Patterns of Disease: Bone

Question 1

What is Osteochondrosis Latens? What is unique about this disease in regards to visual inspection and where it occurs in bone?

What should we remember about growing cartilage?

Answer 1

A lesion causing necrosis of the blood vessels in the epiphyseal (growing) cartilage of the articular epiphyseal complex (AEC).

Unique: It does not affect the overlying cartilage and the underlying bone in regards to where the lesion is. These lesions can only be seen microscopically.

Growing cartilage contains blood vessels versus adult cartilage which does not.

Question 2

What is Osteochondrosis manifesta?

Answer 2

Once you can see osteochondrosis latens grossly, it has now become osteochondrosis manifesta.

When the ossification front reaches the necrotic area, there is grossly visible necrotic epiphyseal cartilage= Osteochondrosis manifesta. This cartilage WILL NOT turn into bone.

Question 3

What is osteochondritis dissecans? What is Joint Mouse?

Answer 3

This is a secondary lesion to OCD lesions.The primary lesion is the OCD lesion where Clefts can form in the OCD lesion and overlying articular cartilage fractures, therefore creating a flap.

If this flap breaks off this is called “Joint Mouse”

This is very painful causing joint effusion and non specific synovitis due to flap penetrating into the bone.

Question 4

What is the function of osteoblasts?

Answer 4

1. Form matrix (osteoid)
2. Initiate bone mineralization
3. Initiate bone resorption

Question 5

What is the function of Osteocytes?

Answer 5

Osteocytes are found in the matrix and detect changes in the mechanical environment and signal to osteoblasts what to do.

Question 6

What is the function of Osteoclasts?

Answer 6

Bone resorption

Question 7

What is osteoid?

Answer 7

This is the organic portion of bone matrix produced by osteoblasts. It is unmineralized and composed of type 1 Collagen fibers and ground substance.

Question 8

What is meant by Micro damage? Give an example.

Answer 8

These are stress fractures which may be preceded by exercise-induced micro damage.

Ex: DMD Dorsal Metacarpal Disease affecting the cannon bone –> causes reduced bone stiffness and periosteal bone formation (extra bone) in the cannon bone (3rd metacarpal)

Question 9

What are two kinds of fractures? Give an example of the latter form.

Answer 9

1. Traumatic due to excessive force.
2. Pathological due to abnormal bone broken by minimal trauma or normal weight bearing.

Pathological examples are

• osteomyelitis (inflammation of the bone marrow), - bone neoplasms,
• metabolic bone disease.

Question 10

Describe the Salter-Harris Classification system and what it is used for. Why is it important to be concerned with young animal bone fractures?

Answer 10

This is used to describe fractures of the growth plate.
Types I-V.

Type I and II: usually have few complications because they don’t penetrate the epiphyseal cartilage.
Types III and IV: cross the epiphyseal plate.
Type V: Growth plate is crushed.

If the plate is crossed or crushed, this can damage the resting cell layer or damage the epiphyseal artery which nourishes the growth plate inhibiting continued growth of the bone (premature growth plate closure) causing limb deformities in young animals.

Question 11

Name the 3 fracture classification systems.

Answer 11

1. Infraction
2. Simple
3. Compound

2 and 3 involve cortical (outer) bone

Question 12

What is an infraction?

Answer 12

Fracture of the trabecular bone ONLY not involved the cortical bone. This is due to inflammation or necrosis predisposition.

Question 13

What is a simple fracture?

Answer 13

The cortical bone has broken and the skin is unbroken.

Question 14

What is a compound fracture?

Answer 14

The cortical bone as broken and the skin has broken. The bone has been exposed to the external environment through the skin.

Question 15

What is a Comminuted Fracture?

Answer 15

Several small fragments.

Question 16

What is an Avulsed Fracture?

Answer 16

Caused by pulling of a ligament.

Question 17

What is a Greenstick fracture?

Answer 17

One side broken, the other side is only bent.

Question 18

What is a Transverse or Spiral Fracture?

Answer 18

Orientation of the fracture line.

Question 19

What is a compression fracture?

Answer 19

Bone folded onto itself. Compacted so it looks bulging in the middle.

Question 20

What is an impacted fracture?

Answer 20

Bone fractured and pushed into itself.

Question 21

What do we want to stabilize a facture?

Answer 21

It is necessary for the fracture ends to be immobilized to give some stability however not sx. fixed.

Question 22

Describe the process of a fracturing a bone.

Answer 22

1. Periosteum tears. (outer membrane of bone)
2. fragments displaced
3. Soft tissue traumatized
4. Hematoma formation

Question 23

How does the body stabilize the fracture immediately after it occurs?

Answer 23

A hematoma is formed at the broken ends. Growth factors are released by macrophages, platelets, and dead bone to stimulate the proliferation of repair tissue.

Mechanical Strength: Weak.

Question 24

How does the body stabilize the fracture 24-48 hours after it occurs?

Answer 24

At this point we get proliferation of undifferentiated mesenchymal cells and neovascularization which penetrate the hematoma. This forms a loose collagenous tissue.

