Condylar fractures are a large part of practice at Hogan Equine at Fair Winds Farm in Cream Ridge, N.J. Owner Patty Hogan, VMD, Dipl. ACVS, repairs about 50 condylar fractures a year. "It's the most common fracture we see in Thoroughbred racehorses," she says.
A couple of weeks before, Harbinger, winner of the 2010 King George VI and Queen Elizabeth Stakes at Ascot, England, was retired after sustaining a similar condylar fracture. Bone scans also revealed that Kentucky Derby winner Super Saver showed marked activity in all four cannon bones, with a major condylar bruise on the left front fetlock, according to a statement from Larry Bramlage, DVM, MS, Dipl. ACVS, Rood & Riddle Equine Hospital, Lexington, Ky.
"It's hard to say if condylar fractures are becoming more frequent," says Carter E. Judy, DVM, Dipl. ACVS, Alamo Pintado Equine Medical Center, Los Olivos, Calif. "At least in California, the type of fractures we're seeing has changed a bit since the advent of artificial surfaces. We still see condylar fractures but to a much lesser degree, and we're seeing a different configuration of the fracture type, with the fractures being shorter and thinner than they were previously. In my opinion, they tend not to be as severe as they were before." Unfortunately, no hard numbers are available to track this potential trend.
"I think these fractures will always be part of our racing scene," Nixon says. "The more you train and race these horses, the more they seem to get microfractures that predispose them to more complete and even catastrophic fractures. I wish we could detect microfractures better before they propagate," says Nixon. "The problem with this fracture is that there are areas that have accumulated stress within the fetlock joint and the metacarpal condyles, primarily along the palmar surfaces."
This particular area is predisposed to a subsequent propagating fracture. As a horse is trained more and runs more races, a change occurs in the way the bone structure is oriented. It is not a common fracture in 2-year-olds but is quite common in 3-year-old horses and older. "Bone scan and MRI may help us pick up the early changes that later lead to more complete fracture," Nixon says.
Data from these diagnostic studies are still being accumulated, but the eventual hope is that these noninvasive studies done without general anesthesia will provide enough warning of impending fracture that training can be tapered to allow recovery. "At this stage, we can't say with complete confidence that a fracture is inevitable, but as MRI becomes more available and more precise, it may well be our best tool for limiting complete condylar fracture," Nixon says.
Occurrence and etiology
"During the last few years, we have gained a better understanding of the disease," Bramlage says. "In general, we find these fractures in the early stages at a much higher rate than we used to." That is because technology such as bone scans and, more recently, MRI have contributed to our understanding of the disease and to our understanding of what we are seeing on radiographs. "Through the use of MRI, it's become apparent that when we can see the fracture on radiographs, it is already well into the disease process. MRI can show a whole lot more pathology than we ever knew was there," says Bramlage.
"We've known for some time that this disease process occurs because of the repetitive trauma to the bottom of the cannon bone that a horse sustains while it's training," Bramlage says. The key thing to understand is that the horse's skeleton has to adjust to the stress of training. "The musculoskeletal system of a yearling is just not capable of withstanding the kind of stress that a racehorse will put on it. As training progresses, the skeleton adapts."
The major places where this adaptation is seen are in the front cannon bones and the tibias. These bones have to get much bigger and stronger. "If the tibias get behind in this adaptation, the horses will develop a stress fracture," Bramlage says. "If the cannon bones of the front legs get behind, the horses will get bucked shins or eventually a stress fracture if they carry on."
These two bones have the advantage of being able to change both their structure (what they are made of—they can get denser) and their shape (the cannon bone and tibia enlarge). "That adaptation also has to take place on the bottom of the cannon bone at the fetlock joint surface," says Bramlage. "The big difference is that the surface at the bottom of the cannon bone doesn't have the luxury of changing its shape. It is a joint surface. The only option for the bottom of the cannon bone is for the bone to change its structure, which becomes denser and denser."
"There are two kinds of vulnerabilities associated with that," says Bramlage. "One is the original process of making that bone continually stronger in response to training, which can create a condylar fracture. The second vulnerability is the extreme density. If you change the bone away from normal porous or spongy cancellous bone to more dense bone, it becomes brittle, allowing fractures to propagate much more aggressively.
"This can be likened to a porcelain coffee cup that has gotten a small crack," Bramlage says. "It still holds coffee, doesn't separate and never seems to be a problem, though if you hit it just right or load it at just the right location, the cup falls apart." In condylar fractures, the bone sustains microdamage over time and continually repairs itself as the bone adapts. If the horse loads a vulnerable area unevenly or heavier than normal, it might result in a condylar fracture.
