Basic Science Flashcards
Articular cartilage consists mainly of what?
-ECM, w/ only a small percentage of chondrocytes, which are responsible for synthesis, maintenance, and homeostasis of cartilage
what are the major components of ECM in articular cartilage?
-Water, proteoglycans, and collagen
What are the four layers of articular cartilage?
- superficial, middle, deep, and calcified
- classified according to collagen orientation, chondrocyte organization, and proteoglycan distribution
Cartilage is an avascular structure in the adult; this has implications for repair and healing
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The breakdown of the cartilage matrix in normal turnover and in degeneration appears to be the action of what?
-Proteinases (their overactivity is implicated in OA)
how does water content of cartilage change w/ aging and OA?
-decreases w/ aging and INCREASES w/ OA
how does proteoglycan content and keratan sulfate concentration change w/ OA?
- they decrease w/ OA
- proteoglycan degradation and chondroitin-4-sulfate concentration INCREASE
what is the principal mode of lubrication of articular cartilage?
-Elastohydrodynamic lubrication
superficial lacerations to cartilage rarely heal; deeper lacerations may heal w/ fibrocartilage
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what are responsible for the macroscopic and histologic changes seen in OA?
-Inflammatory cytokines and metalloproteinases
tendons and ligaments are materials w/ highly ordered hierarchical structure
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the composition of tendons and ligaments is primarily what type of collagen?
type 1 collagen (aligned in the direction of loading, anisotropic)
structural vs material properties?
structural: describe the capacity of the tissue to bear load
material: describe the quality of the tissue
tendons and ligaments are viscoelastic
-their properties are time dependent
several biologic (eg age) and environmental (eg temperature) factors influence the mechanical properties of tendons and ligaments
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tendon/ligament healing phases?
hemostasis/inflammation–> matrix and cell proliferation–> remodeling/maturation
sheathed vs nonsheathed and extra-articular vs intra-articular tendons and ligaments, how does this affect healing?
-nonsheathed tendons and extra-articular ligaments have a GREATER capacity to heal than do sheathed tendons and intra-articular ligaments
how does loading effect tendon and ligament healing?
-for tendon and ligament healing, increased loading can be either beneficial or detrimental, depending on the anatomic location and type of injury
the physical environment influences tissue maintenance: immobilization is detrimental and exercise is beneficial to the biomechanical properties of tendon and ligament
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what is the tendon/ligament enthesis?
-specialized tissue that is necessary to minimize stress concentrations at the interface between two very different materials (tendon/ligament and bone).
Schwann cell myelination
-speeds transmission of action potentials by SALTATORY conduction at nodes of Ranvier
Most motor and sensory nerves are myelinated, except for which ones?
autonomic and slow pain fibers
Nerve organization
-nerve fibers (axons) are surrounded by ENDONEURIUM, collections of nerve fibers (fascicles) by PERINEURIUM, and collections of fascicles by EPINEURIUM
Nerve injury causes loss of distal function in what sequence?
- motor–> proprioception–> touch–> temperature–> pain–> sympathetics
- nerves recover in the inverse order
Neurapraxia
-a reversible conduction block (traction or compression)
axonotmesis
-involves axon disruption w/ preserved neural connective tissue (stretch or crush)
neurotmesis
-complete disruption of a nerve (open crush or laceration)
tissue pressures up to what mmHg can cause paresthesias and increased nerve conduction latencies?
30mmHg
what decreases rate of transmission of nerve signals?
-temperature, age, demyelination, and loss of axons
Fibrillations
-an EMG finding of abnormal spontaneous activity that occur in muscle fibers 2 to 3 weeks after denervation (transient or complete)
nerve repair (neurorrhaphy)
- involves reapproximation of the nerve ends w/ fascicles appropriately oriented under minimal tension using a fine monofilament epineural suture
- group fascicular repair increases scarring at the repair site
nerve grafts
- may be cabled to increase diameter
- they should also be reversed to minimize early arborization of regenerating nerve fibers
muscle fiber
-collection of myofibrils
fascicles (muscle)
-collections of muscle fibers (which are collections of myofibrils)
actin’s binding sites for myosin are blocked by what?
tropomyosin
You must know all bands and lines of sarcomere organization! (A, I, H, M, and Z)
A band: composed of both actin and myosin
M line: central set of interconnecting filaments for myosin
H band: contains only myosin
I band: composed of actin filaments only, which are joined together at the interconnecting Z-line
Site of action of both depolarizing and non-depolarizing drugs?
