Page 360 - The Veterinary Care of the Horse

3 POLYACRYLAMIDE HYDROGEL (PAAG)

PAAG has been successfully used to treat human arthritis for years and recent studies have
VetBooks.ir shown encouraging results when used in horses with osteoarthritis. Over time the gel

integrates with the soft tissues but is not absorbed, so has a long-lasting, cushioning effect
within the joint. A study of 43 horses concluded that it alleviated lameness and joint swelling,

with 90% of owners being satisfied or very satisfied with the outcome 2 years after the
treatment was given.

Risks associated with intra-articular injections

• Joint infection.

• There may be a short-term increase in joint effusion and lameness shortly after injection
due to inflammation of the synovial membrane. This is known as ‘post-injection flare’. It

usually resolves in 1–3 days.
• Further damage may occur within the joint as a result of overuse while the horse is under

medication, particularly with corticosteroids.

Regenerative therapies

The problem with degenerative joint disease is that once articular cartilage has been
damaged, it has very little capacity for repair. As a result, a number of new cell-based

therapies have been developed to try and stimulate healing. These include the injection of the
following into the diseased joint:

• Stem cells derived from bone marrow or fatty tissue. These have the ability to develop
into cartilage and aid repair of the joint surface. A commercially available ready-to-use

stem cell preparation was launched for the treatment of mild to moderate degenerative
joint disease in August 2019.

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• IRAP . When a joint is injured a substance called interleukin-1 is released and causes an
inflammatory response leading to pain and lameness. If this continues it can lead to

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ongoing damage to the articular cartilage. IRAP is an abbreviation for interleukin
receptor antagonist protein, an antibody produced by white blood cells that counteracts

this inflammation. A blood sample is collected from the horse and incubated for 24 hours
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to allow the white blood cells to produce increased amounts of IRAP . This is then spun
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in a centrifuge to separate the serum containing the IRAP from the blood cells. The
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IRAP is injected under sterile conditions into the affected joint where it has an anti-
inflammatory action by blocking the action of interleukin-1. It also stimulates
regeneration of the cartilage cells. It may be used in combination with corticosteroids or