Bramlage notes that anecdotal data indicate artificial racing surfaces are much more consistent than dirt tracks. Horses do not hit irregular spots in the base on artificial surfaces as frequently as they do with dirt, so the number of condylar fractures is reduced with these new surfaces. As long as a horse never hits a vulnerable area just right, it can withstand the microdamage and eventually repair itself. But if it finds an irregular spot in the base of the track or makes an awkward foot plant for whatever reason, a condylar fracture may result.
All horses have this process of damage and repair going on at all times. "The fact that the bottom of the cannon bone is incapable of altering its shape to minimize that stress makes it much more vulnerable throughout the horse's career than the shins, which adapt their size and shape to neutralize the force, or the tibias, which eventually adapt their size and shape and are no longer vulnerable to stress fractures," Bramlage says. "It's a big demand to ask of the bottom of the cannon bone."
According to a Washington state program, every horse involved in a fatality or a breakdown at a Washington state racetrack must be examined at the veterinary school. About three years ago, members of the radiology group at Washington State University's (WSU) College of Veterinary Medicine realized this was a wonderful opportunity. They began to image horses from Emerald Downs, Auburn, Wash., not only to document the areas of injury, but also to look for preexisting diseases everywhere else within the lower skeleton.
According to Tucker, the microfracturing in the contralateral leg was not noticeable when the legs were looked at grossly unlike other regions common for stress fractures where a periosteal reaction is often visible.
Diagnostics that can be performed on the standing horse are preferred. "Although a standing equine MRI used for horses is not as sensitive as the higher field-strength units and not of the same high resolution for diagnostics, it might be a good way to screen for microfractures before the injury advances to a catastrophic fracture," Tucker says.
During this project, nuclear radioscintigraphy was also performed using a radiopharmaceutical that adheres to bone tissue. This technique showed areas of abnormal bone remodeling and is a sensitive way to pick up stress fractures. Nuclear scintigraphy can be performed on standing horses by using a sedative and an external camera.
"With the help of MRI, and now with the use of nuclear scintigraphy, it may be possible to screen horses without risking general anesthesia," Tucker says. "Standing MRI and nuclear scintigraphy can identify an area of general concern. Horses showing a pattern typical of microfracture and/or trabecular breakdown could be put on a lesser regimen of training or rest."
These methodologies are complementary. Nuclear scintigraphy does not replace MRI, and low-field strength MRI is not the same as high-field strength MRI, but they are all helpful to offer some diagnostic possibilities.
Tucker says data from this study showed that it was important to conduct a complete examination on each patient and not only focus on the site of breakdown. Since condylar fractures occur as a result of sclerosis of the distal metacarpus (cannon bone), Wilkinson did a quantitative study in which, by using MRI, he evaluated the degree of sclerosis, or hardening, of the subchondral bone. In joints there is articular cartilage and subchondral bone, not periosteum. The bone plate supports the cartilage. "The subchondral bone is a very delicate substance," Tucker says, "so this is where one sees osteochondrosis, a typical disease in which the bone underneath the cartilage does not form correctly. The cartilage above the bone breaks down, caves in and creates osteochondrosis."
What this study found were specific areas of subchondral bone sclerosis and remodeling, which leads to fissuring. Lateral condylar fractures have a well-known orientation as to where they occur. So horses are at higher risk for condylar fractures based on specific areas of subchondral bone sclerosis. During an MRI examination, the trouble areas light up as distinct patterns. They are red flags. "If a horse with this type of subchondral damage continues to train or race, it is basically running on dangerous wheels and can have a blow out at any time," Tucker says.
"Unless we do more MRIs and more CT scans as a routine matter, we'll never be able to pick out these horses as potential fracture cases," Nixon says. "Quite honestly, I doubt that we're going to be able to convince trainers and owners of the need to anesthetize racehorses in the midst of their campaigns to do a CT or MRI to define an obscure lameness. Standing MRI is probably the answer, but it is not yet sensitive or fast enough to pick up predisposition to these sorts of fractures. The differences in detail on low-field strength standing MRI and the high-field strength MRI units requiring general anesthesia is quite considerable. But the gap is closing. A program of a bone scan followed by a standing MRI or CT may be potentially useful to identify these horses. It's just a question of whether the sensitivity is good enough to separate those that are likely to fracture versus those that are not. Right now the technology is still being developed to be able to do that."
"In order to get out in front of the fracture outcome, we've been looking at scintigraphy and in some cases MRI," Judy says. MRIs are being performed in some racehorses "that come up sore in their ankles." Equine veterinarians are seeing tiny nondisplaced cracks right at the articular surface. "These tell us that something may be going on in the ankle, and we recommend backing off on those horses training a lot earlier than we might have in the past," Judy says. "Those horses have not gone on to fracture those legs after we've given them a period of rest."
