Basic Science Flashcards
Case series
retrospective analysis of a group of patients
no comparison group
Cross sectional study
single time frame sampling of a population
usually a survey
Case-control study
Retrospective comparison of a group of patients with similar conditions
What type of study allows for calculation of an odds ratio?
case-control
Cohort study
Prospective comparison of a group of patients with similar condition
What type of study allows for calculation of relative risk?
cohort
What type of study allows for calculation of incidence?
cohort (bc it is the only study that gathers data prospectively).
Phase 1 FDA
initial drug safety
dose finding
Phase 2 FDA
determine if a drug works
compare to other intervention
Phase 3 FDA
confirm efficacy with large trial
100s of subjects
Phase 4 FDA
long term safety (post-marketing)
What FDA Phase is most common for failure of a device/drug?
Phase 2
Level of Evidence based on study type
1: RCT or meta-analysis
2: cohort
3: case-control
4: case series, cross-sectional
5: expert opinion
Reasons for downgrade of a study (4)
- heterogenous results
- < 80% follow-up
- no blinding
- concerns about randomization
A funnel plot examines…
bias in the results of a meta-analysis.
Relative risk =
risk in exposed/risk in unexposed
measures the incidence
Odds ratio =
probability an event WILL occur/probability an event will NOT occur
What study measures prevalence?
cross-sectional
Channeling bias
subjects unequally given treatment based on their features
ex patients older than 40 having a higher rate of receiving allograft for ACL recon
citation bias
more likely to believe a study in a top journal
publication bias
positive results are more likely to be published
Categorical data
nominal or ordinal
Nominal data
can be labeled into exclusive categories within a variable that cannot be put into a specific order
(ex. blood type, eye color, gender)
Ordinal data
categories that can be ordered
ex. satisfaction level, pain level, SES status, educational status
Continuous data
interval or ratio
What type of statistical test to use for categorical data
Chi square test
or Fischer’s exact test for SMALL groups
How to know if data is normally distributed
either they show you a bell curve (or they tell you)
If there is abnormally distributed data, you will most likely perform a…
Mann-Whitney U test.
What to calculate if you need to determine relationship between 2 variables of continuous data?
pearson correlation coefficient
What to calculate if you want to predict outcomes from variables?
regression
Sensitivity represents…
the ability to detect disease
ability to detect true positives
Sensitivity =
TP/(TP + FN)
Specificity represents…
the ability to detect health
ability to detect true negatives
Specificity =
TN/(TN + FP)
PPV =
TP/(TP+FP)
NPV =
TN/(TN+FN)
Type I Error
false positive
incorrectly conclude that an association exists when it does NOT
only willing to accept this 5% of the time (p < .05)
Type II error
false negative
incorrectly conclude that an association does not exist when it DOES
willing to except this 20% of the time
A high NNT indicates…
low effectiveness.
Power is…
probability of finding a significant association if one truly exists.
5 things that affect power
alpha beta effect size variance sample size
Moment is…
the rotational effect of a force.
Torque is…
the moment perpindicular to the long axis causing rotation.
Mass moment of inertia is…
resistance to rotation.
moment =
force x distance
Stress is…
the intensity of force acting on an object.
Stress = force/area
Strain is…
the deformation of an object due to stress.
Strain = change in height/original height
What are the units for strain?
no units
Hooke’s Law
when a material is loaded in the elastic zone, the stress is proportional to the strain
The yield point is…
the transition between elastic and plastic deformation.
Young’s modulus of elasticity is the ability to…
resist deformation in the elastic zone
represents stiffness
Ultimate strength is…
the maximum stress the material can sustain before breaking.
(BUT this is NOT the breaking point).
Necking represents…
the reduction of cross-sectional area. A local incresase in stress but overall decrease stress.
Necking begins after…
the ultimate strength.
Breaking point is…
the failure of the material.
Fatigue is…
failure of the material BELOW the ultimate strength owing to numerous loading cycles.
Stiffness is…
resistance to change in shape.
Depends on elastic deformation and young’s modulus.
(a higher young’s modulus is a stiffer material)
Strength is…
the load required to break a material
(depends on plastic deformation).
Hardness is…
resistance to localized surface plastic deformation
scratch/dent
Ductility is…
the amount of deformation a material undergoes before fracture.
On the stress-strain curve, ductility is represented by…
the distance between the yield point and the fracture point. (the wider the distance, the more ductile)
Toughness is…
the ability of material to absorb energy.
It is the area under the curve on a stress-strain curve.
Creep
Increased load deformation over time with constant stress
shows increased strain
Stress relaxation
Strain is held constant and stress decreases over time.
Viscoelastic materials are typically stiffer, stronger and tougher when loaded…
over a short period of time.
Hysteresis
ability of a viscoelastic material to dissipate energy between loading and unloading
(the dissipated energy is used to change the shape of the material - meniscus, discs can act as shock absorbers)
Anisotropic
behave differently depending on the direction of force
Pneumonic for Young’s Modulus of Materials
Ceramic CoST Could Cement Polly to Cancel her TeLephone Carrier
What happens to strength and fatigue resistance as metal grain size decreases?
strength and fatigue resistance increase with decreasing grain size.
Bacteria is most adherent to…
titanium alloy.
Bacteria is least adherent to…
tantalum.
Classic combination resulting in galvanic corrosion
stainless steel and cobalt-chrome
Fretting corrosion
due to micromotion during loading of implants
modular THA at head-neck junction
How to protect against corrosion
- use similar metals
- implant correctly
- passivation by an adherent oxide layer
Ceramics are…
compounds of metallic elements bound to non-metallic elements with ionic and covalent bonds
3 key features of ceramics
- brittle/stiff (sensitive to notches)
- insoluble (great for biocompatibility)
- low resistance to fx
Conductivity of bioactive ceramics are improved by…
large pore sizes.
