Basic sciences

Question 1

MRI

Answer 1

• Def application of strong magnetic field and application of strong radio frequency excitatory pulse to manipulate hydrogen protons to generate high contrast imaging
• How it is produced -
  
  • Nuclear spin - assumes every living tissue has got water content and has for hydrogen atom which is constantly spinning on their axis at rest. When place in a magnet two things happen
    
    • Magnetisation vector atoms align in the direction of the magnet - longitudinal magnetisation vector
    • Precession - protons spin on their axis - Out of phase Apply radio frequency pulse application direction of magnetisation changes - from longitudinal to transverse magnetisation vector precession - changes from out of phase to in phase ( synchronised fashion)
    • Take away the pulse - traverse magnetisation vector changes to longitudinal magnetisation vectors Precession goes back to out of phase In this process it releases energy
    • RF coil detects energy emitted and converts in to signals and eventually an image
    • T1 relaxation time - time taken for longitudinal magnetisation vector to recover to 63% of normal once the pulse stops
      
      • T1 weighted image Good for anatomy.
      • Short TR ( <1000 msec) , short TE ( < 60 msec)
    • T2 - time taken for transverse magnetisation vector to decay to 37% of normal
      
      • T2 weighted image Good for pathology ,
      • long TR ( > 1000 msec) , long TE ( > 60 msec )
    • Fat suppression image - if fluid / oedema within bone marrow or fat needs to be isolated
      
      • Water appear dark on T1 and light on T2 Fat appear light on both T1 and T2 Low water content ( collagen , bone , tendon ) appear dark on both T1 and T2 Sequences
  • Spin echos - an echo is produced by a 90 degrees radio frequency pulse followed by one or more 180 degrees pulse .
    
    • `Both T1 and T2 weighted images can be obtained with the SE sequence
• STIR sequence - fat suppression sequence
• MARS
  
  • TR - time to repetition between two radio frequency pulsations in milli seconds
  • A long TR -allows full recovery of T1 phase before next pulsation starts
  • TE - time to echo - time between middle of excitation pulse and the middle of spin echo
  • Fat suppression sequence
  • Gadolinium - a pramagnetic agent with plasma half life of 2 hrs. It strongly reduces T1 times of the tissue and leads to increased signal on T1 image . Used to differentiate solid mass from fluid filled tissues.

Question 2

X rays

Answer 2

X rays - x rays are high frequency energy from electromagnetic spectrum with shorter wavelength than visible light Buzz words

• Thermionic emission - Tungsten ( negative cathode) heated in vacuum to 2200 degrees and this generates electrons.
• They fire away in vacuum and hits another tungsten piece anode and generate energy.
• The electrons hit the anode about half the speed of light on focal spot
• breaking radiation
  
  • Outer electron of the target nucleus - generating heat
  • Inner electron - knocking off out of the orbit - X ray generation
  • The nucleus - causing electron to slow down
  • x rays in the body -
    
    • absorbed
    • attenuated
    • reflected -
• X ray receipts
  
  • Conventional Phosphor crystals( barium lead sulphate and gadolinium oxyzsulphade) stains black - more energy exposed more stain black
  • Digital radiography - Direct radiography - pixelated elements
  • Computed radiography
  • Fluoroscopic receptors - real time images and converts transmitted x rays in to a brightened and visible light images.
• Input window – often convex shaped (minimizes patient distance) and made from aluminium or titanium.
• Input phosphor plate (caesium iodide) – fluorescent function by absorbing X-ray beam and producing light.
• Photocathode – conversion of light photons to electrons.
• Accelerating anode – a series of electrostatic focusing electrodes that accelerate electrons towards the output phosphor screen.
• Output phosphor screen (silver-activated zinc–cadmium sulphide) – conversion of electrons to light photons which are then captured by an imaging device.
• Low beam attenuation - Water / air
• High beam attenuation
• Scattering Precaution
  
