Distal tarsal osteoarthritis is known by many different names—bone spavin, jack spavin, blind spavin, juvenile spavin and occult spavin—but regardless of what you call it, the lower hock is the most common site for arthritis in a performance horse.

Several different options for treatment exist, including laser therapy, surgery and—the most recent innovation—ethyl alcohol injections. But how do you choose which one is best for your horse?

The lower hock joints, made up of the tarso-metatarsal and distal intertarsal joints, are low motion joints, meaning that they don’t have to be able to move in order for the horse to perform. However, those two joints take a lot of torque as a result of the work that we ask our equine friends to do. While in some instances, poor conformation, under-conditioning or overtraining are to blame for lower hock pain, in most cases it comes as an aside to a carefully managed training program.

Unlike upper hock joints, which need freedom of movement in order to function, the focus of treating the lower hocks is generating long-term comfort and relief from pain rather than continued motion and flexibility. That is why treating lower hock disease often involves, whether intentionally or inadvertently, fusing the joints in order to relieve the pain.

Searching For Alternatives

James Carmalt, M.A., VetMB, MvetSc., FRCVS, Dipl. ABVP, ACVS, an associate professor of large animal surgery at the University of Saskatchewan (Canada), is currently working with a team of researchers to determine the success of using ethyl alcohol injections in the tarso-metatarso and distal intertarsal joints to relieve the painful effects of osteoarthritis.

“A colleague and I were sitting around in the office one day trying to come up with the areas of research that were most important and needed work done, and we came up with laminitis first, then bone spavin and then colic,” recalled Carmalt, who credits his colleague for the idea to inject ethyl alcohol into the joint.

“I would love to claim ownership for the idea, but it was actually Dr. Ryan Shoemaker who read about spinal cancer treatments in people and noted how ethyl alcohol was being injected into the spines of terminal patients to kill the nerves, allowing people a decent last few months. It was he who pursued the idea.”

In the 1980s and early ’90s, horses with lower hock joint problems were often subjected to injections of sodium mono-iodoacetate (MIA), which was extremely painful. Many of the horses suffered from lameness for 24 to 48 hours following the procedure, and some even experienced severe soft tissue damage and progression of arthritis in the proximal (higher up) hock joints. Shoemaker thought injecting ethyl alcohol into the joints would help fuse the joint without the pain and suffering associated with MIA.

Not long after the research began in 2007, Shoemaker, DVM, MVSc, Dipl. ACVS, went into private practice and left the project with Carmalt, who currently oversees 34 horses, 11 of which were in the original study.

“So far the horses I’ve worked with have only required a single injection, and the majority were sound following the procedure,” said Carmalt. “I remain cautiously optimistic.”

As news of the procedure began to spread, other veterinarians started experimenting with the injections. Scott Ander-son, DVM, used his sister-in-law’s Appendix Quarter Horse for his first patient.

“She had a young horse with arthritis in its hock joints from how they had formed during growth. I’d read about the procedure on paper and wanted to try it,” said Anderson, of Woodside Equine Clinic in Ashland, Va. “Luckily it went well, and she was happy!”

Anderson has seen the most success with ethyl alcohol injections in young horses with juvenile arthritis or with older horses that aren’t responding well to regular injections of steroid or hyaluronic acid.

“Not every horse is a good candidate for ethyl alcohol injections,” said Anderson. “What I don’t want to see is people doing the injection any time or for the hell of it. It’s not for a hock that does well with an injection of HA or steroid once a year.”

As osteoarthritis progresses, it can become increasingly difficult for a veterinarian to get a needle cleanly into the lower hock joints, which is crucial to injecting with ethyl alcohol.

If some of the material were to accidentally work its way up into the upper hock joints, the animal would become permanently lame.  

To avoid the possibility of error, the procedure is usually performed in a clinic setting where the animal is sedated, clipped and scrubbed. The veterinarian then puts a needle in the lower of the two joints first—the tarso-metatarsal joint—and injects radio contrast material that disperses into the joint. Next, X-rays are taken from two different views to make sure the radio contrast material has distributed through the joint, but not into the upper joints of the hock, which would destroy cartilage. Once the veterinarian is sure the needle is in the proper location, he or she pulls the contrast solution out and injects ethyl alcohol into the joint. The process is then repeated with the upper, or distal intertarsal, joint.

