Damage to the inferior check ligament

The Inferior Check Ligament (ICL) (officially known as the accessory ligament of the deep digital flexor tendon) begins at the back of the knee (carpus) and runs one third of the way down the cannon area where it attaches onto the deep digital flexor tendon (DDFT).

The ICL is concerned primarily with shock absorption and prevention of excessive lengthening of the tendon (DDFT), hence the name check ligament.

Inflammation or injury to the ICL is a more common problem in horses involved in the following disciplines: show jumpers, dressage horses, polo ponies, driving horses and competition ponies.

Injuries to the ligament is more commonly found in horses and ponies over the age of ten years old, and this is thought to be due to age-related degeneration within the ICL.

Typical injuries to the ICL present associated with sudden onset of lameness with swelling, warmth and sensitivity within the tendinous structures at the upper area of the cannon area.

It is important that any injury that presents with these signs is checked by a vet, because when and how the treatment for this injury is instigated will dictate how well the injury will heal.

A definitive diagnosis is carried out through palpation of the affected area and a subsequent ultrasound examination.

Generally it is recommended that an ultrasound examination is not carried out until about seven to ten days after the onset of the problem until the swelling of the leg has subsided.

This is because in the earlier days the extent of any ligament tear will appear less than it really is and the general swelling of the limb can disrupt the image formed on ultrasound.

The ultrasound examination is important in that it tells us a number of things; it quantifies how much damage has been done to the ligament, which then dictates the treatment protocol and rehabilitation programme, and also gives a good idea of the prognosis as to how likely the horse is to recover from the injury.

Following an initial ultrasound exam, subsequent ultrasound examinations may be carried out, typically at eight week intervals.

These subsequent ultrasound examinations give an accurate picture of how the ligament is healing and lets vets tailor the horses’ rehabilitation programme to the quality of the healing.

In addition to this, it is important to compare the injured ICL to that of the other fore limb, to have an objective measure and to check for any subtle differences in either ligament which may be missed otherwise.

It is not uncommon for horses with ICL damage to have concurrent damage to the adjacent flexor tendons in the cannon area and this tends to lower the horses prognosis and chance to return to their previous level of athletic performance.

In the first few days following an ICL injury it is very important that the horse receives anti-inflammatory treatment to limit swelling of the ligament which may ultimately affect how well it heals.

This anti-inflammatory treatment should be in the form of cold therapy eg cold hosing or icing the limb), anti-inflammatory medication such as phenylbute (Bute), and light bandaging of the limb to limit and/or reduce swelling.

The anti-inflammatory medication is important in that it also encourages the horse to load or weight bear on the limb properly, which in turn will prevent any contraction deformities of the fetlock and/or adhesion formation.

During the initial period the horse should be restricted to box rest and controlled walking exercise for up to three months, before then being re-evaluated with another ultrasound scan.

After the first re-evaluation horses typically are then re-examined to monitor the progress of the ICL healing, with full rehabilitation usually taking between six and eight months (but this can vary).

Furthermore any issues regarding foot imbalance should also be evaluated and corrected.

Horses which do not follow the protocol of strict rest and controlled walking exercise tend to have a persistence of lameness and swelling of the check ligament region, as well as the persistence of the ligament tear on ultrasound examination.

In terms of the success of this conservative type of treatment, reports vary from as low as 18% right up to 76% in some research, but this variation in success rates is ultimately based on the type of horse and the severity of the injury.

There are other potential types of treatment, such as shock wave therapy or injecting stem cells into the ligament, which may help to improve the quality of healing of the ligament, but so far no form of treatment will speed up the rate of ligament repair.

Based on current research shock wave therapy has been shown to provide little improvement in the quality of healing.

The injection of mesenchymal stem cells (usually harvested from the horses bone marrow) into the injured check ligament is a therapy which although still in its infancy has yielded some promising results, but this is based on limited reports and ultimately more research needs to be done to clarify this.

Aside from this ultimately early recognition and aggressive treatment are key factors to a successful outcome from a check ligament injury.

In some cases the injury to the ICL can become chronic in nature with recurrent bouts of inflammation and adhesions forming between the check ligament and the neighbouring tendons.

Cases such as these may be candidates for resection (cutting) and removal of a portion of the ICL.

Performing this allows a portion of scar tissue to fill the void, which in some cases gives the healed ligament similar properties in terms of strength and elongation, up to 80% of that of a normal ligament.