There is definitely a population of horses that have condylar sclerosis as seen in MRI results. "We think those horses may be at an increased risk for fractures," Judy says. "We don't have any hard numbers yet, but it is sure suggestive that that may be true." Trainers have started backing off of the horses with a lot of condylar sclerosis, trying to get the bones retrained to tolerate the stress and not become so brittle.
"The treatment for condylar fractures is pretty straightforward these days," Judy says. The screw fixation has been quite successful, not only for keeping these horses alive but also for getting many of them back to the racetrack. "The only debate is whether you take the screws out or leave them in, and everybody has their own opinion about that."
"As far as the repair goes, it is straightforward," Hogan agrees. "It really hasn't changed a lot, though we now realize that we don't have to put 10 screws in a bone. We just need to secure the joint surface. Most routine fractures are repaired with one or two screws."
"I know of one horse that actually had three condylar fractures in its racing career and actually broke three different condyles in three different legs," Judy says. "And after each one, he went on to race and win."
Lining up the fractured bone exactly with the parent bone is something most experienced surgeons can do quite nicely, particularly with the help of digital radiography or fluoroscopic control. "The biggest concern with all of these, particularly displaced fractures, is the damage to the backside of the joint, where the cartilage is lost, because of the small fragments that develop there," Nixon says. "Those crumbly fragments might be only a couple of millimeters across, but they are a key element to returning horses to their true athletic function and should be removed."
The fragments can be difficult to get out or even visualize. And while the bigger fragments can be locked back into position with the screw repair, the smaller comminuted pieces lead to progressive arthritis and need to be removed. "Once you get them out, you're going to get a better response," Nixon says. "Doing the screw insertion is only a small part of the surgery; the key is cartilage repair. I think when we get better at doing cartilage cell grafts, or stem cell grafts, in these areas we'll get a better outcome.
"The surgery ought to be a three-step process," Nixon adds. "First is fracture reduction and screw insertion. Second, fragment removal—the small fragments that are so loose and rattling around in the back of the joint. And the third phase should be a cartilage or stem cell graft after the fragments have been removed. The big issues right now are trying to get better quality cartilage repair at the back of the fetlock."
"One thing I've learned over the years, by using arthroscopy, is that there is a lot more going on than just the resultant fracture," Hogan says. "Early on, I used to just fix the fracture and never look in the joints. But I started to scope every single one because some fractures that I thought would do very well ended up still having some low-grade soreness problems that I really didn't understand." When she started to arthroscopically evaluate the joints, she found out more, and it solidified her opinion that the condylar fracture is just one part of a chain of events occurring in the ankle.
"I found that when I looked in the back of the joint, in about 80 percent of the horses, there was concurrent cartilage erosion or injury of the lateral sesamoid bone—even in the simplest of fractures with no previous history of joint disease," Hogan says. "So that tells me that there is some undue biomechanical stress on that joint. The cartilage is going to show evidence of that first, and then the bone is going break. It's a combination of factors that contributes to the bone breaking. I always arthroscopically evaluate the joint now and consider what the joint looks like on the inside when formulating my prognosis. If the horse has preexisting joint disease, it has overloading in that joint for some reason and will likely continue to do so to some degree."
"We're definitely learning a great deal with the use of CT now," Hogan adds. "We did a lot of that when I was at Ruffian Equine Medical Center, in Elmont, N.Y., last year, where we performed CT on every condylar fracture. Our intern, Sarah Gray, BVSc, presented a paper regarding our findings in October at the ACVS meeting in Seattle. In every single fractured limb that we performed a CT on, there was a measurable difference in bone density between the fractured condyle and the nonfractured one. We could see that there was sclerosis or a brittleness that occurs in the bone. We have all known that this is occurring, but being able to measure it is just one more piece of information that will ultimately contribute to our objective of minimizing this injury in the racehorse. There is more and more that we are finding out as far as preventing these fractures or finding them early. Certainly bone scans have been extremely helpful, when people will do them."
"I do think that condylar fractures are not single-event injuries but a stress accumulation-type of injury," Hogan says. "The more science that we commit to this problem, the more we learn and realize that it's true. It is rarely the 'took-a-bad-step' scenario. These horses have underlying disease that is going on in the bone, in particular the lateral condyle of the cannon bone. This compromised portion of the bone develops a fault line, and then it just breaks."
"We see so many condylar fractures, and some can be really challenging," Hogan says. "Your goal is to get a racehorse back to training and racing."
With the advances in technology and better understanding of these fractures, they may some day be a thing of the past. "The day is coming when I may be out of business repairing condylar fractures because the more we learn about them, the smarter we are about detecting early bone changes," Hogan says. "Very soon, condylar fractures may be one of the less common fractures occurring in the racing Thoroughbred."
Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. He is based in Seattle.