Grading lameness: how it works *H&H VIP*

It is common practice for vets to grade the degree of lameness exhibited by a horse to give an estimation of its severity. The original grade can then be documented, allowing semi-objective monitoring of improvement following treatment.

Your vet may have described your horse’s lameness as “low-grade”, or perhaps it has been assigned a fractional score. Knowing how to put these scores into context can help an owner understand the sometimes complex process of reaching a veterinary diagnosis.

Limiting factors

It is important to recognise that any scheme attempting to grade lameness will have its shortcomings. People vary in their ability to detect lameness, and grading it will always be a subjective assessment.

Additionally, whether a particular grading scale runs from zero to five, eight or 10, there are no strict definitions of what constitutes a specific grade.

The American Association of Equine Practitioners promotes a one to five scale. Each grade does have a specific definition, but this results in most horses with lameness evident when they move in straight lines having a grade three of five lameness — irrespective of the gait characteristics.

Other variables include:

•  Circumstances: the degree of lameness may vary hugely when on the lunge or under saddle, to the left or right, or on a soft or firm surface. Some schemes do not permit comparison between these factors, yet I believe it is important to record these variations.
•  Multi-limb lameness: grading is relatively straightforward if a horse is lame on only one limb. If more than one limb is involved, the grade becomes a less accurate reflection of the actual amount of pain the horse may be experiencing in each of the lame limbs.
• If lameness is similar in either both forelimbs or both hindlimbs, it may not be possible to detect a lamer limb. The severity of the lameness in each limb may only become apparent when the pain that is causing it is abolished by nerve blocks. For example, a horse with a symmetrical short-stepping forelimb gait may exhibit four-eighths right forelimb lameness once the left forelimb is free of pain.
•  Consistency: lameness may be intermittent. A horse with low-grade foot pain may take a few lame steps only on a turn, then appear sound. It would be misleading to say that he was two-eighths lame without qualifying that this was only sporadically apparent.
•  Compensation: horses adapt differently to lameness to try to reduce pain. Signs can be difficult to interpret, with compensatory movement sometimes mimicking lameness in a certain limb when the real source is elsewhere.
•  Adaptation: if a horse is assessed while ridden, there are many adaptations to his gait that may reflect lameness. Similar low-grade lameness in both hind limbs may result in lack of hind limb impulsion and engagement, leading the owner to complain that he lacks power. The horse may be on the forehand and have a tendency to become overbent, especially on 10m circles. These features are difficult to incorporate into a grading scale.
•  Gait alteration: abnormalities of gait may be most evident in canter, with the horse tending to become disunited on circles and turns, or break into trot. Other horses may show gait changes only under specific circumstances — perhaps preferring to land on a certain leg when jumping, or finding flying changes more difficult in one direction. These lamenesses are genuine, but cannot be graded.

Limitations aside, it is useful to grade lameness to provide some framework for measuring recovery.

It is perhaps most constructive when assessing lameness following nerve-blocking, so that before and after grades can be documented. Improvements are then less likely to be missed.

This can be vital in severe cases where it may not be possible to abolish lameness. Documenting progress from six-eighths to three-eighths, however, represents a significant clinical improvement.

The question that then arises is whether the residual lameness is the result of failure completely to abolish pain from a single source, or if there is a second source of pain.

Comparing grades after nerve-blocking various limbs in a multi-limb lameness can increase the likelihood of a more accurate diagnosis.

Pinpointing the problem

Is low-grade necessarily better than a higher-grade lameness? This is not straightforward to answer.

A low-grade — even sub-clinical — lameness may significantly compromise a horse’s performance in certain movements. It may be much more difficult to diagnose the source of pain.

A general practice vet may assess the horse in-hand and on the lunge and be unable to detect lameness, erroneously concluding that he does not have a pain-related problem. Yet a specialist lameness clinician would assess the horse being ridden before nerve-blocking him, using easier performance of the problematic movements as the outcome factor.

Low-grade lameness may not markedly compromise performance in some horses, especially if they are going well within their athletic capacity. A horse who loves jumping and has adequate scope to perform at a given level may cope, but may struggle nearer the limit of his athletic potential. If he continues to over-exert himself, the lameness may deteriorate.

Such a horse may have adapted to the lameness by stiffening his back. Physiotherapy treatment that relieves muscle tension may actually make the lameness more apparent.

The road to recovery

Once lameness is identified and treated, recovery will depend on the underlying cause.

Removal of a stone wedged between the frog and a shoe may result in immediate and complete resolution of lameness, for instance. With some lamenesses, it may take several weeks for normal neural pathways governing foot placement to be restored following relief of the primary source of pain. Subtle gait abnormalities may persist for several weeks, although these may not be discernible.

Ref: Horse & Hound; 12 November 2015