
- potential hyper responsive DTR
What clinical finding could you have with a disc herniation?
- greater potential for mechanic pain since you will have deformation of the the PLL
- Extension could relieve pain
- reduction of stress on the PLL
- closed pack position of the facet allowing for greater stability and stress on annulus
With a disc prolapse what types of pain processes are occuring?
- mechanical deformation with the disruption of the PLL, expansion of the GAG and compression of the vertebral canal structures
- chemical/ischemic with compression of the vasculature of the nerve root and canal vasculature
- edema leading to mechanical deformation and chemical imbalance in the nerve root
The bladder function is most often impaired with prolapses in which direction?
central because it will catch the cauda equina
What are the five most common causes of disc degeneration per OGI?
- nutritional deprivation
- disruption of protein and sugar binding
- build up of wast products
- mechanical damage
- genetic predisposition
Why does will segmental hypomobility lead to disc degeneration?
the disc has no direct blood supply and is dependent on changes in pressure gradients for nutrients and waste to move through the end plate
How do changes in the ionic environment of the disc lead to degeneration?
the integrity of the collagen is dependent on its ionically regulated protein and sugar composition
Why do injuries to the disc create ionic imbalances?
because of the poor vasculature the disc is dependent on lysosomal activity that has a negative ionic charge
What is the difference between a spondylolysis and spondylolisthesis?
-lolysis- dispruption of neural arch
-lolysthesis- forward slipping of the segement
spondylolysthesis does not mean you have a spondylolysis
What is the prevalence of spondylolesthesis?
6% with women greater than men
What anatomical feature is most predictive of spondylolesthesis?
orientation of the facets in the sagital plane
77.9% ???
What are the six most common ways of developing spondylolesthesis?
dysplastic- congenital
isthmic- fracturing of the scotty dog head
degenerative- as the segement becomes more mobile due to a loss of disc height you can get an anterior displacement
traumatic
patholigical
post surgical- following fusion
What x-ray view is used to diagnosis spondylolesthesis?
oblique
How is a spondy graded?
Sacrum divided into four equal parts
What is spondylodiscitis?
a destructive lesion of the disc that often occurs post surgically
What is a Schmorl’s node?
herniation of intradiscal material through the end plate into the spondy body of the vertebrae
During what decade of life are Schmorl’s nodes most prevelent
second decade of life
