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Praca oryginalna Original paper
Normal anatomical developments of the front legs depend on the congruent growth of the antebrachium bones. In dogs, 40% of the growth of the radius occurs in the proximal and 60% in the distal growth plates; while development of the ulna occurs at a rate of 15% in the proximal and 85% in the distal growth plates (1, 5, 7). The endochondral ossification region is responsible for the longitudinal growth of long bones and the epi-physeal cartilage complex is responsible for the forma-tion of the end point of the bone (2, 6, 9). The epiphyseal cartilage ossifies during the endochondral ossification phases and forms the mature individual. During growth, the epiphyseal cartilage divides into 4 parts. These are; the resting, proliferative, hypertrophic and ossifying phases. Calcification of the cartilage occurs in the ossi-fying phase and this layer contains blood vessels origi-nating from the subchondral bone. Osteoprogenitor cells produce osteoids from the calcified cartilage matrix sur-face and bone structure is formed. As a result of the same chain of events, endochondral ossification also occurs in the epiphyseal cartilage region. These phases are mandatory for the normal development of the cells and for endochondral ossification (2, 6).
Due to an unknown reason, unless mineralized carti-lage areas are removed by fagocytes, these areas of car-tilage are slowly surrounded by metaphyseal bone as growth develops (2). These structures, which can also be identified radiologically, are known as cartilage is-lands. The out-of-control state of the problem of clum-ping of cartilage cells not removed by fagocytes is iden-tified as retained endochondral ossification (10, 14) or enchondromatosis (2). This condition is also known as retained cartilage core (9, 11, 12). In retained endochon-dral ossification, chondrocytes are unable to form cell columns; however, they are active and alive. The growth plate may return to normal and provide growth, or re-main as a cartilage nodule in the metaphysis. Most cells are degenerated and are replaced by fibrous tissue. This tissue later turns into either primary bone or fibrous car-tilage. While the reason for this occurrence is not enti-rely known, it has been suggested that genetic factors and feeding may play a role (2, 3, 9, 13, 14). The men-tioned lesion is characterized by multiple cartilagenous nodules reaching from the growth plate into the meta-physis. These cartilage islands in the growth plate have the appearance of hyalin (2, 3, 9).
Retained endochondral ossification
of the distal ulnar growth plate in dogs
KEMAL ALTUNATMAZ, MURAT SAROGLU, OZLEM GUZEL
Department of Surgery, Faculty of Veterinary Medicine, Istanbul University, 34320, Avcilar, Istanbul-Turkey
Altunatmaz K., Saroglu M., Guzel O.
Retained endochondral ossification of the distal ulnar growth plate in dogs Summary
The aim of the study was an early diagnosis of bones with retained endochondral ossification through clinical and radiological examinations, in order to determine the factors causing the etiology of disease and to indicate necessary precautions to be taken in the prophylaxis of the resulting possible deformations.
This study comprised of 51 dogs of different breeds, age and genders, brought to the clinic and complaining of gait abnormality or abnormal bone structure and which were subsequently diagnosed with retained endochon-dral ossification. Radiological examination indicated that while varying degrees of retained endochonendochon-dral ossi-fication were observed in the distal ulnar growth plates in all cases, retained endochondral ossiossi-fication was present in the distal radial growth plate together with the ulna in one case and in all the growth plates in another case. It was established that 22 cases had left their mothers at an early age and been fed meat products and that 17 cases had received additional calcium and phosphorus in their diets. Following clinical and radiological examination, bilateral carpal valgus was diagnosed in 43 cases and bilateral carpal varus in 8 cases. Radius curvus deformation was also observed in cases where the condition had lasted for a long time. Ulnar ostectomy was performed in 18 cases diagnosed with retained endochondral ossification in the ulna and had not yet reached maturity. Seventeen cases in which the lesions were only in the beginning phase were treated by a change of diet. It was concluded that growth ceased temporarily in bones with retained endochondral ossification and that measures should be taken to avoid possible deformation, and, additionally, that feeding played a significant role in the etiology of the disease.
