On the Forefront: Looking at canine angular limb deformities in a new way

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Mar 01, 2007

Angular limb deformities are common orthopedic conditions in dogs, and a wide variety of deformities can occur. These deformities have most commonly been described in the canine antebrachium. Variation in angular conformation of other long bones has been speculated to contribute to other orthopedic conditions, including patellar luxation and cranial cruciate ligament rupture.

Until recently, a common vocabulary did not exist within the veterinary lexicon with which to discuss angular deformities of all affected bones. Different systems of describing the quantity and location of deformities were used for different bones. Furthermore, parameters for normal joint angulation and relationships did not exist, making the goals for surgical correction ill-defined.

RESEARCHING LONG BONE ANGULAR RELATIONSHIPS

A number of ongoing research projects at the University of Missouri–Columbia Veterinary Medical Teaching Hospital (umcvmth) are focused on re-examining a variety of orthopedic conditions that specifically relate to the angular relationship of the long bones. Through this research, a vocabulary is being established from references designed for human application to uniformly describe the quantity, direction, and relationship of all long bone deformities in small-animal patients. This classification system, referred to as the Center of Rotation of Angulation (cora) methodology, was developed by Dr. Dror Paley, an orthopedic surgeon.1 The cora methodology necessitates understanding the affected bone's anatomical and mechanical axes and the relationship of these axes to the adjacent joints.1 When a bone is abnormally angulated, so too are the bone's axes. These axial angles can be used to help consistently localize and quantify deformities, whether the bone in question is a radius or a femur.

ANGULAR LIMB DEFORMITY CLASSIFICATIONS


1. Preoperative and one-year postoperative photographs of an adult male basset hound presented to the University of Missouri-Columbia Veterinary Medical Teaching Hospital for evaluation of bilateral biapical uncompensated (right forelimb) and partially compensated (left forelimb) antebrachial deformities. These deformities, localized and quantified by using the CORA methodology, were repaired with multiple corrective osteotomies.
Abnormal bone angulation can be classified based on the number of deformities present, the direction of the deformities, and the relationship of the deformities to one another (Figure 1).2

Bones with single, dual, or three or more deformities can be referred to as uniapical, biapical, and multiapical, respectively.

Directionality of deformity is described in three planes: the frontal plane as determined on cranial-to-caudal radiographs, the sagittal plane as determined on medial-to-lateral radiographs, and rotationally as determined by physical examination and radiography. Orthogonal radiographs that include the joint above and below the affected bone are obtained; oblique radiographs can be taken as necessary, depending on the amount of the rotational deformity present. Deviations toward and away from the midline in the frontal plane are named varus and valgus, respectively. Cranial bowing in the sagittal plane is named procurvatum, and caudal bowing is named recurvatum. Rotation can either be internal or external.

If a bone possesses multiple deformities, then the relationship between them can also be described.2 For example, a proximal varus deformity and a distal valgus deformity are thought of as partially compensated because they occur in opposite directions, thus representing the complementary developmental adaptation of forces on the growth plates. An uncompensated biapical deformity is one in which the deformities occur in the same direction, and, thus, the angulation worsens along the length of the bone. Some early evidence suggests that chondrodystrophic breeds, such as basset hounds, may have a higher incidence of biapical antebrachial deformities than other dogs do (Fox DB, Appel SL. University of Missouri-Columbia Veterinary Medical Teaching Hospital, Columbia, Mo: Unpublished data, 2007).