Ultrasonograpy of the Equine Foot
ligaments and making subsequent recommendations. It is possible that the combination of ultrasound with other diagnostics results in improved sensitivity and that with improved image quality and feedback from modalities such as MRI we can improve our sensitivity.
HEEL BULB APPROACH
The more distal portion of the DDFT over P2, as well as the collateral sesamoidean ligament (suspensory ligament of the navicular bone), proximal margin of the navicular bone, proximal outpouching of the distal interphalangeal joint (coffin joint), navicular bursa and palmar/plantar aspect of P2 can be seen via the heel bulb approach. A small footprint curvilinear or convex probe is required to fit in the relatively short and narrow depression between the heel bulbs. The majority of the examination is conducted with the probe oriented sagittally (easiest to initially identify structures). However, diagnostic transverse views are possible and should be attempted in all cases. Optimal visualization is obtained when the horse is standing with the forelimb slightly underneath/behind him Visualization and image quality will vary depending on conformation.
The DDFT will be the most prominent structure, and will be visible running distally on the palmar/plantar aspect of the limb, just deep to the skin, subcutaneous layer and portion of digital cushion. It has a reported thickness at this level of .84 cm (Sage and Turner, 2002) The dorsal margin of the navicular bone, when visible, will appear as a short linear hyperechoic echo with a shadow, oriented perpendicularly to the deep flexor tendon. The collateral or suspensory ligament of the navicular bone appears as a short echoic band which can be imaged extending from the region of the navicular bone proximally. It is wider at its base and narrower proximally, resulting in a slightly triangular appearance. It should be followed as far laterally and medially as possible within the window of visualization. It divides two small anechoic fluid pockets, the palmar/plantar being the navicular bursa and the dorsal being the DIP joint. Considerable variation in the normal shape and prominence of the collateral ligament exists between horses, and evaluation of the contralateral limb is recommended in all cases.
Transcuneal evaluation (i.e. through the frog) can be performed on most horses with proper patient preparation. The DDFT insertion, the plantar/palmar border of the navicular bone, impar ligament, navicular bursa, distal recess of the coffin joint and a portion of P3 can be identified.
To begin, the frog should be trimmed so any excess or redundant tissue is removed and the surface is made as flat and smooth as reasonably possible (excluding cleft) to maximize contact. The foot should then be cleaned with a hoof brush and soapy water, then soaked in water in a wrap or foot boot for 30 minutes to 12 hours, depending on situation. The wrap should not be removed until immediately prior to the ultrasound. Depending on foot shape and frog density and dryness, images can be obtained with a variety of probes from a 7.5 MHz linear probe to 3.5 MHz convex abdominal probe. In some horses, images can be obtained without prior foot