Tendon Injuries in the horse
Tendon injuries/breakdown are a significant cause of morbidity, particularly in sports horses and racehorses. They are the most frequent cause of injury during racing with 7 in 1000 starts resulting in tendon damage, with 90% involving the superficial digital flexor tendon and the other 10% commonly being suspensory ligament injuries. In national hunt horses tendon breakdown or damage is more commonly associated with age deterioration injuries, with re-injury occurring in 23-67% of horses.
Tendons function is to transfer forces generated by muscles to the bony attachments in the lower limb, resulting in movement. They support the metacarpal/metatarsal region (around the cannon bones) and store energy for transfer.
The superficial digital flexor tendon supports the fetlock and stores energy. It loses strain energy as heat. The core of the tendon raises to 43-45°C at gallop, this results in 17% strain, but failure of the tendon results at 10%. The ability of the tendon to repair itself decreases with age. Damage to this tendon often results in the appearance of a swollen or “bowed” tendon, often the fetlock can sink, and they are generally painful when palpated.
As horses get older the likelihood of a core lesion decreases and diffuse weakness and fibre disruption becomes more common.
To diagnose damage to the tendon ultrasound examination is the best method available. However, although when the swelling/lameness is initially noticed this is not necessarily the best time to scan. This is because the damage can progress due to the inflammatory enzymes released at the point of trauma. Therefore generally scanning is done 48-72 hours post injury. The horse should be assessed, and will generally be given anti-inflammatories, a supportive bandage may be applied and cold therapy to the limb is often recommended. Monitoring scans can be done every 2-4 weeks initially to assess progression of any identified lesions, and then once exercise is introduced often reassessments are done every 4-8 weeks. This will be determined by your vet and the damage that has occurred to the tendon.
There are a number of additional therapies that can be useful in repair and recovery from tendon injuries. Initially box rest, supportive bandaging and anti-inflammatory therapies are vital, however the additional use of therapies such as static or pulsed magnetic field therapy has been shown to delay maturation of tissue filling in tendon lesions (Watkins et al 1985), laser therapy which increases blood flow/ATP release and endorphin release, therapeutic ultrasound whereby the absorption of acoustic energy leads to thermal effects of increased blood flow, tissue metabolism and has an analgesic effect. Shockwave may also be useful but mainly in cases of tendon damage at a bony interface. Cell therapies such as stem cells may be useful, or platelet rich plasma both of which can be injected into a lesion, but only in core lesions where there is a capsule for the cells to be “stored” whilst they encourage the lesion to heal. These cells or platelets only tend to be found actively in the lesion a maximum up to 3 weeks however this is often sufficient to see a dramatic improvement in the valid use lesions.
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