Tendon and Ligament Strains and Sprains

Tendon and ligament strains and sprains are common injuries in the lower limbs of performance horses. Most commonly damaged are the tendons and ligaments that run from the knee down to the foot - the superficial digital flexor tendon, the deep digital flexor tendon, the accessory ligaments and the suspensory ligament.

Injuries can range from minor inflammation with no lameness, to complete rupture of the tendon strap. Injuries usually result from excessive loading and overstretching, but may also be due to a direct blow to the tendon area.

The risk of tendon and ligament injury is dependent on the type of activity carried out by the horse. Gallopers, showjumpers, eventers and polocrosse horses most commonly injury the superficial digital flexor tendon (SDF) in the front limbs, while in pacers the suspensory ligaments of the hind limbs are most commonly affected. The suspensory ligaments of dressage horses are prone to strain during extended trot, particularly when working in deep sand arenas. Forelimb suspensory ligament injuries are also common in barrel racers, polocrosse horses and campdrafters that have to brake quickly from high speeds and perform quick forehand turns.

What are tendons and ligaments?

Tendons and ligaments are dense bands of fibrous tissue composed mainly of collagen. Tendons connect muscle to bone, while ligaments connect bone to bone. The flexor tendons run down the back of the leg from the knee to the foot and their role is to flex the fetlock and the digit joints. The suspensory ligament lies at the back of the cannon bone, deeper than the flexor tendons, and stretches from the back of the knee to the sesamoid bones in the fetlock. The suspensory ligament provides support for the fetlock, preventing extreme over-extension.

Why are tendons and ligaments so susceptible to injury?

The main action of tendons is to transmit muscle power to the lower leg, and healthy tendons are able to bear extreme stretching forces. Tendons also have elastic properties, allowing them to store 'energy' and absorb minor overloads during exercise. However, any sudden overload exceeding the limits of their ability to stretch can result in tearing of the tendon structure.

Studies have shown that the 'safe' working elastic stretch in a warmed up tendon is about 3%. However, if strain is excessive the tendon fibres behave in a 'plastic' manner, and can be safely stretched up to 8% of their length until their 'elastic' limit is reached. If loading increases, the maximum 'strain' limit is exceeded and the tendon fibres and blood vessels will begin to rupture, beginning within the central core of the tendon. The end result is the inflammation, pain and swelling characteristic of a 'bowed' tendon.

Pre-disposing causes of strains/sprains

Any factor that increases the stress imposed on a tendon or ligament can result in overstretching and strain. Factors such as prolonged training, increasing age and overheating by bandages may also weaken tendons, making them more susceptible to strain. This weakening appears to affect the centre of the tendon rather than the edges, and this central region is the area most likely to be affected by tendonitis.

Conformational weaknesses that transfer weight to the rear of the limb, such as 'back at the knee', 'cut in behind the knee', long, sloping pasterns and 'under at the heels' increase the mechanical loading on tendons during exercise. Horses that are heavy in the shoulders and neck or carry heavy riders also load extra weight onto their tendons during fast exercise or turns.

Inadequate conditioning at slow speed in early training can predispose a horse to tendon strain. Controlled loading by trotting for 4-6 weeks after a spell helps to improve the elasticity, 'stiffness' and strength of tendons. Tendons stretch more without suffering strain when warmed up, as their elastic limit is doubled when warm. Accumulative leg stress from long term training, and in tired horses at the end of fast competition, particularly on heavy surfaces, increases the risk of tendon strain.

Tight or restrictive bandages increase the risk of tendon injury by interfering with blood flow, lubrication and natural elastic 'rebound' behaviour. Always ensure protective and support bandages are firm, but not tight, and include the fetlock and full length of the cannon bone. Bandages should be removed immediately after hard or prolonged exercise, as recent research suggests that tendons accumulate heat when stretched repeatedly (similar to an elastic band!). Although general body temperature may only reach 40-41ºC, if bandages are not removed immediately after exercise, retained heat can increase tendon temperatures to 46-47ºC, damaging and weakening the collagen fibres and increasing the risk of tendon failure.

Treatment of tendon & ligament strains/strains

Immediate first aid should always be applied if there is any suspicion that a tendon or ligament has been injured. First aid aims to limit the degree of internal tendon fibre damage. Following initial first aid therapy it is a good idea to get your vet to 'scan' the tendon ultasonically, if equipment is available, to determine the location and severity of the tendon fibre injury.

First Aid – First 48 hours after Injury

The initial goal in treating a recently injured tendon is to control inflammation. Often early warning signs of injury are missed and inflammation may be well under way by the time a diagnosis of tendonitis is made. Initially injuries may be low-grade and pass unnoticed until further exercise worsens the damage. Even though the horse may not be obviously lame the tendon may be increased in diameter and feel warm and sensitive to the touch. Within hours the swelling (if severe) will produce the typical 'bowed' appearance and lameness. If a tendon starts to swell up, even without pain and obvious lameness, apply appropriate first aid immediately. Do not wait to see if lameness develops!

