Your horse is limping and a detailed visual exam by your veterinarian reveals a small black spot, suggesting a puncture wound. Your veterinarian radiographs the hoof: The X rays confirm the diagnosis, clearly showing the direction and depth of the puncture.
But for other hoof disorders, radiographs can fail to determine a cause of lameness, and your veterinarian might recommend additional diagnostics. Is it a case of overkill--more time and money spent on the job--or do some hoof defects show up on X rays (also called radiographs) while others don't?
The answer might be both. Some defects are easy to spot (such as displaced fractures), while others are mostly invisible to the untrained eye and require an experienced podiatrist to interpret. Also, all radiographs are not created equal--just like photographs, the information they contain is dependent on the practitioner's technique and the subject's cooperation. And that technique will vary depending on what structure(s) the podiatrist wants to highlight; the technique used to image bony problems won't always show soft tissue defects. Yet another consideration is that even an excellent radiograph might not show a problem if it isn't taken at just the right angle; the foot is a complex structure and some parts can hide problems in others.
Although they require skill to take and read, radiographs can provide invaluable information on foot problems.
Diagnosis of foot problems begins with a good physical exam. Says Tia Nelson, DVM, a farrier and veterinarian with Total Dynamic Balance Veterinary Service in Helena, Mont., "The veterinarian's hands and eyes are the most valuable tools he or she has to evaluate balance, pain, and the area of defect, and are vital to the diagnosis and treatment of each case." After that, she might try radiography to confirm or rule out what she suspected from her physical exam.
Her approach is shared by other experts: Ric Redden, DVM, founder of the International Equine Podiatry Center in Versailles, Ky., wrote in the January 2004 issue of The Horse that physical examination is "the single most important aspect of examining the equine foot. With very few exceptions, the objective of the radiographic examination is simply to confirm the findings or suspicions of the physical examination. Relying on radiographic findings without a thorough physical examination and without consideration of the history carries the risk of misinterpretation and error, which can be costly."
What Can You See?
Once a problem area has been identified, radiographs can show what's going on under the skin. An imaging technique employed to evaluate bone and soft tissue, radiography passes X rays through a part of the body to yield an image. Dense areas such as bones block more of the X rays than less dense areas such as muscle; bones are prominently imaged in white on dark X ray film, while muscle and soft tissue show up as gray or black and, consequently, are far less distinctive.
Foot radiographs can show problems in bones, hoof balance, and soft tissues, and they can reveal other injuries such as abscesses and puncture wounds. If a horse's feet are radiographed repeatedly over time, they can also show trends in hoof balance and measurements that might clue you in to problems developing or to the effects of the horse's shoeing. Following are discussions of the types of information one can glean from radiographs of the feet.
Radiographs are especially helpful in looking at bones within the hoof capsule, says Elizabeth Hammer Davidson, DVM, Dipl. ACVS, assistant professor in sports medicine at the University of Pennsylvania's New Bolton Center. Examples of bone pathology visible on radiographs include:
Fractures--Bone breaks appear as dark lines in an otherwise white or light gray bone, and can be non-displaced fractures (where bone pieces are still next to each other) or displaced fractures (where a piece has moved away from its original position).
Ringbone--This refers to additional bone deposition just outside or at the edge of one or both pastern joints as a result of chronic inflammation. It can "ring" partially or completely around a joint, causing pain and lameness, and it is visible as a rough addition to what should be smooth bone surfaces in these locations.
Sidebone--When lateral cartilages harden into bone (usually from chronic trauma), this is called sidebone. Sidebone compromises the hoof's ability to expand and contract, often resulting in lameness. On a radiograph, normal lateral cartilages are much darker than light gray bony sidebones.
Septic osteitis--Infection and inflammation of the coffin bone that begins in its protective membrane, the periosteum, is termed septic osteitis. This disease results in erosion of the bone surface to varying degrees, with extreme lameness. Bruce Lyle, DVM, a primary care practitioner and podiatrist in Aubrey, Texas, says radiographs of these horses might show progressive thickening of the horn-laminar zone (the distance between the laminae and the outside of the hoof wall, which is not exclusive to septic osteitis), loss of sole depth in the affected area, asymmetric collapse of the proximal (upper) hoof wall into the coronary band of the affected area (unless it was recently trimmed and balanced), and a gas density adjacent to the bone.
Lesions such as cysts and navicular bone degeneration--Michael Ball, DVM, of Early Winter Equine Medicine and Surgery in Ithaca, N.Y., notes that pathology known to be related to navicular syndrome includes enlargements of the vascular channels or synovial fossa within the navicular bone, cyst-like (darker) lesions within the navicular bone, mineralization or calcification of the ligaments associated with the navicular bone, bone disease affecting the coffin joint in the area of the navicular bone, degeneration of the flexor surface of the navicular bone, degeneration of the flexor tendon in the area of its passage over the navicular bone, fractures of the navicular bone, and any combination or degree of these pathologies. "It typically takes three different radiographic views to evaluate the navicular area," he says.
Coffin Bone Position
In addition to bone problems, Andrew Parks, VetMB, MRCVS, Dipl. ACVS, professor of large animal surgery at the University of Georgia, states that one of the most useful things radiographs demonstrate is the position of the distal phalanx (coffin bone) in relation to the hoof wall. This can be useful for evaluating a horse with laminitis, as the distal phalanx can separate from the hoof wall and rotate within the foot in a severe case. It can also be useful for evaluating hoof balance.
