Fracture and Healing

8/18/2019 Fracture and Healing

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Section 20: Fracture

Mechanics and Healing

20-1


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20-2 From: Al-Tayyar


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•

• Axial Loading

– ens on

– Compression• Torsion

Bending Compression Torsion

20-3 From: Le


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20-4 From: Le

, , .


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20-5 From: Al-Tayyar


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•

– Compression strengthgreater than

tensile strength

– Fails in tension

20-6 From: Le

.

Trauma, Lippincott, 1994.


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•

axial load – Oblique fracture

– Butterfly fragment

Figure from: Tencer. Biomechanics in Orthopaedic

20-7 From: Le

, , .


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20-8 From: Vanwanseele


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•

– Primary bone healing

– Cutting cones

– Seen with absolute stability

• Indirect – Secondary bone healing

– Callus formation; resorption at fx site;

– Seen with relative stability

20-9 From: Justice


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•

– 1-7 days

•

– 3 weeks

•

– 3 – 4 months

– months => years

20-10 From: Justice


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• Motion between fracture fra ments that is

compatible with fracture healing.• Motion is below the critical strain level of tissue

repa r.

• Promotes indirect bone healing!• xamp es:

– IM nails

–

– External Fixator

20-11 From: Justice


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• Compression of two anatomically

reduced fracture fragments.• No displacement of the fracture under

functional load.

• Promotes direct bone healing!• Examples:

– Lag screw

– Plate => compression, buttress,neutralization

20-12 From: Justice

– Tension band


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B o n e D evelo pm en t an d H ealin gThe process of bone

ossification. There are twotypes of ossification:

en oc rona an

intramembranous.

stages: fracture,

granulation, callus,

lamellar bone, and normalcontour.

20-13 From: Ames

Chapter 5 – The Skeletal System


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Fracture

• Step 1:.

the fracture,

extensive bleedingoccurs. Over aperiod of several

,clot, or fracturehematoma,develops.

B. Bone cells at the site

nutrients and die.The site becomesswollen, painful, andinflamed.

• A. Granulation tissue is formed as the hematoma is infiltrated by

capillaries and macrophages, which begin to clean up the debris.

B. Some fibroblasts produce collagen fibers that span the break ,

cartilage matrix.C. Osteoblasts begin forming spongy bone.

D. This entire structure is known as a fibrocartilaginous callus and it

splints the broken bone.

20-14 From: Imholtz


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Fracture

• Ste 3: A. Bone trabeculae

increase innumber and

fibrocartilaginouscallus into a

bony callus of.Typically takesabout 6-8 weeksfor this to occur.

• Step 4: A. During the next several months, the bony callus is continually remodeled.

B. Osteoclasts work to remove the temporary supportive structures while osteoblastsrebuild the compact bone and reconstruct the bone so it returns to its original

20-15 From: Imholtz

.


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Biomechanics Intact/Healing

one• Hierarchical structure

– Collagen embedded with

apatite

decreased

apatite:collagen ratio• Fibrils organized to resist

force

– Fibers organized intolamellae

–

20-16 From: Justice

make an Osteon


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• Stren th ro ortional to

density2

• Modulus proportional to

ens y

• Age: increased modulus,

bendin stren th from

child to adult, then

decrease

• o es e ec s wea enbone (round better than

square)

20-17 From: Justice

• Strength proportional to

diameter 4


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•

– Moment of inertiaproportional to r 4

. x s ronger

– Increase in radius by

callus greatly

inertia and stiffness

20-18 From: Le

. x wea erFigure from: Browner et al, Skeletal Trauma

2nd Ed, Saunders, 1998. Figure from: Tencer et al: Biomechanics inOrthopaedic Trauma, Lippincott, 1994.


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•

– Callus increases

– Stiffness

increases witht me

– Near normal

days

– Does not Figure from: Browner et al, Skeletal Trauma,

20-19 From: Le

correspond to

radiographs

2nd Ed, Saunders, 1998.


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Remodeling of Bone

• Wolff’s Law

• –

absorption of osteoclasts and bone formationby osteoblasts

– osteoporosis –increase porosity of bone, decreasein density and strength, increase in vulnerability to

– piezoelectric effect – electric potential createdwhen collagen fibers in bone slip relative to one

, – use of electric and magnetic stimulation tofacilitate bone healing

20-20 From: Brown

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