  1. Cold Therapy - Prompt application of cold therapy and pressure bandaging is essential to control inflammation. Application of ice or ice packs to the limb will constrict ruptured blood vessels and slow haemorrhage and bruising within the area. Ice or ice packs should be applied under an elastic bandage such as Vetrap for 20-30 minutes three to four times per day for the first 48 hours.
  2. Bandaging - Injured tendons should be bandaged in between ice treatments to provide counter-pressure against tissue swelling due to haemorrhage and oedema. Constant firm, uniform pressure will reduce the quantity of tissue fluid and blood clots that can accumulate, improving the long term prognosis for maximum tendon repair. Be careful not to apply bandages too tightly as this can cause further tendon damage.
  3. Rest - The horse should have complete rest in a stable or small yard for at least 48 hours after injury to eliminate the risk of worsening the injury. Complete rest should be continued until the inflammatory process is under control. Consult your vet for advice.
  4. Anti-inflammatory agents - A vet examination should be carried out as soon as possible after the injury and a non-steroidal anti-inflammatory agent such as Finadyne or Bute will often be prescribed. Anti-inflammatories help to keep the inflammation process under control, which helps to minimise damage to surrounding uninjured areas of the tendon.

During this early stage of the injury do not apply warming liniments or rubs, as these tend to increase blood flow to the area, which may encourage haemorrhage and further swelling. However topical DMSO products such as Dermcusal, which also contains the anti-inflammatory copper-salicylate complex, may help prevent fluid accumulation and scavenge damaging 'free radicals' produced by the inflammatory process. Dermcusal should be applied twice daily for the first 3-5 days and then replaced with a warming liniment thereafter.

First Aid – 2- 28 Days following Injury

After the first 48 hours the tendon injury enters the 'sub-acute' phase. The aim of treatment in this phase is to minimise the spread of inflammation to undamaged areas of the tendon, to reverse the effects of acute inflammation to try to minimise permanent damage to the tendon, and to assist the repair process.

  1. Alternating temperature therapy - After the first 48 hours coagulation should have occurred in the damaged blood vessels and the risk of internal tendon bleeding will have decreased. Inflammatory substances will still cause tissue fluid to accumulate and the aim of treatment at this time is to control and remove these inflammatory substances and the fluid that they accumulate. The application of alternating hot and cold therapy will help to dilate and then constrict the vessels in the area, pumping the inflammatory fluid into the circulation and away from the injury. The warm intervals should be 3 times as long as the cold intervals and the cycle should be repeated as often as possible each day for 4-6 days after the initial injury.
    After 4-6 days cold therapy should be stopped and warm therapies alone should be used to improve the circulation and to speed repair. Prolonged warming can be generated by the use of a topical liniment such as Vetsearch Spirit Liniment or Old Timer’s R-Iodine. If Dermcusal or other DMSO based liniments have been used in the early phase of treatment, wash the leg well with warm water before applying warming liniments to avoid any interaction between the ingredients.
  2. Pressure Bandaging - Pressure bandaging should be continued for 2-3 weeks to counteract lower limb swelling and accumulation of tissue fluids around the inflamed area. Bandages should be firm but not too tight!
  3. Anti-Inflammatory Agents - Bute or other non-steroidal anti-inflammatories should be continued based on your vet’s advice, to minimise any ongoing inflammatory damage.
  4. Exercise - Stall rest should be continued until tissue fluid accumulation and swelling is halted. Once this inflammatory process is under control, controlled gentle exercise can be started. Mild, non-injuring exercise helps to stimulate tissue fluid movement and improves circulation throughout the tendon. The horse should be hand-walked for 15 minutes twice a day during the first month following injury. Horses should be housed in stables or small yards and not turned out into larger paddocks, as the risk of further injury is high if the horse over-exerts the tendon.

Long Term Rehabilitation

Although lameness may disappear in a few weeks the tendon fibres will take at least 6 months to heal and you should discuss the best rehabilitation programme for your horse with your vet. In all cases tendon 'overloading' must be avoided until the tendon has healed and regained its strength and elasticity, as the risk of re-injury is high.

Specific nutrients may improve the elasticity of tendons, which not only helps to reduce the incidence of tendon problems, but also encourages the repair of damaged tendon tissue. Daily supplementation with Vitamin A, Vitamin D, selenium, copper, zinc and manganese is recommended. All of these nutrients are provided by a daily dose of Feramo-H. In addition a supplement of good quality protein such as 2 cups per day of soyabean, canola or lupin meal is recommended to provide amino acid building blocks for tendon repair.

When bringing a horse back into work after recovery from a bowed tendon, it is very important that adequate tendon strengthening work is carried out. Six to eight weeks of slow trotting work on a hard, even surface such as a roadway for 10-15 minutes each day may help to strengthen the tendon. Always warm-up a horse that has had a tendon injury for 10-15 minutes at the trot before fast work or turning exercise to improve tendon elasticity and lower limb blood flow.

Special support bandages such as Equisport are useful for horses known to have suffered a previous tendon injury. However it is very important that bandages are applied correctly (consult your vet or the manufacturer’s instructions when applying support bandages). Remove bandages immediately after exercise to allow tendon cooling. Regularly examine suspect tendons after exercise and apply an ice pack for 10-15 minutes after exercise to try to avoid a flare-up of a previous injury.

By Virbac Animal Health - Last updated 16 November 2012

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