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What are the mechanisms of wear

third body


What are the 5 forms of lubrication

  • elastohydrodynamic
    • main mechanism during dynamic joint function
    • elastic deformation of articular surfaces
    • thin films of lubricant separate the surfaces 
  • boundary (slippery surfaces)
    • bearing surface is non-deformable
    • lubricant only partially separates surfaces
    • superficial zone proteins have a role in this lubrication mechanism
  • boosted (fluid entrapment)
    • concentration of lubricating fluid in pools 
    • trapped by regions of bearing surfaces that are making contact
  • hydrodynamic
    • fluid separates surfaces when one surface is sliding on the other
  • weeping 
    • fluid shifts out of articular cartilage in response to load
    • surfaces separated by hydrostatic pressure


What changes occur in aging cartilage

  • increases in
    • chondrocytes size
    • protein content
    • stiffness (passive glycation leads to increased stiffness of collagen) 
    • increase in ratio of proteoglycan keratin sulfate to chondroitin sulfate
  • decrease in
    • absolute number of cells (becomes hypocellular, despite the fact that individual chondrocytes are increasing in size)
    • water content (differentiates from osteoarthritis where water content actually increases)
    • solubility
    • proteoglycan size
    • elasticity


What are the 5 forms of articular cartilage

hyaline or articular cartilage
fibroelastic cartilage (meniscus)
fibrocartilage (at tendon and ligament insertion into bone)
elastic cartilage (trachea)
physeal cartilage (growth plate)


What is the function of cartilage

  • decreases friction
  • distributes loads
  • cartilage exhibits stress-shielding of the solid matrix components
    • high water content
    • incompressibility of water
    • structural organization of the proteoglycan and collagen molecules


What are the extracellular components of cartilage

  • water
    • makes up 65% to 80% of mass of the cartilage 
    • accounts for 80% of the weight near the surface 
    • 65% at the deep zone
  • collagen
    • makes up 10 to 20% of total cartilage mass
    • type II collagen accounting for 90% to 95% of the total collagen content. 
    • functions to provide cartilagenous framework and tensile strenth
    • small amounts of types V, VI, IX, X, and XI collagen are also present
  • proteoglycans 
    • makes up 10 to 15% of cartilage 
    • functions to provide compressive strength and attract water   
    • produced by chondrocytes
    • composed of GAG subunits 
      • chondroitin sulfate
      • keratin sulfate
  • noncollagenous protein


What are the zones of articular cartilage

  • Superficial zone (tangential zone) 
    • Type II collagen orientation is parallel to joint 
    • Has flattened chondrocytes, condensed collagen fibers, and sparse proteoglycans
    • only zone where articular cartilage progenitor cells have been found 
  • Intermediate zone
    • Type II collagen has an oblique or random organization
    • Is the thickest layer with round chondrocytes, and abundant proteoglycan content
  • Deep layer (basal layer) 
    • Type II collagen is perpendicular to joint and crosses tidemark;  has the highest concentration of proteoglycans
    • Round chondrocytes arranged in columns                     
  • Tidemark
    • Is deep to the basal layer and separates the true articular cartilage from the deeper cartilage that is a remnant of the cartilage anlage, which participated in endochondral ossification during longitudinal growth in childhood.
    • The tidemark divides
      • the superficial uncalcified cartilage from the deeper calcified cartilage
      • division between nutritional sources for the chondrocytes  
    •  The tidemark is found only in joints 
    •  Most prominently in the adult and nongrowing joint
  • Subchondral Bone  


What nurishes cartilage

surface - synovial fluid

subchondral bone at base


What are the 8 components of SF-36

physical functioning
bodily pain
general health perceptions
physical role functioning
emotional role functioning
social role functioning
mental health

36 questions; SF17 is a more condested version


What are the 4 components of the HHS

  • pain
    • no pain given 44 points
  • function
    • no limp, walks without aid, and can walk more than six blocks given 33 points
  • function activities
    • no disabilities given 14 points
  • physical exam  
    • based on range of motion with max score of 9

out of 100


What are the components of the WOMAC score




total score

30 questions on a likert scale; scored out of 100


Compare observational and experimental designs for research studies

  • observational 
    • researchers observe patient groups without allocation of intervention
    • may be either prospective or retrospective
    • may be descriptive or analytic 
      • descriptive 
        • useful for obtaining background information for more advance studies
        • examples 
          • case reports
          • case series
          • cross-sectional studies
      • analytic 
        • explores the association between a given outcome and a potentially related variable
        • examples 
          • case-control
          • cohort
          • meta-analysis
  • experimental 
    • researchers allocate treatment
    • allows the evaluation of efficacies of therapeutic interventions
    • examples 
      • double-blinded, prospective, randomized clinical trial is the gold standard for evidence based medicine


