Understanding tendon injuries

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A “blown” or damaged tendon has signalled the end of many horses’ successful racing or competition careers, and there is currently some confusion surrounding tendon injuries and the best way to treat them.

One of the most startling true facts about tendon injury is that the degree of lameness is not related to the degree of inflammation in the tendon itself. Confusingly, some horses can have quite extensive damage without being very lame, or the affected limb being very swollen. Equally, subtle thickening in the cannon region may be related to substantial tendon damage.

“Essentially, a damaged or ‘bowed’ tendon occurs when one of the tendons or ligaments responsible for supporting the leg has been torn by being overloaded. Although this is a sudden event, the harbingers would have been laid down many months beforehand,” says Roger Smith, professor of equine orthopaedics at the Royal Veterinary College.

“A useful metaphor is to think of the tendon or ligament as an old rope fraying. At any point in time, the tendon can tear and as soon as it does there’s a large inflammatory response with bags of swelling,” continues Prof Smith.

Vets generally organise tendon or ligament injuries into three levels of severity — mild, moderate and severe — and generally the more severe the damage, the poorer the prognosis.

When a vet sees a horse with swollen soft tissues at the back of the cannon bone, they have to decide which structures are damaged and how severe the damage is.

The tendons and ligaments in the horse’s lower leg include:

  • the extensor tendon at the front of the leg

  • the superficial and deep digital flexor tendons at the back of the leg
  • the suspensory ligament which runs between the bones and flexor tendons
  • the check ligament, just below the knee

The superficial flexor tendon and suspensory ligament support the fetlock. Damage to other structures such as the check ligament can occur in conjunction with injury of the superficial flexor tendon.

Injury to the check ligament tends to result in swelling centred closer to the cannon bone than with an injury to the superficial flexor tendon, which displays the classic “bow” at the back of the leg.

Damage to the suspensory ligament can occur in many sites and the clinical signs may vary. Damage that is limited to the proximal (top) part of the ligament may show only subtle lameness with minimal swelling and is common in the sport horse. This condition can be hard to detect, whereas damage lower down the suspensory usually shows more obvious swelling.
Injury to the deep digital flexor tendon is unusual but when it does occur it is normally at the level of the fetlock or below, within the tendon sheath. There is a much poorer prognosis with injury to this tendon and, frequently, persistent lameness.

The first step of diagnosis will be palpation, which will give the vet a good idea of which structure is involved, but it will be hard to tell how bad the damage is.

Next, the vet will examine how the fetlock on the injured side behaves in comparison to its pair. If there has been significant damage to the flexor tendons, the fetlock will drop towards the ground. If the suspensory ligament is severely damaged, the fetlock will be nearly on the floor.

Examination by ultrasound is the final stage of diagnosis and should take place around one-week after the injury occurred to be of most use.

Prognosis following injury depends primarily on the level of damage and the horse’s job, according to Prof Smith.

“The problem is that tendon heals well with fibrous tissue but this is not as good as the original tendon tissue and the horse will always be at risk of re-injury. It is very difficult to give an accurate prediction of the outcome. Quoted success rates range from 2%-90%.”

  • This article was first published in full in Horse & Hound (18 December 03)

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  • Understanding tendon injuries

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    The tendons and ligaments that run down the back of the horse’s leg below the knee are important structures – the equivalent of the tendons that enable us to bend our fingers.

    In the horse, they have the essential role of holding the bonesand muscles of the leg together, so enabling the whole limb to work properly.

    Bowed tendons

    Sprained, or “bowed”, tendons is one of the most common causes of premature retirement in horses, particularly from racing and eventing.

    It tends to be the superficial flexor tendon that becomes damaged by repeated strain during fast work. This is what is usually involved when a horse is said to have broken down. The body weight of the horse is carried largely on the forehand, resulting in stress on the forelegs at fast paces, which is why these injuries occur more frequently on the front legs.

    Fibrous tissue

    Tendons are strong bands of fibrous tissue which attach muscles to bones, while ligaments are similar structures that support joints and are not directly attached to muscles.

    Tendons and ligaments work together in the lower limb of the horse. Although the superficial flexor tendon is the most well known, other structures, such as the check ligaments are as important.

    Damaged ligaments

    Check ligament desmitis (inflammation) appears to be most common in older horses more than nine years old, which are doing athletic work, particularly jumping.

    Check ligament damage is not necessarily associated with the fast work that traumatises the superficial flexor tendon, but possibly more with twisting and turning.

    The main indicators of check ligament injury are:

  • Slight to moderate lameness, usually occurring during, or shortly after, exercise, although some horses are not obviously lame.

  • Swelling, and then thickening, of the inferior check ligament – at the back of the leg, below the knee.

  • Heat and pain in the area of injury.

    If you notice any suspicious soft tissue swelling at the back of the leg, particularly below the knee, call your vet.

    One of the frustrations with tendon and ligament injuries is that the horse may not be obviously lame, or there maybe a bout of lameness which resolves rapidly.

    If the severity of the injury is not recognised and the horse resumes work as soon as the lameness disappears, there is a high risk that the ligament injury will end up being serious.

    Time to heal

    Another difficulty with tendon and ligament injuries, but particularly those involving the check ligaments in older horses, is the length of time they take to heal.

    In general, horses with check ligament injuries require at least six months’ rest from full work, while others will not be sound for 15 to 18 months.

    An ultrasound scan is the best guide to when it is safe to start proper work.. Carefully controlled exercise is essential.

    Treatment

    There are two critical aspects to treating check ligament injuries.

  • The first is to reduce the formation of scarring – adhesions. Prompt aggressive treatment in the first 48 hours after injury is vital.

    This means rest and cold treatment by hosing or ice packs, plus anti-inflammatory drugs. A pressure bandage should be applied in between cold treatments to help reduce the swelling. This needs to be done in the early stages to limit damage.

  • The second is patience. There is no magic treatment and time is the best healer. Drugs will help repair the tissues that make up the ligament, for example, Adequan.
  • Not all check ligament injuries return to soundness.

    One survey of 18 cases showed that only seven returned to their original level of performance.

    If there is only limited damage to one check ligament and a controlled exercise programme is followed to stretch any adhesions and allow proper repair, the chances of recovery are good.

    Problems are more likely if there is recurrent damage to that ligament, or damage to other parts of the leg, such as the superficial flexor tendon, or to the check ligament on the opposite leg.

    In many cases, the injured area will remain thickened even though the horseis sound.

  • Originally published on horseandhound.co.uk