Equine Lameness

Lameness evaluation in horses

No hoof, no horse. No limb, no horse. Lame horse, money lost (they are expensive lawn ornaments). We spend a lot of time evaluating horses for lameness. Sometimes the owner doesn’t recognize the horse is lame but maybe just not performing up to snuff or not happy about the work. Horses may also be presented for a prepurchase examination in order to verify soundness (no lameness) prior to being purchased by a new owner. The goal is generally to localize the lameness in order to target advanced diagnostics and to be able to reassess the horse at a later date.

The main parts of a lameness examination

The history

When evaluating lameness, context is crucial. Beyond the presenting complaint and a general health history, we also need to know  a lot about the situation.

What is the horse supposed to be doing? Backyard pleasure? Grand Prix Jumper? When is it supposed to be doing this? Tomorrow? Next year? Owners may have high hopes and unrealistic expectations but good to know what they are.

How hard and how frequently the horse is worked?  Horses may be lunged (worked in a circle) in soft footing as a warm up -this is tough work! How long do they do this? How many does of the week does the horse work? How often is it shown? How long is each work out? What is the footing?

Horse owners also tend to medicate their animals. Is the horse currently on medication? Has it received any medication? What type and for how long? Did it make a difference? Is the horse on any supplements? Note: they may not consider these medications!

Horses may be outside 24 hours a day or inside most or all of the time. Standing is a stall is different from free choice exercise. What is the horse’s environment. Note: If the horse has been prescribed stall rest, ask open ended questions. Horse owners will often give up on stall rest and be reluctant to admit it directly.

Horses are also athletes and some get regular therapies. It is very useful to know if the horse has had surgery or joint injections before and when the last treatment was. Hooves grow over time. If the horse is due for a hoof trim (most get trimmed every 6-8 weeks) or needs a shoe reset, that can change your interpretation of radiographs and can affect treatment plans.

Weight shifting does need to happen when a horse is lame. Owners might notice secondary shoulder pain (foot issue) or back pain (hock issue).

The visual examination

left forelimb held forward, “knobby” carpus

Prior to nearing the horse or touching the horse, the overall appearance, conformation, stance and symmetry should be evaluated (along with attitude). Is the horse shifting weight equally between limbs? Shifting weight excessively? Not putting weight on a limb? Pointing a limb? Are any limbs or parts of limbs swollen or atrophied?

 

 

The passive examination

The passive examination is performed with the horse standing still, often during history collection. The horse is palpated from poll to toes and assessed for range of motion of joints (how well do they bend), lumps and bumps, fluid in tendon sheaths and joints, and warm or painful areas. Knowing the palpable anatomy is crucial. Hoof structure, shoe wear and tear and hoof balance is also evaluated. Abnormalities are recorded for consideration after the active examination. Not all will turn out to be significant.

Hoof tester examination

Generally, hoof testers are applied as part of the passive examination.  Large tongs are used to pinch the hoof. A consistent response (withdrawal of the limb each time the hoof tester is applied) is indicative of pain. [A single withdrawal means the horse doesn’t want this exam but doesn’t necessarily mean pain.] Pain over the heel region is often associated with navicular bone issues. Pain in other areas could be a hoof abscess, sole bruise or laminitis. Pain all over (no distinct area) is often a hoof abscess or a fracture.

using hoof testers – great images

The active examination

Rusty midtrot. LF and RH on the ground.

The horse is evaluated at a walk and a trot as part of most examinations. Occasionally the horse is worked at a canter and/or ridden. The trot is a two beat gait which allows overall shifts in weight to be evaluated since one hind foot and one fore foot are on the ground at one time. At a canter, the horse can protect a lame limb by using one “lead” – one leg starts the stride, the other 3 follow. Horses with significant lameness will prefer to canter rather than trot.

Note: If you are worried about a fracture (from the history, level of pain), DO NOT TROT the horse. Incomplete fractures can become complete fractures. 

