Lameness: Tendon and Ligament Problems Articles

Healing the Bowed Tendon The Lowdown on High Suspensory Disease (Proximal Suspensory

Desmitis)

 

Healing the Bowed Tendon

by Maria L. Lewis, VMD

          When people say a horse is "bowed", or that it has a "bowed tendon", they are generally referring to tearing of the superficial digital flexor tendon in the middle of the cannon bone region. This tear causes a curved, bow-like swelling on the back of the leg between the knee and the ankle. Although the swelling is usually in the middle of the cannon bone, it may be behind the knee, at the level of the ankle, or it may extend from the knee to the pastern. Most people think tendon injuries such as "bowed tendons" only happen to racehorses. In reality, any breed or type of horse, performing almost any activity, can be at risk for tendon injury. Tendon injuries can be more serious than some types of fractures because the tendon heals very slowly and replaces torn tendon fibers with fibrous scar tissue. The healed tendon is less elastic, leaving the tendon vulnerable to re-injury. When there is a significant injury, the horse may not be able to return to its previous level of performance due to persistent weakness of the tendon.

The superficial digital flexor tendon is made of protein fibers that are arranged longitudinally, forming a long attachment between the muscle above the knee, and the long and short pastern bones just above the hoof. The tendon fibers are somewhat elastic, but will tear if stretched or loaded beyond their limits. Improper positioning of the leg in relation to the horse's body weight can tear the tendon fibers. This configuration may occur when the horse lands after a fence or as the horse becomes tired and changes its gait. Any unbalanced loading of the tendon, uneven footing, poor conformation, and/or improper shoeing can also contribute to tendon damage. In some cases this overload can be the result of a single misstep, and in other cases it can be the result of cumulative stress or fatigue of the fibers.

Once the tendon fibers tear, bleeding within the tendon causes acute swelling, heat, and pain. The horse may or may not exhibit lameness. In fact, many horses with serious tendon damage are never lame. Swelling also occurs around the tendon due to an accumulation of fluid (edema). In the short term, ice or cold hosing and bandaging the leg should decrease the local inflammation and swelling. The horse should be confined to its stall with only hand walking exercise. If the horse is sore or significant swelling is present, consider speaking to a veterinarian about using oral phenylbutazone for a short period of time to decrease the swelling and discomfort. Since palpation of the leg is not a reliable method of determining the presence of tendon damage, contact a veterinarian to make arrangements for an ultrasonographic evaluation of the swelling.

Ultrasonography allows a veterinarian to evaluate the integrity of the tendon fibers as well as other important parameters, including the cross-sectional area of the tendon, the alignment of its fibers, and its echogenicity. The echogenicity of the tendon is related to its density. The\ normal tendon appears bright white or echogenic, and the abnormal tendon appears various shades of gray (hypoechoic) or black (anechoic). Based on the ultrasonographic findings, a veterinarian can confirm the presence of tendon damage and determine its severity. Subtle tendon damage may display an increase in the tendon cross-sectional area due to edema, without actual fiber tearing. Serious damage may consist of total tendon rupture with complete loss of the tendon fibers, a marked increase in tendon cross-sectional area, and loss of support in the limb. Most tendon injuries fall somewhere in between with a discrete area of fiber tearing visible on the ultrasound image (black or dark gray hole), and enlargement of the total tendon cross-sectional area. The hole seen on the ultrasound is actually an accumulation of blood and granulation tissue within the tendon where the tendon fibers have torn apart.

If your horse has suffered a tendon injury, a veterinarian will work with you to develop a rehabilitation plan. Most horses need stall rest with restricted exercise for at least two months

(possibly up to eight months), depending on the degree of injury and the horse's temperament. This confinement, coupled with a controlled exercise program, will encourage healing of the tendon while preventing re-injury. Initially, the horse should only be walked in hand. Once the tendon has been cooled out, cold hosing is no longer necessary or helpful. Topical application of DMSO may help decrease residual swelling in the leg, but the tendon will remain persistently thickened in the majority of cases.

A veterinarian will need to ultrasound the horse's leg approximately every sixty days after the initial exam to determine if the tendon has healed enough to allow for an increase in exercise. An increase in exercise may entail up to five minutes of jogging exercise or turnout in a small paddock. This exercise will gradually increase over a period of months; depending on the improvements seen during the follow-up ultrasound exams. Tendon rehabilitation is a slow process that can be frustrating if your horse suffers any setbacks due to re-injury. Monitoring the horse's progress with regular ultrasounds can eliminate these setbacks.

Recent research in veterinary medicine has focused on ways of improving the outcome of tendon injuries. Surgical treatments that include tendon splitting and superior check ligament desmotomy have been found useful. Other treatment modalities such as therapeutic ultrasound, low-power laser, acupuncture, hydrotherapy and electromagnets are also thought to promote tendon healing. In some cases, the use of intralesional medication, such as ACELL, may be beneficial in improving the quality of tendon repair. A veterinarian can help choose the best treatment for each individual horse.

