Ah, the well-turned pastern: slender, shapely, yet incredibly strong, the bearer of thousands of pounds of pressure relentlessly imposed during the million steps of a lifetime. So much rides on the pastern, and so little goes wrong with it, at least compared to the fetlock above and the ever-challenged hoof below. Accidents, including fractures, cuts and abrasions, do afflict the area, for sure, and strains and pulls of tendons and suspensory ligaments crisscrossing the pastern do occur. But only two abnormalities--ringbone and sidebone--pop up on the pastern often enough to have earned labels in common stable parlance.
Both "bones" are evidenced by visible irregularities on the pastern, yet neither is always or even often the cause of lameness. Sidebone, especially, is usually more a matter of abnormal appearance than of altered function. Ringbone, on the other hand, does disable horses, sometimes temporarily, sometimes permanently.
Your greatest ally in deciding the seriousness of a pastern irregularity is the horse himself: You can bet that no matter how awful the landscape there may look to you, if the horse isn't limping, there's no cause for panic. Even if he is "off," the lumpy pastern may well be blameless in the lameness, an unfortunate concurrence with another painful place in the lower leg. By familiarizing yourself with the normal pastern landscape and function, you'll be prepared to determine which lower-leg lumps are harbingers of trouble and which are merely blemishes.
The two bones called phalanxes or phalanges that make up the pastern are equivalent to your two longest finger bones. Your third phalanx resides within your fingertip and the horse's within his hoof, where it's called the coffin or pedal bone. So little movement takes place in the pastern joint connecting the long and short pastern ones that casual observation would lead you to believe a single bone links the fetlock and hoof. Yet the joint is visible just below a pair of dimplelike depressions on the inside and outside of the pastern two or more inches above the hoof. This pair of hollow spots is one of the "good" irregularities you'll find on the normal pastern. The joint connecting the short pastern bone and the coffin bone is not visible and barely palpable because it's just within the hoof capsule and overlaid, on its sides, by thick cartilage pads (collateral cartilages).
Flexibility is the primary feature of your own joined phalanxes, allowing you to curl your fingers to grasp and manipulate. In contrast, the equine design requires rigidity between the upper two bones so the pastern can act as a stiff strut and firm anchor for the soft-tissue "straps" that hold the leg bones in line. Because of the tendons' pulleylike action, which wouldn't be possible without an immobile pastern joint, the fetlock and the coffin joints rotate in concert with each other and the larger hinges up the leg during the touchdown, support, liftoff and airborne portions of each stride.
The tendons and ligaments on a weight-bearing pastern are difficult to discern because they hug the bone surfaces so tightly. If you lift your horse's leg and manipulate his hoof while palpating the pastern with your other hand, you should be able to feel the play of the extensor branches of the suspensory ligament angling forward over the sides of the pastern just below the fetlock. The deep digital flexor tendon lies along the rear aspect of the pastern joint: The one small window of opportunity for palpating it is in the vaulted arch formed by the superficial flexor tendon where it encircles the deep tendon just above the cleft between the heel bulbs. The extensor tendon, the strap that advances the in-flight foot to its landing position, runs down the front of the pastern toward the tip of the toe. On fine-skinned horses, these supporting structures are discernible not as bulges or lumpiness but as clean-edged ridges slanting across the bones.
The joining of hoof wall to skin is accomplished at the coronary band or coronet, the raised, rather hard area encircling the foot from heel to heel. Just inside the coronet, on the sides and toward the heels, are the cartilage pads overlying the coffin joint. These collateral cartilages, so called for their location on each side of the hoof, are partly within the hoof wall and partly above it. In addition to serving to smooth the transition between the slender column of the pastern bones and the wide "mouth" of the hoof capsule, these cartilages contribute to shock absorption and circulation. Rigid enough to protect the blood vessels and nerves passing through them to the hoof's interior, these cartilages are just sufficiently flexible to participate in the hoof's expansion and contraction during weight bearing and flight. Normal collateral cartilages are readily visible and palpable as smooth, somewhat "giving" bulges that are wider and higher near the heels and taper toward the toe. Draft horses and other individuals with blocky, upright pasterns may have collateral cartilages that, even when healthy and functioning normally, are quite prominent.