  • Time - reduce the time
  • Distance - increase the distance
  • Shield -
• IRMER 2000 ( ionising radiation ( medical exposure ) regulations 2000 -
  
  • Duty holders Employer - provides frame work
  • Referrer - orthopaedics clinicians
  • Practitioner - involve justifying and authorising each exposure undertaken
  • Operators - carries our any practice aspect of the radiological investigations

Question 3

Consent

Valid consent

Section 1 (2) of the Mental Capacity Act 2005 states that ‘a person must be assumed to have capacity unless it is established that he lacks capacity’ Given by a person with the capacity to make the decision in question •

Given voluntarily

Based on appropriate information (informed) and understood

Answer 3

The consent discussion

In practice, this means that surgeons should provide information about:

• The patient’s diagnosis and prognosis
• The right of the patient to refuse treatment and make their own decisions about their care
• Alternative options for treatment, including non-operative care and no treatment
• Advice on lifestyle that may moderate the disease process
• The purpose and expected benefit of the treatment
• The nature of the treatment (what it involves)
• The likelihood of success
• The clinicians involved in their treatment
• Potential follow-up treatment
• The material risks inherent in the procedure and in the alternative options discussed (for materiality, see Section 4.3)
• For private patients, costs of treatment and potential future costs in the event of complications.

Question 4

MATERIAL RISK

• The Bolam test is whether the person seeking consent ‘has acted in accordance with a practice accepted as proper by a responsible body of medical men skilled in that particular art’. This placed the opinion of medical practitioners at the centre of any judgement about the breach of duty.
• • The new test for materiality is ‘whether, in the circumstances of the particular case, a reasonable person in the patient’s position would be likely to attach significance to the risk, or the doctor is or should reasonably be aware that the particular patient would likely attach significance to it’

Answer 4

KEY PRINCIPLES

• The aim of the discussion about consent is to give the patient the information they need to make a decision about what treatment or procedure (if any) they want
• The discussion has to be tailored to the individual patient. This requires time to get to know the patient well enough to understand their views and values
• All reasonable treatment options, along with their implications, should be explained to the patient
• Material risks for each option should be discussed with the patient. The test of materiality is twofold: whether, in the circumstances of the particular case, a reasonable person in the patient’s position would be likely to attach significance to the risk,or the doctor is or should reasonably be aware that the particular patient would likely attach significance to it.
• Consent should be written and recorded. If the patient has made a decision, the consent form should be signed at the end of the discussion. The signed form is part of the evidence that the discussion has taken place, but provides no meaningful information about the quality of the discussion
• In addition to the consent form, a record of the discussion (including contemporaneous documentation of the key points of the discussion, hard copies or web links of any further information provided to the patient, and the patient’s decision) should be included in the patient’s case notes. This is important even if the patient chooses not to undergo treatment.

Answer 6

• Bone is a composite dynamic form of specialised connective tissue
• Comprised of cells 10% and Matrix 90%
• Cells include
  
  • Osteoblasts - Osteoblasts are derived from undifferentiated mesenchymal cells, they are bone forming and lay down osteiod (type 1 collagen) Activate Osteoclasts to resorb bone via the RANK Ligand system. These processes is controlled by cytokines, growth factors and BMP.
  • cytes
  • clasts - Osteoclasts are from heamopoetic monocyte cell lineage – they are multinuclated giant cells that resorp bone. They have a ruffled brush border. They can sit in small pits called Howships Lacunae, on the bone surface, or lead cutting cones that tunnel through the bone.
• Matrix has organic and inorganic components
  
  • The organic matrix resists tension forces and is mainly made up of type 1 collagen. This is a triple helix structure made within osteoblasts and fibroblasts.
  • The inorganic matrix resists compression forces and is mainly calcium hydroxyapatite crystals. Ca10 (PO4)6 OH2

The crystals are formed during mineralization at specific pore and hole regions of the collagen fibrils.

