OTTB Health Series:

Horse Health Topics This is part of a new series on OTTB health exploring common injuries, issues and concerns of interest to prospective Thoroughbred owners. A Disclaimer: Of course we’re not veterinarians; we urge you to speak with a qualified professional about the prognosis of the particular horse that you are considering. We simply want to provide some informational resources for your review.

Chips…A Common Occurrence in OTTB Joints

What are bone chips and how do they occur?

Bone chips or chip fractures of horses’ joints are properly termed “osteochondral fragments.”  Osteo (Latin for bone) and chondral (Latin for cartilage) describe the make-up of the fragments that can cause irritation and lameness in a horse’s joint.  In horses, the major component of the fragment is normally bone.  In people, cartilage pieces are more common.

Fragments (chips) occur for two main reasons:  1) Defective development of the bone (sometimes called osteochondrosis) where the bone fragments under normal loads; or 2) Uneven loading or trauma to normal bone, where the bone fragments are under uneven pressure.  — Larry R. Bramlage, DVM, MS, DACVS, on behalf of the American Association of Equine Practitioners’ (AAEP) On Call Program.

If you have looked at CANTER listings you may have noticed that it is fairly common to see Thoroughbreds listed that have bone chips, especially in the knee, or ankle joints of the front legs.

In this article we’ll reference some material on bone chips and “slab fractures” to help the prospective buyer or adopter evaluating a horse with a chip injury:

1) How do these injuries occur?

2) What questions should you ask the vet about the horse’s injury

3) What the long-term prognosis might be for the horse that you are considering

We have tried to gather together information from a variety of reputable sources–but, as always–no article will substitute for x-rays and a veterinary opinion on the specific horse that you are considering.

So please, if you are looking at a horse known to have a knee, or ankle chip, please get a set of diagnostic films and discuss the horse’s suitability for your needs–including how much necessary treatment might cost, with a qualified veterinarian…As always: we recommend a pre-purchase exam for any as a horse as the horse may be asymptomatic at the time your are considering your purchase.

How Do Bone Chips Occur?

As noted in Dr. Bramlage’s quote, above: chips may be the result of bony imperfections, or the result of excessive stress on normal bone. Osteochondrosis, or “OCD”, is a fairly common in Thoroughbreds.

At full racing speeds Thoroughbreds can exerts thousands of pounds of force on their bones, so mechanical injury to joints is common. The horse may tire; weakened muscles may not support proper leg alignment and the horse’s knee hyperflexes backward, or the fetlock joint snaps down too far–the result can be a flake or “chip” in that knee or ankle joint.  “In 3-year-olds, knee (carpus) problems–such as carpitis (knee inflammation) and chip fractures–were the most common causes of lameness, although fetlock injuries were also important in this age group.” [1]

You may also see horses with “slab fractures” in the knee if you are on the backside looking for a horse. A slab fracture is a fracture extending from one articular surface to the opposite articular surface. Horses with slab fractures show more lameness than with chip fractures, and x-rays are used to confirm the diagnosis..

What Questions Should You Ask the Vet?

If you are looking at a horse with a chip, or slab fracture it is important to consider a few things to be discussed with the trainer and with the veterinarian evaluating the animal:

1. What bone(s) are affected? And to what degree?
2. If it is a knee, is the chip in the upper, or lower joint?
3. Is it articular, or non-articular (in the joint, or outside of it)?
4. Are any of the supporting structures in the joint damaged (e.g. if the horse with an ankle chip, is the suspensory apparatus affected?)
5. Is there evidence that the joint was previously injected?
6. How new is the injury?
7. How was it sustained: in training, or during an actual race?
8. When was the injury discovered? (Sometimes a horse may come back from a race and not manifest lameness until the next day, for example)
9. How has the injury been treated?
10. Is it a re-injury to the same area; e.g. a chip in a knee which already had chips or arthritic changes?
11. Does the horse have any other physical issues?
12. Does the horse have the temperament to do well on stall rest for a period of time?

The vet may need to do a series of several x-rays on the affected joint in order to get the best picture of the injured area. In evaluating the horse it is critical that the vet understand the intended use of the horse, your degree of knowledge, and willingness/ability rehabilitate a  horse.

Should I Even Consider a Horse with a Chip?

There is no blanket “right answer” to this question. You need to take into account your circumstances, the degree of injury/impairment, the long-term prognosis, current degree of lameness, if applicable.