What structures affect the mechanical properties of polymers?
structure of long chains
- longer/linear are stronger
- cross-linked are stiffer/harder/stronger
Gamma-irradiation of PE acts to…
promote cross-linking and improves wear but decreases strength, etc.
Heat generated from cement depends on…
thickness of cement mantle.
Vacuum mixing of cement…
decreases porosity and increases strength.
Dextro-lactide monomer is associated with…
more rapid degradation and potential for inflammatory response.
What ceramic is responsible for the stiffness and strength of bone?
hydroxyapaptite
What matrix component is responsible for the toe region of ligaments?
elastin
What determines the stiffness of a screw?
core diameter
What 3 features maximize screw pullout strength?
large outer diameter
small core diameter
fine pitch
The stiffness of plates is proportional to…
the 3rd power.
Stiffness of plates increases with…
increasing screws and with decreased working length.
The stiffness of a nail is proportional to…
the 4th power.
Reaming allows for…
increased torsional resistance.
What form of lubrication is the mechanism for articular cartilage?
elastohydrodynamic lubrication
The instant center of rotation of the ankle is…
the talus.
What are the properties of the annulus fibrosus and nucleus pulposus?
AF: tensile
NP: compressive
Osteoporosis of the spine involves…
loss of horizontal trabeculae with resulting loss of vertebral stiffness.
Axis of rotation of the elbow
center of trochlea
Instant center of motion of the wrist
head of the capitate
Lead toxicity inhibits the effects of…
parathyroid hormone-related peptide (PTHrP) .
What is the primary mode of bisphosphonate excretion?
renal
Callus formation is biomechanically beneficial because it…
increases the outer diameter of bone, leading to increase in stiffness, torsional strength, moment of inertia, and decreases strain.
Cells of the innate immune system
- natural killer cells
- mast cells
- eosinophils
- basophils
- macrophages
- neutrophils
- dendritic cells
Cells of the adaptive immune system
- CD8+ T lymphocytes
- T helper cells
- B cells
- plasma cells
Orthopedic surgeons who are seropositive for which 3 pathogens need to inform patients prior to scheduling an exposure prone procedure?
- HIV
- Hep B
- Hep C
What part of the x-ray machine should be as close to the patient as possible to decrease scatter to personnel?
image intensifier receptor
What percentage of RA patients test positive for RF?
80-90%
The rank of ultimate strength (or tensile strength) from highest to lowest is:
- cobalt chrome
- titanium
- stainless steel
- cortical bone
What percentage of bone weight is collagen?
20-25%
What region of the physis does type X collagen play a prominent role?
zone of hypertrophy
What dominant intracellular proteins become directly phosphorylated as a result of BMP binding to receptors?
SMADs
Woven bone is seen in…
fracture callus or pathologic states (infxn, malignancy)
Woven bone demonstrates…
random organization of osteocytes, not stress oriented, increased cellularity.
Differentiation of osteoprogenitor cells depends on oxygen and strain:
High strain –> fibroblast
Medium strain, low O2 –> chondroblast
Low strain, high O2 –> osteoblast
3 key transcription factors of osteoblast development
- beta-catenin
- runx2
- osx
In response to mechanical stress, osteoprogenitor cells release…
Wnt –> binds to receptors and cause production of beta-catenin
Beta-catenin controls production of…
runX2 which then controls OSx for terminal differentiation to osteocytes.
Osteocytes inhibit osteoblasts via…
sclerostin.
Tartrate resistant acid phosphate (TART)
secreted by osteoclasts to lower the pH
What is one of the major proteolytic enzymes that digests organic matrix at the ruffled border?
cathepsin K
Cathepsin K mutation leads to…
pyknodysostosis.
Calcitonin is produced by…
parafollicular cells of the thyroid.
It directly binds to osteoclast to slow bone resportion.
Most abundant non-collagenous matrix protein
osteocalcin
US can help to heal bone via…
producing nano motion.
Electrical bone stimulator MOA
increase osteoblast activity by reducing O2 concentration and increasing local tissue pH.
PTH normally acts to…
increase calcium and decrease phosphate.
Calcintonin normally acts to…
decrease calcium.
Vitamin D normally parallels the actionof…
PTH and increases reabsorption of calcium in the kidneys.
Rickets occurs in which zone of the growth plate
zone of provisional calcification
Dose of calcium and vitamin D for osteoporosis tx
Ca: 1200-1500 mg/day
Vit D: 800-1000 IU/day
Raloxifence
- estrogen based
- reduces osteoclast activity
- can be used for osteoporosis
Romosozumab
sclerostin antibody
thick sarcomere filaments
myosin
thick is the longer word
thin filaments
actin
Energy substrates for different exercise time
0-10 sec –> ATP and creatine phosphate
1-4 minutes –> glycogen and lactic acid
4+ minutes –> glycogen and fatty acids
Spondyloepiphyseal Dysplasia - Congenita
- short trunks/limbs
- normal hands, head, mentation
- type II collagen disorder
TNF-alpha blockers
Etanercept (receptor fusion protein)
Infliximab (chimeric IgG antibody)
Adalimumab (monoclonal antibody)
Tocilizumab
anti-human IL-6 receptor antibody
What gene in staph aureus allows for adhesion to titanium?
fibronectin
What antibiotic is not recommended for kids because it has been shown to cause arthropathy in animal models?>
ciprofloxacin
A bone scan after well funcitoning TKA may demonstrate increased uptake for up to…
1 year.