“After the procedure, the horse is comfortable right off because the alcohol causes nerves in the joints to die,” explained Anderson. However, the joint does not fuse immediately; it takes an average of three to six months for the joint to start to “spot weld.”

“This is not an immediate fix,” said Carmalt. “I’ve had two clients say their horses were better within 48 hours, but the majority will take about three months to get back to a decent degree of soundness.”

“I’ve followed up with about 25 percent of my patients with X-rays down the road, and what I see is that there are areas where the joint has fused, but not the whole joint. However, it’s enough for the horse to be comfortable. Maybe if I were to X-ray those same horses a year or so later the joint may have fused entirely,” Anderson added.

Exercising Caution

While ethyl alcohol injections may sound like the best lower hock treatment on the market, some veterinarians remain skeptical. Craig T. Roberts, DVM, believes that few horses are good candidates for the procedure and fears that owners may rush into treating their lame companion with the new drug when corticosteroid injections are all that they need.

“The only horses to consider for fusion are ones that have such severe changes that they can’t be managed with steroid injections,” insisted Roberts, referring mainly to horses who had crushed tarsal bones as foals and severely compromised joints. “Most horses with lower hock conditions get five to six months out of the [steroid] injections, and it’s not uncommon for horses to go their entire career with one or two treatments a year.”

And although some horses may need as many as three steroid injections a year, many questions must be asked
before turning to ethyl alcohol. First, it’s important to find out what your veterinarian is injecting into the hock joint. If he or she is only using hyaluronic acid or triamcinolone (Vetalog), then a stronger steroid may be necessary. Also, are both joints (the distal intertarsal and tarso-metatarsal) being injected?

“There is the big debate as to whether these two joints communicate or not,” said Roberts, who sees the majority of his patients in the Ocala, Fla., area. “Studies have been done, but the literature is not definitive on this subject. Rather, it is likely a variance between individuals as to whether these two joints share joint fluid between them. Thus, I inject both joints individually to be certain I am doing the best I can to treat both locations. It honestly seems that some horses only injected in the tarso-metatarsal joint don’t get as good as or as long a response as those injected in both joints.”

Roberts added that it’s a rare case of lower hock arthritis that can’t be managed with steroids. “I would caution people to get a second opinion if they are being told their horse has severe radiographic changes and may require more aggressive therapy than the standard,” he said. “I review lots of cases where a horse has been diagnosed with severe changes, and upon review their films are not all that bad. Somewhere down the line there’s been more of an exaggeration as far as the severity of the condition.”

And just as not every human responds in the same way to pain, neither does every horse. Some may show no radiographic changes in their hocks, but respond well to injections, while other horses may show changes in films, but aren’t clinically bothered.

This is partly because the hock is not a high-motion joint. Along with the pastern joint and certain joints in the neck, the lower hock doesn’t have to move in order for the horse to be an athlete. However, once pain and inflammation have set in, medical intervention is almost always necessary to keep the animal operating at its peak level of performance. But the selection of medications to manage arthritis in a low motion joint is not governed by the same decision making process of high motion joints.

“Interestingly, we sold the idea for 40 years that steroids were bad for joints, which is not entirely true. The benefits of steroid therapy in joints can be tremendous for their long term care, used judiciously,” Roberts said. “Similarly, the radio-graphic changes seen in lower hocks do not always correlate with the amount of clinical discomfort a horse may have.”

He said horses with changes in the lower hocks at 4, 5 and 6 years will have the same radiographic changes when they’re injected later in life.

“Similarly, initiating steroid injections in lower hock joints does not necessarily mean your horse will have greater problems later in life,” Roberts said. “If anything, addressing the inflammation early often slows the joint’s deterioration. People say they don’t want to start injecting a younger athlete. However, if the clinical concerns are there, at any age, treatment is advisable. Being a bit of a comic, I often say, ‘Well, when your horse is old enough to be sound, give me a call.’ ”

So what makes Roberts so wary of treating lower hock pain with ethyl alcohol?

