Flashcards in Bone injury, fracture healing and bone regeneration Deck (69):
what does osteoinductive mean?
a material that induces the differentiation of stem cells into osteoblasts. you want to implant this into your site and see if it induces bone
what does osteoconductive mean?
Material conducts bone formation over the surface of the implant.
what does osteointegration mean?
should only be used to describe the appearance of the interfaceand simply implies bone growth up to the surface of the implant.
what does bone bonding mean?
Direct chemical link between implant and bone
what demographic is normally affected by bone cancers?
what does a joint implant need to have ?
if it is going into a chilled then it needs to have a sliding region that allows it to increase in size as the patient grows
how does the survival rate of implants relative to age>
- the longer you have the distal femoral replacement, the more likely you are to have to have it replaced due to aseptic loosening- at 10 years after implant there s a 68% survivorship
what are generally used to treat bone cancers?
implants such as distal femora replacement
are old implants osteointegrated?
no the implant normally becomes loose
how can telemetry be used to help implant design?
- it allows the force put on the implants to be measured- the forces and moments that occur as you walk on an implant
what did telemmetry tell us about the way in which load was being transferred over time?
load becomes distributed more towards the tip of the stem as the implant becomes loose.- to the shaft
what happens at the interface of fold implants over time?
- a fibrous tissue occurs between the implant and the bone and doesn't become osteointegrated. This results in a change in load over time.
how did they seek to promote osteointegration with the implants in order to prevent damaging load changes? what happened as a result ?
- they engineered a porous collar to the end of the implant with the hope that bone would integrate into it. But this didn't work- became encapsulated by fibrous tissue and the fiction was not stabilised
due to the act the porous collar did not promote oseointegration, what did they use instead?
they used a hydroxyapatite covered implant (applied by spray) this is the mineral component of bone. They found that bone grew into his prosthesis
how did putting a hydroxyapetite coating on the implant improve the survivorship of implants against aseptic loosening?
it was improved for the ten year period to 88%, from 68%. If you subdivide this into those that got oseointegration at the shoulder of the implant - 98% of these cases survive but when you dont it is reduced. This shows that oseintegration at the shoulder is very important
why is oseointegration at the shoulder so important?
you prevent the load moving to the shaft of the implant and you load the bound in a more physiological manner. the stem of the bone is protected from being over loaded.
how can mesenchymal stem cells be used in bone cancer treatment generally?
take these cells and implant them with the implant in the hope that they promote osteointegration at the implant interface
how does mesenchymal stem cells turn into oteocytes?
- run 2 an OS X for pre osteoblast, then b-catenin for and osteoblast and then an osteocyte if it becomes trapped.
how can you mark mesenchymal stem cells?
- see if they express STRO-1, see if they will become bones when applied to osteogenic supplements. See if they produce rnx-2 and AP
how did they measure wether mesenchymal stem cells were affected by chemotherapy?
they exposed rats to chemotherapy and not the controls- they then broke a bone and fixated them. They then had 3 different groups t look at the repair: osteotomy only, osteotomy with just fibrin glue and then osteotomy with MSC and fibrin glue they show that MSCs could be maintained in fibrin glue)
what does chemotherapy do, how can this be treated, how was this shown?
It reduces bone formation- which is bad because if you are treating someone with bone cancer you want high bone formation because you want to promote regrowth. But when you add mesenchymal stem cells in a glue to a fracture- you find that bone formation increases to the same levels as those without chemotherapy
how can MScs be applied to implants?
a spray- they checked that they could be sprayed and remain viable first.
what did they find when they spray MSCs?
there is an initial reduction in viability and then it increases
describe the experiment used to investigate whether a spray of MSC onto an implant can improve osteointegration.
they sprayed it onto surface of the implant and they used an animal model which was a tibial replacement in the sheep- they looked at a group with stem cells and some without and as early as 2 months you could see differences in the amount of bone formation. - the found that the more cells you integrate the better the response. These cells were all autogenic cells.
what is the problem with using the autogenic MSC spray into implant approach? how can this be circumvented?
you are taking cells from a cancer patient so you may be spraying back on cancerous cells. You can use the same model but with allogenic cells and also with cells that have been differentiated down the osteogenic lineage.
what were the results of trying to circumvent the problem with using autologous cells within the spray MSC approach?
