Joints Developmental - Pathology

()Map MUSCULOSKELETAL SYSTEM (Map) JOINTS

Hip dysplasia

• Mainly large and giant dog breeds, especially with stocky conformations
• Seen in cattle - Herefords
• Subluxation of hip joint due to maldevelopment
• Not present at bith
• Inherited + environmental factor involvement (nutrition, exercise)
• Pelvic muscles are behind the bone development in rapidly growing dogs -> lack of restraint of the joint -> excess movement before acetabulum is fully mature
• Usually develops within first 6 months of life
• Varying degrees of severity
• Pathogenesis:
  • Joint laxity / acetabular dysplasia
  • -> Flattened femoral head +/- mild or severe periarticular osteophyte formation
  • -> Thickening of femoral head + degeneration of articular cartilage
  • Eburnation
• Predisposes to DJD
• Round ligament of femoral head may rupture -> luxation

Elbow dysplasia

• = Ununited anconeal process
• In dogs, especially German Shepherd Dogs, St. Bernards, Labradors
• Occurs during first few years of life
• Failure of anconeal centre of ossification to unite with the ulna
  • Normally, they unite between 4-6 months of life
• May partially or totally separate from each other
• Intra-articular irritation -> DJD with osteophyte formation within the joint

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

Arthrogryposis

• Persistent congenital flexure of a joint in conjunction with muscle contraction
• Caused by:
  • Inactivity or paralysis in utero
  • Spinal dysraphism
  • Intrauterine viral infections
  • Toxic plants (poison hemlock, lupine)
  • Cause persitent contraction of uterus -> fetal compression
• Arthrogryposis and palatoschisis in Charolais cattle