Medycyna Wet. 2006, 62 (1) 41
In the endochondral ossification phase, due to a re-gional obstruction occurring both in the matrix calcifi-cation and in the vascular penetration in the epiphyseal cartilage, this area remains cartilage instead of ossi-fying (2, 6).
Contrary to lesions occurring in the joint cartilage, the morphological appearance of the lesion in the growth plate occurs after the obstruction in endochondral ossi-fication. When this obstruction occurs, the cartilage is formed of hypertrophic chondrocytes. Most of these lesions recover without problem. However, angular deformation may be encountered in relation to patholo-gical fractures in the growth plate or incongruent growth in the antebrachium (6).
The aim of this study was to early diagnose the bones with retained endochondral ossification by clinical and radiological examinations, to determine the factors in ethiology of disease and to point out necessary precau-tions to be taken in the prophylaxis of the possible de-formations occurring.
Material and methods
The material of the study consisted of 51 dogs of different breed, age and gender, brought to our clinic with a complaint of gait abnormality or abnormal bone structure. History of each case was taken, feeding methods, age, gender, condition of littermates, where present, were established and recorded in detail.
Radiographs of the antebrachiums and suspected other bones of all cases were taken. Blood samples were collected and calcium and phosphorus values were examined. Ulnar ostec-tomy was performed in 18 cases diagnosed with retained endo-chondral ossification in the ulna and had not yet reached matu-rity. Seventeen cases in which the lesion was only in the begin-ning phase, were treated by changing their diets. It was recom-mended that these dogs were fed commercial pet food for adult dogs, which had a lower proportion of calcium and phospho-rus. In order to monitor possible changes occurring, radio-graphs were taken of the related regions. Of the remaining cases, owners of 13 were told that ulnar ostectomy was neces-sary and 3 were told that corrective osteotomy was necesneces-sary. However, treatment could not be carried out due to owners not giving their consent.
Results and discussion
In this study, retained endochondral ossification was encountered in a total of 51 dogs of which: 22 were mixed breed, 17 Anatolian Sheepdog, 4 Great Dane, 2 St. Bernard, 2 Spanish Cocker, 2 English Setter, 1 Si-berian Husky and 1 was an Irish Setter. Ages of the dogs changed between 4-7 months and bodyweight between 8-28 kg. Of the cases, 40 were male and 11 female.
Following radiological examination, while varying degrees of retained endochondral ossification was ob-served in the distal ulnar growth plates of all the cases, retained endochondral ossification was also seen in the distal radial growth plate together with the ulna in one case (fig. 1) and in all the growth plates in another case. Presence of the lesion was also noted in 3 littermates as well as 2 other littermates. In other cases, no similari-ties were found between littermates with respect to the disease. In radiographs of dogs with retained
endo-chondral ossification, the growth plate appeared to be cystic in some cases (fig. 1), like a radiolucent line in some cases and al-most closed and degenera-ted in some cases (fig. 2).
It was established that, 34 dogs with lesions had been confined to a closed area and did not have sufficient
Fig. 2. Radiographs in a 6-month old Anatolian Sheepdog; A) medio-lateral radiograph of bilateral antebrachium and ap-pearance of retained endochondral ossification in both distal ulnar growth plates (white arrows), B) radiographic appe-arance of retained endochondral ossification in both distal ulnar growth plates (white arrows) and anterio-posterior ra-diographic appearance of bilateral carpal valgus, C) medio-lateral radiographic appearance of bimedio-lateral ulnar ostecto-my, D) appearance 7 months after ulnar ostectomy
Fig. 1. Medio-lateral and cranio-caudal radiographs of the right antebrachium of a 5-month old Anatolian Sheepdog with retained endo-chondral ossification (middle phase) in both the distal ulnar and radial growth plates (white arrows)
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space to exercise. It was determined that, 22 of the cases had left their mothers at an early age (at 10-25 days old), had been fed concentrated meat products and that in 17 cases additional calcium and phosphorus had been included in the food. The feeding methods of the other dogs could not be ascertained, as the owners had tried several different diets before and after the lesions appeared.