- you use cells that are allogenic and some cells that have been differentiated down the osteogenic line
- you find that the allogenic cells in this system didn't work. bu t when you use autogenic stem cells tat have been differentiated partially down the osteogenic pathway then you get a better response.
- it is thought that the allogenic cells caused some kind of immune response/ infammatory which caused bone resorption.
how can you use autogenic stem cells for implantation?
if you aren't using cells from a cancer patient
how did they test whether hey could use this application of stem cells to hip replacements?
they applied he cups used in the replacement wit fibrin glue containing the MSCs. They measured the length of fibrous tissue along the acetabular cup. They found that towards the periphery of the cup you get less fibrous tissue and more oseointegration.
why are osteointegration needed for hip replacements?
1 in 10 need revisions due to ascetic loosening.
how can they promote osteointegration in hip replacements to prevent revisions?
they remove the cup and then put on a morcelised allograft (bone chips from femoral heads) this is pasted onto the region and this is impacted onto he surface and then they insert another cup and hope that new bone forms around the cup.
- they asked if they could improve implant fixation by applying MSCs with impacted allograft - they first has to check whether impaction resulted in the cells being killed. The measured the forces and found 30 KN. and the graft sees 9kn force. they find that this force depresses the proliferation of these stem cell int he graft.
- then took this impacted graft and inserted it into the spinal muscles of a sheep and monitored spine formation. This gives a test of how osteoinductive these tissues are.
- get over 100% difference in bone formation
- then they mixed bone chips(allograft) with mesnehcmal stem cells (autologous) and with plasma to form a clot that could be handled, then impacted the one chips onto the al lot the femar. They fond that this caused bone formation after 6 months increases by 60%
has MSC been used in patients yet?
no - not in humans yet.
what is an osteoclast?
stem derived from a different lineage from osteoblast and osteocytes- the haematopoeiic
what is the role of the osteoclast?
- produces acid pH in a bit which resorbs the calcium phosphate material and at the same time it produces an enzyme called casthespin K which is a MMP which operates at low pH which also helps tp resorb the organic part of t eh bone
how do the osteoblast and osteoclast interact? what does this mean?
the osteoclast and the osteoblast are very closely linked- they dont operate without the other - the skeleton is being completely remodelled
what is the role of the osteblast?
the cell that will give rise to the bone
what percentage of your bone is remodelled each year?
what has to happen for a osteclast to be formed~??
to produce a multinucleate osteoclast which is able to resorb bone, it has to some into contact with the stromal cell (osteoblast)
what is the process by which the osteoclast is formed?
- the RANKL system
- RANKL is on the osteoblast and is essentially a membrane bound antagnoist and not he osteoclast there is RANK. when they come together , they initiate the formation of a multinucleate cell
- they need m-CSF which is produced by osteoblasts which is required for the osteoclast to form
how is the osteoclast needed for the osteoblast to form bone?
- when the bone is removed there are cytokines which are released which stimulate the osteoblast which enables the osteoblast acts
- they also directly interact by binding of ephori's (ephrin B2 is on the osteoclast )
why is it important that bone is continuously remodelled?
the bone can gain micro cracks during life and can join together which can result in stress fractures
what is the treatment for osteoporosis? what re the downsides about this treatment
bisphosphonate- they prevent osteoclastic action- this can result in the formation of an atypical fracture because the cell is unable to remodel bone and so fractures can occur
what is a bone multicellular uni?
the unit of the osteocytes and osteblasts
what is a cool thing that osteocasts do ?
they detect strain and send signals to the osteoblast to activate it and influence bone remodelling- they release sclerostin
- when you get to a micro fracture he caniculi are fractured
- this causes apoptosis which prevents the release of sclerostin and allows the osteoblasts to become an productive cell.
how do osteclasts mediate the action of the osteblasts ?
