Diagnosing lameness in your horse 

Veterinarians develop their own protocols in assessing lameness but the following steps give an indication of the process.

  • Review medical history - the Vet will ask you questions relating to past and present difficulties of your horse. He or she will also enquire about excercise or work requirements and any other pertinent information.

  • Appraisal at rest - in a visual appraisal at rest, the vet will study conformation, balance and weight bearing and look for any evidence of injury or stress. 

  • Evaluation in motion - the vet will watch the horse walking and trotting and in some cases it may be put onto a lunge. Observing the horse from the front, back, and both side views, the veterinarian notes any deviations in gait. 

  • Hands-on-exam - the vet will palpate the horse, checking muscles, joints, bones and tendons for evidence of heat, swelling or any other physical abnormalities. Pulses in the blood vessels of the lower limb frequently yield useful information about infections or inflammation in this area. Points to check are forearm, knee, cannon bone, fetlock, pastern, coronet and hoof.

  • Hoof & joint tests - hoof examination normally includes a careful visual inspection of the weight bearing surface of the foot when it is picked up.

  • Flexion test - flexion tests help to assess the capsule surrounding joints together with the associated ligaments and tendons and bone ends. The veterinarian holds the limb in a flexed position for a short period and then releases the leg. As the horse trots away the vet watches for signs of increased lameness.

  • Lunging - frequently the vet will want to watch the horse being lunged in a circle on hard ground. This generally puts more pressure on the inside leg (front or back) and makes subtle lameness more obvious.

  • Nerve blocks - local anaesthetic can be used to help isolate the area of lameness by numbing the region and improving the lameness. These are called nerve blocks. They allow the vet to focus expensive imaging tests in the affected area. 

  • Imaging tests - Once the source of the pain has been localised, a range of imaging techniques may be used to further identify the cause. These include ultrasound scans and X-rays. In more difficult-to-diagnose or high value cases, bone scans, MRI (Magnetic Resonance Imaging) and Scintigraphy may also be used. 

 

Determining which leg is lame

Except in severe lameness, assessment takes place when the horse trots. It is more usual to examine a horse’s gait for lameness in front when it is coming towards you and hind limb lameness when it is going away.
In general a horse will drop its weight onto the unaffected leg. The head will appear to nod onto this leg.

Forelimb lameness:

With left forelimb lameness, for example, the horse will come down more heavily onto the right foreleg and its head will appear to nod onto this leg.

Hindlimb lameness:

This is more challenging to diagnose.  Looking from behind, with a left hindlimb lameness, the hip goes through a greater range of vertical motion and appears to be carried higher than the right hindleg.  It is possible that the head will drop onto the opposite (right) foreleg.

 What is a Nerve Block and why does my horse need one?

If your horse is lame, a nerve block can be used to help pinpoint the source of pain. The nerve block numbs a joint or larger area of the leg, so if the horse goes sound after the injection, the vet can say that the source of the problem is in that area or joint. Diagnosis will only be effective if the horse is sufficiently lame for the vet to notice a difference after administering the nerve block. The vet will undertake an initial assessment of your horse to identify the lame leg and the degree of lameness. This will be done by trotting your horse in a straight line on a hard, level surface or on a lunge in both directions.

The process of nerve blocking will then commence, with the vet typically starting at the lowest point of the leg and working upwards. Once the nerve block has been administered, and the anaesthetic has taken effect (usually 5 to 10 minutes), the horse will be trotted up again.

If there is a significant improvement, the vet will know that the cause of lameness is within the target area of the nerve block and will focus their attention in this area. Conversely, if there is no real improvement, the vet will need to wait until the anaesthetic has worn off (approximately 20 minutes) before applying another nerve block further up the leg. Your horse will then need to be trotted up and assessed again. This whole process may be repeated several times and can be very time consuming.

Once the nerve block (or blocks), has indicated the general area of the problem, the vet can then use other diagnostic techniques to more accurately determine the cause of lameness. This may involve the use of x-rays, ultrasound scans or specialised techniques such as Magnetic Resource Imaging (MRI). 

Diagnosing lameness using nerve blocks

So what will the Vet do?

A nerve block involves anaesthesia of a nerve or nerves supplying part of the body to assist diagnosis or treatment of a condition. Nerve blocks are most commonly used to diagnose lameness in horses and can be divided into two broad categories:

  1. Articular blocks where local anaesthetic is injected into a joint, tendon sheath or bursa (small cavity between soft tissues).
  2. Regional blocks where local anaesthetic is placed adjacent to nerves to numb larger areas of a leg.

Will my horse need sedating?

Most horses are fairly amenable to nerve blocks but some individuals are not. With articular nerve blocks, horses must remain still due to the sensitive area the needle is going into. In this case, light sedation may be needed to allow the nerve blocks to be placed. However, this can affect the way the horse moves on re-examination of the lameness which can make results more difficult to interpret.To ensure a safe procedure for both vet and horse, the vet will assess the best way to proceed based on the nature of the lameness and temperament of the horse among other things.

What should I do after the nerve block?

Your vet will probably instruct you to watch your horse for 24 hours after a nerve block procedure for any signs of increased lameness and contact them if you are worried. Your vet may also advise you to keep your horse stabled after local anaesthetic has been used, so that it has time to wear off. While anaesthetic is still present in the horse’s system, the horse will not know precisely where its limb is and it may cause further damage to itself. Your vet will advise you how long to
stable the horse for. If possible, stable bandages should be applied to the leg for the first 12 - 24 hours after the block to minimise development of any swelling. Again, your vet will advise you.

Are there any risks associated with nerve blocks?

Risks are low with nerve blocks.With regional blocks, local anaesthetic is put adjacent to the nerve. The vet will clean the area with a surgical scrub or spirit to reduce the number of bacteria on the skin and risk of infection. Occasionally, a low grade infection may start in the area of injection which will cause some local pain for 24 to 48 hours, but the horse’s body will usually sort this out for itself. If not, antibiotics may be required.

The risks are slightly greater with articular blocks as the needle is going into highly sensitive structures such as joints and tendon sheaths. The vet will often prepare this area as if for a surgical operation by clipping and scrubbing the area with a surgical antiseptic. They may also prepare their hands for surgery and may even wear surgical gloves. The assistant will not be allowed to touch the syringe, needle or bottle of anaesthetic unless they are similarly prepared.

All these preparations are to reduce the risk of infection. If numerous nerve blocks are performed, there is also a risk of the leg swelling.  

(Source: Dechra) 


equine vets