Straightening Crooked Legs
It is not unusual for foals to be born with some level of angular limb deformity, but this becomes a problem when the deformity is severe and doesn't self-correct quickly. If the deviation is relatively minor, it might be resolved with stall rest, corrective shoeing, and/or a splint. However, if the conservative approach fails, the solution might involve surgery--periosteal stripping, transphyseal bridging, or in serious cases both of these surgical procedures.
"Over the past 10 years, the surgical techniques for correcting angular limb deformities preferred by the major surgical and teaching centers have changed several times," says Mark Robinson, DVM, of Alpine Veterinary Service in Billings, Mont. "As we watched the various recommendations, comments, and observations from the institutions and noted surgeons evolve, we have also modified our own methods of surgically managing these cases in the setting of our rural private practices."
Causes of Angular Deformity
"The angular limb deformity (deviation of the foal's legs away from the normal axis of the limb)," he says, "is classified as varus or valgus, depending on whether the deviation is medial (toward the animal's midline, or varus) or lateral (away from the animal's midline, or valgus). These deviations are further described by their location on the limb. Specifically, they are classified from the joint where the problem begins. For example, a foal whose pastern angles outward (lateral) from the fetlock down is said to have fetlock valgus. If the fetlock angles inward (medially) from the fetlock downward, the foal is said to have fetlock varus."
Causes of angular limb deformities are many and varied. According to a paper on equine pediatric orthopedics by Pamela C. Wagner Von Matthiessen, DVM, previously of Oregon State University (OSU), and Barbara J. Watrous, DVM, also of OSU, there are five predisposing defects that lead to angular limb deformities.
"These are poor conformation, which cannot be treated; laxity of the joint; immature bones in the carpus or tarsus; growth imbalance of the physis (growth plate); and trauma to the growth plate," write Wagner Von Matthiessen and Watrous. "All of these problems lead to uneven stress, and thus uneven growth at the plate (more on this later). Once the uneven weight-bearing begins, it becomes a continuous cycle. The angled leg causes more stress on the already stressed portion of the plate, making it worse. The cycle must be broken by redistributing the weight on the plate with external splints, corrective trimming and shoeing, or surgical manipulation of the unequal growth rate."
Growth plates are highly specialized areas at one or both ends of a bone at which all of the bone's longitudinal growth occurs. If this plate is or becomes asymmetrical, the longitudinal growth of the bone will be crooked, hence owners' and veterinarians' interest in treatments that reestablish symmetry as quickly as possible.
Correcting Angular Deformities
Angular limb deformities can be challenging to a veterinarian, partly because there is a relatively narrow window of opportunity for correction. The general rule of thumb for veterinarians is that if an angular limb deformity does not show any sign of improvement within 10 to 14 days after birth, some form of action--possibly including surgery--should be taken.
Wagner Von Matthiessen and Watrous have this to say about treatment of these non-self-correcting deformities: "Free exercise may worsen the deformity, and stall rest is recommended. Hoof trimming and splints are some recommended conservative therapies.
"Early surgical treatment is also recommended," their paper continues. "Because of growth plate closure times (age of the horse when the plates completely ossify into non-growing bone), angular limb deformities at the fetlock must be treated by four weeks of age, and those in the carpus (knee) or tarsus (hock) by four months. After this time, even surgery may not completely correct the deformity."
It's important, says Robinson, to consider the location and cause of the angular limb deformity when deciding on the appropriate treatment approach. The following conditions, he says, should be ruled in or out prior to developing a treatment plan:
- Incomplete ossification (conversion of cartilage into bone) of the small cuboidal (cube-shaped) bones of the carpus or tarsus (see photo on page 109);
- Laxity of the surrounding soft tissue structures supporting the joint; and
- Abnormalities of epiphysis (end of a long bone), physis (growth plate), and metaphysis (the wider part at the extremity of the shaft of a long bone) of the long bones entering the joint.
"Incomplete ossification of the cuboidal bones," Robinson says, "can be due to abnormalities occurring before birth, causing a delay of the ossification process of the small bones located in the hock or carpus. A shortened gestational period may lead to the same problem. The foal with incomplete ossification of the carpal bones should be diagnosed and treated as soon as possible to attempt to minimize malformation of these bones as post-natal ossification progresses. The improper angle of the limb leads to improper loading of the soft, cartilaginous cuboidal bones. This, in turn, leads to an irreversibly malformed bone at the completion of ossification."
Radiographs, he says, can quickly provide a diagnosis of incomplete ossification. On the X rays, cuboidal bones of the knee or hock will appear poorly mineralized and rounded in appearance. In addition, when the joint is manipulated, it can be pushed straight or to the opposite deformity.
Laxity of the surrounding soft tissues of the abnormal joint, he says, also can be easily diagnosed with radiographs and digital manipulation.
"We manage incomplete ossification and soft tissue flaccidity non-surgically," Robinson says. "Foals with incomplete ossification of the carpal bones are managed with stall rest and splint application. Due to the associated risks, we are reluctant to apply casts unless we are unable to maintain proper alignment of the leg with splint application.
"When splints are used, we change them every three days to provide dry padding and check for rubs or pressure sores. We change casts every 10 days and try to move the foal into a splint if it is practical. We apply the splints or casts until the ossification of the cuboidal bones appears sufficient. We confine the foals with incomplete ossification of the cuboidal bones strictly, but allow the foals with laxity of the soft tissue structures to walk with their mothers for 10 minutes twice daily."
However, Robinson says, when the problem is with the distal (lower) end of long bones, surgery might be needed.
Primarily, two surgical techniques are employed. One is periosteal stripping, which is the simpler of the two. The other is transphyseal bridging, which is more involved but often brings about a more rapid resolution of the problem.
