- 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
- In dogs:
- 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
- Grossly:
- Retained cartilage cores
- 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