William F Bennett MD

Injured Tissue-The Basics of
Healing
Requires Cells and Growth Factors
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Tissue repair relies on vascularity and cellular migration
Blood escapes, hematoma
Platelets, pluripotential stem cells form scaffold for neocellular proliferation
Cells respond to Growth Factors(Bioactive agents)
Some cells respond different to growth factors based upon tissue

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At the time of injury released, Gfs bind to receptors and effect cellular function.
Part of inflammatory response.
Proteins
Anabolic/catabolic
Cytokines-extracellular proteins
• Effect cell to cell mediation
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Examples- Interferon/interleukin/tumor necrosis factor

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Transforming Growth factorbeta(TGFB)-Largest group
• Over 100 members
• Anabolic effect on all components of
Musculoskeletal tissue

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Bone Morphogenic proteins-BMP ’ s
• Osteoprogenitor derived cells-promote bone growth
Platelet Derived Growth Factor-PDGF
• From platelets and stimulates angiogenesis, chemotactic influence and mitogenic
Insulinlike Growth Factor-IGF-1
• From variable cells, broad anabolic effect
Fibroblast Growth factor-bFGF
• Early differentiation of cells and tissue and in repair process

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Epidermal Derived Growth Factor-
EGF
• Proliferates ectoderm and mesoderm
Growth and differentiation Factor-
GDF-5
• Chondrocyte, fibroblast and mesenchymal cell expansion

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Two clinically available BMP ’ s -stimulates bone growth
• rhBMP2-Recombinant BMP(Infuse, Medtronic Sofamor
Danek, Minneapolis, Mn.)
• BMP 7(osteogenic protein-1- OP1)
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Stryker, Biotech, Hopkinton, Ma,
LMP1 -Lyophilized Mineral protein
• Stimulates BMP
PDGF and Platelet Rich Plasma may interfere with bone healing
BMPs help reduce non-union rate, spinal fusion rate and possibly open wedge osteotomy non-healing

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BMP2 and OP1 have been shown to aid in the tendon to bone healing
Although the exact mechanism for this repair process is not well known

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Mechanism not well defined
GDF5 may play a role
IGF1 and PDGF2
• Increased collagen synthesis
These factors can be found in augmentation tissues like porcine submucosa, bovine, equine collagen and human allograft dermis
Cascade - shows to repair tissue- platelet rich plasma !!!!!!!!!!!!!!!

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Cell Proliferation, Type 1 Collagen
• and proteoglycan synthesis are stimulated by bFDF, PDGF and bTGF
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Method of delivery will be a geneenhanced delivery system via fibroblast cells transduced by plasmid or virus carrying these growth factors

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Meniscal tears heal better when ACL reconstruction is done at the same time.
Suggests that something in the blood augments healing
Arnozcky has shown a fibrin clot to help healing.
Platelet Rich Fibrin Matrix(PRFM)
• Cascade- ultracentrifuge of blood
• Platelt rich ultracentrifugate is further centrifuged down to a volume-stable suturable fibrin matrix

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Articular cartilage is Hyaline cartilage
• Type 2 collagen
Heals to injury with fibrocartilage
• Type 1 collagen
• No vascular supply
• No nerves
• More of a scar tissue than normal tissue

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Fissuring- chondroplasty, smooths edges only, no healing
Osteochondral defects- microfracture technique or marrow stimulation techniques-forms fibrocartilage
Cartilage-growth factors
• Bmp2/1IGF/bTGF
• Add these to cell colonies, like genzyme cell cultures- get better hyaline cartilage

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Lavage and debridement
Chondroplasty
Microfracture
Oats
Polymer bone plugs
Osteochondral allografts
Cartilage cultures- Genzyme only
• Cambridge Ma

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Carticel- Genzyme-using chondrocytes, cartilage cells as opposed to stem cells.
• Bx, 4-6 weeks later can replant with cultured cells, use periosteal patch, open surgery, collagen membrane 2 nd generation……using presently.
• Next gen Carticel, MACI-matrix impregnated with cells, no periosteal patch

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Both an evolution and a revolution in modern biomedicine.
Concept is rather than introduce organ transplant, one would implant certain population of cells to allow regeneration
Bone marrow transplantation is intermediate between organ and stem cell transplant.

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Bone Marrow transplant- for radiation loss of blood cells and their progenitor lines.
Stem cell skin grafts for burn victims.
Corneal stem cell implants.
Pancreatic islet cell implantation.

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Genetically corrected stem cells used to treat;
• Muscular dystrophy
• Other disease processes
• Future will be in musculoskeletal areas as well.

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Adult stem cells identified from brain to muscle.
Fetal Stem cells- aborted fetuses or umbilical chord
Embryonic stem cells-
• Discarded from in vitro fertilization
• Somatic Nuclear Transfer- a nucleus from a normal body cell is placed into a fertilized egg with its nucleus removed.
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The fertilized egg has the effect of “ resetting ” the nucleus to a primordial state.
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No ethical considerations with fetuses here!

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Embryonic-
• Ubiquitous component of the embryo.
• Defined by position in the embryo
• Divide in culture without changing charcteristics.
• Single cell can give rise to a colony of cells.
Adult-
-rare, difficult to identify, unknown origin, partially understood function and life history
-defined by complex list of features.
-can not divide indefinitely.

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Maintain undifferentiated phenotype until exposed to appropriate signals.
With signals can differentiate into specialized cells that have structure and function
Mesenchymal Stem cells are of this type-MScs- bone marrow.
Mesenchymal is from a layer in the developing embryo.

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Know some signals
Don ’ t know all intermediate steps
Don ’ t know how exactly how one cell changes to another.
Don ’ t understand the microenvironment completely.
Adult and MSC have limited differentiation potential compared to embryonic stem cells and limited number of replication cycles.

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Stem cells may be exhausted
Has been shown to happen in degenerative conditions, especially osteoarthritis.

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Over next 5-10 years there will be major commercial development in the area of stem cell enterprises.