The mesenchymal cells come from the perisoteum, endosteum, and stem cells in the medullary cavity

Mechanical Strength: Weak.

Question 25

How does the body stabilize the fracture 36 hours after it occurs?

Answer 25

Now the first woven bone is visible. A callus is also formed: unorganized meshwork of bone that forms after a fracture. Mechanical Strength: Weak.

Question 26

How does the body stabilize the fracture 4-6 weeks after it occurs?

Answer 26

A primary callus is formed which consists of woven bone and possibly hyaline cartilage. Mechanical Strength: Moderately Strong.

Question 27

How does the body stabilize the fracture over months to years after the it occurs?

Answer 27

A second callus is formed: Woven bone is replaced by strong, mature lamellar bone. The size of the callus can be reduced in size over a period of year by osteoclastic activity to restore the normal shape of the bone. Mechanical Strength: Almost Normal

Question 28

What is the histological difference between woven and Lamellar bone?

Answer 28

Lamellar bone is smooth and organized. Osteoid has been deposited. A smooth blue line indicated osteoid has just been deposited. Woven bone is disorganized with clumps of osteoblasts dispersed.

Question 29

What is a callus, what is its purpose, and how is it formed?

Answer 29

Callus is formed to bridge the gap between the fracture ends, it encircles the fracture site, and stabilizes the area. The reason it encircles the site is because although it assists in stability it is weak still at that site, therefore it is developed to a large size to help compensate. It will eventually undergo endochondral ossification. Callus' contain cartilage if the blood supply is less than optimal. They are externally formed by the periosteum and internally by the medullary cavity and bone ends. (Growth factors assist in proliferation)

Question 30

What are the complications associated with fracture repair?

Answer 30

1. The bony ends can move in a pocket of fibrous tissue which acts as a false joint (pseudoarthrosis). 2. Inadequate blood supply causing cartilage formation. 3. Instability allowing excessive movement will cause the development of a fibrous callus. 4. Fibrous tissue does not stabilize the fracture and does NOT act as a template for bone formation like cartilage does.

Question 31

Ideally and realistically, What are we looking to achieve during rigid fracture repair?

Answer 31

a. Ideally, we want contact (direct) healing where there is direct osteonal bridging therefore no callus will be formed. b. However, realistically a gap ( 1 mm will form woven bone and must be modeled into osteonal bone.

Question 32

What is Osteitis?

Answer 32

inflammation of bone

Question 33

What is periostitis?

Answer 33

inflammation of the periosteum

Question 34

What is osteomyelitis?

Answer 34

inflammation of the bone marrow or spinal cord involving the medullary cavity.

Question 35

What is Sequestrum?

Answer 35

Fragment of dead bone isolated from blood supply surround by exudate.

Question 36

What are different portals of entry into bone?

Answer 36

1. Direct | 2. Hematogenous

Question 37

Describe the different "direct" entry ways into bone..

Answer 37

1. Directly through the periosteum and cortex. 2. Trauma that may/ may not break the bone. 3. Direct extension

Question 38

What is direct extension? Give an example.

Answer 38

Entry into the bone from a contiguous focus of infection. Example: Actinomyces bovis= causes lumpy jaw in cattle. It is introduced into the oral mucosa by a penetrating injury (i.e. wire). From there it invades bone causing sever suppurative (neutrophil abundant) osteomyelitis.

Question 39

Describe Hematogenous entry into bone.

Answer 39

This is entry via a blood borne infection. Blood gains access to marrow cavity of diaphysis and metaphysis via nutrient foramen. In young animals it enters the epiphysis via the epiphyseal artery and small branches of cross the epiphyseal cortex. The entry into bone occurs at the physis (growth plate ) or Articular-epiphyseal cartilage complex.

Question 40

Describe how hematogenous entry into the bone causes infection. Does it affect young or older animals?

Answer 40

Hematogenous bacterial osteomyelitis is common in young animals such as foals, neonatal ruminants and pigs. It can be due to a bacterial infection where purulent exudate in the medullary cavity increases pressure and can compress vessels causing thrombosis and infarction as well as increased bone resorption. Perinatal transmission occurs via umbilicus or oro-pharyngeal origin. The entry into bone occurs at the physis (growth plate ) or Articular-epiphyseal cartilage complex.

Question 41

Discuss the factors which contribute to capillary entry into bone allowing Bacteremia causing infection at the epiphysis or growth plate.

Answer 41

Capillaries loop and enter the bone to join the medullary veins at the AE complex and metaphyseal growth plate. Factors contributing to infection at growth plate: 1. Slow flow and turbulence of blood in larger descending limbs 2. Lower phagocytic ability 3. Discontinuous endothelial cells. 4. No anastomoses, therefore thrombosis results in infarction favoring bacterial localization.

Question 42

What is embolic osteomyelitis?

Answer 42

An embolus lodges in the capillary loop at the metaphysis. This inflammation causes lysis of the metaphyseal bone and growth plate cartilage causing mechanical instability. The periosteum will produce reactive woven bone in response.