Diagnosing Equine Shoulder Pain

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Sometimes perceived shoulder pain is a symptom of real pain elsewhere.

In a series of 59 horses presented to a specialty orthopedic referral clinic for suspected shoulder problems, only half actually turned out to have pain in the shoulder area. Severe pain in the lower leg, usually foot-pastern-ankle area, is often misinterpreted as shoulder pain.

This is either because the owner or trainer sees that the horse is unwilling to bring the leg forward freely, or because the shoulder area muscles are tense. Shortening of the stride is typical for any cause of pain in the lower leg. The tightness of the muscles comes from is involuntary splinting against the pain.

Reliable signs of possible shoulder problems include:

• Pain when placing pressure in the shoulder area.

• Swelling in the area of the joint.

• Pain when the shoulder is pulled forward, back or out away from the body without flexing the joints of the lower leg.

• Reluctance to advance the leg. In extreme cases, this will be obvious if the leg is brought any farther forward than the neutral, standing position. In others, the horse will move the leg forward but feel the pain when the leg is in motion off the ground and will put the leg down earlier than normal, without finishing the full stride.

• When pain is felt on elevating the leg, the horse may swing the leg in an arc to the outside to advance it, rather than straight up and forward. This type of gait abnormality needs to differentiated from knee pain, which often causes the same thing.

• With chronic cases, you may see atrophy of the chest and shoulder muscles, as well as an upright and smaller foot on the involved side, but these are not specific.

• Failure of the lameness to improve with local anesthetic blocks to the knee and lower legs.

• Improvement of the lameness .with local anesthesia to the shoulder area.

Those last two items may seem pretty obvious, but it can’t be emphasized enough that in many cases it’s absolutely imperative to use diagnostic local anesthesia to locate the problem area. It’s one thing if you have a hot, swollen, obviously tender shoulder or lower leg, but often that’s not the case. Painful hoof problems and even nondisplaced fractures elsewhere on the leg may show little in the way of outwardly visible signs.

Types of Problems

Actual arthritis in the shoulders is rare. Ponies and miniature horses may be born with shoulder dysplasia, similar to hip dysplasia in dogs. Like the hip, the shoulder is a ball and socket joint. A large knob of bone on the top of the humerus (upper arm bone) fits into a cup on the lower edge of the scapula (shoulder blade).

With dysplasia, the cup is shallower and flatter than normal. This conformation can lead to anything from arthritis caused by the head of the humerus having more motion than normal inside the joint, to actual dislocations. This causes a severe lameness that is sometimes treated surgically by putting plates and screws or nails across the joint to prevent movement. These animals are then usually pasture or breeding sound (although since it is likely genetic they really shouldn’t be bred).

Shoulder arthritis in full-sized horses is not of the ”wear and tear” type we run into in other joints. Infectious (septic) arthritis can occur following puncture wounds. Arthritis may also develop as a result of osteochondrosis dessicans, a developmental bone disease where the transition zone between bone and cartilage is abnormal. As a result, cysts may form in that area, or sections of cartilage that are loosely attached can become cracked, form flaps or even break off into the joint. The irritation caused by the unstable cartilage eventually results in arthritis, although the osteochondrosis itself is often painful enough that the diagnosis is made before arthritis even develops.

Damage to the joint from septic arthritis is often quite severe, and the prognosis is poor, but treatment may be attempted by flushing the joint and treatment with antibiotics, both directly in the joint and systemically. Left untreated, the prognosis for osteochondrosis in the shoulder joint is also poor and progression to arthritis is expected, although horses with only minor changes may improve to some degree with time and be used as pleasure horses.

Arthroscopic surgery to remove any abnormal cartilage is the treatment of choice. In one series of 15 cases with relatively minor (but painful) lesions, 12 returned to athletic use. Prognosis is worse for horses with lesions in more than one spot in the shoulder, or those that are already developing arthritis. With or without surgery, other customary treatments, such as Adequan or Legend systemically, and local injections of hyaluronic acid, may also be recommended.

By far the most common cause of shoulder pain is injury to the soft tissues of the shoulder. A large bursa, the bicipital bursa, sits between the two prominences of bone on the humerus, and the tendon of the biceps muscle runs over the top of this. The tendons of the supraspinatus and infraspinatus muscle insert in the shoulder region, with another bursa located under the tendon of the infraspinatus muscle.