Laminitis with coffin bone rotation--"You can see displacement of the distal phalanx (coffin bone), the defining feature of chronic laminitis, on radiographs," says Parks. "Later on in laminitis, you may see very clearly the changes in the curvature and the thickening of the hoof wall that accompanies abnormal hoof growth."
However, rotation can be a tricky thing to measure unless there is already a radiograph of the horse's feet when they were sound. The reason for this is that there is considerable variation in conformation between individual horses, just as with people. Thus, a specific range of values for coffin bone angles in "normal" and "rotated" feet doesn't really exist, as rotation is relative to the angle the coffin bone had before disease occurred. In particular, horses with club feet will have steeper coffin bone angles that can look like rotation, but they're really just normal angles for those horses.
Once the initial radiograph is taken, successive radiographs can help monitor any progressive rotation or treatment success.
Foot imbalance--"A weight-bearing radiograph view through the phalanges will show a lack of balance when the joint space is compared from medial to lateral (viewed from the front)," explains Nelson. "The space should be equally wide on both medial and lateral sides. If it is pinched or closer on one side than the other, balance should be carefully examined. Disorders associated with lack of hoof balance include lameness, stress fractures of the hoof, abscesses due to pressure, arthritis, and toe or quarter cracks."
Parks notes that bone alignment seen on a lateral radiograph (from the side) can also give some insights into tendon tension. "Increased tension (of the deep digital flexor tendon, implied by the "heels" of the coffin bone being dropped toward the ground) results in increased pressure on the navicular bone," he says. "This conformation and increase in pressure is one factor that leads to the development of navicular disease."
Other Hoof Pathologies
Other defects often seen radiographically, Parks says, include white line disease, keratomas, pockets or lines of gas (which can be associated with laminitis or abscesses), avulsions where pieces of hoof wall are missing, and sometimes cracks.
A change in the location of the very thin, slightly darker (on X rays) line at what's probably the junction of keratinized and non-keratinized tissues signals hoof problems. "This line is normally about at the junction of the outer 60% (stratum medium of the wall) and inner 40% (stratum internum and soft tissues)," Parks says. "If that line is no longer at this location, it implies that one of the other two layers is thicker. In horses with acute laminitis, the inner layer of the wall becomes edematous (fluid-filled) and is thicker than normal."
Puncture wound tracts can often be seen on radiographs, and many practitioners prefer that any penetrating object be left in the foot if possible for radiographing, so they can see how deep the injury goes. Once the object is pulled out, the injury will be harder to see.
Hoof Repair and Radiographs
Although they're not often a problem, hoof repair materials can cause problems when evaluating radiographs, notes Davidson, who presented her observations of how various hoof repair compounds affect radiographic findings at a New Bolton Center hoof symposium. Adds Nelson, "If the internal structures you want to visualize cannot be seen due to the repair material, then it will be difficult to confirm diagnoses and assess treatments." She says thin layers of repair material aren't usually problematic.
"If the hoof wall repair incorporates metallic compounds such as screws or wires, they will definitely appear on the radiographs, impairing the ability to evaluate the underlying bony structures," Davidson says. "Additional oblique radiographic views may be indicated under these circumstances."
Another material sometimes used on the hoof is iodine. "Iodine on a hoof and under a patch can certainly be a little misleading on radiographic images," Parks states. "Iodine casts a radiodense shadow wherever it is. If I know that it's there, I just allow for it and don't worry about it, but a veterinarian should be made aware of it."
Radiographs as Preventive Care?
Beyond deworming, dentistry, and foot care, one veterinarian believes that annual lateral radiographs of your horse's front feet (and interpretation by your horse's veterinarian in consultation with his farrier) should be included in your preventive care program. Richard Mansmann, VMD, PhD, of Central Carolina Equine Practice in Chapel Hill, N.C., notes that this program is a systematic way to make the owner aware of any potential or existing foot problems, a basis from which the farrier, now armed with a radiograph, can make more informed shoeing decisions, and a means to encourage positive interaction among the owner/veterinarian/ farrier team.
Beyond Standard Radiographs
When a physical exam and radiographs can't tell the whole story, your veterinarian will likely turn to additional diagnostics. A venogram (radiograph that provides an image of the foot's veins after contrast dye is injected into a vein) tells if a horse lacks circulation in an area, Davidson says. "If the lack of circulation is quite severe, it's possible we have a laminitic horse. An area without circulation suggests that the health of the foot in that area is poor," as blood flow is key to the health of the tissues.
Areas of poor circulation could indicate damage or areas of increased pressure that are compromising blood flow, but aren't causing problems yet, much like your arm turning white when you press your fingertip on it for a few minutes. These areas could be due to poor balance or some other cause of unbalanced stresses in the foot, and could cause problems if not addressed. (For more information on venograms, see www.TheHorse.com/ViewArticle.aspx?ID=4076).
Other diagnostic techniques such as nerve blocks, flexion tests, and stress tests (such as lifting the toe off the ground) are helpful in pinpointing a diagnosis. "Finding the painful area or area of defect is important," Nelson says. "Any tool or clever idea to resolve that question is useful."
Radiography is just one tool in the veterinarian's arsenal of foot diagnostics, but it's a valuable one. It can provide essential information in times of crisis or minor lameness. If your veterinarian radiographs your horse's feet, ask for an explanation of what he/she finds. The insight you'll get into your horse's feet can help you better understand how to manage his feet and treat any problems.
See the Lameness (Hoof) and Shoeing category at www.TheHorse.com, and the Radiography category under Diagnostic Imaging.
About the Author
Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.
POLL: Colic Surgery