Osteochondrosis

Question 1

What is the definition of osteochondrosis?

Answer 1

• Defect in endochondral ossification
  
  • Endochondral ossification = the process by which epiphyseal cartilage becomes bone
• ​​Non-inflammatory cause of arthritis

Question 2

What are the different regions of growing bone?

Answer 2

• Diaphysis
• Metaphysis
• Physis
• Epiphysis

Question 3

Long bone growth occurs from the ________ and the ________.

Answer 3

growth plate; epiphysis

Question 4

What is the relative contribution of the physis and epiphysis to bone length?

Answer 4

The growth plate is responsible for ~80% of the length; the epiphysis provides the other ~20% (though this can vary between bones and species)

Question 5

T/F: Most of the bone growth occurs by 12mo

Answer 5

FALSE

Most of the bone growth occurs by 26wks, or ~6mo

Question 6

When does the epiphysis usually ossify by?

Answer 6

At the end of ~6mo, the epiphyses have ossified though the growth plates are still open

Endohondral ossification occurs in both locations but it is the second that is the issue in OCD

Question 7

Explain the terms “center of ossification” and “ossification wave”

Answer 7

• Center of ossification = section of epiphysis where endochondral ossification begins
• Ossification wave = ossification travels outward and anastomosis continues

Question 8

Describe the transfer of blood supply to the epiphysis from the perichondral plexis to the metaphysis

Answer 8

• Cartilage blood supply: perichondral plexis
• Blood supply to metaphysis comes from medullary canal
• Ossification wave: anastomoses form
  
  • Perichondral plexis
  • Epiphyseal bone supply

Question 9

How can an error/interruption during the transfer of blood supply during bone growth lead to thicker epiphyseal cartilage?

Answer 9

• Small defects may ossify by other means
  
  • Intramembranous ossification
  • Lesion resolves, not a clinical problem
• Failure to ossify–> thickened cartilage
• Thickened cartilage acts as ‘stress riser’
• Necrosis–> cleft between cartilage and bone
• Focused stresses over cleft–> fracture of cartilage

Question 10

How can thickened epiphyseal cartilage become a flap of cartilage at the joint surface?

Answer 10

• Too much breakdown –> ischemia and necrosis of cartilage
• Because endochondral ossification is not progressing normally in this area–> thicker cartilage (failure of endochondral ossification)
• If bigger area, might persist as growth continues
• Might still undergo intramembranous ossification as bone continues to mature
• Fissure can develop between bone and cartilage
• If fissure extends to the joint surface, it results in a flap of thickened cartilage –> osteochondrosis dissecans (OCD)

Question 11

How can a fissure between the thickened cartilage and subchondral bone trigger DJD?

Answer 11

• Necrotic cartilage induces repair
• Inflammation is first stage of repair
• Defect in joint surface accelerates DJD

Question 12

What is the etiology of OCD?

Answer 12

Multifactorial

• Genetics/heredity
• Non-genetic/environmental factors
  
  • Nutrition
    
    • Vitamin D
    • Ca
    • Energy
  • Trauma
• Both genetic and non-genetic factors must be present for disease to manifest

Question 13

What are the breed and gender dispositions of OCD?

Answer 13

Males predisposed

Large/giant breed dogs

Question 14

What is the significance of heritability in OCD?

Answer 14

Heritability 10-45%

DON’T BREED

Question 15

What is the relationship between dietary Ca and vitamin D levels and OCD?

Answer 15

• High vit D/Ca promotes errors in endochondral ossification in Great Danes
• Direct causation of OCD not established
• High Ca/vit D linked to other ortho diseases

Question 16

How does dietary energy relate to the development of OCD?

Answer 16

Promotes development of bone and muscle

Increases stress on developing cartilage

Question 17

What is the difference between microtrauma and macrotrauma as related to OCD?

Answer 17

• Microtrauma–normal weight-bearing stress
  
  • Abnormal cartilage more prone to injury
  • Lesions occur even with normal stress
• Macrotrauma–athletic, high-impact stress
  
  • May cause subclinical to become clinical
  • No direct evidence in dogs
    
    • Shown to be a factor in human OCD

Question 18

What does the phrase “developmental orthopedic disease” signify?

Answer 18

Presents at an early age and continues to develop/progress over time

Question 19

What is the biphasic age distribution of OCD?

Answer 19

• 2 stages of diseaes
  
  • Immature–inflammatory arthritis
  • Mature–secondary degenerative disease
• Frequently bilateral (assume bilateral until proven otherwise)
• Heritable: DON’T BREED

Question 20

What are the common locations of OCD (dogs)?

Answer 20

• Shoulder–caudolateral humeral head
• Elbow–medial humeral condyle
• Hock–medial or lateral talar ridge
• Stifle–medial or lateral femoral condyle

Question 21

What radiographic findings are compatible with OCD?

Answer 21

Flattening contour of the joint

Question 22

What are the recommended preventative measures for OCD?

Answer 22

• Any puppy of a breed susceptible to developmental ortho disease should be fed a diet relatively restricted in energy, vitamin D, and Ca (“large breed puppy” diets)
• Might not encourage extreme activity in predispositioned breeds (ex: jumping 10ft to catch a frisbee)

Question 23

What are the indications for conservative treatment of OCD?

Answer 23

• Small lesion
• Young patient (ossification incomplete < 6mo)
• Clinically silent or mild lameness
• Poor surgical outcome–site dependent

Question 24

What are the components of conservative management for OCD?

Answer 24

• Diet
• Exercise restriction
• Weight control
• +/- NSAIDs or other therapies

Question 25

Describe the most common surgical treatment for OCD and the difference in the type of cartilage that forms as the defect heals

Answer 25

* Fragment removal and subchondral bone debridement * Usually arthroscopic * Healing by second intention * Replacement of articular cartilage with fibrocartilage * Imperfect * Osteochondral transplants (OATS)