Biomechanics and Biology

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Biomechanics and biology of fracture healing in
osteoporotic boneProf. Dr. Peter
AugatInstitut für BiomechanikBerufsgenossenscha
ftliche Unfallklinik MurnauParacelsus
Medizinische Privatuniversität Salzburg
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Age related changes in musculoskeletal tissue

• decrease in the amount of tissue
• altered molecular composition
• accumulation of degraded molecules
• reduced synthetic capacity of differentiated
  cells
• altered levels of circulating hormones, growth
  factors and cytokines
• altered ability of the cellular response
• alterations in the loading patterns of the tissue
  or the tissues response to loading

Freemont, J Pathol 2007 211 252259
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Age related changes in hormones

• Growth Hormones Insuline Like Growth Factors
• IGF-1 production decreases
• Growth Hormone production decreases
• Sex hormones
• Androgens decrease
• Oestrogens decrease
• Cytokines
• Increase in TNF-a, IL-1 and IL-6

Freemont, J Pathol 2007 211 252259
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Age-associated cellular senescence

• Replicative senscence
• Teleomere shortening
• Stress-induced premature senescence (SIPS)
• mitochondrial injury

Age-associated stem cell changes

• Reduction of MSC stem cell pool
• Changes in differentiation characteristics
• Preference of adipogenteic pathway (mediated by
  PPAR?)
• Reduction of regeneration response

Freemont, J Pathol 2007 211 252259
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• Age related changes in
• bone quality and quantity
• bone volume
• bone architecture
• porosity
• geometry
• mechanical properties

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• reduction in bone volume
• change in bone architecture

images courtesy of R. Müller
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peak bone mass
BMD
age in years
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changes in the cortical geometry

• endosteal resorption
• periosteal apposition

• increase of intramedullary width
• reduction of cross sectional area
• (i.e. tibial diaphysis 7 per decade)
• cortical thinning
• (i.e. vertebral body cortex 450µm
  250µm)

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Increase in cortical porosity
R2 0.5
pore diameter in µm
Wachter K., Bone 2002
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Aging of cortical bone
old osteons are stiffer increased
brttleness accumulation of microcracks reductio
n in thoughness
Schaffler MB, BONE 1995 Burr D, OI 2003
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osteoporosis and fracture
"Bone failure not implant breakage is the primary
mode of failure inosteoporotic boneCornell J
AAOS 11109 (2003)
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Screw fixation in osteoporotic bone

• Cancellous screws (humerus, femur)
• Cortical screws
• Cortical locking screws
• Lag screws (femoral head)
• Pedicle screws

Augat et al. JOR 16(5) 2002
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Implant fixation in osteoporotic bone

• Proximal humerus plates
• Anterior cervical plates
• Vertebral body replacement
• Hip implants (nails, DHS, pins)
• External fixators (tibia)
• Locking plates (proximal tibia)

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affected / not affected by BMD
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Bonnaire et al. OI 16(S2) 2005
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The Basic Principles
How to fix implants in osteoporotic bone ?

• long splintage
• angular stability
• reposition and compression
• augmentation

Hertel R, Jost B in An H 2002
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(1) long splintage

• large distance between screws
• large distance of screws to fracture zone
• elastic implants (i.e. titan vs steel)
• diverging screws

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(1) long splintage
H.S., w., 82 J. subtroch femur fx, long Gamma
nail
E.L., w., 83 J. prox. humerus fx, T2 nail
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(2) angular stability
breakage during screw insertion -gt irreversible
deformation -gt loss of primary stability failure
of bone implantat interface -gt cut out -gt
implantdislocation -gt los of secondary stability

• conventional plate

angle stable plate
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(3) reposition and compression

• increase of primary stability
• improvement of retention
• load sharing

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(3) Reposition
H.S., w., 80J. lateral neck fracture, DHS
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(4) augmentation

• bone cement
• PMMA
• Calcium Phosphat cement
• bone transplant
• autograft
• allograft
• crystaline HA
• polylactid

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Osteoinduktive Cytokines

• Osteogenic protein-1 (OP-1, BMP-7)
• Bone Morphogenic Protein-2 (BMP-2)
• local increase in BMD
• acceleration of healing

Valentin et al, 2nd Distal Forearm Workshop of
the ISFR, Rome 2005
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Implants for osteoporotic bone

• high primary stability
• minimal trauma
• good retention
• load sharing
• fracture healing with biomechanical concepts
• acceleration of healing

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