Angular Limb Deformities (ALD)
Any deviation of the horse’s limb from the normal (straight) axis is considered an angular deformity. For the purpose of this article, we will be discussing limb deviations relative to the saggital plane of the horse; these are typically assessed by viewing the affected limb(s) from the front of the animal.
Angular deformities are categorized as one of the following:
Most animals will exhibit some degree of rotational limb deviation (i.e. “twisting” of the limb) in conjunction with angulation. This is typically displayed in foals with valgus angulation as an outward rotation of the feet (splayed feet) and in foals with varus angulation as an inward rotation of the feet (pigeon toes).
As a consequence of disproportionate growth higher up in the limb, it is common for the first phalanx (P1) to develop compensatory opposing angular deformity. Although this response may result in a straightening of the overall limb axis, abnormal orientation of the distal articulations (joints) is encountered.
PERINATAL FACTORS. These conditions are present during the later phases of gestation or in the immediate perinatal period.
Incomplete Ossification. A variety of complications such as placentitis during pregnancy, severe metabolic disease, heavy parasite infestation, colic and premature delivery may jeopardize the intrauterine environment of the foal and result in incomplete ossification of the long and/or cuboidal bones. These bones are susceptible to pressure-induced deformity which deleteriously affects the correlating limb’s axis.
Foals with Hypoplastic Cuboidal Bones generally have mild to moderately severe angular limb deformity that is inconsistent in severity. Manipulation of the affected limbs reveals an impression of ligamentous laxity, though the force needed to create deformity is greater than in foals with ligamentous laxity. Radiographic assessment confirms the presence of inadequately ossified cuboidal bones and a geometric pivot point within the joint.
In severe cases, there may be persistence of the proximal growth plates of the metacarpus and metatarsus (cannon bones); these should be closed before birth. Deviation in the front limbs usually occurs in a medial-to-lateral direction; in the rear limbs, however, abnormality is best visualized from the side.
The presenting complaint in horses with cuboidal bone hypoplasia is often moderate to severe angulation with a sudden (acute) onset. These foals usually have swelling over the carpus or tarsus and frequently object to manipulation of the affected joints. Radiographs reveal misshapen but completely ossified cuboidal bones with a geometric pivot point located within the joint.
Angular limb deformities caused by cuboidal bone hypoplasia carry the potential for the poorest prognosis. Chronic arthritis often occurs secondary to cuboidal bone hypoplasia, even in cases that have been "successfully" managed.
Foals with underdeveloped cuboidal bones should be restricted to box stall confinement. Additional support in the form of a splint or tube cast can help to mechanically protect the essentially cartilaginous cuboidal bones in particularly active individuals.
Flaccidity of Periarticular Structures. Some foals suffer from excessive laxity of soft tissue structures responsible for supporting and stabilizing joints. In many cases, more than one joint is affected concomitantly. Abnormal loading of affected articular surfaces results, often inducing moderate to severe ALD.
Angular limb deformities due to ligamentous laxity are typically present and most pronounced at birth. The carpal and tarsal joints are most commonly involved. Examination of the foal at rest reveals excessive medial to lateral mobility of affected joints. At a walk, the deformity may be consistent or variable with regard to both severity and direction. Manipulation does not elicit a painful response. Radiographs are morphologically normal and the geometric pivot point is located within the joint.
The majority of angular deformities due to ligamentous laxity resolve spontaneously over the first few days of life. Splints and casts are contraindicated in cases of ligamentous laxity as the added support often exacerbates the problem.
DEVELOPMENTAL FACTORS. These conditions influence limb angulation during growth of the foal up to approximately 18 months of age.
Disparity in Long Bone Growth. Angular deformities most commonly arise from disproportionate growth of the metaphyses (growth plates) of the distal radius (above front knee), the distal tibia (above hock) and the distal third metacarpal / metacarpal (cannon) bones. The most common deformity is a lateral (valgus) deformity originating at the carpus.
Physical examination will reveal a constant angulation. Palpation and manipulation does not elicit a painful response and there is no swelling or laxity of affected joint(s). Radiographic evaluation confirms the presence of normally shaped cuboidal bones and the geometric pivot point is located proximal (above) the joint.
