Developmental diseases of the MSK system

Question 1

What is endochondral ossification?

Answer 1

The formation of bone from a cartilage precursor.

Question 2

Where does endochondral ossification occur post-natally?

Answer 2

In 3 locations

• Physis where it is responsible for the majority of longitundinal bone growth
• Articular-epiphyseal cartilage complex (AECC) primarily responsible for the radial expansion of the epiphysis
• Cuboidal bones (the majority of these bones ossify from a single centre)

Question 3

What is shown in blue?

What is shown in yellow?

Answer 3

Blue = bone

Blue with XXX = bone just formed by endochondral ossification

Yellow = “growth cartilage” = cartilage that is involved in endochondral ossification

Question 4

True or false: cartilage is avascular

Answer 4

True

Question 5

True or false: growth cartilage is avascular

Answer 5

False: growth cartilage (unlike articular cartilage) is vascularised.

Cartilage canals are channels within cartilage that supply the blood whilst it is growing.

Question 6

Osteochondrosis

Answer 6

a developmental skeletal disorder that affects bone and joints due to the failure of the process of endochondral ossification.

It is of unknown aetiology.

Question 7

What does this image show?

Answer 7

Osteochondrosis

• Indentation of the ossification front
• Columnar arrangement disrupted
• Fissures and necrosis of deep layers

Question 8

T/F: the following terms can be used interchangeably:

Osteochondrosis

Osteochondritis

Osteochondritis dissecans

Answer 8

False - sometimes in practice they are used interchangeably but they are not equivalent!

• Osteochondrosis: failure of endochondral ossification
• Osteochondritis: extension of lesions to the articular surface causing inflammation of the joint
• Osteochrondritis dissecans: presence of a dissecting osteochondral flap (see image below)

Question 9

How does osteochondrosis occur?

Answer 9

• For reasons unknown, the cartilage canal blood supply fails, creatug lesions.
  
  • These are focal areas of ischaemia, which lead to chondronecrosis and necrotic canal vessels.
• The necrotic regions do not ossify. They become incorporated into subchondral bone as growth continues and may form cysts.
• Trauma or weight-bearing may cause the formation of dissecting lesions.

Question 10

What are some common sites of OCD in the horse?

Answer 10

• Tibiotarsal joint
• Femoropatellar joint
• Fetlock
• Stifle
• Shoulder and hip in Shetlands, rare in other horses

Question 11

What are some common sites of OCD in dogs?

Answer 11

• Shoulder
• Stifle
• Elbow