Identifying the exact source of trouble in the stifle may not be a simple process.

If you know that your horse has been kicked or has hit a fence hard on cross-country, diagnosing a stifle problem shouldn’t be a problem. But stifle injuries may involve soft tissues, the bones, or both—which can sometimes make diagnosis and treatment challenging.

Rick Mitchell, DVM, of Fairfield Equine Associates in Newtown, Conn., said that in most athletic horses, hind limb injuries more commonly involve the hock and suspensories rather than the stifle.

“But the stifle should always be considered when diagnosing a serious hind limb lameness,” he said.

The stifle is a large, complex joint composed of four bones, two menisci (crescent-shaped discs of fibrocartilage attached to the joint surface) and 14 ligaments. It is one of the strongest and most well-supported joints and is actually three separate joints—the medial femoro-tibial joint, the lateral femoro-tibial joint and the femoro-patellar joint. The stifle also has three distinct joint compartments filled with lubricating fluid.

Is It The Stifle?

One of the classic signs of stifle lameness is a shortened anterior phase of the stride. “The horse may or may not demonstrate a mild toe drag. In severe cases the horse may appear to be on the toe, unwilling to put the heel down—meaning he doesn’t want to extend the leg,” said Mitchell, explaining that the horse is trying to protect the joint by keeping it flexed.

“Some horses with more subtle stifle lameness merely have a reduced willingness to bend toward the affected side. They lose suppleness and flexibility on that side. Additionally they may have an irregular or roughened canter, more often when moving away from the affected side,” he added.

The horse may demonstrate back and croup soreness, including discomfort and sensitivity while being groomed and saddled. “All of these signs are non-specific for hind limb lameness; none are truly specific for the stifle,” Mitchell said.

Without the presence of a known injury like a kick or some other type of blow to the joint, and without the presence of severe swelling/enlargement and sensitivity at the stifle, the only way to be sure the stifle is the site of injury is to eliminate other causes of lameness.

When evaluating a lame horse, Mitchell almost always wants to see it work under tack. “This is a big aid. Working under tack may sometimes accentuate lameness, and it can also help us learn a great deal more about the lameness. You don’t need to do this with every hind limb lameness, but it’s a valuable tool. There are a number of horses that you must see working under tack in order to determine level and type of lameness,” he said.

Certain flexion tests can guide a vet to the appropriate joint, but the hoof and lower leg must first be eliminated as the source of lameness through nerve blocks. “Then you are centering on the stifle as a likely cause,” said Mitchell. “In a more specific examination you can do joint articular blocks on the stifle itself to determine the source of lameness.”

Ultrasound and radiographs can help the veterinarian pinpoint and evaluate the area of injury, but it’s important to first try to narrow it down and localize it, as with nerve blocks.

Once the stifle has been determined to be the problem, X-rays may be taken of the joint to rule out cyst formation, fracture, osteochondral fragmentation or chronic arthritis.

“If the horse has had problems for a long time, with arthritic changes, this can be determined with an X-ray,” said Mitchell.

Soft tissue inflammation or damage, however, won’t show up on radiographs, so this emphasizes the need for careful examination and comparison to the other joint. Blocks within the joint, to eliminate lameness, and then ultrasound as a means of evaluating the joint, can be more helpful than radiographs if it’s a soft tissue injury.

“In this day and time, it’s becoming increasingly important to consider using ultrasound examination of the joint. Not every veterinarian has the technical expertise to do this. With a stifle injury, the owner or trainer of the horse needs to request consultation with a veterinarian who possesses expertise in examining this joint,” said Mitchell.

“With ultrasound you can look at a number of the ligaments, the medial andlateral menisci, the synovial membranes, the surface of the end of the femur, etc. This can rule in or rule out soft tissue problems,” he added.

This technology might help determine a treatment plan that could include injecting the joint.

Treatment Options

“If there’s no evidence of radiographic abnormality and lameness has been located accurately to the stifle joint and is a grade 2 or less, I don’t think it’s irresponsible to go ahead and treat the horse—and just assume it’s a soft tissue injury. It can be treated with an intra-articular injection and systemically with anti-inflammatories to try to reduce the inflammation,” Mitchell said.

If it is indeed a soft-tissue injury, this may be all the treatment that’s needed. Sudden lameness with joint swelling often responds to rest, cold therapy (ice or cold water hosing), systemic use of non-steroidal anti-inflammatories such as phenylbutazone or topical anti-inflammatory medication.

“In the event it fails to respond to anti-inflammatory therapy or responds temporarily, followed by return of lameness, then you need a consultation—realizing that the horse might need surgery. It is best, however, if you can try to determine the first time around, if possible, what is actually going on in the joint. In any event, if the horse responds to therapy with a return to lameness, don’t just keep treating it. Go a little farther with diagnostics to try to figure out exactly what’s going on,” he said.

Arthroscopy is the gold standard for determining what’s going on in the joint. “It’s the only way to definitively determine what’s in there—short of doing a postmortem examination,” said Mitchell.
Thus arthroscopy must be considered as a diagnostic as well as a therapeutic tool.

“My philosophy is that if you’ve identified a stifle problem and ruled out gross soft tissue abnormalities (the problem is not apparent on ultrasound), you’ll treat the joint, and if it does well, that’s the answer. If the horse responds well but subsequently becomes lame again, it’s a candidate for arthroscopy,” he said.

Most of the things your veterinarian will look for with arthroscopy in a sport horse—especially a middle-aged sport horse—involve soft tissue problems. These include damage to the articular cartilage, damage to the menisci, and/or damage to the ligaments that support the joint.

“If we can identify the area of damage, it’s possible to sometimes treat or modify those tissues by cleaning up the debris and the injury by trimming the torn ligament or trimming and cleaning up the torn meniscus just like we do in human knee surgery. You take the irritating things out of there,” said Mitchell.

What the veterinarian finds in the joint and how it is cleaned up (how much debris or damaged tissue must be removed) also determines how much recovery time the horse will need.

After diagnosing and possibly deciding upon arthroscopy, this must all be put into perspective regarding the age of the horse.

“Is this a young horse, or is he 19? Where are we, in trying to salvage the athletic future for this horse?” asked Mitchell. “What level of work can he be returned to? This determination may also depend on how long he’s been lame. If he’s been lame a short time, the older horse may merely have a soft tissue injury that’s just as easily repaired as in a 4-year-old.”

In addition to the surgeries being done, there is also some work now involving stem cells placed in the joint to encourage healing of the damaged tissues after they are cleaned up. Another alternative to injecting the joint with corticosteroids and/or sodium hyaluronate is use of autogenous conditioned serum. This is a commercial process, referred to as IRAP (interleukin receptor antagonist protein).

“This is used as an anti-inflammatory,” said Mitchell.

The horse’s own blood is utilized to make the serum, and then multiple injections of the ACS are put into the joint over several weeks.

“By treating the blood in an incubator in a specially treated syringe, white blood cells are stimulated to produce interleukin receptor antagonist protein and a whole soup of cytokines—which are cellularly active substances. These inhibit inflammation and stimulate repair and healing. Some of these cytokines, because they are growth factors, may also have a stimulatory effect on healing. This is very new and we don’t yet know the full effects of all of these substances, but it is a commercially available therapy,” said Mitchell.