The window of opportunity for dealing with deformities arising from the distal radius/ tibia is large. The degree of urgency is somewhat increased when addressing distal cannon deformities, however, because there is little growth potential in these bones after the foal is 100 days of age.
Nutritional Imbalance. Problems associated with imbalanced nutrition in the foal include flexural deformities, osteochondrosis and ALD. Osteochondrosis as a consequence of zinc toxicity or copper deficiency may cause ALDs.
Excessive Exercise. In some cases, the level of exercise can exceed the foal's ability to appropriately adapt to the applied stress(es). Microfractures occurring within the growth plates may result in collapse of local proliferative zones, causing premature closure. This type of injury has been classified as a Salter Harris Type V fracture.
Trauma. Fractures within the growth plate can also stem from external trauma. Most epiphyseal fractures result in some degree of ALD due to the loss of viability in one or more associated physeal regions.
Diagnosis is generally made through careful clinical (visual) examination of the foal.
In some cases, radiographic images are acquired to more accurately depict the degree of angulation as well as identify a specific cause. However, artifactual angulation is commonly observed during radiographic examination due to alteration(s) in x-ray beam orientation relative to the limb. We therefore must stress the importance of careful visual evaluation.
It is important to note that the majority of foals with angular limb deformities caused by growth disparity of the long bones will spontaneously correct. The challenge for the veterinarian is to identify which foals are likely to require more aggressive intervention and to implement corrective measures while there is still sufficient growth to allow correction.
STALL REST. Foals with incomplete ossification of the long or cuboidal bones should not be turned out. Applied stress experienced by partially ossified carpal and tarsal bones may result in abnormal mineralization of the bones and the development of degenerative joint disease. Foals with flaccidity of the periarticular supporting structures can also benefit from this form of therapy.
SPLINTS & CASTS. The purpose of these devices is to maintain proper limb alignment while waiting for the cartilage template along the cuboidal joint surface(s) to ossify and mature enough to handle normal weightbearing load without consequence.
We do not recommend splinting or casting of youngsters that lack evidence of incomplete ossification of the cuboidal bones of the carpus or tarsus. Not only is this technique ineffective, it usually results in the formation of pressure sores in the skin (see below).
It is extremely important that the foot not be incorporated within the splint or cast so as to avoid weakened flexor tendons, dropping of the fetlock and/or osteopenia.
Affected limbs should be well-padded prior to application of any splinting or casting device, as foals have a strong predilection towards skin compromise due to excessive external pressure. Damage will occur if the external pressure imposed by the device exceeds the capillary pressure within the skin, even if only for a short period of time. It is for this reason that we discourage cast or splint use in foals with normal cuboidal ossification.
Read more about bandaging considerations HERE.
Casts or splints should be changed frequently (every 3-4 days) to prevent associated complications. The carpi ulnaris and ulnaris lateralis muscles quickly become flaccid in a casted/ splinted environment, necessitating the continued use of soft bandages for several days following removal.
CORRECTIVE TRIMMING & THE APPLICATION OF EXTENSIONS. The farrier correctively trims ALD foals with the following goals in mind:
To reposition the foot back under the limb in a valgus setting. This is accomplished via trimming of the lateral (outside) half of the wall relative to the inside half.
To reposition the foot back under the limb in a varus setting. This is accomplished via trimming of the medial (inside) half of the wall relative to the outside half.
To reestablish normal foot balance in a valgus setting. In many cases of valgus angulation, the inside wall is shorter than the outside wall. This results in a "tilting" of the coronet band and outward rotation of the foot. Trimming lateral toe-quarter and medial heel quarter is often performed to reestablish normal foot balance in this scenario.
To reestablish normal foot balance in a varus setting. In many cases of varus angulation, the outside wall is shorter than the inside wall. This results in a "tilting" of the coronet band and inward rotation of the foot. Trimming medial toe-quarter and lateral heel quarter is often performed to reestablish normal foot balance in this scenario.
When trimming alone is not sufficient, your farrier may also apply extensions to amplify the effect of corrective trimming and further stimulate correction of the angular deformity. Extensions are generally comprised of polymethylmethacrylate glue (PMMA or Equilox®), corrective shoes or a combination of both.
