Equine Science Update
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Comparing navicular therapies.
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Which treatments for navicular syndrome are effective? Many different therapies have been advocated. A recent study assessed the value of three commonly used treatments.

Dr Mike Schoonover and colleagues at the Oklahoma State University `s College of Veterinary Medicine have been evaluating heel-elevation shoeing, phenylbutazone administration and the injection of corticosteroid into the distal interphalangeal joint (coffin) joint.

Navicular syndrome is a chronic forelimb lameness associated with pain in the navicular bone or closely related structures. In the past it has been thought of as a single disease. In fact it probably includes a number of different conditions. It is typically insidious in onset, often affecting both fore feet.

In the past the response to treatment has been assessed largely by subjective means. Now, quantitative gait analysis techniques allow a more objective assessment to be made.

Dr Schoonover and his colleagues used force plates embedded in the ground to measure the peak vertical ground reaction force (PVGRF) - the force generated as the foot hits the ground. Lame horses strike the ground with less force than normal. To take the weight of the horse into account they expressed the PVGRF as a percentage of its body weight (%BWF). The more lame the horse, the smaller the %BWF.

Twelve horses chosen for the study showed lameness of both forelegs, associated with pain in the heel area. The lameness improved after blocking the nerves that innervate the palmar third of the foot. Changes typical of navicular syndrome were present on radiographic examination. Each horse had been lame for between 1 month and 2 years. At a pre-treatment assessment they identified the foreleg with the lowest %BWF, which they called the lame leg. This was the leg that would be treated with the triamcinolone injection.

Three treatments were used in sequence:

3° heel elevation shoes only.

Wide web aluminium horseshoes with a 3° wedge were nailed on after trimming and balancing the feet. The shoes decrease tension in the deep digital flexor tendon, reducing pressure on the navicular bone. They provide extra support to the heels by extending the shoe wide at the quarters and further back at the heels.

3° heel elevation shoes + phenylbutazone (PBZ).

Phenylbutazone is a commonly used non-steroidal anti-inflammatory drug. Horses were given 4.4mg/kg by intravenous injection twice daily for 5 days.

3° heel elevation shoes + intra-articular cortisone.

Triamcinolone acetonide (6mg) was injected into the distal interphalangeal joint.

3° heel elevation shoes +PBZ + intra-articular cortisone.

Finally they assessed the effect of all three treatments together.

Three horses improved 24 hours after the heel elevation shoes had been applied. However there was no improvement in the group as a whole. Indeed some horses had lower %BWF values - they were actually lamer. But after 2 weeks, there was a significant improvement in lameness in both fore feet. Dr Schoonover points out that this indicates the need for a period of adaptation after therapeutic shoeing for the full benefit to be realised.

Further improvement was seen after phenylbutazone administration. There was a significant increase in the %BWF of the lame fore leg in eight horses, indicating that the lameness had improved. The opposite foreleg showed a slight improvement in five horses.

When the results for all twelve animals were considered together, triamcinolone injected into the DIP joint gave no additional benefit over heel -elevation shoeing. However, six horses did show a significant improvement after triamcinolone. So joint injection combined with heel elevation may help individual horses.

Dr Schoonover concludes that 3° heel-elevation shoeing, alone or with phenylbutazone, may reduce the lameness of horses with navicular syndrome. However, he concedes that some horses will not respond and may require other treatments such as different shoeing techniques, or injection of the navicular bursa with corticosteroids or hyaluronate.

For more details see: Quantitative comparison of three commonly used treatments for navicular syndrome in horses. Mike J Schoonover, Henry W Jann, Margaret A Blaik. Am J Vet Res. (2005) 66, 1247 - 1251.
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