Once a diagnosis of a problem with the navicular bone, the deep digital flexor tendon or one of the other soft tissue structures associated with the navicular bone is made, one of the treatment options is to inject the navicular bursar with cortisone as an anti-inflammatory. The navicular bursar is the fluid filled pouch between the navicular bone and the deep digital flexor tendon.
The procedure involves injecting with a long needle between the heel bulbs, through the deep digital flexor tendon and into the navicular bursar. This is best carried out under x-ray guidance. First of all a radiograph is taken of the foot with a marker that shows up on the image, to identify the exact location of the navicular bone within the hoof, a mark is made on the hoof wall with a marker pen to be used as an aiming marker for the needle advancement. Often a nerve block will be placed at the palmar digital site to totally desensitise the heel region of the foot, sometimes just the location of the injection site is desensitised with local anaesthetic.
Once the injection site is desensitised the heel region is meticulous cleaned and then aseptically prepped. A 10cm spinal needle with a stylet is placed through the skin between the heel bulbs and advanced towards the navicular bone, roughly parallel with the ground, using the marker on the hoof wall as a guide to the angle of approach. As the needle is advanced it is possible to gently feel it contact the back of the navicular bone. At this point a second radiograph is taken to make sure the needle placement is correct. If the needle is in the right place behind the navicular bone and through the deep digital flexor tendon, then the stylet is removed from the needle and the cortisone is injected into the bursar. Mixed in with the cortisone is a radiopaque substance which shows up on x-rays, a third x-ray is taken to demonstrate filling of the drug within the pouch at the back of the navicular bone and therefore the drug within the navicular bursar, after the needle has been removed.
Following injection the heel region is bandaged to keep it clean for 24 hours. The patient is kept box rested also for the first day after the injection, then hand walked for a further 2 days, followed by an ascending exercise program dependent on what the actual diagnosis was.
It is important that this procedure is carried out as aseptically as possible as to avoid the introduction of infection into the navicular bursar. It is also important to be as accurate as possible with the needle placement, if we know from the series of images obtained that the needle was correctly positioned and that the cortisone was injected into the navicular bursar, then we know if the horse does not become sound it was not due to inaccurate drug placement and that a different treatment option is required.
Navicular bursar medication is only one treatment option available to us for the treatment of navicular disease syndrome. This technique should be used in conjunction with other medications such as Tildren (Equidronate), aspirin, isoxoprine, etc. Probably the most important aspect of treatment is the farriery and obtaining a correct and appropriate foot balance.
Dr. E.A.Lyall, BVetMed, CertEM (StudMed), MRCVS