bone healing and fracture management

Question 1

strain

Answer 1

strain= change in length
More pieces broke into=lower strain at each individual fracture site
bigger gap=lower strain

Question 2

bone healing depends on

Answer 2

-the type you getdepends upon the size of
the gap between fragments and the
amount of motion at the fracture site

Question 3

types of bone healing

Answer 3

• Secondary (indirect) healing
• Primary (direct) healing:
   Contact healing
   Gap healing

Question 4

secondary healing (indirect healing)

Answer 4

endochondral ossification; healing by callus formation)
* Healing via a sequence of tissue types that make progressively stiffer matrix
* Occurs in fractures that have some movement and/or more than a 1 mm gap

Question 5

secondary healing (indirect healing, endochondral ossification steps)

Answer 5

steps:
1fracture
2 hematoma followed by fibrin clot
3 fibrous tissue fomation
4 fibrocartilage formation
5 cartilage mineralization and blood vessel ingrowth
6 bone formation
7 remodeling

Question 6

wolffs law

Answer 6

-Bone remodels in response to stress: it is
laid down where it is needed and resorbed
where it is not needed

Question 7

Growth Factors Influencing Bone Healing

Answer 7

• Bone morphogenetic proteins (BMPs)
• Insulin-like growth factor
• Transforming growth factor β
• Platelet-derived growth factor
• Fibroblast growth factors
• Vascular endothelial growth factors

Question 8

Primary (Direct) Healing requires

Answer 8

• Formation of bone without intermediate tissues coming first
• Requires close apposition of fragments, a blood supply, and rigid stabilization

Question 9

primary healing: contact healing

Answer 9

• Requires direct contact between fragments
• Bone multicellular units (led by cutting cones) form spot welds
• Then remodeling of laminar bone occurs

Question 10

primary healing: gap healing and steps

Answer 10

• Gap of 1 mm (or less) between fragments, and fracture is rigidly stabilized
• Hematoma->connective tissue/blood
  vessels->osteoblasts lay down lamellar bone in gap->cutting cones go across new bone

Question 11

Blood Supply to Bone

Answer 11

-Nutrient artery-> medullary canal and endosteum
* Metaphyseal blood vessels
* Periosteal blood vessels
* Extraosseous blood supply of healing bone
-Extraosseous blood supply to bone comes
from muscle attachments—so try not to
disrupt them when fixing a fracture

Question 12

anatomic repair

Answer 12

• Perfect alignment and apposition of fragments is the goal
• Some early weight transmission may be possible through reconstructed bone, sparing the apparatus
• Usually requires generous exposure and direct manipulation of fragments
• Disrupts blood supply/early healing response to some extent

Question 13

anatomic repair indications

Answer 13

• Choose only for fractures which CAN
  be reconstructed!
• Appropriate when you expect
  fracture to heal slowly under the
  best of circumstances
• Appropriate when callus is
  undesirable

Question 14

biological repair

Answer 14

• No big attempt to reconstruct the fractured bone
• Minimal disruption of blood supply
• Hardware bears all the forces until fracture heals
• Either closed or “open but do not touch” (OBDNT) approach to fracture reduction
• Limb is pulled out to length and angular and
  rotational deformity are corrected
• Bone generally heals more
  rapidly, BUT…
• Until healing has occurred, the hardware bears all of the forces of weightbearing

Question 15

biological repair indications

Answer 15

• Appropriate for fractures with a good blood supply that you expect to heal rapidly
• Appropriate for fractures you
  can’t reconstruct
• Not a good choice in situations
  where callus is not your friend

Question 16

assessment of repair and healing AAA

Answer 16

*Alignment and reduction (or apposition)
*Apparatus
*Activity: how is the animal using the limb? how is the fracture healing?

Question 17

What influences fracture healing?