Most vets use the AAEP 5 point scale. This allows someone else to evaluate the horse and determine if the lameness has changed. Grade 5/5 is nonweight bearing, while grade 1/5 is a lameness seen only under certain conditions.

AAEP Lameness scale

0: Lameness not perceptible under any circumstances.

1: Lameness is difficult to observe and is not consistently apparent, regardless of circumstances (e.g. under saddle, circling, inclines, hard surface, etc.).

2: Lameness is difficult to observe at a walk or when trotting in a straight line but consistently apparent under certain circumstances (e.g. weight-carrying, circling, inclines, hard surface, etc.).

3: Lameness is consistently observable at a trot under all circumstances.

4: Lameness is obvious at a walk.

5: Lameness produces minimal weight bearing in motion and/or at rest or a complete inability to move.

Horses are evaluated from the rear, the front and the side. We are looking for symmetry, stride length, foot flight and foot placement.

When a limb is painful, the horse will try to adjust his/her weight to avoid much pressure on the limb. This shifts the head and body to other limbs, changes how long the horse stays on the lame limb and often changes how much the horse raises and lowers the limb (minimizing joint bending). The weight and timing shifts are what we look for. A “head nod” means the horse is shifting the weight of its head to change the weight on the sore limb. If the horse is lame on the left forelimb, it will throw its head up and back when the left fore is weight bearing. Newton tells us the head will have to come back down (equal and opposite force). So we see a nod downward when it does; and this is when the opposite forelimb is on the ground. Hence we say “down on sound”.  We can often hear the harder landing on the sounder limb, as well.

https://www.thevetexpert.com/a-complete-guide-on-lame-horse-identification-and-treatment/

For the hindlimb, we look for hip excursion. Normally the hindlimb joints bend and the hip doesn’t move up and down much. However, if the hock joint hurts, the horse will try to avoid bending it. To lift the foot, the horse has to lift the whole leg (raising the hip more). A greater hip excursion is usually found on the lame limb. With these horses, the greater drop in the hip is usually in the lame leg, while a hip “hike” may be observed in the sound leg.

Rule of sides

Occasionally a horse will throw its head forward with a hindlimb lameness. Due to how the trot works, this can look like a forelimb lameness on the same side. If the horse throws it’s weight forward with a left hindlimb lameness, the head will be nodding down at the same time the right fore is hitting the ground. Down on sound means we can interpret this a left fore lameness. Just keep in mind it could also be a left hind lameness! Rule of sides – if it looks like a LF nod, consider LH too; if it looks like RF nod, consider RH too.

 

There are now tools that can help identify more motion on a limb, making lameness exams more objective. However, the more we know the more confusing it can get!

Horses may be worked on both hard and soft footing. Hard footing emphasizes weight bearing issues (a bone bruise will be worse on hard footing), while soft footing emphasizes soft tissue issues (a tendon injury will be worse on soft footing).

Horses are also worked in a circle (lunged). Lunging exacerbates weight bearing issues on the inside limb and soft tissue issues on the outside limb. A horse that is bilaterally lame won’t show as much lameness on a straight line as the horse can’t pick a limb to more extra weight on. We may not see a nod or change in hip excursion. Often we just see a short, choppy gait. When the horse is lunged, however, now one leg is working much harder than the other and we can see lameness. We lunge the horses in both directions to ensure we have found all the affected limbs.

Stress tests are used s to try and confirm lame limbs or to localize the limb. Taking full limb radiographs on a horse would cost over $1000 so we need to better define what we want to image. We do this noninvasively through flexion tests (bend the limb and stress the joints) and wedge tests (a bar is put under different parts of the horse’s foot to stress different areas).

The distal limb will be flexed on both fore and hindlimbs, usually for 30 seconds. The lower limb is bent to stress the coffin joint, pastern and fetlock joints. It is impossible to flex these joints individually. The person flexing the limb avoids putting pressure on tendons or ligaments as pain in these regions could complicate the interpretation. After 30 seconds, the horse is trotted off and the lameness reassessed. Often the first 1-2 steps will show pain; these are generally ignored and the examiner focuses on the later steps. Persistent lameness is called positive.

