Tendon injury is common in sport horses, particularly those that compete at speed and jump (racehorses, eventers and show jumpers). Horses with tendon injury may or may not be lame, but the tendon will be hot, swollen and painful on palpation. The most commonly affected tendon is the superficial digital flexor tendon (SDFT). Tendon injury occurs due to overstrain of the tendon or as a result of a direct blow to the tendon often from another limb. The SDFT is designed to act as a biological spring, stretching by up to 12.2% of its original length during limb loading and returning elastic energy to the limb which assists in forward motion. The video illustrates the fetlock (and hence SDFT ) loading following landing from a fence. High speed training results in repetitive loading of the tendon which can lead to degeneration of the tendon structure leading to injury. Alternatively, a ‘one-off’ event such as a stumble at speed may cause overstrain. The injury involves breakdown of the normal tendon structure or ‘matrix’ and results in a lesion which is filled with inflammatory mediators and fluid, further distorting the tendon matrix. Tendon injuries vary from very mild injury with some ‘filling’ but no disruption to the tendon fibres through to ‘core’ lesions where the centre of the tendon has a visible hole or where large regions of the tendon are affected. Unfortunately, tendon healing tends to be slow with scar tissue formation that results in the repaired tendon being more prone to reinjury and stiffer, less effective as a biological spring. Reoccurrence of tendon injury is high.
On suspecting a tendon injury first aid involves rest, cooling (to reduce inflammation), compression (bandaging) with the use of analgesia and/or anti-inflammatory medication if necessary. After 5-7 daysthe initial swelling will have subsided and the vet can then ultrasound scan the tendon to try and ascertain the extent of the injury, enable the most effective treatment plan to be devised and advise on the likely length of time for recovery. This scan forms a ‘baseline’ to which serial scans every 2 to 3 months can be compared. Rest and controlled exercise are the only treatment needed for many injuries, but in certain circumstances the vet may recommend additional treatment such as stem cell treatment, PRP, corticosteroid injection. Physiotherapy may be advised to aid the horse’s return to work and prepare the body for the weight of a rider after a long lay off. Controlled exercise is advised and this can be done one of two ways, horses may be turned out in increasingly large spaces, but have free access to very a low levels of exercise all day, or they can be box rested with controlled exercise in hand, on a walker or on a treadmill.
Tendon Injury Case Study
Flat racehorse with left fore superficial digital tendon injury with a core lesion.
Diagnosis: Superficial digital flexor tendon lesion incurred during training.
Treatment: Immediately post-injury the limb was cold hosed for at least 10 minutes 3 to 4 times a day (to minimise inflammation) and then stable bandages applied to both limbs (to apply compression in order to reduce oedema). Anti-inflammatory medication was given. One week following injury the vet carried out an ultrasonographic examination of the lesion to establish the extent of the injury. Based on this scan, the vet advised implantation of autologous mesenchymal stem cells (MSCs) followed by a controlled exercise programme.
14 days post injury bone marrow was aspirated from the sternum under standing sedation. The sample was then sent to a laboratory (Biobest, Penicuik, Edinburgh) where the stem cells are cultured for 10-14 days prior to implantation into the core lesion using ultrasound guidance which was carried out 26 days post injury.
Rehabilitation: Following implantation the horse had two weeks of box rest, then two weeks of hand walking, before beginning a period of controlled exercise on the treadmill. In the early stages of rehabilitation (first 4 weeks) post exercise cooling using a cold and compression machine (Zamar) was applied (the thermal images show a cooler limb post Zamar treatment). Work was gradually increased over the twelve weeks post implantation to 40 minutes of walking on the high speed treadmill split into 2 sessions (am and pm). Between weeks 13 and 32 trot work on the treadmill was introduced (in small bouts of just a minute at a time at first), but by week 32 the horse was able to do 50 minutes of work in total including 30 minutes of trotting. The horse was discharged at the end of week 32 to begin canter work and gradually return to full work by week 48 post implantation.
Outcome: This horse was still racing in 2014, being placed in 5 out of 6 races run that season, winning £46k post discharge.
Before cooling During cooling After cooling
Down Hill Jump
Tendon Injury Questions
1.Look at the thermal images of the horse pre and post cooling with a cold and compression unit. By how many degrees is the skin surface cooled following Zamar treatment in this horse?
2.Find out how hot the tendon core can get during galloping.
3.Research the structure of a tendon – how does tendon structure alter post injury?
4.What is meant by the following terms?
5.How is an image created using diagnostic ultrasound.