Chondrodysplasia in Bouviers Radiographic findings in Bouviers with a radius curvus syndrome Drs. T. Oudenes Project Tutors: Dr. E. Auriemma Prof. Dr. G. Voorhout Abstract Bouviers are a popular breed of dog in Holland. Since some time the breed association has noticed that in different litters pups were born with deformed forelimbs. The abnormalities seen in different degrees in the young Bouviers include: outwardly turned feet, inwardly turned elbows and short legs, some of the dogs show symptoms of lameness. The defect appears to be hereditary and seems to fit into the syndrome of chondrodysplasia. Lameness in the front limbs is a common complaint for owners to seek out veterinary help. The causes can be categorized into congenital anomalies, developmental disorders, traumatic, idiopathic, infectious, nutritional, metabolic and neoplastic disorders. The first two are more common and can have a genetic basis. 28 Bouviers, both with and without the skeletal anomaly, have been clinically and radiographically examined. The age ranged from 6 weeks to 11 years. The most prominent abnormalities found, include (sub)luxation of the radial head and bowing of the proximal radius in a caudolateral direction, bowing of the ulna, a shallow trochlear notch, a widened olecranon fossa and (sub)luxation of the ulna at the level of the carpus and valgus deviation of the front paws. The abnormalities show a lot of similarity with CEL type 1 as reported by Kene et al (1982). 2 Table of Contents Abstract 2 Introduction 3 Normal anatomy and development of the forelimb 3 Disorders of the forelimb in the growing dog 7 Asynchronous growth of the radius and ulna 7 Retained cartilaginous cone 9 Congenital elbow luxation 9 Materials and methods 11 Results 12 Discussion & conclusion 17 References 21 3 Introduction Bouviers are a popular breed of dog in Holland. Not many hereditary disorders circle in this population. Since some time however dog owners have noticed that in different litters pups were born with deformed forelimbs. The number of litters with pups showing this defect appears to have grown. For that reason the breed association (Nederlandse Bouvier Club) contacted the faculty of veterinary medicine in Utrecht. The faculty set up a couple of dates at which a number of Bouviers (both healthy and with the defect) were clinically and radiographically examined. The abnormalities seen in different degrees in the young Bouviers include: outwardly turned feet, inwardly turned elbows and short legs (Hazewinkel 2008), see figure 1. Some of the dogs have problems in the elbow joint, causing them to show symptoms of lameness (Hazewinkel 2008). The defect appears to be hereditary and seems to fit into the syndrome of chondrodysplasia, a congenital lessening of cartilaginous growth (Hazewinkel 2008). Lameness of the forelimb is a frequently seen problem Figure 1 – Bouvier with abnormal front limbs in dogs under 1 year of age. Many causes are known (Cook 2001). The causes can be categorized into congenital anomalies, developmental disorders, traumatic, idiopathic, infectious, nutritional, metabolic and neoplastic disorders (Cook 2001). The first two can have a genetic basis and could be the cause of the lameness in the Bouviers. Infectious, nutritional, metabolic and neoplastic causes are infrequently seen (Cook 2001). Much research has been dedicated to deformities of the limbs in dogs and a lot of articles have been published on the topic. The syndrome seen in the Bouviers does not seem to fit the most commonly described anomalies. There also seems little known about the defect in the Bouviers; no specific literature is available on growth disorders in the forelimb of Bouviers. The goal of this article is to describe and inventory the abnormalities seen on the radiographs of the front legs of the Bouviers and to find clues for an etiology (and thus pointing out areas for further research). I will start by describing the normal development and anatomy of the forelimb. After that I will recount what is written in the literature on growth disorders that could fit the abnormalities seen in the Bouviers. Next I will describe the defects seen on the radiographs, followed by a discussion of similarities and differences with the literature and the possible etiologic factors. Normal anatomy and development of the forelimb The forelimb is built up of the brachium, antebrachium, carpus and manus. The brachium or upper arm consists of the humerus. At the proximal end of the humerus there is a round caput that contacts the glenoidal cavity of the scapula (Dyce 2002). The tuberculum major and minus, separated by the intertubercular groove, border the caput (Dyce 2002). A spiral groove runs over the lateral side of the shaft (Dyce 2002). At the lateral side of the shaft the deltoid tuberositas is located and connected to the tuberculum major through a prominent ridge (Dyce 4 2002). On the medial side