Just as normal human ankles range from fleshy to fine, stumpy to fragile, horses' pasterns exhibit a variety of normal "looks." By studying the lower limbs of many horses carefully with your eyes and your fingers, you'll come to appreciate the array of structural possibilities, from the long, sloping, slender model to the short, stocky, upright tree trunk. Versed in the normal landscape of bones, joints, soft-tissue supports and cartilage pads, you're set to recognize the lumps that could spell trouble.
An angry streak of scar tissue running over one heel. An unyielding ridge jutting above the coronet at the quarters. A disorderly blossom of bone on the front surface of one pastern. A squishy bulge just above the cleft of the heels. These are some of the sights that can stop you cold when they pop up within your herd or show up on a prospective purchase. Unfortunately, looks alone aren't reliable indicators of each condition's implications for present and future soundness. Even before you engage a veterinarian to examine and x-ray these questionable sites, you can deduce a lot of vital information about a lump's seriousness from its location and characteristics.
Location: The where of the case indicates which type of tissue and which particular structure are currently or were once inflamed by a single traumatic event or chronic wear and tear. The possible sites include a joint surface, cartilage, a tendon or ligament, and skin and connective tissue.
The pastern provides two opportunities for joint-associated swellings. When the pastern joint is involved, the condition is called high ringbone. The bulge appears one to two inches above the coronet, usually with the greatest swelling on the pastern's front surface. Low ringbone affects the coffin joint, with the lumpiness appearing at the coronet, most often in the toe region. "True" ringbone (veterinarians call it "articular" ringbone) arises from joint edges or surfaces, with bone eventually proliferating in response to damage to the cartilage. Some articular ringbones are painful and progressive; others are "silent" for years or a lifetime.
"False" or "periarticular" ringbone is a similar response to bone-surface damage in the vicinity of, but not within, the joint. Direct injurious blows are the usual cause. Strains and tears of tendon and ligament attachments near the joints and periosteum-damaging wounds also can trigger the inflammatory process responsible for "false" ringbone. Only a radiograph can show for sure if the ringbone is true or false.
Hard ridges above the coronet at one or both quarters of the hoof tell you that the collateral cartilage(s) there have ossified, or converted to bone. A foot affected by sidebone, as the condition is called, may look boxy and upright and have contracted heels. When you apply finger pressure on the heels behind the pastern, you'll feel the resistance of bone rather than the slight give of cartilage.
A bulge or swelling at the back of the pastern just above the heel bulbs reflects wither tendon strain or inflammation of the tendon sheath through which the deep digital flexor tendon passes. These rear supports structures run all the way from the coffin bone to the knee/hock, and through the tendons are more likely to "blow out" from excess stress. Filling of the usual hollow between the long pastern bone and the side of the digital flexor tendon indicates strain of the inferior sesamoidean ligament.
Characteristics: The lump's appearance, feel and effect on the horse indicate how recently the problem has arisen and how painful it is.
- The swelling's consistency reflects both the structure being affected and the strength and stage of the inflammatory response. A fluid-filled swelling is most often a sign of current inflammation in which the injured tissues are awash with healing juices. Sometimes injury or infection causes fluid-producing joint capsules and tendon sheaths to develop bulges that remain even after inflammation subsides. Bone-hard lumps are exactly that, calcification gone awry in reaction to a months-earlier disturbance in the bone's covering of cartilage or periosteum. Scarring of the skin tells of crises on the surface months or years ago.
- Temperature of the tissues is a useful gauge in assessing the current activity of a lump. Heat is swelling's partner in inflammation, a sign that something is definitely amiss and an indication that there still may be an opportunity to halt the destruction. A cold lump is set, and though it's probably painless, it's unlikely to go away on its own.
- Sensitivity to palpation indicates whether the lump is inflamed, the injury is recent or resolved and if pain is affecting the gait at least a little. The presence or absence of sensitivity is crucial to your veterinarian's diagnostic procedure: Palpation, flexion tests, temporary nerve blocks and having the horse jog in circles and sharp turns on a variety of footings all help pinpoint sensitivity in pastern structures.