The other osteocalcium phosphate (brushite is also present)

Question 7

Muscle fibre types

Answer 7

Type 1 – slow oxidative fibres:

• slow contraction velocity – low myosin ATPase activity; • high concentration of myoglobin (red in colour);
• • high concentration of mitochondria;
• • high capillary density;
• • oxidative;
• • very fatigue resistant;
• • low force generation – small diameter fibres.

Type 2a – fast oxidative fibres:

• fast contraction velocity – high myosin ATPase activity; • intermediate myoglobin concentration;
• high mitochondria concentration;
• intermediate capillary density;
• oxidative and glycolytic;
• fatigue-resistant;
• high force generation – large diameter fibres.

• Type 2b – fast glycolytic fibres:

• • very fast contraction velocity – high myosin ATPase activity; • low myoglobin concentration (relatively white in colour);
• • low mitochondria concentration;
• • low capillary density;
• • glycolytic;
• • fatiguable;
• • very high force generation – large diameter fibres.

Question 8

Calcium metabolism

Answer 8

Question 9

Bone screw

Answer 9

Question 10

Stage I

Haematoma and inflammation

Up to 1 week

Answer 10

• Haematoma from ruptured blood vessels forms a fibrin clot. Damaged tissue and degranulated platelets release signalling molecules, growth factors and cytokines Migration of inflammatory cells into the haematoma occurs, responding to local growth factors and cytokines (IL-1, IL-6, TGF-β superfamily including BMPs, PDGF, FGF, IGF)
• Proliferation, differentiation and matrix synthesis as haematoma is replaced by granulation tissue. There is capillary in-growth (angiogenesis), recruitment of fibroblasts, mesenchymal cells and osteoprogenitor cells. The periosteum plays an important role in this process
• Cell types involved include polymorphonuclear neutrophils, macrophages and then fibroblasts
• At the necrotic bone ends, bone resorption is mediated by osteoclasts and removal of tissue debris by macrophages

Question 11

Bone healing

Stage II

Soft callus

1–4 weeks

Answer 11

• Increased cellularity with proliferation, differentiation and neovascularization
• Callus is a combination of fibrous tissue, cartilage and woven bone Intramembranous (bony/periosteal) callus is a primary callus response: Type I collagen (osteoid) is laid down from periosteal osteoblasts in the cambium layer as periosteal bony callus or woven bone. This is hard callus, but it does not bridge the fracture
• Endochondral (fibrocartilaginous/bridging) callus is a bridging external callus: Multipotential cells differentiate to form chondroblasts and fibroblasts within the granulating callus that produce the type II cartilaginous and fibrous elements of the matrix (chondroid). Chondroblasts then calcify the chondroid matrix they have produced, creating calcified fibro-cartilage or soft callus Medullary callus: This is a later process and can slowly unite the fracture if external callus fails

Question 12

Stage III

Hard callus

1–4 months

Answer 12

• Calcified soft callus is then resorbed by chondroclasts and invaded by new blood vessels. These bring with them osteoblast precursors that produce the bony (type I) elements of the matrix (osteoid) and then mineralize it to form woven bone
• Soft calcified chondroid callus becomes hard mineralized osteoid callus.
• Bony bridging continues peripherally as subperiosteal new bone formation. At this point the fracture is united; it is solid and painless on movement

Question 13

Stage IV

Remodelling

Up to several years

Answer 13

• Once the fracture has united, the hard callus is remodelled from woven bone to hard, dense lamellar bone by a process of osteoclastic resorption, followed by osteoblastic bone formation. The medullary canal reforms at the end of this process This is the same mechanism as for direct cortical, osteonal or primary bone healing, seen following fracture fixation with absolute stability
• Bone assumes a configuration and shape based on stresses acting on it (Wolff’s law)
• Electrical fields may play a role in Wolff’s law, with osteoclastic activity being predominant on the electropositive tension side of bone and osteoblastic activity on the electronegative compression side

Question 14

diamond concept

Answer 14

• Mechanical stability
• Osteoprogenitor cells
• growth factors
• an adequate scaffold to create a ‘biological chamber’ active enough to support efficiently all the necessary physiological processes for successful union