We have seen many horses with “old chips” who go on to do just fine in second careers. Many with  newer injuries have been successfully rehabilitated: in some cases after a surgery to remove the chips, in others on stall rest alone. But there are certainly cases we’ve seen where horses do not go on to second careers as a result of knee, or ankle chips. It depends upon the animal, the injury and even on that particular horse’s sensitivity to discomfort.

If you are considering a horse with bone chips, be sure to discuss treatment and maintenance options with the vet during the PPE.

New treatments–both surgical and pharmacological–are being developed and prospective owners have options available.

Surgical Options often run into thousands; but there have been significant advances in arthroscopic surgery over the past two decades, offering many horses the chance for a return to high-performance careers. Here is a description of how arthroscopic knee surgery is often done in horses:

“Small incisions are made to insert the arthroscope into the joint capsule to allow for visualization of the joint as well as to utilize the necessary instruments needed to remove the lesions. The camera projects the image inside the joint onto a monitor for more convenient evaluation of the site by the surgeon. A steady stream of fluid is pumped through the joint during the procedure to aid in the removal of debris and to keep the surgery field clear. Generally only a minimal number of sutures are required to close the small surgical incisions and a protective bandage is applied to the area for the horse’s recovery from anesthesia.

The usual hospital stay is three days. Horses are admitted to the hospital one day prior to surgery and released one day after. Hand walking can begin seven to ten days post surgery and horses with simple chips can be back to work within 6 weeks. Many horses return to work earlier, under the direction of their veterinarian, without complication.” [2]

As noted below, other factors within the horse’s affected joint will have a bearing on long-term prognosis:

“Based on follow-up studies with carpal chip fragments, 75% come back and race successfully at the same or better level than before. Not all the 25% in the unsuccessful group fail because of carpal problems. Other problems happen to the horses that contribute to this figure. The success rate does vary depending on the amount of articular cartilage damage in the joint. However, it was a pleasant surprise to find that we can tolerate up to 30% articular cartilage loss off a bone that has fractured without lowering the success rate. Once we get to 50% cartilage loss or a significant amount of subchondral bone loss, then the success rate comes down to 50%.” [3]

Non-Surgical options to manage the development of inflammation and arthritis in the joint that may be associated with bony injuries include the use of intra-articular injections using lubricating agents (hyaluronic acid, or “HA”) or corticosteroids. Medications frequently prescribed to address joint problems and for maintenance include: Legend,  an intravenous formulation of HA which helps in joint lubrication; and polysulfated glycosaminoglycans (PSGAGs) such as Adequan (used where there is cartilage damage, and it has also been used to prevent day-to-day loss of cartilage components)

NSAIDS such as phenylbutazone (or “bute”) are used to minimize inflammation and may help to address any periodic discomfort and during the recovery process though they do not act on the bones themselves.

Speak with your vet about which options would offer the horse the best outcome; they may recommend a combination of therapies.

If the Chip Is “Old”, or the Horse Seems Sound…

We’ve seen many CANTER buyers have a PPE done where chip(s) show up on x-ray on an otherwise asymptomatic horse. The vet examines the films to find that there many be one or more chips–whether old “set” chips, or newer bone damage that is not causing a significant lameness but may explain a horse’s less than stellar racing form.

In fact, Bramlage notes: “Estimates place the prevalence that a horse will have a chip fracture in one of its joints sometime in its life between 20 percent and 50 percent. About 15 percent of horses have some type of chip that occurs during adolescent play and spontaneous competition, even before they begin training.”

Bramlage notes that bony fragments can often be sequestered and neutralized–much as a pearl is formed when an irritant is introduced into the oyster’s shell.

As noted in the article from McIlwraith, an important influencing factor is the condition of the cartilage.

If there is minimal damage and the chip is non-articular, stable and not causing discomfort or lameness, the vet may “green light” the prospect for your intended use.

Some Reference Articles:

Bone Chips in Joints (www.thehorse.com does require registration to access articles free of charge)

Bone Chips Fall Into Different Categories

Traumatic Joint Injuries and Disease

Treating early osteoarthritis-Orally administration hyaluronic acid can be a new arrow in practioner’s quiver, but few efficacy studies exist (an older article, but interesting info on use of HA in joints)

References:

1. “Racing Toward Injury”, by: Ray Geor, BVSc, PhD, Dipl. ACVIM, September 01 2002, Article # 3787 on www.thehorse.com

2. Peterson & Smith Equine Hospital, LLC website

3. “Traumatic Joint Injuries and Disease”, C. Wayne McIlwraith, BVSc, PhD, Orthopedic Research Center, Colorado State University