Chapter 73 Osteochondrosis

Question 1

What is osteochondrosis?

Answer 1

Disorder of endochondral ossification

Question 2

Where can you find clinical manifestations of OCD in dogs?

Answer 2

• Humeral head
• Medial aspect of humeral condyle
• Lateral or medial femoral condyle
• Medial or lateral trochlear ridge of talus

Question 3

Growth plates contribute to ____% of final bone length
Epiphyses contributes to ___% of final bone length

Answer 3

Growth plate: 75-80%
Epiphyses: 20-25%

Question 4

At what age does growth plate fusion occur in proximal epiphysis of humerus? Distal epiphysis?

Answer 4

Proximal: 10-13 months
Distal: 6-8 months

Question 5

At what age does growth plate fusion occur in proximal epiphysis of radius? Distal epiphysis?

Answer 5

Proximal: 6-11 months
Distal: 8-12 months

Question 6

At what age does growth plate fusion occur in the olecranon of the ulna? Distal epiphysis?

Answer 6

Olecranon: 6-10 months
Distal epiphyses: 8-12 months

Question 7

At what age does growth plate fusion occur in proximal epiphysis (head) of the femur? Distal epiphysis?

Answer 7

Proximal: 7-11 months
Distal: 8-11 months to shaft, 3 months condyle to trochlea

Question 8

What are the 4 zones of a growth plate?

Answer 8

1. Resting zone
2. Proliferative zone
3. Hypertrophic zone
4. Mineralization zone

Question 9

Which zone of the growth plate is vascularized?

Answer 9

Resting zone, penetrated by chondro-epiphyseal vessels

Question 10

What hormone acts directly on stem cells in resting zone and what is its effect?

Answer 10

Growth hormone, promotes differentiation of stem cells into daughter cells capable of producing IGF-1

Question 11

Amount of cartilage volume increase during growth plate enlargement is determined by what?

Answer 11

• chondrocyte proliferation
• chondrocyte enlargement
• matrix formation

Question 12

What constrains the circumferential expansion of the growth plate?

Answer 12

Perichondral ring of Lacroix

Question 13

What are the two layers of the articular-epiphyseal complex?

Answer 13

Thin outer layer - avascular, develops into mature articular cartilage
Thick inner layer - similar to growth plate responsible for epiphyseal enlargement

Question 14

What are the two main differences between the thick inner layer and growth plate?

Answer 14

1. Inner layer is disorganized without zonal or columnar arrangement
2. Abundant vasculature throughout the inner layer (not just resting zone)

Question 15

What is a type I OCD lesion?

Answer 15

Occurs at center of affected articular surface away from vascular attachments

Eg. caudal humeral head, med humeral condyles, lat/med femoral condyles

Question 16

What is a type II OCD lesion?

Answer 16

Occur at joint margin and retain a vascular attachment

Eg. med/lat trochlear ridge of talus, FMCP

Question 17

Describe the 4 grades of OCD lesions in the proximal humerus

Answer 17

I - cartilage surface normal, cartilage slightly thickened, miniscule subchondral defect
II - cartilage surface mottled, cartilage thickened, small cleft b/w cartilage and subchondral bone
III - discoid elevation of cartilage surface, large cleft, underlying sclerotic subchondral bone
IV - partially detached cartilage flap or separated flap and joint mice

Question 18

What is a retained cartilagenous core and where does it most commonly occur?

Answer 18

Local thickening of growth plate, most commonly distal ulnar growth plate

Many heal spontaneously