Angular and flexural limb deformities (Proceedings)
Foals are often afflicted with limb deformities, and they are classified as flexural or angular deformities. Occasionally, rotational deformities are also present.1,2 Many of the congenital angular limb deformities correct with no treatment or with only conservative treatment. In some cases of severe orthopedic disease in young horses, the supporting limb can develop an acquired angular deformity, but angular deformities are generally congenital or developmental. Flexural deformities are grouped into congenital and acquired deformities; congenital refers to deformities that are present at birth, while acquired deformities develop later in life.3 Both types of deformities will be discussed along available treatment options.
ANGULAR LIMB DEFORMITIES
Foals with angular limb deformities (ALD) have either a valgus or varus presentation. Valgus deformities deviate laterally distal to the origin of the deformity, while varus deformities deviate medially distal to the origin. Carpal valgus is the most common ALD seen, followed by fetlock varus.4,5 The etiology of ALD is not fully understood in every case and is likely multi-factorial. We do know that unequal growth can occur across the metaphyseal growth plate, or physis. Most of the long bone growth occurs at this level and with disparate growth, deformities can occur. It is theorized that perinatal as well as developmental factors can influence the occurrence of ALD.1 Trauma (or irregular pressure) across the physis may be a reason for incongruent growth rates. Abnormal pressure on the physis could occur due to joint laxity, malposititioning in utero, excessive exercise in young foals, or lameness in the opposite limb.1,5 It is also possible that nutritional factors may lead to excessive or anomalous growth in some cases. Another cause for ALD is incomplete ossification of the cuboidal bones. In premature or dysmature foals and in twins, the carpal or tarsal (cuboidal) bones may not be completely ossified. The carpal/tarsal structures consist of cartilage instead of bone when this occurs, and even normal weight bearing can deform the cartilage template. The bones then ossify in that crushed shape and the consequence can be an ALD of the carpus or tarsus.ALD: DIAGNOSIS
Angular limb deformities are diagnosed based on physical exam. Examination of the leg or legs involved can be done from different angles to evaluate the deformity. Radiographs are also performed in most cases to determine the source(s) of the deformity as well as to determine if crushing of cuboidal bones is present. Manipulation of the limb can also aid in diagnosing joint laxity, or flaccid supporting structures. Most foals are born with some degree of angular deformity, and many will correct over time. Foals also have small chests and long legs, which make many foals appear "close-kneed" because of their toed-out posture. A good physical exam can determine if and where there is a serious deformity. Diagnosis of fetlock and phalangeal deformities should be made and treatment initiated as early as possible. The distal metacarpal or metatarsal physis has little remaining growth potential after 60-90 days. Moderate carpal or tarsal deformities with no cuboidal bone involvement can be treated at a later age, as the growth plates of the distal radius and tibia have substantial growth occurring for up to a year.
ALD: NON-SURGICAL MANAGEMENT
Conservative management can sometimes be very useful in treating foals with ALD. Stall rest or restricted exercise (small periods of turnout or hand walking with the mare) is a technique that will allow many, if not most foals to correct. Frequent hoof trimming is recommended for all cases, both surgical and non-surgical. Valgus cases should have the outside or lateral wall of the hoof trimmed slightly shorter (lower), while varus deformities need the medial aspect of the hoof slightly shorter. This results in the longer side of the foot hitting the ground first, and rotating it "away" from the deformity (i.e., medially for a valgus deformity). In addition, shoes or composite material may be used to extend the foot medially for valgus deformities and laterally for varus deformities. These extensions prevent wear on that aspect of the hoof as well as assisting in the foot contacting the ground first on that side. Splints and casts have limited use in foals with ALD unless they have incomplete ossification of the cuboidal bones, and decreasing weight-bearing in those cases has ideally been implemented before a significant ALD is present.
Foals with incomplete ossification of the cuboidal bones must be on strict stall rest, and in some cases sleeve casts, splints, braces or slings may be warranted. These adjunctive therapies may help reduce weight-bearing and deformation of cartilage template as mentioned above. Most neonatal specialists advocate repeated radiographs every 2 weeks to monitor ossification of the bones.
If the bones are ossified, foals with carpal or tarsal deformities can be treated with stall rest and trimming for several months if there is no worsening of the condition. If the foals are improving with stall rest and limited turnout (from one to a few hours a day), even 4-6 months is an acceptable period to wait. I have treated foals as old as 9 months of age, and still had successful results after transphyseal bridging in those that did not eventually correct with conservative management. It typically takes foals of this age longer to correct. It must be noted however, that it is important to identify foals with cuboidal bone abnormalities, joint laxity, and deformities that worsen over time to recommend a different course of treatment than only conservative management for this length of time.
In foals that have fetlock deformities, surgical treatment is encouraged early (~ 3-4 weeks of age), as the window for manipulating growth with surgical procedures is much smaller. As such, we generally do not recommend stall rest as a treatment option in these cases. Foot trimming and extensions, if warranted, are included in the treatment for these cases as well.