Ataxia is incoordination and can originate from the vestibular system, the cerebellum or the proprioceptive system, the latter primarily consisting of muscle-nerve stretch and feedback to the spinal cord and the brainstem.
By far the most common cause of ataxia in horses is spinal cord compression and, in particular, in the neck – so-called wobblers syndrome or cervical vertebral malformation / malarticulation (CVM).
It is unknown exactly how common compression of the spinal cord in the neck is. A 2009 study found it present in around 1 in a 100 of thoroughbred horses in the UK, and it is probably slightly more common in warmblood horses. Horses with diseases affecting their balance and coordination can be dangerous to ride and are usually euthanised or retired.
Subtle gait deficits whether it is lameness or ataxia are well known to be difficult to appreciate clinically, even for experts, and sometimes the chronically mildly lame horse that cannot be blocked with local anaesthetic nerve blocks may be ataxic or have a so-called root-signature lameness. It is well established that the asymmetry originating from lameness can be measured using a miniature portable gait laboratory, so-called inertial measurement units (IMUs). Thilo Pfau of the RVC’s Structure and Motion Laboratory has developed the IMU system used at the RVC for lameness detection.
Several groups have attempted to detect ataxia using force plates, motion capture or IMUs. Both force plates and motion capture have been shown to be helpful for detection of ataxia in horses however this equipment is expensive and the systems can only measure 3-5 strides at the time. Further it is time-consuming to obtain results from these measurements. It is therefore ideal to use a portable gait measurement system like the IMUs because they can measure for an unlimited number of strides at the time and processing is faster with immediate results.
A study from RVC Equine and the Structure and Motion Laboratory, published in 2017 in the Equine Veterinary Journal, showed that motion capture and reflective markers placed just above the fetlocks were able to detect ataxia in horses due to an increased variation in the cranio-caudal movement of the swing phase during walk. This variation was increased for ataxic horses when they were blindfolded suggesting that the eyes correct for some of the coordination-challenges in horses. We are in the process of analysing the data from our IMUs in that study so that we can use IMUs to assist us with assessment of the ataxic horse.
Assessment of ataxia is important not only due to rider safety but also to get objective ways of looking at effects of interventions such as changes over time, articular process joint injections, various forms of rehabilitation, surgery for wobblers disease (basket surgery) and also holds an important perspective for dogs with ataxia from intervertebral disk disease, wobblers syndrome and understanding how they change their gait over time as well as effect of treatment interventions.