of the shaft the tuberositas teres major is located (Dyce 2002). The distal end of the humerus consists of an articular condyle, divided in a medial area (trochlea) for the ulna and a lateral area (capitulum) for the radius (Dyce 2002). The caudal part of the trochlear groove is continued proximally in a deep fossa olecranon, that offers space for the anconeal process of the ulna (Dyce 2002). Proximal of the articular part are a medial and a lateral epicondyle (Dyce 2002). The foramen supratrochlearis perforates the bottom of the fossa olecranon an opens in the hollow fossa radialis in the cranial part of the shaft (Dyce 2002). The antebrachium or lower arm is formed from two bones: radius and ulna. In the standing animal the ulna is caudal from the radius in the proximal part of the antebrachium, but lateral in the distal part (Dyce 2002). The radius and ulna only make contact at the ends, making pronation and supination (up to 45°) possible (Dyce 2002). The radius is shaped like a rod, widening at the proximal end, where it articulates with the humerus, and at the caudal side with the ulna (Dyce 2002). The shaft is cranio-caudally compressed and slightly bowed in length (Dyce 2002). The distal end is somewhat enlarged and has a slight concave oval form, allowing for abduction, adduction and rotation in the carpus (Dyce 2002). Medial to the carpal joint the radius is lengthened and forms the medial styloid process (Dyce 2002). The ulna has a small shaft and is lengthened proximal to the elbow by the olecranon process (Dyce 2002). Distal to the olecranon on the cranial border is the anconeal process and further distally there is a facet for articulation with the radius (Dyce 2002). The shaft is equal in length to the radius and both bones are separated by a membrane crossing the interosseus space (Dyce 2002). The distal end has a facet for articulation and ends in the lateral styloid process (Dyce 2002). The short carpal bones are located in two rows. The proximal row contains the radial, ulnar and accessory bone (Dyce 2002). The accessory bone extends caudal from the carpus (Dyce 2002). The distal row is numbered 1 through 4 (Dyce 2002). On the medial side of the carpus is a small sesamoid bone (Dyce 2002). Most movements in the carpus occur at the level of the antebrachiocarpal joint, some in the intracarpal articulation and almost none in the carpometacarpal articulation (Dyce 2002). The first signs of the developing limbs are paired projections growing from the ventrolateral surface of the embryo. In dogs these can be seen from the fourth week of gestation (McGeady 2006). The growing extremity consists of a mesenchymal core and an outer layer of ectoderm (Dyce 2002, McGeady 2006). The first indication of the skeleton consists of a thickening of the central mesoderm forming a core in the limb bud, that later develops into a series of cartilage models shaped like the future mature bones (Dyce 2002, McGeady 2006, Bingel 1977). In the next stage the cartilage is replaced by bone tissue. The ossification in a typical long bone takes place through two processes (Dyce 2002, McGeady 2006). The first process is intramembranous ossification. The perichondrium around the middle of the shaft lays bone on the cartilage within a connective tissue membrane, this causes a tubular bone layer (a collar) to form around the centre of the shaft, that slowly expands to the ends (Dyce 2002, McGeady 2006). With the second process the cartilage in the centre of the shaft degenerates and the matrix is impregnated with calcium salts (Dyce 2002, McGeady 2006). Next connective tissue from the periosteum grows into the isle of dead cartilage, bringing with it several cell types with different functions responsible for the process of endochondral ossification (Dyce 2002, McGeady 2006). The balanced construction and destruction change the middle of the shaft into the primary or diaphysary centre of ossification (Dyce 2002, McGeady 2006). Later similar centres of ossifications are formed at the two extremities of the cartilage model: secondary or epiphysary centres of ossification (Dyce 2002, McGeady 2006). Bone growth is more complex then described above. The required size and shape can only be 5 obtained by remodelling the bone, a combination of bone deposition and resorption (Dyce 2002, McGeady 2006). Eventually only two plates of the original cartilage remain: the epiphisiary or growth plates, situated between the primary and secondary centres of ossification. (Dyce 2002, McGeady 2006). Interstitial growth of the cartilage in these growth plates ensures the lengthening of the bone, as long as the growth speed equals the speed of endochondral ossification (Dyce 2002, McGeady 2006, Hazewinkel 1998). With the aging of the animal the replacement of cartilage by bone goes faster than the cartilaginous growth, causing the plate to thin and eventually disappear (Dyce 2002, McGeady 2006).