There are some advantages to periosteal stripping compared to transphyseal bridging, according to Robinson. For one thing, he explains, periosteal stripping requires minimal instrumentation, no expensive surgical implants, and can usually be performed at a reasonable cost for the client.
This procedure involves exposing the periosteum--the tough, thick, fibrous membrane that covers the bones--and incising (cutting) and elevating it away from one side of the bone (see "Surgical Options for Limb Straightening" on page 104). By so doing, Robinson says, "We are able to cause that side of the bone to grow more rapidly and thereby push the limb below the joint in the opposite direction."
In valgus (away from the midline) deformities, Robinson says, the periosteal stripping should be performed on the lateral (outside) side of the long bone entering the joint to allow that side's growth to "catch up" to the medial (inside) side. In varus deformities, it would be just the opposite--the procedure would be performed on the medial (inside) side of the long bone entering the joint.
However, he says there are times when this procedure won't get the job done in a timely manner.
"We feel," he says, "that hemicircumferential transection and periosteal stripping are slower and less likely to cause complete resolution of angular limb deformities than growth retardation techniques (transphyseal bridging)."
Age of the patient also becomes a factor. Robinson says that he is less likely to perform periosteal stripping alone on knee or hock deformities of foals that are more than two months of age or on fetlock deformities of foals more than four weeks of age.
"Since the time necessary to let the limb straighten (before the growth plates close, or stop growing) is the limiting factor in surgical treatment of angular limb deformities," he says, "the degree of deformity must be considered when picking a surgical protocol for the treatment of the deformity. Severe angulations should be treated by growth retardation techniques (transphyseal bridging) or combinations of growth retardation and acceleration (periosteal stripping)."
Thus, these two techniques designed to accomplish the same thing--proper alignment of limbs--work in opposite ways. Periosteal stripping promotes growth where the periosteum is incised, and transphyseal bridging retards growth where the implants are inserted.
"We have tried several techniques for retarding the growth at the physis in foals," Robinson says. "All of the techniques involve bridging across the physis with surgical implants in order to restrict expansion of the physis. The hardware is always applied to the long (convex) aspect of the bone. All of the techniques we have tried have had good results at resolving the angular deformity if the procedure was performed early enough to provide adequate time for a response."
Robinson explains the following transphyseal bridging techniques:
Transphyseal Bridging Using Staples--Robinson says that although this technique has been successfully employed by a number of surgeons, it is not the procedure of choice for him. There is an increased likelihood of soft tissue blemishes and a possibility of staple legs spreading during growth, he says.
"We haven't utilized the stapling technique in our practice," he says, "due to the necessity of specialized equipment that could only be used in this procedure. We are also concerned about the potential for operator error on the driving of the staples. Exact staple placement is important and less forgiving than screw and wire techniques. Since two staples are recommended, the area of surgical exposure is relatively large."
Transphyseal Bridging With Screws and Wire--This procedure, Robinson says, begins with radiographs to determine the relative width and shape of the area of the physis to be bridged.
"A 25-gauge needle is inserted into the physis. If the original X rays showed an exceptionally wide or deformed physis, we will take intra-operative X rays at this time. To ensure correct placement of our screws, we will use the needle or the needle and intra-operative X ray to help guide placement of our screws. The screw in the epiphysis (between the growth plate and the end of the bone) is inserted halfway between the physis and the articular (joint) surface. The second screw is positioned about three to four centimeters proximal to (above) the plate.
"The screw size and type are variable with the surgeon. We use a 4.5-mm x 35-mm self-tapping cortical bone screw. Normal techniques for drilling and insertion of screws are followed. Before the screws are tightened, two figure-eight loops of 18-gauge Cerclage wire are applied between the screws and tightened. Further driving of the screws increases the tension on the wire."
The foals on which this technique is used remain confined with their mothers until the surgical implants are removed. Timing is important concerning removal of the implants, Robinson says. The implants must be removed immediately when the leg becomes straight, or the growth retardation will continue and the joint will again become deformed--in the opposite direction.
Utilizing Screws and Wires Through a Tunneling Technique--This is one of the newer approaches to transphyseal bridging in which the implants are the same as with the screw and wire technique, but the approach has been modified.
"The physis is located with a sterile needle," says Robinson. "Then a small incision of about one centimeter is made through the skin centered halfway between the physis and the articular (joint) surface of the epiphysis. A second incision is made about three centimeters above the physis. The subcuticular tissue is elevated by tunneling between the two incisions. The skin should be rotated to the site of the incision prior to making the incision so that when the skin is released, the incision will not be directly over the implants. This will decrease the risk of infection, pressure necrosis, and dehiscence (splitting open of the healing incision)."
The technique greatly reduces the size of the surgical incision, Robinson says, and the degree of post-surgical swelling and irritation, always a concern with transphyseal bridging, appears to be minimal.
"We have been able to reduce our overall costs with the tunneling technique and are happy with it," he concludes.
The Screw and Plate Technique--This technique, Robinson says, works very well at his clinic. The approach is similar to that for screws and wire; here a 2.7-millimeter bone plate is conformed to the contour of the bone and implanted using two cortical bone screws. The procedure, Robinson says, requires about the same amount of time as the screw and wire technique.
"In our hands," Robinson says, "the procedure was quite successful and seemed to provide a better cosmetic effect with less irritation."
However, he adds, this surgical approach requires a relatively large incision and the cost of the surgery is increased due to the increase in the cost of the implants.
Because time is of the essence in dealing with angular limb deformities, Robinson maintains, it's important that owners who observe this problem contact their veterinarians immediately. It is also important, he says, that the veterinarian aggressively diagnose and treat angular limb deformities. A wait-and-see attitude, he says, "could greatly affect the chances for a positive outcome regardless of the type, reason, or origin of the deformity."
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
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