What are the key aspects of a randomized control trial

  • Definition
    • a study in which patients are randomly assigned to the treatment or control group and are followed prospectively 
    • provides the most compelling evidence that the study treatment causes the expected effect on human health 
    • randomization minimizes study bias 
  • Crossover design
    • administration of two or more therapies, one after the other, in a random order
    • susceptible to bias if washout period is inadequate   
    • single blinded study vs. double blinded study 
      • double = participant and administrator
  • Analysis 
    • intent-to-treat analysis
      • outcomes based on the group into which they were randomized, regardless of whether the patient actually received the planned intervention
      • minimizes non-responder bias
    • per protocol 
      • excludes patients who were not compliant with the protocol guidelines 


What are the key aspects of a cohort study

  • Definition
    • a study in which patient groups are separated non-randomly by exposure or treatment, with exposure occurring after (prospective), or before (retrospective), the initiation of the study
  • Evidence
    • Level II or III evidence
  • Analysis
    • results usually reported as relative-risk
  • Example
    • you want to determine if smoking is a risk factor for the development of lung cancer.  You identify a group of smokers and a group of non-smokers, and follow them over time measuring the desired outcome, in this case, lung cancer.


What are the key aspects of a case control study

  • Definition
    • a study in which patient groups are separated by the current presence (cases) or absence (controls) of disease and examined for the prior exposure of interest
  • Evidence
    • Most are Level III evidence
  • Analysis
    • usually reported as odds-ratio
  • Example
    • you want to determine if smoking is a risk factor for the development of lung cancer.  You compare the smoking history of individuals with lung cancer (cases) and those without (controls).


What is a cross-sectional study

  • Definition 
    • study group is analyzed at a given time ("snapshot") with no follow-up
  • Example 
    • you want to determine the prevalence of baseball injuries during the 2003 little-league season

Example of an observational study


What are the levels of evidence

  • Level 1
    • Randomized controlled trial (RCT) 
    • Meta-analysis of randomized trials with homogeneous results 
  • Level 2   
    • Prospective comparative study (therapeutic) 
    • Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results 
  • Level 3
    • Retrospective cohort study
    • Case-control study 
    • Meta-analysis of Level 3 studies 
  • Level 4
    • Case series
  • Level 5
    • Case report (a report of a single case) 
    • Expert opinion
    • Personal observation


What are some of the most common surgical medical errors

  • Communication errors are the leading cause of wrong-side surgeries, medication errors, diagnostic delays or loss to follow-up     
  • Wrong site surgery
    • involve the patient in identifying correct side 
    • response when performed
      • address by immediate discussions with family revealing errors 
      • apologize and accept responsibility, but not blame   
  • Surgical "time-out" should include the following according to JCAHO     
    • identify correct side, site, and patient
    • verify the correct procedure
    • surgeon is most effective OR team member at reducing complications when using surgical checklist and "time-out"
  • Medication prescribing errors
    • reduced when physicians use computerized order entry 
  • errors in medical documentation
    • It is illegal to alter the medical record for any reason 
    • no one has the authority to authorize a physician to alter the medical record
    • errors can be noted and addendums can be added


What is the definition of medical negligence

  • Negligence is the failure to provide the standard of health care resulting in medical injuries
  • A second-opinion physician has an ethical obligation, but not legal obligation, to disclose if the standard of care has been breached by a treating physician. 
  • A successful patient-plaintiff lawsuit for medical negligence against a physician requires that the following FOUR elements be alleged and proven in a court of law 
    • duty
      • the duty of the physician is to provide care equal to the same standard of care ordinarily executed by surgeons in the same medical specialty.
    • breach of duty
      • breach of duty occurs when action or failure to act deviates from the standard of care.
    • causation
      • causation is present when it is demonstrated that failure to meet the standard of care was the direct cause of the patient’s injuries.
    • damages
      • damages are monies awarded as compensation for injuries sustained as the result of medical negligence


Definition of workers compenstation

  • A workmans' compensation patient is determined to reach maximum medical improvement when further restoration of function is no longer anticipated and can then settle his/her claim.   
  • Ability for worker's compensation patients to choose their own physician varies by the statutes of each state. 
  • Legal definitions
    • impairment
      • loss of function resulting from an anatomic or physiologic derangement. 
    • disability
      • limitation of an individual’s capacity to meet certain personal social or occupational demands.