Question 15

Bone graft substitutes

Answer 15

• Cell-based - bone marrow aspirate contains osteogenic precursors, but this is an inefficient method as most of what is obtained is red blood cells
• Factor-based, e.g. BMP-7 and BMP-2 are now produced and sold commercially. Platelet-rich plasma as an autologous additive to bone grafts has been used predominantly in maxillofacial surgery, theoretically supplementing the levels of growth factors.
• Calcium phosphates:
  
  • bulk, e.g. tricalcium phosphate (which undergoes partial conversion to hydroxyapatite in vivo), hydroxyapatite and combinations of the two. These materials degrade at a very slow rate
  • injectable, e.g. Norian SRS:
• Calcium carbonates, e.g. BiocoraTM: chemically unaltered marine coral that is resorbed and replaced by bone.
• Coralline hydroxyapatite, e.g. Pro-OsteonTM: calcium carbonate skeleton undergoes a thermo-exchange process to convert this into calcium phosphate.
• Calcium sulphate, e.g. OsteosetTM: osteoconductive calcium sulphate pellets.
• Silicon-based, e.g. bioactive glasses, glass-ionomer cement: used as delivery systems for osteoinductive compounds.
• Synthetic polymers, e.g. polylactic acid and polyglycolic acid: problems include the production of acidic degradation products.
• Ceramic composites, the primary inorganic component of bone is hydroxyapatite, and calcium phosphate-based ceramics attempt to mimic this material, e.g. CollagraftTM: calcium–collagen graft material – an osteoconductive composite of hydroxyapatite, tricalcium phosphate and collagen used as a bone graft substitute or expander, mixed with autologous bone marrow to provide cells and growth factors.

Question 16

Osteoinductive agents

Answer 16

Transforming growth factor-beta

• • Super-family of growth factors found in platelets and many cell types.
• • Broad range of activity within bone and fracture callus.
• • Induces synthesis of type II collagen and proteoglycans.

Bone morphogenetic proteins

• Family of at least 20 glycoproteins able to stimulate ectopic bone formation.
• BMPs 2–7 and BMP 9 have been found to possess independent osteoinductive
• activity.
• Induce differentiation of mesenchymal cells to osteogenic lineages.
• BMP 2 and BMP 7 (OP-1) have been approved for clinical use, such as in tibial non-union.

Fibroblast growth factor

• Mitogenic for many cell types.
• • Released from endothelial cells.
• • Stimulates angiogenesis and callus formation.

Platelet-derived growth factor

• • Potent chemotactic activity following fracture.
• • Released from platelets and monocytes after trauma.
• Stimulates deoxyribonucleic acid (DNA) synthesis.

Question 17

Bone banking

Answer 17

• Donor consent
  
  • Living donors: consent is needed in order to cover retrieval, testing and access to medical records.
  • Cadavers: the prerequisite is lack of objection from the next of kin.
• Donor screening
  
  • Medical and behavioural history: this helps to pick up certain donors that may need to be excluded, e.g. intravenous drug abuse. The history is usually obtained from the next of kin for living donors and from general practitioner notes for cadavers.
  • Blood tests: performed for hepatitis B and C, HIV, syphilis and Rhesus status.
• Exclusion criteria
  • HIV.
  • Hepatitis B and C.
  • Malignancy.
  • Systemic disorders that may compromise biological or biomechanical integrity of graft, e.g. rheumatoid arthritis, autoimmune disease, long-term steroid treatment.
  • Diseases of unknown origin, e.g. Alzheimer’s disease, Creutzfeldt–Jakob disease, multiple sclerosis.
• Allograft processing - Allografts are processed to remove superfluous proteins, cells and tissues in order to decrease immune sensitization and disease transmission. Processing also allows better graft preservation.
  