In many cases, angular deformities can be successfully addressed by the farrier alone (with no veterinary assistance). Since bone growth is manipulated to produce the desired effect, it is best to implement corrective measures when the foal is relatively young (less than 6 months of age) and has still has plenty of growing to do.
You can review a detailed article on CORRECTIVE TRIMMING in CASES of ANGULAR DEFORMITY HERE.
The majority of foals with angular limb deformities caused by growth disparity of the long bones will spontaneously correct. The challenge for the veterinarian is to identify which foals are likely to require more aggressive intervention and to implement corrective measures while there is still sufficient growth to allow correction. Exercise restriction and corrective hoof care are consistent treatment recommendations that help to reduce the biomechanical stress on the angled limb. In many cases, this conservative approach is sufficient to allow resolution of the deformity. Foals that are severely affected or foals that fail to respond to confinement and corrective hoof trimming are candidates for surgical treatment.
SURGERY. In all cases of surgical intervention, we manipulate the foal's growth to produce the desired effect. This means that we either accelerate growth along the short side of the bone and/or decelerate growth along the long side of the bone. The difference in growth rate between treated and untreated sides of the bone results in overall straightening of the limb.
These techniques speed up growth along the concave aspect or short side of the bone with the intent of eventually allowing it to "catch up" to the other (longer) side.
Periosteal Stripping. This procedure is performed on the concave aspect of the limb and is designed to accelerate bone growth along the "short" side. This procedure typically requires that the patient be generally anesthestized.
Technique: The periosteal layer along the bone is transected (cut) and elevated off of the underlying bone. In many cases, a portion of the elevated periosteal tissue is also resected (removed).
By cutting the periosteum, we potentially reduce its tethering effect on underlying bone growth, thereby allowing the bone to grow at a faster rate.
Although this procedure gained tremendous popularity in previous years, it is now considered to be relatively ineffective. We no longer recommend periosteal stripping for treatment of angular limb deformity at The Atlanta Equine Clinic.
Foiling. This technique entails the infusion of counterirritant (typically 2% iodine in almond oil) within the periosteal tissue along the concave (short) side of the bone. Increased irritation and blood flow resulting from the counterirritation increases activity within the adjacent growth plate, thereby accelerating growth.
This procedure, which is generally performed in the standing/ sedated foal, has proven to be extremely effective in our hands. On average, three treatments are administered at 3-week intervals.
Multiple limbs and multiple sites on each limb can be "foiled" simultaneously. Moreover, no change in the foal's turnout schedule nor exercise routine is necessary during the treatment period.
These techniques slow down growth along the convex aspect or long side of the bone, thereby allowing the other (shorter) side of the bone to catch up with respect to growth. The goal is to create compression across the physis, retarding the growth on that side of the limb. The physis at the concave side will not be affected.
Growth retardation is performed either in young foals (less than 3 months of age) with severe ALD or in foals with significant ALD in a bone after its rapid growth rate is completed.
Transphyseal Bridging. This technique involves the placement of a staple or two screws connected by wire or a plate across the growth plate along the convex aspect of the limb.
The transphyseal bridge compresses the growth plate, restricting growth while allowing the slow growing side to essentially catch up, thereby resolving the angulation. The transphyseal bridging techniques are effective; however, a second surgery is required to remove the implants when the limb is straight.
Transphyseal Screw Insertion. A single screw is placed through the growth plate on the convex aspect of the limb, thereby arresting bone growth uniaxially (along one side). As growth on the other side of the bone catches up, the limb progressively straightens.
As in other transphyseal bridging techniques, a second surgery is required to remove the implant when the desired effect has been achieved. However, in the case of transphyseal screw insertion a much better cosmetic result is achieved.
Corrective Osteotomy or Ostectomy is used for correction of angular limb deformities in older foals with growth plates that have already closed. In these cases, the surgeon is unable to utilize limb growth to achieve normal angulation.
This technique is also used to treat patients with rotational and diaphyseal deviations, primarily of the cannon bones. This procedure is effective; however, economic constraints often limit its application.