By Stuart Pearson BVM&SCertAVP(ESO)MRCVS – CHESHIRE EQUINE CLINIC
The Purpose of Tendons
The function of a tendon is to transfer energy in order to propel the horse forward. A large amount of energy is stored in the tendons down the back of the leg as the fetlock extends/sinks. This “energy store” is similar to slowly stretching an elastic band and then releasing it quickly. Tendons will also provide support to joints and offer some “shock absorption”. For the purpose of this article I will concentrate on the superficial digital flexor tendon that runs down the back of the cannon bone and fetlock and provides a large propulsive energy store while supporting the fetlock.
Anatomy
Simply speaking tendons are made up of dense collagen that is specially arranged in a “crimping” pattern allowing for a greater degree of stretch – which results in an increase in the energy stored alongside a corresponding increase in strength. The most similar human tendon in structure and function would be the Achilles tendon and interestingly much research in veterinary treatment of equine flexor tendons relates to human treatments and visa versa.
Effect of Ageing and Prolonged Exercise
Unfortunately, long-term exercise and age causes degeneration in tissue, and tendons are not exempt from this. The centre of the tendons change with age and the fibrils (small fibres) shorten and therefore elasticity is lost, increasing the likelihood of damage. Once a horse reaches 3 years of age a damaged tendon has limited capacity to regenerate or repair itself without scar tissue (a much less elastic tissue with “rope- like” quality).
Tendon Injury
Two main types of injury can occur: direct trauma where the tendon is damaged from another object, such as a fence or “struck into” by a foot, or even a slipped bandage. The other is an overload strain injury, sometimes from a mis-step on uneven ground or an accumulative effect in a horse usually exercising or working for a longer distance.
Tendon Healing
To allow for successful treatment of an injured tendon we must recognise and understand the different overlapping phases of tendon healing. There are four phases of tendon healing that occur
Phase 1: Subacute, no visible signs as inflammation not present. This explains why the signs of damage are often noticed the day or two after the horse has been worked.
Phase 2: Acute Inflammation, there are the usual markers of inflammation; heat, pain and swelling as blood supply is increased to the damaged area. This is the time the horse is rested with cold therapy and anti-inflammatory medication and will last approximately 2 weeks.
Phase 3: Repair phase lasts 3 weeks when the body produces scar tissue type collagen This phase overlaps with the inflammatory phase 2.
Phase 4: Re-modeling phase lasts several months and converts this weaker collagen into a stronger type. Exercise in a controlled fashion to stimulate the muscle to tendon junction is of great importance at this stage.
Treatment for a Tendon Injury
Orthopaedic injuries can typically be treated in two ways – surgically or conservatively. Traumatic injuries that result in significant tearing of the tendon may need surgical repair in the form of interlocking suturing. More commonly, however, a more conservative approach is chosen, bearing in mind the phases of healing that will take place.
The first job is to reduce inflammation and fluid accumulation in the tendon: cold therapy using iced boots, spa or even cold hosing will reduce heat in lower leg. Twenty minutes of cold hosing will reduce the temperature of the horse’s lower leg for 8 hours. In addition, anti-inflammatories and bandaging will help reduce swelling.
The next step would be to consider treatment of any lesion or hole within the tendon. This is done with a needle to decompress the hole, and then medication is administered directly to the damaged area. These medications can simply be saline to flush out the degrading enzymes and prevent further tendon loss, or synthetic products such as hyaluronic acid aimed at healing the damaged tendon itself. Regenerative therapies are another option aimed at healing and regenerating the damaged tendon. These are usually derived from the horse itself, such as Stem cells (from the horses bone marrow) or platelet rich plasma (from the horse’s own blood). All of these products have different costs and implications associated with them. Careful evaluation of the most recent studies about their potential effectiveness needs to be considered before embarking upon treatment with these medications.
Regardless of which treatment type is employed, there is absolutely NO substitute for a targeted and controlled exercise program to achieve maximum tendon strength. Walking is increased before trotting, and then eventually cantering is introduced over a period of several months. During this time evaluation using ultrasound is useful to monitor the healing and regeneration process and allow for alterations to the rehabilitation process. The aim is to maximise the regeneration of the “elastic” tendon and minimise the “inelastic rope-like” scar tissue.
Prevention
Prevention is always key and attention to foot balance is important for preventing many injuries including tendon strains, for instance: the long-toe low-heel conformation puts more strain down the back of the tendons and should be avoided. An appropriately fit horse will be less prone to injury and achieving this fitness should not be rushed. Hard exercise on firm ground will increase the likelihood of tendon injury and care must be taken in these conditions. Lastly get to know your horses legs, in this way any changes in size, heat and swelling can be picked up early before damage has occurred or it becomes irreparable. The old adage will always hold true, “prevention is better than cure”.
For more advice on tendon injuries or other orthopeadic injuries please contact Stuart at office@cheshireequineclinic.co.uk or 01829 770 999