- they release scelrostjn which keeps the osteoblasts in a resting state
what are the two ways that bone can be formed in fracture?
- intramembranous ossification
- endochondrial ossification
where does intramembranous ossification occur normally?
- in the skull
what is the process of intramembranous ossification?
- the mesenchymal stem cells come along and differentiate on the collagen mesh into osteoblasts and form bone directly
what is the type of bone remodelling that occurs in the body other than the skull?
what is the process of endochondrial ossification?
- get cartilage which turns into bone
- at the top of the growth plate (the region nearest the joint) you get cartilage which is in a resting zone - these chondrocytes dont produce any cells themselves
- below this zone there is a proliferative zone where the chondrocytes are in a proliferative state
- they move down the growht plate as the patient grows
- as it does this it becomes hypertrophic and lays down calcified cartilage
- this leads to the calcification zone where matrix become s calcified and in the ossification zone osteoblasts despite ECM and osteoclast remodel the bone. The capillary loops allow the osteoclasts and osteoblasts to differentiate from mesnehcymal stem cells
what family of TFs are involved in endochondrial bone formation?
what produces the calcified cartilage?
how can bone grow in girth?
has the periosteum membrane surrodungin the bone with stem cells in it which produce osteoblasts and chrondrocytes and will first produce hyaline cartilage and woven bone which will be replaced with lamellar bone via endochondrial ossification
how does strain affect bone formation?
if you have limited strain then you will get intramembranous ossification and if you get a lot of movement you get endochondrial ossification
what forms when there is over 10% strain? what is the result of this?
granulation tissue forms and you get non union and fibrous tissue forms between the two broken bones
what is it called when there is fibrous tissue forms din the break due to too much movement?
hypertrophic non union
how can hypertrophic non union be prevented?
- using a fracture fixation device
whata re the general stages of fracture healing?
- because damage blood the blood coagulates
- then MSC come in from several sources and yo u get release of osteocytes too which can become osteoblasts
what are the three outcomes of fracture fixation?
what is direct healing (intramembranous bone formation)?
- bone forms across the gap- the gap is small= no scar
what is indirect healing (endochondrial formation)?
- the surface of the bone bulges - associated with set cells being recruited from the periosteum which forms a cartilage fracture callus -stabilistabilises the fixation
in a fracture where do the progentor cells come from?
- endosteum (covers internal part of the bone)
- bone marrow
what Tfs control the production of osteoblasts mainly?
why is strain so important? what experiment showed this?
they took MSC and cultured on different strange: elastic substrate= muscle, stiffer= cartilage or bone, very low stiffness= brain
how can the stiffness be linked to the bone fracture?
different stiffness= bone or cartilage. depending on the stiffness in the fracture - you needed togged different tissues developing - fibrous tissue= high tension
how can you use computer models to predict likelihood of healing in a bone fracture?
- can look at strain and gap and predict what the outcome will be
How can you manipulate strain to improve repair and why does this work, when does this need to be done?
distraction osteogenesis: pull the fracture apart at a certain rate per day and you can change the amount of bone formed by changing the rate of strain. Lower strain rates result in less bone forming by higher strain rate. You can take a fracture that you dont think will heal which will lead to a better repair. need to do this very soon after fracture
how can you use stem cells fix a bone defect?
l. Bone regeneration in a massive rat femur defect through endochondral ossification achieved with chondrogenically differentiated MSCs in a degradable scaffold
- Porous PLGA scaffold seeded with MSCs pre-differentiated in vitro into cartilage-forming chondrocytes then placed the scaffold side which resorbed away and resulted in a bone forming between the two ends
how can circulating stem cells be used in fracture?
- you induce a fracturw which is healed by stem cells which are circulating within the bodies vasculaure- you promote the release do them GSCF or ADM3100
-these released cells will migrate back to regions where SDF-1 is being released which is at the break site injury