Bone chips in a horse’s movable joints can compromise the animal’s ability to perform, and, in some cases, they can even end the animal’s career. However, not all bone chips are created equal. Some are so innocuous that they cause little or no hindrance to the horse’s well-being or ability to perform.
Unfortunately, the equine joint is fragile and complicated in design and construction. The knee joint, for example, operates with eight building-block-type bones that are subjected to severe concussion when the horse is running at speed. Sometimes the stress is more than the bones can tolerate, and a piece of bone–which can vary in size from a tiny speck to something as large as the tip of a man’s finger–will “chip” off.
Fortunately for horses and their owners, when the chip causes serious problems, a veterinarian can remove the chip through arthroscopic surgery and allow the joint to return to normal (if the damage is not too severe).
We’ll take a step-by-step look at what happens when there is a bone chip, and the manner in which the problem is solved. Sources include Larry Bramlage, DVM, MS, Dipl. ACVS, a board-certified surgeon at Rood & Riddle Equine Hospital in Lexington, Ky., and an on-call veterinarian for the American Association of Equine Practitioners (AAEP); Steve Adair, MS, DVM, Dipl. ACVS, an associate professor of surgery at the University of Tennessee; and we’ll include information from a white paper released by the Equine Research Coordination Group (ERCG), with C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, Dipl. ACVS, of Colorado State University, listed as the author. (The Equine Research Coordination Group is comprised of researchers and organizations that support equine research, including the AAEP Foundation, American Horse Council, American Quarter Horse Association Foundation, Grayson-Jockey Club Research Foundation, Maxwell H. Gluck Equine Research Center, Morris Animal Foundation, Havemeyer Foundation, United States Equestrian Federation Foundation, and a number of university researchers.)
Chipping Away at the Problem
Bramlage, who is an expert on the subject of bone chips, explains them this way: “Bone chips or chip fractures of horses’ joints are properly termed osteochondral fragments. Osteo (Latin for bone) and chondrol (Latin for cartilage) describe the makeup of the fragments that can cause irritation and lameness in a horse’s joints. In horses, the major component of the fragment is normally bone. In people, cartilage pieces are more common.”
While chip fractures can occur in any breed and discipline, they seem to be most prevalent in racing Thoroughbreds, perhaps because of the high-speed work they do or because of their owners’ financial ability to look for chips.
Bramlage points out there are two basic reasons for a bone to chip or fracture. One reason involves defective development of the bone (sometimes referred to as osteochondrosis), in which case the bone fragments under normal loads. The second reason involves repetitive cyclic trauma to normal bone. In this case, the bone fragments because the rate of damage due to repetitive loading exceeds the rate of repair (subchondral bone, which is the bone beneath articular cartilage, is constantly is a state of remodeling and repair).
The excessive loading, our experts say, can be the result of poor conformation, as with a horse that is back at the knee. The rate at which a young horse is developed on the training track or in the arena can also contribute to chips. Too rapid a progression with training when joint bones are not yet able to keep up with the damage can play a role in the development of bone chips.
Bramlage tells us if the chip fracture or fractures happen when a horse is still growing or during a period of rest, the joint will try to isolate the fragment. It does this by surrounding it with scar tissue in an effort to render it smooth and nonirritating, in the sort of way an oyster makes a pearl from a grain of sand.
He adds that the size of the chip is not of particular significance, but the amount of debris the chip sheds is highly significant. The debris serves to irritate the joint and, if the shedding continues, can cause ongoing inflammation, resulting in arthritis. On the other hand, if the debris shedding ceases, there is a strong possibility the joint will heal.
Bramlage adds this about the shedding of debris: “Acute bone chips in high- motion areas shed a lot of debris because the two raw bone surfaces rub together like two rocks, shedding little bits of sand into the joint. This debris causes pain, lameness, and poor performance. Because chip fractures seldom come totally free in the joint, but remain at their site of origin, this rubbing and debris shedding continues with the joint motion. The more strenuous the motion, the more lameness (usually occurs).”
Chip fractures can occur in all joints, but our experts agree they are most likely to be found in the fetlock and knee joints, particularly among racing Thoroughbreds. The reason for this appears obvious. When a horse is running at speed, the knee and fetlock joints absorb a great deal of concussion. At one point during each stride, all of the horse’s weight is suspended on one front limb.
Bramlage estimates the possibility for a horse to develop a chip fracture in at least one of his joints during his lifetime ranges between 20% and 50%. About 15% of horses, he says, have some type of bone abnormality and fragmentation that occurs during adolescent growth and spontaneous competition, even before they begin training.
