2/26/2010 Friday - More on Flash's lameness

Vet tip of the Day: Understanding the lameness exam

Key Words: splint bone, cannon bone, fracture, sclerosis, lysis

Today I’m going to continue following the trail of Flash’s lameness which remains unsolved. A quick review of the initial findings: an acutely grade 4 lame 11 year old gelding with history of trauma to the medial  left front mid-metacarpus . There was hot painful swelling mid-way down the splint bone, no other pertinent findings on physical examination.

The American Association of Equine Practitioners has established a uniform grading system to describe equine lameness. If you Google - AAEP lameness - you can read more on how veterinarians evaluate lameness. Here is the scoring system:

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.

While this grading system is useful, it does not specifically describe the characteristics of an individual horse’s lame gait. When watching Flash move, what concerned me was not only the degree of lameness – clearly visible at the walk, but the inconsistency of the lameness. When turning, or stepping onto uneven ground Flash would occasionally take steps that were almost non-weight bearing. The veterinary vernacular for this type of gait is “fracture lame”. When walking carefully on a flat surface Flash’s gait would improve to a fully weight bearing walk.

When evaluating a lame horse it is important not to develop tunnel vision. While Flash had obvious evidence of trauma to the splint bone area of the forelimb, the character of the lameness was not characteristic of that produced by a splint bone fracture. I was immediately concerned that there might be a non-displaced fracture (a crack, more or less) of the cannon bone or first pastern bone, although these injuries are uncommon. Also the occasional “bad steps” suggested pain in the hoof. Flash wore shoes with full pads, making it impossible to apply hoof testers to his foot reliably to check for a signs of pain originating from the foot.

A second concern when examining a horse with a grade 4 lameness is making a bad situation worse. If a diagnostic nerve block is performed which eliminates the pain, the horse may no longer protect the injured area and in bearing full weight, cause a non-displaced fracture to become unstable, or comminuted, with disasterous consequences. So, on my first examination of Flash I broke the rules of lameness evaluation that you learned in yesterday’s blog. I skipped the diagnostic nerve blocks and only evaluated the gait at a walk. I completed a careful examination of the limb and went straight to x-rays to rule out a fracture.

Radiographs of the medial splint bone and cannon bone ( MCII and MCIII – see blog archive from Feb 7th for review) did not reveal a fracture, although there was obvious enlargement of the splint bone at the swelling site. So what to do? Small, fresh, non-displaced fractures are not always immediately apparent on radiographs, even with excellent quality digital x-rays. Keeping the veterinary code of “above all else, do no harm” foremost, I decided to treat Flash conservatively and repeat the x-rays in two weeks. There were no open wounds or swollen joints, so the chance of infection requiring immediate treatment was minimal, and if there was a non-displaced fracture present that I had failed to detect, it was best treated with stall rest and observation at this point.

I prepared an anti-inflammatory “sweat” containing furacin, glycerin and DMSO and instructed the trainer to apply it daily to the swelling under a bandage. I prescribed a low dose of phenylbutazone to decrease pain and inflammation. The dosage was very conservative because I did not want Flash to feel too comfortable and not protect his leg. I instructed the trainer to call me immediately if the lameness worsened or did not improve somewhat over the next 2-4 days, and scheduled a recheck in two weeks barring complications.

Hopefully the past two blogs have helped illustrate some of thought processes we employ when approaching lame horses. The take home message: for chronic, low grade lamenesses, we use a systematic approach:

Step 1: physical examination

Step 2: gait evaluation

Step 3: diagnostic nerve blocks

Step 4: Diagnostic imaging

When evaluating acute, severe lameness, additional concerns come into play which may alter this plan. Two important things to keep in mind: 1: Do No Harm, 2: Don’t get tunnel vision.

More on Flash on Monday – what do you think the answer is?

Enjoy your weekend – the 4th chapter of Veterinary Tales will be ready next week, introducing one of my favorite clients, getting Sticky’s histopathology results, and treating a horse with a mysterious swelling!

Tuesday, February 7: The Fetlock and Metacarpus

Vet tip of the Day:

First a quick review: we've looked at the anatomy of the bones in the pastern and foot and the attachment of the deep flexor tendon onto the back of the second pastern bone and coffin bone. We've discussed how irregularities in the navicular bone can contribute to heel pain by irritating the flexor tendon and navicular bursa as the tendon slides up and down against the back of the navicular bone. And we've reviewed ring bone, an arthritic condition that occurs at the P1-P2 and P2-P3 joints.

Today we will move on to the bones and major soft tissue structures between the knee (carpus) and the pastern. The cannon bone, with a much smaller splint bone on either side, spans this distance. The bottom of the cannon bone rests on the top of P1, the long pastern bone, and forms the fetlock joint. The cannon bone and the splint bones are all metacarpal bones, which correspond to the bones in your hand between your wrist and your knuckles. At the level of the fetlock joint, just behind the cannon bone, lie the sesamoid bones. The suspensory ligament, which arises from the back of the knee, lies along the back of the cannon bone and splits just above the sesamoids, with one branch attaching to the top of each sesamoid bone. The deep and superficial flexor tendons originate behind the knee and attach at the level of the pastern. The deep flexor tendon attaches to the back of P1 and P2 (the long and short pastern bones), and the superficial tendon to P2 and P3 (the short pastern and coffin bones).

The distal, or lower cannon bone, suspensory branches and fetlock joint are like an amazing suspension bridge which is critical in supporting the weight of the horse during exercise. They are very common sites of injury in athletic horses. You may have seen pictures of the x-rays of Barbaro, whose catastrophic injury involved not only a fracture of the end of the cannon bone, but also his sesamoid bones, suspensory ligament and pastern. In our less extreme athletes, small strains in the suspensory branches, chip fractures in the fetlock, and inflammation of the sesamoid bones are all relatively common causes of lameness.

Pick up your horse's right front leg and hold the foot in your left hand. Place your right thumb on the inside, and your index finger on the outside, of the cannon bone mid-way between the knee and the fetlock. Squeeze firmly and let your fingers slide over the structures moving toward the back of the leg. The suspensory ligament is difficult to feel because it is very firm and lies closely attached to the back of the cannon bone. However, it is easy to feel the deep and superficial digital extensor tendons which lie just under the skin. Learn to distinguish between them, and then move your hand up and down the leg, feeling the length of each tendon from knee to fetlock. Just above the fetlock, on the inside and outside, it is possible to clearly palpate the branches of the suspensory ligament where they attach to the top of the sesamoid bones. Your hands are very sensitive indicators of changes in the soft tissue structures of the leg that can alert you to the presence of injuries.