Osteochondrosis

Osteochondrosis in pig elbow (Image sourced from Bristol Biomed Image Archive with permission)

Osteochondrosis dissecans (Image sourced from Bristol Biomed Image Archive with permission)

• Defect in cartilage growth (i.e. dyschondroplasia)
• In growing animals: large breeds of dogs (4-8 months), pigs (5-7 months) and horses (weeks - 2 years)
• Involves both the growth plate and the immature joint cartilage
• Multifactorial:
  • Trauma
  • Genetic
  • Rapid growth
  • Ischaemia
  • Nutritional
• Essentially idiopathic
• Failure of endochondral ossification
• Lesions bilateral in 70% of cases but lameness often unilateral, sometimes no clinical signs
• Some authors consider this condition more generalised, in which case e.g. ununited anconeal process would be part of osteochondrosis syndrome

Different manifestations include:

• 1. Osteochondrosis dissecans (OCD):
  • Retained cartilage cores
    • White, wedge-shaped areas of retained cartilage in the metaphysis
    • Clefts -> separation of cartilage from bone -> flaps or free joint mice
    • May interfere with joint function
  • Lysis → bone cysts
  • Focal disruption of endochondral ossification
  • -> Angular limb deformities and degenerative joint disease
  • May be present together with synovitis
  • Predilection sites:
    • In dogs:
      • Proximal humerus
      • Lateral femoral condyle
      • Coronoid process of ulna
    • In pigs:
      • Humeral and medial femoral condyles
      • Anconeal process of elbow
    • In horses:
    • Medial femoral condyle
    • Distal tibia
  • Osteochondrosis dissecans in dogs:
    • Grossly:
      • Lesion in central part of the caudal aspect of developing ossification centre in humeral head
    • Histologcally:
      • Lesion filled with granulation tissue (fibroplasia)
      • Surrounding thickened bone spicules
      • Cap of thickened articular cartilage over the defect
      • -> May fragment - joint mice
      • Calcified cartilage fragments may be in the posterior pocket of joint capsule
        • May grow through synovial fluid nourishment

• 2. Epiphysiolysis
  • Not associated with retention of cartilage
  • Separation of epiphysis from the metaphysis
  • Likely to be due to trauma to degenerated growth plate
  • Possibly the basis of ununited anconeal process and ununited coronoid process in dogs