  • Physical debridement of unwanted tissue.
  • Ultrasonic processing with or without pulsatile washes to remove remaining cells and blood.
  • Ethanol treatment to denature cell proteins and reduce bacterial and viral load.
  • Antibiotic soak to kill bacteria.
  • Irradiation to sterilize tissue, particularly if contaminated or if not processed in a sterile manner (but this affects collagen and alters mechanical strength).
  • Demineralization, produced by acid extraction of allograft cortical bone. Demineralized bone matrix (DBM) contains type 1 collagen, which provides the osteoconductive scaffold for osseous in-growth; and osteoinductive growth factors like BMPs, FGF, IGF, PDGF and transforming growth factor-β (TGF- β).
• Allograft preservation
  
  • Fresh: - most immunogenic.
  • Fresh-frozen at -70°C:
    • has least impact on mechanical strength; • decreases immunogenicity;
    • preserves BMPs.
  • Lyophilized (freeze-dried):
    • least immunogenic;
    • lowest likelihood of disease transmission;
    • BMP depleted;
    • may structurally weaken during rehydration.
• Examples of products available from bone banks
  
  • Fresh-frozen femoral head: a whole femoral head, retrieved from a living donor, which is unprocessed and greater than 50 g in weight. Available only frozen, and supplied only to hospitals that collect fresh-frozen femoral heads for tissue services when limited stock available.
  • Cancellous cubes: approximately 1 cm3 in volume. Available freeze-dried and irradiated in packs of five.
  • Cortical struts: struts of cortical bone from femoral shafts that are cut to various lengths from 2 to 22 cm. Available as freeze-dried or frozen and sterilized by gamma-irradiation.
  • Massive bone allografts: grafts prepared with articular cartilage and soft tissue removed. Available frozen and irradiated. A small stock of proximal and distal femora and proximal tibiae is normally maintained.

Question 18

Levers

Answer 18

First-class lever

• the fulcrum lies in between the applied force and the load.
• Mechanical advantage is gained by increasing the force arm length in relation to the load arm length.
• An example is the atlanto-occipital joint as the fulcrum,

Second-class lever

• Second-class lever: the fulcrum is at one end of the lever, with the applied load force at the other end and the load in between.
• The force arm length is always greater than the load arm length.
• An example is the act of standing on one’s toes, with the toes as the fulcrum, the weight of the ankle offering resistance being the load, and the counter-force being applied by the calf muscles. An everyday example is the use of a nutcrack

Third-class lever

• The fulcrum is at one end of the lever, but the load is at the other end, with the applied force in between.
• The load arm length is always greater than the force arm length, and so a greater force is needed to move the load.
• This is the most common type of lever found in the human body.
• An example is the elbow joint as the fulcrum,

Question 19

Vascio elastic property

Answer 19

The underlying mechanisms responsible for the viscoelastic behaviour

• friction internally, as microelements in the structure move against each other as a material is stretched, as described previously in the unfurling of collagen fibres.
• Second, the movement of interstitial fluid through a material that is a semi-porous matrix creates a drag, which produces viscoelastic behaviour. The femur exhibits features of viscoelastic behaviour in terms of stress relaxation.

Question 20

The second moment area

Answer 20

• is a variable that describes the spatial distribution of a material within a structure.
• The type of material does not affect the SMA.
• The SMA is affected by the organization and shape of the material
• For materials with rectangular cross-sections, the perpendicular distance away from the neutral axis (h) has a third power effect on the SMA.
• For materials with a solid circular cross-section, the radius (which is the distance from the neutral axis) has a fourth power effect on the SMA.
• For materials with a hollow circular cross-section, the total SMA equals the SMA of the solid outer portion minus the SMA of the missing inner hollow portion.
• Rigidity in bending is a particularly important concept when choosing metal plates for fracture fixation:
• Bending rigidity = SMA X Youngs modulus

Question 21

The polar moment of inertia or polar moment area (PMA) is a variable parameter related to the size and shape of a structure but not the material from which it is constructed

• polar moment varies to the fourth power of the radius.

Answer 21

Torsional rigidity is a measure of the resistance of a material in a particular size and shape to torsional forces.

