Osteoarthritis

Question 1

What are the 2 pathways for osteoarthritis?

Answer 1

• one involved abnormal stresses on normal cartilage and the other involves normal stresses on abnormal cartilage
• both pathways can be triggered by repetitive trauma, resulting in either cartilage damage or bone microfractures
• in young horses, OCD results in abnormal cartilage, including thinning, and micro fractures, and in old horses the cartilage begins to degenerate and lose its elasticity
• abnormal stresses occur with some diseases, including articular fractures and collateral ligament injuries
• the end result of both pathways is the same: degradation of proteoglycans and collagen, and reduced synthesis of the matrix
• this weakens the cartilage and causes inflammation, continuing the cycle

Question 2

Clinical signs of OA

Answer 2

Varying levels of severity/tissue involvement
- synovitis
- partial thickness cartilage erosions
- full thickness erosions
- subchondral bone lesions
- peri-articular new bone
- peri-articular soft tissue damage (including collateral ligaments)
- peri-articular fibrosis
- joint ankylosis

Question 3

OA CS - what is different in the horse to other species?

Answer 3

• high motion joints such as the DIPj, fetlock, tarsocrural and stifle joints can be significantly affected by mild dz and can have a poor prognosis for return to function
• small changes, e.g. small osteophyte formation can be clinically significant in high motion joints
• low motion joints such as PIPj and distal tarsal joints can sometimes tolerate quite significant changes, but unpredictable -> severity of radiographic signs doesn’t always relate to severity of CS
• radiographic signs in low motion joints can include lysis, new bone formation and ankylosis, and can look quite aggressive

Question 4

Use of joint fluid analysis for OA in horses

Answer 4

• not often that helpful
• protein levels may be normal or slightly increased, same for cell count
• the main changes seen usually relate to viscosity