26.5.4: Osteoarthritis of the coffin joint

Question 1

Signalment for coffin joint osteoarthritis

Answer 1

• Progressive degenerative joint disease so seen in middle to older horses
• Common!
• Coffin joint OA seen in all types of horses
• More commonly affects front feet than hind

Question 2

What is another name for the distal interphalangeal joint?

Answer 2

Coffin joint

Question 3

What is another name for the coffin joint?

Answer 3

Distal interphalangeal joint

Question 4

What is another name for the proximal interphalangeal joint?

Answer 4

Pastern joint

Question 5

What is another name for the pastern joint?

Answer 5

Proximal interphalangeal joint

Question 6

What is meant by ‘high ringbone’ vs ‘low ringbone’?

Answer 6

High ringbone = proximal interphalangeal joint osteoarthritis.
Low ringbone = distal interphalangeal joint osteoarthritis.

Question 7

Signalment for proximal interphalangeal joint osteoarthritis?

Answer 7

• Uncommon
• Seen in heavier breeds: cobs, hunters
• Hind feet more commonly affected than front

Question 8

Predisposing factors to coffin joint OA

Answer 8

Question 9

History associated with coffin joint OA

Answer 9

• Low grade lameness - often bilateral forelimb lameness
• Often insidious onset but can be sudden
• Reduced performance without obvious lameness
• Disease progresses subclinically prior to the development of clinical signs (lameness develops when “threshold” of the disease is reached
• Need to know the horse’s workload, both recently and longer term

Question 10

Clinical exam findings in the horse with coffin joint OA

Answer 10

• Effusion in the coffin joint -> palpate fluid 1cm proximal to the coronary band on the midline
• Careful attention to hoof balance and shoeing: broken back hoof pastern axis; long toe low heel conformation

Question 11

Dynamic exam findings in the horse with coffin joint OA

Answer 11

• Usually sound at walk
• Mild lameness at straight trot -> may be bilateral
• Lameness more obvious on lunge with lame limb to inside of circle (i.e. LF lameness on left rein)
• Worse on hard ground
• Usually moderate positive response to distal limb flexion

Question 12

Which nerve block is shown here and how long will it take to work?

Answer 12

Question 13

Which block is shown here and how long will it take to work?

Answer 13

Question 14

Which nerve blocks might you use to determine if a horse has coffin joint OA and what response would you expect to each of them?

Answer 14

• Partial improvement with palmar digital nerve block. May completely block if there is no pathology on the dorsal surface of the joint.
• Block completely to abaxial sesamoid nerve block
• Block completely to coffin joint block

Next step: radiograph.

Question 15

Which radiographic view is shown here and what features of coffin joint OA can you see?

Answer 15

• Lateromedial view
• Green arrows - sharp spur development of the short pastern and pedal bone
• Blue arrow - irregular, lucent modelling of the dorsal aspect of the short pastern bone at the attachment site of the joint capsule
• There is also foot imbalance to correct here

Question 16

What pathology can be seen here?

Answer 16

Coffin joint OA
* Irregular new bone formation on the dorsal surface of P3
* Possible increased radiopacity palmar and distal to navicular bone - may indicate joint effusion

Question 17

Why might MRI / CT be of benefit in a case of coffin OA?

Answer 17

• MRI / CT not always required to achieve diagnosis
• Will show degree of joint effusion and cartilage degeneration
• Allows diagnosis of additional pathology e.g. oedema in the distal phalanx

Question 18

What options are there for analgesia of coffin joint OA? What are the pros and cons of each?

Answer 18

Question 19

What options for intra-articular medications are there, aside from corticosteroids?

Answer 19

• Hyaluronic acid - lubricant, given with corticosteroids in high motion
• Polyacrylamide gel (Arthromid) - hydrogel filler with cushioning and lubricating effect
• Stem cell allograft
• Platelet rich plasma
• Interleukin 1 receptor antagonist (IRAP)
• Bone marrow aspirate concentrate (BMAC)

Question 20

What are SADMOD?

Answer 20

Slow Acting Disease Modifying Osteoarthritic Agents
* Many exist; evidence lacking
* e.g. oral joint supplements
* e.g. Pentosan polysulphate (Cartrophen)

Question 21

What are the benefits of Cartrophen for coffin joint OA?

Answer 21

Cartrophen = pentosan polysulphate
* Accelerate chondrocyte and synoviocyte metabolism
* Stimulates proteoglycan synthesis
* Reduces MMP production
* Overall: anti-inflammatory and cartilage repair effects

Question 22

What corrective farriery would be suitable for horses with coffin joint OA?

Answer 22

Question 23

Surgical treatment options for coffin joint OA

Answer 23

Question 24

What should you advise the owner about long-term management of coffin joint OA?

Answer 24

• OA is managed rather than cured
• Horses can continue to have happy active lives, but expectation should be reduced
• Workload must be managed
• Be careful what surface the horse works on
• Veterinary treatment and corrective farriery are likely to be ongoing