What are factors that contribute to radiation exposure from flouro in the OR

  • Factors which increase radiation exposure levels during use of fluoroscopy   
    • imaging large body parts
    • positioning extremity closer to the x-ray source 
    • use of large c-arm rather than mini c-arm 
    • radiation exposure is minimal during routine use of mini-c-arm fluoroscopy unless the surgical team is in the direct path of the radiation beam 
  • Factors to decrease radiation exposure to patient and surgeon 
    • maximizing the distance between the surgeon and the radiation beam
    • minimizing exposure time
    • manipulating the x-ray beam with collimation (coning)
    • orienting the fluoroscopic beam in an inverted position relative to the patient 
    • strategic positioning of the surgeon within the operative field to avoid direct path of beam
    • use of protective shielding during imaging


What are the risk of HIV and hepatitis transmission in orthopedics

  • Risk of HIV transmission
    • needlestick  
      • seroconversion from a contaminated needlestick is ~ 0.3% 
        • exposure to large quantities of blood increases risk
      • seroconversion from exposure to HIV contaminated mucous membranes is ~0.09%
    • frozen bone allograft 
      • risk of transmission is <1 per million
      • donor screening is the most important factor in prevention
      • no reported cases of transmission from frozen bone allograft since 2001
    • blood transfusion
      • risk of transmission from blood transfusion is 1/500,000 per unit transfused
      • seronegative blood may still transmit virus due to delay between HIV infection and antibody development
  • Risk of Hepatitis B transmission
    • needlestick
      • 37% to 62% eventually seroconvert following needlestick
      • 22 to 31% develop clinical Hepatitis B infection following needlestick
  • Risk of Hepatitis C transmission
    • needlestick
      • 0.5 to 1.8% risk of transmission


What are the major and minor criteria for fat emboli syndrome

  • Major (1) 
    • hypoxemia (PaO2 < 60)
    • CNS depression (changes in mental status)
    • petechial rash
    • pulmonary edema
  • Minor (4) 
    • tachycardia
    • pyrexia
    • retinal emboli
    • fat in urine or sputum
    • thrombocytopenia
    • decreased HCT
  • Additional 
    • PCO2 > 55
    • pH < 7.3
    • RR > 35
    • dyspnea
    • anxiety


What is virchows triad DVT

venous stasis
hypercoagulable state
intimal injury


What is the pathophysiology of clot formation

  • stasis
  • fibrin formation 
    • thromboplastin (aka Tissue Factor (TF), platelet tissue factor, factor III, or CD142) is released during dissection which leads to activation of the extrinsic pathway and fibrin formation 
  • clot retraction
  • propagation


What are primary hypercoagulopathies

factor V Leiden mutation   
antithrombin III deficiency 
protein C deficiency
protein S deficiency
activated protein C resistance


What are secondary factors that contribute to DVT


  • malignancy 
    • recently been associated with up to 20% of all new diagnoses of VTE
  • elevated hormone conditions 
  • recombinant erythropoeitin 
  • hormone replacement
  • oral contraceptive therapy
  • late pregnancy
  • elevated antiphospholipid antibody conditions 
  • lupus anticoagulant
  • anticardiolipin antibody
  • history of thromboembolism
  • obesity
  • aging
  • CHF
  • varicose veins
  • smoking
  • general anesthesics (vs. epidural and spinal)
  • immobilization
  • increased blood viscosity


What are aquired risk factors for DVT in athletes

  • Hemoconcentration
    • dehydration, trauma, immobilization, travel, blood hyperviscosity, OCPs
      • Recent travel >4 h have 4x risk of VTE; however, varying results of studies…
  • Marathon running + air travel >4h
    • acute hypercoagulable state exaggerated with increasing age >35
    • add in a thrombophilia and you have even higher risks
  • Hypoxia at high altitude
    • body increases RBC production
    • hyperviscocity – risk in climbers
  • Females on OCPs have 4x the risk
    • those with inherited thrombophilias and on the OCP have even higher risk (up to over 30 fold, they say..)


What are the increased risk for DVT with various thrombophilic diseases

  • Factor V Leiden mutation
    • Heterozygous 7×
    • Homozygous 80×
  • Prothrombin G20210A mutation 2.8×
  • Antithrombin III deficiency 5–20×
  • Protein C deficiency 2–10×
  • Protein S deficiency 2–10×
  • Hyperhomocysteinemia 2.5×
  • Elevated factor VIII 5×
  • Elevated factor XI 2.2× 


What are prevention strategies for DVT in athletes

  • screening
    • prior to race
    • family history
    • previous VTE
    • medications (OCP)
  • Prevention
    • LMWH for high risk situation
    • hydration
    • early mobilization after surgery
    • avoidace of high risk situations