Although tendon injuries are serious, most horses can recover and return to athletic function if given enough time. Even in the case of a severe tear, it is likely that a horse will be able to return to a less strenuous activity. The best way to ensure a successful outcome is through prompt ultrasonographic diagnosis, treatment, and careful monitoring of the tendon by a veterinarian.

Dr. Lewis, a 1991 University of Pennsylvania School of Veterinary Medicine graduate, is currently in private practice limited to equine diagnostic ultrasound in Unionville, PA. She trained in diagnostic ultrasonography with Dr. Virginia Reef at New Bolton Center for several years; and served as an Imaging Specialist at the 1996 Atlanta Olympic Games and at the 1999 Pan American Games in Winnipeg.

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posted: 7/10/2002. Last updated: 7/18/2005.

 

The Lowdown on High Suspensory Disease (Proximal Suspensory Desmitis)

by Sue Dyson, FRCVS, AAEP member

         

Sue Dyson, FRCVS, AAEP member

 

INTRODUCTION

The suspensory ligament can be divided into three separate regions, all of which can become injured: the proximal (upper) part, the body and the branches. Proximal suspensory desmitis (PSD) or high suspensory disease, is a common injury in both the forelimbs and the hindlimbs of athletic horses and may occur in one limb or in both the forelimbs or both the hindlimbs at the same time.

LAMENESS EXAMINATION

Proximal suspensory desmitis in the forelimb results in a sudden onset of lameness which can be remarkably temporary, resolving within 24 hours unless the horse is worked hard. Lameness varies from mild to moderate and is rarely severe unless the lesion within the ligament is extensive. PSD in both front limbs may result in loss of action rather than observable lameness. This occurs more commonly in racehorses, probably because of the failure to recognize earlier, subtle lameness of just one limb.

Lameness is usually worse on soft ground, especially with the affected limb on the outside of the circle. When subtle, the lameness may be more easily felt by a rider than seen by an observer. Lameness may not be apparent at working trot but may be detectable at medium or extended trot. Flexing the lower limb often temporarily worsens the lameness. It may be undesirable to work the horse hard to reproduce lameness because of the risk of worsening the injury.

NERVE BLOCK (LOCAL DIAGNOSTIC ANALGESIA)

If PSD is suspected, local diagnostic analgesia is indicated. This should result in substantial improvement in, or complete alleviation of, lameness within about 10 minutes, assuming PSD is the only cause of lameness. However, none of the different ways of blocking the proximal suspensory ligament are necessarily specific. That is, pain in other structures such as the knee or foot may also be alleviated. On the other hand, it is possible for the blocking solution to be injected into structures next to the proximal suspensory ligament. Thus, even if the lameness was not improved or alleviated with a PSD block, the lameness may still be due to this condition.

ULTRASONOGRAPHY

Diagnostic ultrasonography is essential to accurately diagnose PSD. The limb should be evaluated in two different planes and careful comparisons should be made to the opposite limb. High quality images are needed since lesions can be subtle and easily missed. Measurements of the ligament may be extremely valuable since, especially in acute cases, enlargement of the ligament may be the only detectable ultrasonographic abnormality. It may be difficult to evaluate an acute case accurately if the horse has had a previous injury to the suspensory ligament because the tissue may not have healed fully. Also, local diagnostic analgesia may allow air to enter the area, making visualization difficult.

The degree of ultrasonographic abnormality usually reflects the severity of the lameness. In acute cases the ultrasonographic abnormalities may be very subtle. Since they may worsen over the next 10 to 14 days, re-evaluation may be useful to confirm the diagnosis.

OTHER IMAGING TECHNIQUES

There are usually no detectable radiographic abnormalities of the cannon bone in acute cases of PSD. In chronic cases however, certain parts of the bone may appear "whiter" or "darker" in certain views. When these secondary bony changes occur in a forelimb, a more guarded prognosis is given. Nuclear scintigraphy is generally unnecessary for diagnosis if good quality ultrasonographic images are obtained, but it may add information about secondary bony changes.

It should be kept in mind that there may be more than one source of pain contributing to lameness. For example, PSD and foot pain occur together quite commonly. There may also be hindlimb lameness occurring at the same time as PSD, especially in the opposite hindlimb, so it is important both to assess and to re-evaluate the horse as a whole.

TREATMENT

Most cases of acute forelimb PSD respond well to stall rest and controlled walking exercise for three months. Attention to correct foot balance is important. Although starting the horse back to work too soon usually results in recurrent injury, approximately 90% of horses do resume full athletic function without injuring themselves again. More chronic cases may require longer rehabilitation; in a small proportion of cases lameness persists. Extracorporeal shock wave treatment has been successful in some chronic cases which had failed to respond to conservative management.

In some horses the lesions disappear completely upon follow-up ultrasonography. In others, the appearance of the suspensory ligament never returns to normal. Rest should be continued until the appearance of the ligament on ultrasound remains stable.

posted: 6/18/2002. Last updated: 6/18/2002.