“With ethyl alcohol, you are working to accelerate the arthritic process and destroy the joint cartilage in order to try and fuse the joint,” he explained. “If it completely fuses the joint, great, it might make the horse more comfortable. But, if you only get half the joint fused, then you make the problem harder to manage with other treatments. At the end of the day, there aren’t a lot of horses being retired because their lower hock pain can’t be managed. The bigger picture should be to question the medications and techniques being used.”

Surgical Options

If joint injections are no longer working and ethyl alcohol seems too risky, there’s always the option of surgery to help get your horse back on track. While many different surgical techniques exist, intra-articular drilling is one of the most widely used.

Surgical drilling involves making a small incision through which the cunean tendon is cut. The surgeon then takes a drill and, with X-ray control, drills three different paths through each of the distal intertarsal and tarso-metatarsal joints to a depth of approximately 3 centimeters. The goal of the tracts is to remove cartilage from opposing joint surfaces, which allows bony union to prevent motion of the joint, thereby decreasing pain.
John Madison, DVM, dipl. ACVS, uses the surgical drilling technique on several equines a year and finds that in most cases, horses are sound following the rehabilitation period.

“I generally tend to perform surgery on the horses [on which] injections don’t last long anymore,” said Madison, referring to horses who are injected three, even four times a year. “It becomes difficult to get in the joint when you’re injecting them repeatedly. Just from a purely financial standpoint, if you’re injecting a horse four times a year, then it’s worth doing surgery at that point.”

An average rehabilitation period is about six weeks, during which the horse is confined to stall rest. Following the short recovery period, most horses can go back in light work, although they may need the help of an anti-inflammatory such as phenylbutazone. By six months, however, the horse should have made a full recovery.

“Radiographically, these joints don’t look much different than normal joints even though they’re functionally fused,” said Madison. “A lot of times you can’t tell, even several years later, especially if the joints were fairly normal on X-rays before the surgery.”

Another surgical option for treating the lower hock, which is much different than drilling, is using a laser to facilitate arthrodesis (fusion) of the distal tarsal joints. The technique involves placing a laser fiber into the dorsomedial (meaning inside and toward the front) aspect of the joints while another needle is placed at a distant location to serve as an egress for smoke produced by the laser. The goal of the procedure is to boil the synovial fluid until it vaporizes, thus causing chondrocyte death and a collagen shift in the joint capsule and intertarsal ligaments before leading to the eventual collapse and fusion of the joint.

And while laser-facilitated arthrodesis may sound uncomfortable, postoperative pain is minimal. This is likely because the superheating causes thermal damage to nerve endings and diminishes the perception of pain. In addition, the laser seals small blood vessels during the surgery, resulting in decreased bleeding and minimal post-operative swelling.

 Chad Zubrod, D.V.M., M.S., dipl. ACVS, has been performing the laser surgery since 2000. “I don’t think the initial costs to laser as opposed to surgical drilling are that much different. I’m not much of a surgical drilling fan because the horses don’t get sound as quickly after the surgery as I would like them to. To me the financial advantage to laser comes in because you’re able to use the horse sooner after the surgery.”

This is in part because a decreased amount of inflammation in the bone and soft tissues results in faster healing of tissue, which in turn leads to a faster return to use. On average, horses that have laser surgery are back under tack in two months and in full work by four months.

“I do find that the horses get pain relief before the joints are ankylosed,” said Zubrod. “I’ve had about an 80 percent success rate with the procedure. There’s always the possibility of complications, such as infection, as there are for all techniques, as well as the possibility of skin necrosis from heating around where the laser goes in, but neither of these are very common anymore.”

Nowadays, Zubrod performs fewer laser-facilitated hock surgeries out of the Oakridge Equine Hospital in Edmond, Okla., than he did five years ago. That’s not to say that the laser isn’t effective, but not every horse is a good candidate for the procedure.

“I’m not jumping to do the laser surgery,” admitted Zubrod. “I don’t think that even though it sounds appealing never to have to inject again that it’s always the best option. Everything has a risk associated with it—the risk of fusing and the stresses associated with it aren’t without possible complications because you’re essentially changing the biomechanics of the leg. We’ve backed off on how quickly we recommend surgery to our clients. Still the safest and most effective way to treat the lower hock is by injecting a steroid and not by jumping to any form of ankylosis until you no longer get a response from the steroid.”