Why the Chips Fly
To better understand why chips occur, we turn to Adair, who also has written and spoken extensively on the subject, for a description of what occurs in bone development: “Long bones develop from cartilage by a process of endochondral (with cartilage) ossification. The centers of ossification (bone formation) develop in the center of the future long bone (diaphysis) and at the ends of the long bones (epiphysis). As ossification proceeds, a bony epiphysis develops, as does a bony diaphysis. Between the two centers of ossification is the metaphyseal growth plate, and this is what enables the limb to lengthen after birth as the foal grows. There is a second growth plate, called the epiphyseal growth plate, that forms as the epiphyseal ossification center advances toward the ends of the bone and what is destined to be the articular surface of the joints.”
Along the way as the bones grow and develop, lesions and deformities sometimes develop within the bone. A great deal of research has been conducted, but no one has come up with any definite conclusions as to the specific cause of osteochondrosis and developmental orthopedic disease in general, other than the problem is multifactorial. Those factors can include everything from mineral imbalance to genetics, overfeeding, rapid growth, endocrine problems, nutrition, mechanical stress, and trauma.
In some cases, lesions within the developing bone can be the precursors of bone chips when the horse continues to grow and develop and moves into a training program with what might be a weakened spot or spots in the developing bone.
The good news is that veterinarians often detect bone development problems when a horse is young through X rays and, in many cases, these problems can be successfully treated. Veterinarians take radiographs of the joints of many yearlings that go through major Thoroughbred sales, and it is there veterinarians often notice problems with bone development. The wise horse owner will also be on the lookout for any signs of inflammation in the joints.
Once a horse develops a chip fracture, the clinician must decide which treatment protocol is best. Chips that might be causing some inflammation, but are not serious enough to cause lameness, might well be treated with an injection of joint fluid supplement, such hyaluronic acid or an anti-inflammatory agent.
Still another factor in determining the treatment of choice can involve age. For example, Adair explains, the bones of a 2-year-old horse are much more malleable and resilient than those of a 7-year-old. He says this means that a clinician might have a bit more latitude in deciding a course of action with a young horse, as compared to an older animal.
The chip’s location is also a key factor, Bramlage and Adair state. If it is in an area of strenuous joint motion, it is more apt to cause lameness, and the veterinarian might recommend arthroscopic surgery as the course of action.
Arthroscopic surgery has been instrumental in solving many bone chip problems since it came onto the equine scene in the 1970s.
Here is how the ERCG white paper describes the procedure, in part: “Arthroscopic surgery involves inserting a 4-millimeter in diameter instrument known as an arthroscope through small stab incisions to view and complete surgery within a joint, such as removing a cartilage fragment. Use of the arthroscope for diagnosis of equine joint disease commenced in the mid-1970s, while performing surgery under arthroscopic visualization began in the late 1970s. By 1984, both diagnostic and surgical arthroscopy were being performed clinically in the horse with arthroscopic techniques completed successfully in the carpus (knee), fetlock, hock, and stifle joints, with techniques for other joints following shortly thereafter. Currently, arthroscopy is used to diagnose and treat diseased joints more successfully than with incisional techniques used earlier. More than 50 joints and conditions can now be operated on arthroscopically.”
A key element in successful arthroscopic surgery, Bramlage says, involves a period of rest in the wake of the surgery to promote healing. Required recuperation time varies horse to horse, depending on the severity of the injury.
Arthroscopy received a strong public relations boost in 1985 when Spend a Buck scored a wire-to-wire six-length victory in the Kentucky Derby only five months after McIlwraith performed arthroscopic surgery for removal of a small fracture fragment in one knee.
Still another success story is the Thoroughbred Grindstone, winner of the 1996 Kentucky Derby. The colt had bone chips in both front fetlocks and both knees at age 2. Bramlage removed them with arthroscopic surgery. The colt won the Derby, but he sustained a bone chip in the right knee in the process and was retired. At stud he sired Birdstone, who, in turn, sired 2009 Kentucky Derby winner Mine That Bird. In the 2009 Preakness Mine That Bird finished second to Rachel Alexandra, a filly that had fetlock chip fractures removed as a 2-year-old.
Generally speaking, Bramlage says, veterinarians have found that horses with fetlock bone chips often have a positive prognosis for recovery and an ability to compete after surgery. The success ratio is not as high when the bone chip is in the knee, especially if it occurs in the lower knee joint. However, he adds, location and duration of injury figure prominently into the equation of how well the horse does athletically after surgery.
There also have been cases where horses have raced and won with bone chips present. The most notable case in point is War Emblem, winner of the 2003 Kentucky Derby and Preakness, but a horse that lost the Belmont after he stumbled at the start. War Emblem raced with bone chips in both front ankles and a knee.
A common goal of today’s horse owners is to determine early on if a joint problem involving a bone chip exists, and to treat it in the early stages with nonsurgical methods if possible, and surgical methods if necessary.
Article Reprint from horse.com