In the forelimb, the carpus can be flexed by itself. This flexion is held for 60 seconds. In the hindlimb, the reciprocal apparatus makes it impossible to flex any normal joint all by itself. The distal limb, stifle and hip will flex when the hock is flexed. The upper limb flexion is often called a spavin test.  This test is not terribly specific so we are trying to determine if it is markedly worse than the distal limb flexion. A positive spavin that was worse than a distal limb flexion would suggest hip, stifle or hock pain.

A heel wedge test is similar to a very big (horse sized) hoof tester and puts pressure on the caudal heel structures. A toe wedge test places strain on the flexor tendons.

 

 

Local blocks

Once we have identified the limb, we usually still need to confirm the region causing the pain. In most cases, we start at the hoof and move up. We numb each region and reassess the lameness at a trot. When the lameness goes away (or moves to the other limb), we know that the pain is coming from the region we just blocked.  If we start too high, we numb large regions and are back to needing to localize further but now we have to wait for the local anesthesia to wear off. Knowledge of anatomy is again crucial!

Example :The horse is lame on the left forelimb. If we block the palmar digital nerves and the horse is still lame, we can assume the lameness is not in the heel region (orange shading in the image). Then if we perform an abaxial nerve block  (blue shading+ orange shading) and the horse goes sound, we can say the pain is in the region below the fetlock and above the area blocked by the palmar digital nerve block. In the image, this would be the blue area above the orange.   This “subtraction” means it is important to move up the limb and to do so carefully so we don’t have a large region to evaluate (radiograph, ultrasound.).

 

Joint blocks above the foot are an exception. Local anesthesia injected into the joint generally numbs the joint and not much else if the horse is evaluated sooner rather than later (later the local anesthetic leaches out and finds nerves). If the carpus is swollen on a racehorse, we may just radiograph it. However, if it is swollen but not painful or painful on flexion but not swollen (eg unclear diagnosis), we will often inject it to see if it is the source of pain. If this doesn’t resolve the pain, we can still do effective distal limb nerve blocks.

It is not uncommon for the horse to change which limb is lame during a series of blocks. Lameness is often bilateral as it is typically related to wear and tear and conformation issues. Once we numb the pain on one side, the horse can now show us the lesser pain on the other side. The veterinarian needs to carefully check which limb is showing pain at each step! In the example above, the horse would typically go lame on the right forelimb rather than becoming sound.

A response of 50% (50% better) is pretty poor. A response of 100% is rare. Once we have the lameness improved to the point where we can no longer tell a difference, we have made significant improvement, or the horse is getting tired of needles, we will move to diagnostics such as ultrasound or radiographs.

Note: if you cannot see the lameness consistently, it will be hard to tell if your local blocks help. Try a different modality!

Scintigraphy

If the horse will not tolerate local blocks, if multiple limbs are lame or if the examination is pre-performance, it may be more effective to perform a bone scan. The horse is injected with a radioactive substance that collects at areas of remodeling bone (some do soft tissue too). The highlighted areas (hot spots) are then evaluated more closely, generally with radiographs.

Imaging

Most lameness exams end with diagnostic imaging. Radiographs are best for bony structures; ultrasound for soft tissue. The foot has both and is best evaluated with MRI.

Resources

LAMENESS EXAMS: Evaluating the Lame Horse, AAEP. Date unknown – short and sweet synopsis

2018 Sporthorse lameness exam, TA Turner, FAEP- lots of great hints and explanation

Manual of clinical procedures in the horse. Eds: Costa & Paradis- Chs 27 and 28- how to’s with lots of pictures

Adams & Stashak’s Lameness in Horses, 6th edition; Ed: Baxter.
Lameness in the Horse; 2nd edition; Eds: Ross & Dyson.

Other examples

Lameness Locator info

 

License

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Large Animal Surgery - Supplemental Notes by Erin Malone, DVM, PhD; Elaine Norton, DVM PhD; Erica Dobbs, DVM; and Ashley Ezzo, DVM is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.