Answer 17

-location of the fracture
-the bone fractured
-degree of soft tissue disruption
-Strain and motion at the fracture site
-type of healing affects speed which strength returns
-limb use
-species
-age

Question 18

Strain and motion at the fracture site when assessing healing

Answer 18

*A little axial tension or
compression promotes bone
healing, too little strain is bad
*Too much tension is bad
*Any torsion/shear at all is terrible

Question 19

Guidelines for uncomplicated fracture healing expectations
(dogs and cats) different ages

Answer 19

*2-5 months of age: 2-4 weeks
*6-12 months of age: 4-8 weeks
*Adult: 6-10 weeks
*Geezer: 12-16 weeks

Question 20

Radiographic union: primary (direct) healing

Answer 20

Question 21

Radiographic union: secondary (indirect) healing

Answer 21

Question 22

Radiographic vs clinical union

Answer 22

*Remember that first, resorption of dead bone occurs
*In adults it takes about 6 weeks for callus to mineralize
*Feel for fracture getting “sticky”

Question 23

technical error in fracture healing

Answer 23

• If the repair method chosen is insufficient to
  neutralize forces acting on the fracture, the
  repair will fail

Question 24

quadriceps contracture

Answer 24

• Tends to follow delayed femoral fracture
  union
• Common after splinting of femoral fractures
• Might be associated with compartment
  syndrome
• Common in young dogs (and cats)
• Best avoided: make sure you have solid
  fracture repair and aggressive, early physical
  rehabilitation

Question 25

malunion

Answer 25

* Fracture healing with abnormal alignment * Malalignment may be angular, axial (shortened), torsional, or a combination * Malunion may or may not be a clinical problem * Bone length can be affected...but up to 20% loss of femoral length is well tolerated in dogs and cats * Up to 15 degrees self-correction of angular malalignment may happen over time * Rotational malalignments do not self- correct

Question 26

corrections of malunion: Osteotomy

Answer 26

* Osteotomy is making a cut in a bone. * Ostectomy is removing a piece of bone. types are: closing wedge opening wedge oblique dome step can also use distraction osetogenesis

Question 27

delayed union

Answer 27

fracture has not healed within the expected time (usually 3-5 months)

Question 28

nonunion

Answer 28

-no healing well beyond the expected maximal time (~6 months in adult dogs and cats)

Question 29

causes of delayed and nonunion

Answer 29

* Excessive motion of fracture fragments * Infection * Excessive gap between fragments * Devitalized bone * Poor blood supply to fragments

Question 30

Vascular (Hypertrophic) Nonunions

Answer 30

treat by rigid stabilization of the fracture

Question 31

Avascular (Atrophic) Nonunions

Answer 31

Question 32

Treatment of Avascular (Atrophic) Nonunions

Answer 32

1) Encourage ingrowth of new blood vessels * Remove offending hardware * Resect fibrous tissue, sclerotic bone ends from fracture site * Open up medullary canal (drill longitudinal holes) to encourage blood vessel ingrowth 2) Rigid stabilization, under compression if possible

Question 33

management of atrophic nonunions

Answer 33

3) Stimulate bone growth * Cancellous bone graft * Bone morphogenetic protein or other growth factors * Mesenchymal stem cells * Omentum! * Bone transport (via distraction osteogenesis

Question 34

bone grafting

Answer 34

* Transplantation of bone to stimulate healing or replace bony deficits * Autografts come from the same animal * Allografts come from a different animal of the same species * Xenografts come from other species

Question 35

bone grafting type of bone

Answer 35

* Cortical: used to replace big bone defects and provide physical support * Cancellous: provide little to no physical support but stimulate healing

Question 36

What Cancellous Bone Grafts Provide

Answer 36

* Osteogenesis: mesenchymal precursor cells in the graft differentiate into active osteoblasts * Osteoconduction: Graft provides a scaffold for osteoblasts to lay down new bone upon * Osteoinduction: Growth factors in the graft recruit more cells to turn into osteoblasts and lay down new bone

Question 37

Collection of Cancellous Bone Graft

Answer 37

* Make a small hole in the donor bone with a pin or drill * Use a curette to scoop out cancellous bone * Store cancellous bone in a bloody sponge, in the dark, in a safe place until implantation

Question 38

places to get cancellous bone for graft

Answer 38

* Proximal humerus * Proximal tibia * Femoral condyle * Ilium (especially in cats) * Sternum (horses and cattle and birds

Question 39

when to use cancellous bone grafts

Answer 39

* Delayed unions and nonunions * Long bone fractures in adult animals that you expect to heal slowly * Places where there are bone deficits * Osteomyelitis * Arthrodesis

Question 40

Bone Graft Substitutes

Answer 40

* Injection of bone marrow into a fracture/delayed union site * Calcium phosphate cements * Bioglass (for example, Consil, made by Nutramaxx laboratories) * Coral (I am not making this up!) * Bone morphogenetic proteins in carrier substances