New Navicular Bursa Injection Technique Validated
Horses with chronic navicular pain might benefit from analgesic (pain-relieving) injections in the navicular bursa, a tiny space nestled between delicate structures within the hoof. But getting a needle into that space can be tricky. Not only do veterinarians need to hit the right—and very small—spot but they also need to avoid hitting other structures to get to it.

A new ultrasound-guided technique, however, is showing promise, said Knut Nottrott, DVM, of the Pole Equin at VetAgro Sup in Marcy L’Étoile (Equine Teaching Hospital of Lyon), in France.

Currently, practitioners take one or more X rays during needle positioning to check needle placement before injecting. Despite the common use of ultrasound guidance in other needle placement techniques, traditionally this modality hasn’t been useful for visualizing within the hoof because the wall blocks the ultrasound waves, Nottrott said. So radiography has been the imaging technique of choice.

Scientists recently tried a new technique, however, by first placing the hoof in a 60° flexed position—a navicular or Hickman block position (a special block in which the horse rests a hoof while the veterinarian takes a navicular bone X ray). Then by accessing the foot laterally through the tissue above the hoof on the side, the scientists were able to “see” the needle via ultrasound entering the navicular bursa without interference from the hoof wall. This led not only to successful injection but also to reduced risks for both horse and veterinarian.

“By eliminating the need for radiographic control of needle position used in current techniques, we are no longer exposing staff to the radiation,” said Nottrott. “Plus, the ultrasound technique requires less repositioning of the needle and would theoretically take less time than an X ray-guided technique, meaning reduced risk of infection and probably lower levels of stress for the horse.”

It also means avoiding trauma to the deep digital flexor tendon (DDFT), he added. Efforts to reach the navicular bursa through the back of the pastern (to avoid the hoof capsule) require passing the needle through the DDFT.

Nottrott and his fellow researchers tested the technique using cadaver forelimbs placed in the flexed position. They then used an ultrasound probe positioned just below the fetlock to guide the needle placement into the navicular bursa in 62 hooves. To test their correct needle position, they injected the tissue with a radiocontrast agent and then verified that agent’s placement using radiographs.

Then, they carried out the same procedure in 26 live horses’ forelimbs (52 injections).

In the cadavers, they also injected a second agent—methylene blue—as they pulled the needle out of the foot. This allowed them to trace the needle’s pathway when they opened the cadaver hoof to explore the effects of their work.

They successfully placed the contrast agent into the navicular bursa in 91% of the 114 total limbs; in 78% of the cases, the agent made it to the navicular bursa alone without affecting other structures, Nottrott said. When they didn’t get the agent into the navicular bursa, it was usually related to a poor ultrasound image, he said.

The technique described in a 2013 study that also aimed for a lateral approach to avoid the DDFT had good results, but requires multiple X rays to check the needle position.

“That study showed that repositioning the needle is required several times (three times per horse on average), and a radiographic contrast medium has to be injected each time to be visualized on a ‘one-moment’ X ray,” he said. “This means that several X rays need to be taken before the navicular bursa is reached successfully, which exposes the staff to radiation. The frequent repositioning of the needle might cause trauma to surrounding soft tissues.”

With the ultrasound-guided technique, the practitioner can follow the needle on the screen in real time, so needle repositioning is less frequent—an average of 1.1 times per horse in the current study, he said.

“So, this could further minimize inadvertent tissue trauma, and no contrast medium needs to be injected to localize and verify the needle tip within the navicular bursa,” he added.

To succeed in reaching the navicular bursa via ultrasound, practitioners must recognize the importance of good hoof positioning, correct transducer (ultrasound probe) alignment, and competent anatomic structure knowledge, all of which are essential for success, he said.

Now validated, the technique is currently used on a regular basis at the Equine Teaching Hospital of Lyon (Clinéquine, VetAgro Sup) in Lyon, France, Nottrott said.

The study, “An ultrasound-guided, tendon-sparing, lateral approach to injection of the navicular bursa,” was published in the Equine Veterinary Journal.