TENDON INJURIES

Tendons attach muscles to the bones on which they act. Most tendons are short and infrequently damaged, however, the long tendons of the limbs are prone to damage during exercise or as a result of direct trauma.

There are two main flexor tendons that run down the back of the leg from the level of the knee (or hock): the superficial digital flexor tendon, and the deep digital flexor tendon, beneath these lie the suspensory and check ligaments. The superficial flexor tendon is most vulnerable to injury.

The tendons themselves are composed of longitudinally arranged bundles of fibres. Blood supply to tendons is poor compared to muscles and other tissues.

Damage to flexor tendons occurs commonly during exercise. Moderately strenuous exercise can result in tearing of fibres in horses that are not fully fit. Even in fit horses, over stretching of tendons can occur, during fast work, work on uneven ground or jumping at speed. The degree of damage can range from minor, with little fibre damage to very severe with total tendon rupture occurring. Most often, a proportion of fibres are damaged forming a discreet “hole” which extends for a variable length of the tendon.

Direct trauma to a tendon, e.g. being galloped on, may result in slight bruising or more severe damage possibly even tendon rupture. Sharp trauma such as a cut can also result in anything from minor damage to severing of the tendon. Injuries involving tendon sheaths are potentially very serious as infection in these structures may be life threatening.

Damage to a tendon causes inflammation, heat and swelling. Mild strains may not cause lameness. In severe damage, the limb may become very painful and swollen and the horse may be quite lame. If the tendon is ruptured, the horse may walk with the toe tipped up. If a tendon sheath becomes infected, the horse will be very lame.
If you suspect that your horse has a tendon injury, you should give us a call. A clinical examination may confirm or relieve your concerns, however, it can be difficult to assess the extent of damage by look and feel alone. Ultrasonographic examination (‘tendon scan’) allows visualisation of the structure of the tendon and any damage. It also allows assessment of healing processes.

There are several treatments for tendon injuries but none is guaranteed to result in permanent soundness. Damaged tendon heals by producing irregularly arranged fibres. This repair is weaker than normal tendon and re-injury is common. In the early stages anti-inflammatory treatment such as the application of cold, support bandaging and administration of drugs such as phenylbutazone etc. is useful. Adequate rest is vital. Turning a fit horse out into a paddock is not resting its tendon. Most tendon injuries require at least 3 months of restricted exercise (e.g., walking in hand or on a horse walker). Repeat tendon scans are invaluable for assessing healing before exercise levels are increased. In many horses, it is a year before they are fit to compete again.

Attempts have been made to speed up healing and to improve the quality of the repair tissue by injection of substances into the tendon itself. Many different therapies fall in and out of favour. Several years ago, use of “Bapten” was hailed as the next break through in promoting a better quality tendon repair, its use has now almost ceased. The current trend in therapy involves use of stem cells to improve tendon healing. While this kind of treatment is showing some promise, it must be remembered that its use is still experimental, with long term objective studies still being completed. At present, no specific treatment is available to speed the rate of repair.
Both tendon “firing” (application of a hot iron) and blistering (application of chemical irritants) are also examples of treatments previously used to “cure” tendon injuries. The leg invariably swells and is quite painful. There is no scientific evidence to indicate that these painful procedures results in stronger tendons.

While we are always pursuing new treatment options, and many may offer some potential improvement in outcome, a useful rule of thumb still seems to hold true, that is, most minor tendon injuries carry a good prognosis in spite of what is done with them and most severe tendon damage carries a guarded long term prognosis despite what is done with them. Also an adequate rest period is the mainstay of any and all treatment options.

After an adequate period of rest and ultrasonic evidence of healing has been demonstrated the horse should be introduced to a gradually increasing program of exercise. As repaired tendons do not achieve the same strength as undamaged tendon, the horse may not be able to maintain same intensity of exercise as before the injury but may be suited to less rigorous pursuits.