The ability to accurately locate and inject the cervical vertebral facet joints, the joints that lie between the transverse processes of the vertebrae, has significant advantages, including the performance of regional nerve blocks and intra-articular (within the joint) injection treatments. Unfortunately, unlike humans, horses don’t have readily palpable cervical facet joints. Therefore, intra-articular facet joint injection requires guidance of an imaging system such as ultrasonography. Reports of its accuracy for this use in horses are lacking. Therefore, researchers at the Royal Veterinary and Agricultural University of Copenhagen in Denmark, including Lise Berg, DVM, and J.V. Nielsen, DVM, conducted a study to determine the accuracy of ultrasound-guided intra-articular injection of cervical facet joints in horses. They wanted to estimate the factors that influence accuracy.

Two operators with no previous experience in either ultrasound-guided procedures or cervical facet joint injections performed the procedures. Eight cadaver necks with intact cervical vertebrae from C2-C7 were used. The facet joints were localized using a 5 MHz curved linear array transducer with or without a needle guide attachment. “Both options were tested in case the needle attachment increased our success with injections,” explains Berg, “But we found it was just as easy to work without it.” A 14-gauge needle was inserted, the joint capsule penetrated, and a mixture of dye and gel injected. The joint was immediately dissected to check dye placement.

Results indicated that 72% of injections were intra-articular as intended. Moreover, as both operators gained experience, the percentage of intra-articular injections increased, with some necks having 92% accurate intra-articular injections. Obviously, it is difficult to extrapolate data from cadavers to live horses, and to predict how a live horse would tolerate the procedure. Berg expresses concern about the practicality of heavily sedating a horse for this procedure. This might “mask pain and make injection results difficult to interpret.” However, Berg says mild sedation might ease the procedure “by helping the horse stand still and allowing for manipulation of the neck into the optimal position for injection.” In addition, “A small amount of local anesthetic at the site of the injection might ease the procedure, as long as injection depth is adjusted so relevant structures aren’t influenced.”

Berg is currently working on her PhD, and she is involved in stem cell research focused on equine cartilage biology with hopes of moving into the area of emerging gene therapies