Blackthorns are the bane of many hunters, because of the vicious thorns that act almost like poisoned arrows.

These nasty thorns can penetrate the soft tissues taking all sorts of bacteria in with them to cause potentially catastrophic infections. Location is key for blackthorn punctures — even though they are tiny, it is where they end up that causes problems.

There are multiple joints, tendon sheaths and bursae in every horse’s limb, which are relatively superficial, beneath the skin, so they are alarmingly vulnerable.

All these vital structures are closed pouches of synovial fluid, which are designed to lubricate the horse’s joints every time his limbs move. This normally works well until an injury allows a blackthorn or any other foreign body to penetrate a synovial cavity.

Any such puncture wound allows bacteria to invade and produce a potentially very serious infection. This produces obvious pain and lameness because of the inflammatory reaction, which causes swelling within the synovial cavity. This can cause career-ending damage to surrounding tissues, such as joint cartilage or surrounding tendons.

Effective management of these injuries requires prompt recognition of the condition and appropriate treatment right away. If a horse has a blackthorn inside a joint, then the best treatment is keyhole surgery (arthroscopy) to look inside the damaged area, then flush and remove debris and infection from the joint.

Best chance of success

The University of Liverpool vet school has recently published a review of more than 200 horses treated in this way, to identify the factors that may be associated with survival.

To confirm that a joint or similar is affected, a vet will collect a fluid sample, commonly called a joint tap. The research showed that when this had higher levels of total protein — meaning it was more inflamed — this was a bad sign. Similarly, the presence of moderate to severe inflammation at surgery was also not good, especially as such cases are likely to require multiple surgeries.

An interesting finding was the increased likelihood of survival where an obvious wound was present. This may be related to the injury being noticed sooner, but also because an open joint wound may allow drainage of inflammatory fluid, thus reducing detrimental joint swelling and build-up of damaging inflammatory mediators.

Surprisingly there was no significant link between time from initial injury to treatment, the level of white blood cells (pus) measured or the presence of bacteria cultured in the sample.

It was found that when anaesthesia was induced out of normal working hours, it was not advantageous to horse outcome. Instead it seems that there are benefits to stabilising the patient prior to anaesthesia and not going for immediate emergency surgery.

The good news is that overall survival rates were good.

Ref: Horse & Hound; 22 January 2015