Following examination of the blood samples, calcium values were seen to have risen significantly in 13 cases with retained endochondral ossification and had addi-tional minerals included in their diets. Of the remaining cases, phosphorus values had risen in 16 cases.
Following clinical and radiological examinations, bilateral carpal valgus was diagnosed in 43 cases and bilateral carpal varus in 8 cases. In cases where the lesion had been present for a long time, the deforma-tion, radius curvus was also observed. The degree of the formed carpal varus or carpal valgus varied depen-ding on the time between formation of the lesion and referral to the clinic and whether or not ulnar ostectomy had been carried out. In later period check-ups of 18 cases which had undergone ulnar ostectomy, the defor-mity formed before ostectomy was seen to continue, however, that its advance had been prevented (fig. 2).
While mentioned among osteochondrosis lesions only briefly (6), the obstruction in the endochondral ossifi-cation of the growth plate responsible for the longitudi-nal growth of long bones, appears in a way similar to the cellular changes in osteochondrosis.
While it has been reported that, genetic factors play a role in the ethiology of the disease (2, 3, 9), retained endochondral ossification was observed in only 5 dogs belonging to 2 separate mothers. It was interesting that, these dogs had left their mothers at an early age (10-14 days old) and had been fed unbalanced diets. Different to previous reports, in one of the cases, retained endo-chondral ossification was present in the ulna as well as in the distal radial growth plate (fig. 1).
While retained endochondral ossification has been reported to be a disease of mostly large breed dogs (4, 12, 14), our cases consisting of mostly mixed and medium breed dogs were not parallel to other studies. However, results of the study suggested that, the role of feeding after birth was more important in the forming of the disease than the breed factor. Among our cases, 22 had left their mothers at an early age and 17 had been given additional calcium and phosphorus in their diets. This additional calcium in the diet has been re-ported to cause the parotid gland to be less active than normal and that, in turn, this causes delay in bone deve-lopment and lead to problems in endochondral ossifica-tion (2). Hedhammar et al. (8), produced hypertrophic osteodystrophy and osteochondrosis (retained cartilage core and Wobblers Syndrome) by feeding Great Dane puppies a diet rich in calcium and phosphorus.
In agreement with Koper et al. (11), most of our cases were also male (4 : 1).
Different to previous reports (10, 11), the radiogra-phic appearance of the lesion in the distal ulnar growth
plate had a cystic structure in some cases and was in a radioluscent line in some other cases.
In the long-term follow-ups of cases with retained endochondral ossification and treated only with a chan-ge of diet, it was seen that the growth plate returned to normal with dietary arrangement and that the bone con-tinued to grow. However, it was determined that, as re-ported in literature (1, 2), this temporary pause occur-ring in the distal ulnar growth plate caused partial de-formation (radius curvus).
Incongruent growth of the radius and ulna is the most common reason of deformity in the front legs of dogs. It has been reported that, symmetrical or unsymmetrical closure or retained distal ulnar and radial growth plates results in abnormal development (1, 4). In our cases, which were not treated, it was seen that severe radius curvus and carpal valgus occurred due to the obstruc-tion in ossificaobstruc-tion in the ulna. When cases, which had undergone ulnar ostectomy, to prevent or stop future de-formation, were compared to those, which had not had an ostectomy, this procedure was seen to present positi-ve results (fig. 2).
It has been concluded that, growth is temporarily ceased in bones with retained endochondral ossifica-tion, necessary precautions should be taken to prevent possible deformation occurring and that feeding plays a significant role in the ethiology of the disease.
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Authors address: Assoc. Prof. Dr. Kemal Altunatmaz DVM, PhD, Surgery Department, Faculty of Veterinary Medicine, Istanbul University, 34320, Avcilar-Istanbul/Turkey; e-mail: altunatmaz@hotmail.com
