Thorn penetration by blackthorn is a common injury in horses hunting over country with fields separated by hedges containing blackthorn (Prunus spinosa) bushes. This type of injury is treated at Oakham Veterinary Hospital on a regular basis throughout the hunting season due to our proximity to the Leicestershire packs. As a result, we have developed a huge amount of experience and a high level of expertise in the treatment of these injuries.
Which joints are commonly affected?
The thorns tend to penetrate areas of the limbs passing through the hedge as it is jumped. Most commonly the front of the knees(carpii), the front of the fetlocks in both front and hind legs. Thorns and thorn fragments can also be found in other joints (stifle, hock), tendon sheaths, bursas, tendons, ligaments, muscle and simply under the skin. The majority of these sites require careful thorn location with ultrasonography and removal the thorn fragments often requires advanced endoscopic surgical techniques.
Irrespective of the injury site the principle for treatment remains the same; if the thorn material is removed the horse will recover well.
Why do thorns cause so much trouble?
Clinical research undertaken at Oakham suggests that the painful tissue reaction to blackthorn injury is not caused by infection. In fact, contrary to popular belief among the equine veterinary community, the joint is sterile after a thorn penetration. The substances that make blackthorns black are alkaloids, and this thorn contains more alkaloids than other plants. Our research indicates it is this that causes the severe tissue reactions. When the pain and lameness reduces in cases that are untreated, it is likely that the residual lameness is due to a foreign body reaction to the plant material.
How do we diagnose and treat thorn penetration injuries?
The injury can be divided into 2 simple categories-
- Extra-synovial (not into a joint, tendon sheath or bursa)
- Intra-synovial (into a joint, tendon sheath or bursa)
The area affected tends to swell and be hot, 3-12 hours after hunting. Pain is quite variable and can be severe initially but will generally subside. Extra-synovial injuries can be divided into 3 areas
• ‘in and out’ - frequently no thorn material is left in the tissue. In these cases, the initial inflammation will subside spontaneously, irrespective of treatment.
• Subcutaneous - thorns can frequently be felt under the skin and squeezed out between thumb and fore finger, or encouraged to work their own way out by application of a poultice.
• Deep sub fascial - If the thorn has penetrated under the fascial layer, it is unlikely to be able to be removed via its entry hole, as the multiple tissue layer holes will not line up unless the limb is in the exact position that it was when it penetrated.
In all of these cases, high resolution ultrasound is used to identify the thorn. We then use an ultrasound guided technique developed at Oakham, to enable accurate identification and removal with minimal trauma. These techniques are performed under local anaesthesia if possible, but in some cases general anaesthesia is necessary.
The horse is usually severely lame within 3 hours of hunting, with heat and swelling of the affected structure. Interestingly the lameness does usually reduce but not resolve over the following 12 hours.
Arthroscopic surgery is used to identify and remove the thorn material and flush the synovial structures. We use specific techniques that we have developed at Oakham. All cases require general anaesthesia.
When treated by the techniques we have developed at Oakham, and once all the thorn debris has been successfully removed the majority of horses are sound 48 hours after surgery and discharged from the hospital after 5 days. Post-surgery recovery time is short and the horse can return to the hunting field in as little as 2/3 weeks.