SPAVIN - FUSED HOCKS
“Spavin” is a lay term to describe arthritis of the lower hocks. This is a degenerative process that ultimately can progress to fusion of the hocks. However, this does not always predictably happen unless provoked by invasive procedures.
Spavin can be painful and cause lameness to more or lesser degree. Once the hocks are fused, horses seem more comfortable.
How do they develop Spavin?
There could be many reasons why horses can develop spavin. From younger horses brought into work where there may be a developmental problem, to older horses for various reasons.
We must not forget that conformation and concurrent problems (i.e. kissing spines) can play an important role (picture 1).
A healthy functional lower hock should look like the picture below.
Picture 1: Sickle hocks can predispose to spavin. Corrective shoeing can help to help prevent it.
The main mechanism is damage to the cartilage, which subsequently affects the bone underneath (subchondral bone) altering the architecture and impairing the anti-concussive properties. This is a cycle. Ultimately when cartilage disappears, both joint surfaces can become fused.
How long does it take to fuse?
The timeline process of fusing as seen in the above x-rays is unpredictable. In most of the cases it either doesn’t quite happen, or is very slow in progress.
When lameness occurs, pain would have to be managed. Generally the use of oral anti-inflammatories or intra-articular medication of long acting steroids would encourage progressive fusion of the joints. However on occasion, horses can become too sore to be ridden and they may need time off.
Regarding treatment there are other types of medications (aiming to regenerate rather than regenerate). The merits of these options should be discussed with your vet.
Can hocks can be fused with treatment or surgery?
When conservative treatment fails, there are options of provoking fusion to manage pain long term. This is not something to take lightly. It is invasive and there are important conditions to consider before deciding.
There are several methods:
1- Drilling across joint surfaces
2- Use of laser
3- Controlled injections of monoiodoacetate (MIA)
4- Injection of ethyl alcohol (or ethanol)
There are pros and cons for each technique. We want to achieve an optimal treatment with minimal pain, maximum effect arthrodesis, minimal side effects, short convalescence and cost effective. Ethyl alcohol would generally be a good choice. They tolerate this procedure better than MIA. The other procedures require general anaesthesia with the associated complications such as fracture in recovery which I personally experienced in one case.
Ethyl alcohol causes neurolysis and proteinolysis causing cell death and “cartilage damage”, precipitating joint fusion. It also affect nerves similar to a nerve block, which explains why horses had minimal to no lameness associated with the procedure. It has been used in humans for nerves medium to long term for pain blockade in cancer patients.
What can go wrong with ethyl alcohol fusion?
The hock has two main compartments that encompass the different joints. One in the lower hock connecting the less mobile joints and the other in the upper hock which communicates with the most mobile joints. The important point of this procedure is that it should be aimed to the lower tarsal joints only (turquoise colour on the right picture). If the alcohol reaches the more upper mobile joints (marked as red) it can cause severe arthritis and chronic lameness.
It is of the upmost importance to ensure both lower joints and upper joints are not communicating which they can randomly be. A contrast injection should be performed prior to injection of alcohol. An x-ray should be taken (see picture below). If there is communication, the procedure should not be done. Also, the clinician should not apply overzealous pressure when injecting intra-articular as this could force alcohol to an unwanted place.
There may also be disadvantages where the alcohol may not reach the full joint surface and therefore achieving limited fusion.
Contrast x-rays:
Left picture with normal communication of lower hock.
Right picture shows communication with upper hock joints.
What does ethyl alcohol treatment involve?
The procedure is a simple intra-articular injection under x-ray guidance where firstly a contrast medium is injected, followed by ethyl alcohol.
Horses generally display swelling over the next 24 hours which quickly improves by 2 weeks. There is a persistent swelling on the site of injection for a maximum of 4 months.
The fusion of the joints are visible on x-rays at about 1 month’s time and achieve fusion at around 4 months. Following treatment horses are on box rest and walk in-hand for 1-2 weeks, followed by paddock rest for 6 weeks, and then they can start walk and trot for another 6 weeks if they continue to improve.
What is the success rate?
In a published study of 24 horses from different clinics in the UK, it was found that 52% improved the degree of lameness, 19% deteriorated and 8% developed serious complications
Adding to that study, I have compiled 20 cases. Of those 25% improved to allow previous level of performance, 15% partly improved but not fully (so 40% go better one way or another), 30% did not improve longterm and 10% were found to have other concurrent problems that were more relevant. I couldn’t follow 20% of those cases which may have improved the statistic. I haven’t experienced any serious complications.
The keys to make this treatment a more successful choice are:
1- They have to have a clear response to nerve block. Many of the cases that weren’t successful didn’t in general have a clear response to analgesia initially.
2- Take in consideration conformation or concurrent problems as they can affect the outcome. Therefore it is important to reach a clear diagnosis.
Please get in touch with us if you want to know more about this procedure.
