1. History

2. Observe at rest
3. Observe while moving (walk, trot and canter)

4. Palpate and manipulate limbs

if lameness not yet localised:

5. Diagnostic nerve / joint blocks

6. Diagnostic imaging 

•   Some aspects are common to all history-taking, as discussed in your

  communication sessions: allow owners to describe the problem as they see it; start by asking “open” questions, ask whether owner has any questions, outline what you plan to do next.

•   Age / breed: some conditions are related to age (e.g. OCD)

•   What is the horse used for? May range from brood mare (not ridden,. lives out all

  year, probably not shod, may have low-grade lameness without anyone noticing)

  to competition horse (ridden daily, expected to be completely sound)

•   Briefly ask about concurrent disease (coughs, colic etc)

•   Are vaccinations up to date?

•   Is horse insured * (loss of use, veterinary fees)?

•   If recently purchased, was the horse “vetted”?

•   Previous lameness?

•   Which limb(s) does the owner think is affected (owner may be mistaken, but do

  give them benefit of doubt to begin with)

•   Duration of this lameness

•   Severity of lameness

•   Wound(s)?

•   When was the horse last shod? If shoes have been removed, this is likely to

  rapidly cause (additional) lameness at exercise

* If the horse is insured, warn the owner that some companies require notification prior to lameness investigation or referral. 

While taking the history it is useful to observe the horse, so you will already have noted: General demeanour, body score, whether shod or not.
Horses commonly rest either hindlimb; they do not normally rest a forelimb.

Next:
With the horse weightbearing evenly on all 4 limbs, walk right around the horse while assessing for muscle wastage, conformational abnormalities and obvious swellings e.g. over joints / tendon sheaths
Common conformational abnormalities include:

low heel – long toe conformation
fetlock / carpal / tarsal valgus or varus (angular limb deformities) mediolateral foot imbalance
asymmetry between feet
hyperflexion or –extension of distal limb

Detailed inspection and palpation can be performed now or, as the author prefers, following trot-up when the level of lameness & limb(s) affected have been established. 

Assess at the walk for obvious lameness (in which case trotting probably not required).
All horses swing their head slightly with every stride as they walk – do not confuse this with a “head nod” indicative of lameness.
Pay particular attention to the horse turning – this may be the only moment when the horse shows a lame stride, or when mild ataxia is evident (see neurology lectures).
The hind feet should be placed in the same spot, or in front of, where the fore foot was (“tracking up”)

The trot is the best gait for determining which limb(s) is lame (Why?)
The handler should trot the horse using a slack lead-rope at a steady speed towards and away from the observer, on a level hard surface.
The key to recognising forelimb lameness is the head nod.
In hindlimb lameness, asymmetric movement of the gluteal regions is the cardinal sign 

instead, establish the rythmn of the head nod first (saying “now” with each nod may help) then look for which foot is landing on the beat. Markers placed on the tuber coxae can help detect asymmetric motion. 

A moderate to severe hindlimb lameness 

can mimic forelimb lameness, because as the horse tries to shift weight away from the painful limb it extends its head and neck forwards and down. A hindlimb lameness graded at 3 / 5 or above can therefore appear like a lameness of the ipselateral forelimb. However, observation from behind will confirm greatly increased unilateral gluteal excursion, which doesn’t occur with forelimb lameness. This may sound complicated but is actually quite easy when you see it. 

The lameness should be graded. Common scales are 1-5 and 1-10. The grading systems are subjective and can vary between different clinicians, but so far no objective method of measuring lameness has found its way into clinical practice, although gait analysis systems are available. The lameness may be intermittent. Subtle lameness can become more apparent when the horse is lunged. In-hand trotting or lunging on hard and soft surfaces or on a slope may be used to exacerbate a subtle lameness. Ridden exercise is rarely useful, takes extra time and can mask a subtle lameness, so avoid unless the lameness / equitation problem is clearly associated with having a rider on board.

• Shortened stride length of the affected limb, best observed from the side

•   Increased fetlock extension (dropping) on sound(er) limb, also best seen

  from side

•   Many causes of hindlimb lameness result in medial swinging (“plaiting”) of

  the affected limb as it is carried forward; best observed from behind

•   Some hindlimb lameness results in toe-dragging due to reluctance to flex

  the hock(s)

•   The sound foot often makes a louder noise on landing, which some

  clinicians find useful (not this one though) 

0. The horse may be lame on 1, 2, 3 or even all 4 limbs!

   The lameness may vary, depending on medication, periods of rest, type of surface horse is moving on

   If the lameness is very subtle or intermittent, diagnostic blocks may be hard to interpret so best not to embark on that process if you cannot see a clear lameness 

0. As with other aspects of examination, sticking to the same routine when palpating a horse’s limb helps preventing errors of omission. Most clinicians start with the foot and move proximally, paying particular attention to common sites of pain such as joints and insertions of ligaments. This is where familiarity with normal functional anatomy is vital.

   The horse may respond to pressure at the site of pain – the most important example of this is the response to hoof testers.

   
   
   

0. Flexion tests are routinely used to help localise the source of lameness, with a positive response being one where the horse trots away more lame than before. They are very non-specific, especially in the hindlimb where all joints flex when the limb is raised. In the forelimb it is possible to flex the joints distal to the carpus separately from the proximal limb. Flexion tests are not a substitute for nerve blocks unless the response is very exaggerated but may help indicate which region is painful. Similar tests used occasionally include placing a wedge under the heel for palmar foot pain (extension test) and valgus/varus stress tests (useful to confirm stifle pain). The use of flexion tests in pre-purchase examinations is controversial as their interpretation varies between clinicians. 

If the location of the pain is not apparent from the above 4 stages, then the use of blocks becomes necessary. This should be explained to owners, who often wonder why the veterinary surgeon “doesn’t just x-ray the leg”. With very few exceptions, lameness cannot be diagnosed by the gait alone, although it is often claimed that a horse has, for example, “a shoulder lameness”. Such horses almost always block out to their feet. Horses with laminitis do have a characteristic stance and gait because they usually have pain in both front feet, but other conditions can cause a similar gait, and laminitis can occasionally affect only one foot, or be mild in its effects.

In general, diagnostic nerve blocks are performed starting distally and progressing proximally. The highest nerve blocks are performed just above the carpus and the hock. Once nerve blocks have localised the region, joint blocks can be used to further narrow down the possible sources of pain.

A new graduate can be expected to know in detail how to perform nerve blocks of the foot (palmar digital and abaxial sesamoid nerve blocks). You should be aware of other nerve blocks and joint injections, but do not need to memorise their locations. 

Although a diagnosis may be evident from steps 1 – 6 above, diagnostic imaging is often required to determine the severity of the lesion, give a prognosis and formulate a treatment plan. The most common techniques used and radiography and ultrasonography. Scintigraphy (bone scanning) has been used for the past 30 years to help localise regions of abnormal bone turnover and more recently magnetic resonance imaging (MRI) has become possible in the standing, sedated horse and has allowed far greater differentiation of the various causes of foot lameness.