NMJ
maximal force production is proportional to what?
-muscle physiologic cross-sectional area (PCSA)
phosphagen energy system
-has enough ATP for approximately 20 seconds of activity
Delayed onset muscle soreness (DOMS)
- peaks at 24 to 72 hrs post-exercise
- most common in type IIB fibers
- associated primarily w/ ECCENTRIC exercise
Eccentric contraction
-generates the highest tension and greatest risk for musculotendinous injury
muscle strain
-most likely in muscles that cross two joints
The intervertebral disk
-allows motion and provides mechanical stability of the functional spinal unit
intervertebral disk nutrition
-mostly avascular and depends on diffusion through pores in the end plate to provide nutrition to the disk cells
Nucleus pulposus cells
-more synthetically active in a hypoxic environment
nucleus pulposus
- normally rich in aggregating proteoglycans (aggrecan and versican), which attract water and help maintain disk height
- nucleus pulposus has a higher concentration of type II collagen than the anulus fibrosus
anulus fibrosus
-well organized laminated fibrous tissue composed primarily of type I collagen
what happens to intervertebral disk as it ages?
- with increasing age, the disk cells produce less aggrecan and type II collagen, leading to decreases in proteoglycan and water content
- as the nucleus pulposus dessicates, disk height is lost and the anulus fibrosus develops fissures
what percentage of asymptomatic individuals older than 60 yrs have MRI evidence of disk degeneration?
-90%
Genetics plays a strong role in disk degeneration, but this seems to involve a multifactorial process that does not fit a Mendelian pattern.
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Disk degeneration is NOT necessarily a painful condition
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Diskography
-has a high false positive rate in pts w/ abnormal psychometric testing results
what is the most common general infectious symptom?
PAIN localized to the site of infection
-it is rare for pts to not report pain as a presenting symptom of infection
Septic arthritis in adults (most common organisms)
- most commonly associated w/ N. gonorrhea in otherwise healthy pts
- S. aureus is the second most common pathogen causing adult septic arthritis
triad of symptoms strongly suggesting Clostridial myonecrosis
- progressively severe pain out of proportion to obvious injury
- tachycardia not explained by fever
- crepitus
how much bone loss is required before the classic signs of osteomyelitis (bone resorption, destruction, periosteal elevation) can be seen on radiographs?
bone loss of 30-40%
The most sensitive imaging tool for diagnosing osteomyelitis?
MRI
what are the classic findings on MRI of osteomyelitis?
- signal change that is due to the increased edema and water content in bone, which is manifested as a reduction in T1 and an increase in T2 marrow signal
- the increased signal intensity on T2 images results because the fatty marrow has been replaced by inflammation
Synovial fluid WBC count strongly indicative of infection in a TKA?
-WBC count > 2,500/mm3 or w/ > 90% PMNs
S. aureus is protected from host immune defenses by what 3 mechanisms?
- excretion of protein A, which inactivates IgG
- production of a capsular polysaccharide, which reduces opsonization and phagocytosis of the organism
- formation of a biofilm (a “slime” containing an aggregation of microbial colonies embedded within a glycocalyx matrix that most commonly develops on THA/TKA implants or a devitalized bone surface), which also secludes the organism from host defense mechanisms
modes of action of penicillin and cephalosporins?
-inhibition of cell wall synthesis
modes of action of clindamycin
-binds 50s ribosomal subunit
tuberculosis treatment
-extended triple drug therapy of isoniazid, rifampin, and pyrazinamide for 6 to 12 months has shown to be effective w/ osseous extra-pulmonary involvement
treatment of choice for MRSA?
vancomycin
3 types of bone grafts
-osteogenic, osteoinductive, osteoconductive
bone healing stages
early (inflammation)–> middle (reparative)–> late (remodeling)
bone healing may be affected by host and local factors
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what is the gold standard bone graft material?
autograft
reported rate of potential HIV transmission from allografts?
1 per million
Demineralized bone matrix (DBM)
- have been shown to have significant interproduct and interlot variability
- predominantly osteoCONDUCTIVE
bone marrow aspirates
-provide potential access to osteoGENIC mesenchymal precursor cells
Ceramics
-inorganic compounds consisting of metallic and nonmetallic elements held together by ionic or covalent bonds
BMPs
-potent osteoINDUCTIVE factors of the TGF-b superfamily
T of F: several forms of electromagnetic stimulation may facilitate bone healing?
True