Any of these structures, as well as the bone to which they attached, can become inflamed or torn and cause pain. The biceps bursa and tendon, located at the point of the shoulder, are the most frequently involved. Injuries occur when the leg is behind the horse and the shoulder joint is trying to flex to bring it forward. Horses going up hill, on slippery ground, or wearing shoes that don’t provide good ground traction are most at risk, as are horses making many sharp changes of direction at speed, and horses that are working in harness and pulling weight rather than being ridden.

Because the bicipital bursa is the most commonly involved structure, it’s fairly common practice to inject this structure with cortisone or another corticosteroid as the first step in treatment of horses with easily detected pain on palpation around the scapula. If all goes well, this injection coupled with rest is usually successful.

However, ultrasound of the shoulder area as a first step will guarantee that the problem actually is located in the bicipital bursa, and the examining veterinarian can also use ultrasound as a guide to guarantee the steroid is being deposited where it should be. Horses that aren’t examined by ultrasound first and do not have as good a response as anticipated to the steroid injection should really be ultrasounded before being injected again. Tendon tears also cause heat and pain. This is a more serious injury that requires more time to heal, and repeated steroid injections will only slow that healing.

In addition to the prescription drugs and specific treatments your vet will do, there are many ways you can help your horse recover from a shoulder problem.

Ask your veterinarian to be very specific about time frames for rest, when your horse can have hand walking or turn out, and how much.

Use anti-inflammatory/pain-relieving drugs to get g ood control of initial inflammatory reactions but think long and hard about long-term use. They control symptoms but can interfere with true healing and lead to the horse doing more than he should for the stage of healing.

• Ask your vet for a general scheduled of ”land marks” your horse should reach at various stages of healing. Find out when you can expect heat/swelling to be gone, when you can stop pain and anti-inflammatory medications, how comfortable you can expect the horse to be.

Also establish guidelines regarding when it is advisable for the horse to be examined again, both routinely to monitor progress and what are the red flags that mean things may not be going as they should.

• Use cold and heat therapy to minimize the amount of drugs you need. The shoulder is a difficult area to treat without actually standing there and holding things in place, but investing in an Stretchies Shoulder Guard ($38.95, www.valleyvet.com, 800-419-9524) allows for hands off treatment.

These are stretchable Spandex and nylon front-end protectors with a yolk that extends between the legs. They will hold your hot or cold packs in place and provide gentle support.

The gel packs that can be used both warmed or cold are about $8 each for the individual, reuseable packs (MacKinnon, www.mackinnonicehorse.com, 800-786-6633).

In general, cold should be used for as long as there is obvious heat and inflammation in the area, as well as for an hour or so after exercise when rehabilitation begins. Use a 30- to 60-minute heat treatment before exercise, and several times daily after the acute inflammation has calmed down.

• Once approved by your vet, gentle stretching exercise to the front and back, after a heat treatment, can usually begin after the acute inflammatory stage is over. These can often begin before the horse is released to walking and are a good warm-up before the horse leaves the barn.

• Our choice for a nonirritating, anti-inflammatory and analgesic liniment is Equilite’s Sore No-More, (www.equilite.com, 800-786-6633, $16.95/16 oz.). This product is safe to use with hot or cold, under the shoulder guard, and won’t damage fabrics. Use along with cold therapy after exercise sessions to help prevent any back sliding.

• If the problem involves the shoulder joint itself, you can supplement with joint nutraceuticals as you would for any other joint problem.

Hyaluronic acid gel is our favorite performer for active inflammation, with Conquer Gel leading the pack (Kinetic Technologies, www.kinetictech.net, 877-786-9882). The liquids, with Equi-Aide’s Lube All Plus (www.equiaide.com, 800-413-3702) a favorite, also work well. Use until the acute problem quiets down, then go to your favorite joint supplement.

• Soft-tissue problems like bursitis and tendon/muscle injuries do not respond to joint nutraceuticals. Heat/cold can provide safe symptomatic release, while stretching, controlled exercise and (most importantly) time will eventually bring true healing.

There is also a growing body of controlled experimental evidence that low level laser therapy speeds early stages of healing, improves strength and improves ultimate functional outcome in tendon injuries.

Wavelengths of from 648 to 904 nm have been effective, at low to moderate dosages of 1 to 5 joules/cm2. True lasers are required for this, since light therapy equipment using only LEDs (light emitting electrodes) will not penetrate deeply enough to reach the problem area.

If your horse has a documented shoulder tendon injury and you want to try this therapy, ask your vet if he/she can recommend a therapist or be sure to work with a reputable and knowledgable company such as Respond Systems (www.respondsystems.com, 203-481-2810). Three-month rentals are available.

Article by Eleanor Kellon, VMD.