No single characteristic will tell you that one pastern lump is benign and another is a career stopper. Instead, it's the convergence of characteristics with location and the horse's reaction to it that speaks of the present and long-term implications of the abnormality. The swelling, heat and pain associated with a superficial rope burn on the pastern can be intense enough to cause the horse to limp, yet good nursing care will make the lower leg as good as new. Conversely, a little on-again, off-again choppiness arising from a gradually developing ringbone won't look like much early on but later can mean the end of the horse's usefulness under saddle.
The Bad and Just Ugly
Owners of conformation horses don't want to see even the tiniest nick blemishing their animals' pasterns, but the critical issue for most other lines of work is whether an abnormal lump has or will have soundness implications. The joints are the most likely sites of lameness-associated swellings. Because high ringbone affects a joint with almost no mobility anyway, its prognosis is more optimistic, in many cases, than the outlook for low (within the hoof) ringbone. If articular inflammation eventually fuses the pastern joint (in a process called ankylosis) or if surgery produces the same effect through the use of screws and plates, the horse may return to his previous performance level. However, neither of these "cures" is swift, painless or, in the case of surgical intervention, without risk of complications.
On the other hand, low ringbone is a diagnosis you'd never like to hear for your horse. Given the need for a smoothly operating hinge at the coffin joint and its location within the hoof capsule, swelling, pain and diminished movement there really affect the horse's soundness. Painkillers help control the discomfort, but nothing will reverse the joint restriction, which translates into permanent gait deficits.
Tendon and ligament damage signaled by a soft lump or a hard "filling" on the back of the pastern just above the heels is less common but possibly as debilitating as low ringbone. Strains and tears of the support tissues are quite painful and often more sluggish about healing than bone fractures. Lengthy rest, restricted movement and pain management may encourage resolution of the inflammatory reaction, but injured tendon tissues never regain their previous flexibility and strength. Patience can be rewarding in cases of strained sesamoidean ligaments, which heal to soundness with 12 to 18 months of quiet pasture rest.
When a pastern irregularity does not involve the joint surfaces, tendons or ligaments, it rarely affects the horse's soundness. Scars from accidental injuries--the wire cuts, abrasions, rope burns and such that are so common on horses' lower legs--remain blemishes so long as they involve just the skin and immediate subcutaneous tissues. Wounds that disturb deeper structures, such as the periosteum and joint capsules, trigger calcification in all the wrong places and may or may not affect soundness. You can distinguish the just ugly from the bad by palpating the area: If the scar or lump moves feely over the underlying hard tissues just as the normal, surrounding skin does, it shouldn't limit the horse's movement or cause him pain.
Nonarticular bony lumps rarely are anything but blemishes. The calcification most likely occurred in response to a traumatic event, but, located away from a joint, it doesn't produce pain or impede movement once inflammation has turned to bone.
Rarely does sidebone cause lameness. Ossification of the collateral cartilages may be a normal aging-related change that robs the foot of some of its elasticity. Lateral hoof imbalance and injury of the quarters also produce the characteristic bony ridges just above the coronet. Only when the area is actively inflamed, with signs of heat and sensitivity to pressure, can a lameness possibly be linked to sidebone. Radiographs won't reveal the "truth," as many horses have bony changes in that area without exhibiting any gait changes. If someone points to sidebone in a lame horse, look elsewhere for the cause of the limp.
Preventing pastern injuries is part good management and part wise stock selection. Keeping your horse's lower legs out of injurious entanglements with wire, animal burrows and the like and assuring him sage footing beneath functionally balanced feet will protect him from the majority of pastern-damaging accidents. When selecting or breeding horses for activities high on concussion, quick, lateral moves and abrupt stops, avoid the conformation that makes the pastern vulnerable to breakdown.
For vulnerable horses in risky occupations, train and compete conservatively, and heed the earliest warnings that the joints and support structures are being hit with more stress than they can endure. Better to give the pastern-weary horse a restorative rest, improve his working conditions and maybe even change his occupation. This stretch of anatomy may sport a bunch of bumps and lumps that look worse than they really are in terms of their effects on function, but once the truly serious pastern conditions become entrenched, there's no curing them.
This article originally appeared in the March 1997 issue of EQUUS magazine.