Question 22

Osteolysis

Answer 22

• Osteolysis represents a histiocytic response to wear debris
  1. particulate debris formation
  2. macrophage activated osteolysis
  3. prosthesis micromotion
  4. particulate debris dissemination

Question 23

Wear -

• Abrasive wear - Hard on soft - Ploughing on soft surface
• Adhesive wear - strong intermolecular bonds
• Fatigue wear - Delamination

Answer 23

• the progressive loss of bearing substance from the material secondary to mechanical or chemical action
• Mode 1: the generation of wear debris that occurs with motion between the two primary bearing surfaces, as intended by the designers.
• Mode 2: a primary bearing surface rubbing against a secondary surface, not intended as an articulating surface, e.g. a femoral head articulating with an acetabular shell following wear-through of the polyethylene.
• Mode 3: two primary bearing surfaces with interposed third-body particles, e.g. bone, cement or metal.
• Mode 4: two non-bearing surfaces rubbing together, e.g. back-sided wear of an acetabular liner, fretting of the Morse taper, stem-cement fretting or neck of femoral component impinging on rim of cup.

Question 24

Half life

Answer 24

Apixaban - 12 hours Direct factor Xa inhibitor

Dabigatran - 12 hrs - Direct thrombin inhibitor – Direct thrombin inhibitors (DTIs) prevent thrombin from cleaving fibrinogen to fibrin

Warfarin

Baseline testing — Prior to starting warfarin, it is appropriate to obtain the following baseline testing, if not already done:

●Prothrombin time (PT) with international normalized ratio (INR) and activated partial thromboplastin time (aPTT), to obtain a baseline value for monitoring and to identify any underlying abnormalities

●Complete blood count (CBC) including platelet count, to obtain a baseline and identify thrombocytopenia

●Serum creatinine, to estimate the glomerular filtration rate (GFR)

●Liver function tests, to identify potential alterations of warfarin metabolism (or hemostasis)

●Urine (or serum) pregnancy test for women of childbearing potential (due to risks of teratogenicity)

Fondaparinux - highly sulfated pentasaccharide derived from the minimal antithrombin (AT)-binding region of heparin. It is an indirect factor Xa inhibitor (figure 1). It acts by binding to and inducing a conformational change in AT that increases the ability of AT to inactivate factor Xa

Question 25

Metals

Answer 25

Microstructure: 1. Crystalline latice (pure form) * Body Centred Cubic BCC * Face Centred Cubic FCC * Hexaognal Closed Packed HPC Then molten form grains * Grains Size ( Larger Grain size --- easier to fail due to bigger dislocations) * Alpha Phase --- Orignial alloy * Beta phase --- Added elements to alloy ( weaken the strength)

Question 26

**Cleanliness**

Answer 26

* standard plenum ventilated operating theatre lying empty, there should be less than 35 CFU of bacteria/m3 of air and less than 1 CFU/m3 of Clostridium perfringens and Staphylococcus aureus. * During operative procedures, there should be less than 180 CFU of bacteria/m3. * In ultra-clean laminar flow theatres, there should be less than * 20 CFU/m3 at the periphery of the enclosure and * less than 10 CFU/m3 at the centre.

Question 27

Ventilation - High- efficiency particulate air (HEPA)

Answer 27

* Plenum - pressure inside the theatre is greater than that outside. * air from contaminated areas should not enter the aseptic zone. * Laminar airflow characteristics involve the entire body of air within a designated space moving with uniform velocity in a single direction along parallel flow lines.Laminar flow theatres deliver around 300–500 air changes per hour. * Horizontal laminar flow. * Vertical laminar flow. * Ex-flow or exponential flow (Howorth enclosures).

Question 28

**Nerve reconstruction ladddr**

Answer 28

* Neurolysis * Nerve repair * Neurotisation * Nerve graft * tendon transfer * *

Question 29

DCP

Answer 29

Hole is shaped in angled cylinder