Osteochondritis dissecans (OCD) of the humeral head is a manifestation of osteochondrosis involving the scapulo-humeraljoint, and in particular, the caudal portion of the humeral head, in which an osteochondral flap separates and then detaches completely, exposing the underlying subchrondral bone. The condition affectsmedium, large and giant breeds of dogs during the growth period. OCD of the shoulder causes varying degrees of lameness of the fore limbs and is usually bilateral. Of all the forms of OCD, that involving the shoulder has the best prognosis.
AETIOPATHOGENESIS
Osteochondrosis is a defect of endochondral ossification, which is the mechanism responsible for the longitudinal growth of long bones. The aetiopathogenesis of osteochondrosis seems to be multifactorial, and predisposing factors and triggers act simultaneously to cause the problem: overeating, excessive nutritional supplements, genetic factors, excessive movement associated with heavy body weight and rapid growth. During the course of osteochondrosis, the cells of the metaphyseal and epiphyseal growth cartilage fail to differentiate correctly and do not undergo normal calcification and ossification. The cartilage, therefore, continues to grow and becomes thicker and less resistant to mechanical stress.
In the case of OCD, a crack first appears in the thickened part of the cartilage, an osteochondral flap separates from the underlying bone and the subchondral bone becomes exposed (Fig. 1). Excessive movement or even only microtrauma from normal physical activity can lead to the osteochondral flap detaching completely and becoming a loose body in the joint. This flap can undergo various fates: very rarely it is reabsorbed, otherwise it can migrate into the caudal cul de sac or proximally into the bicipital groove. The flap can grow and calcify by drawing nutrition from the synovial vascularisation and become discernible on X-rays (Fig. 2). Contact between the synovial fluid and subchondral bone triggers a series of biochemical and biological reactions which lead to the development of synovitis. It is usually at this point that the first clinical signs can be observed. The osteochondral flap floating free in the joint can be a source of continuous irritation and contribute to the development of the synovitis. The cartilage defect is repaired by the formation of fibrocartilage.
EPIDEMIOLOGY
OCD of the humeral head occurs in medium, large and giant breeds of dogs during the growth period between 5 and 12 months of age, with a peak incidence between 6 and 7 months of age; male dogs have a greater predisposition to develop the condition. The breeds most involved are Border Collie, Dogue de Bordeaux, Cane Corso, English Setter, German Shorthaired Pointer, Great Dane, Rhodesian Ridgeback, Boxer, Newfoundland, Retriever, Bernese Mountain dog, Schnautzer, German Shepherd, Belgian Shepherd, Rottweiler and Dalmatian.
CLINICAL SIGNS
OCD of the shoulder is a cause of fore limb lameness of variable severity and often with a sudden onset. In most cases OCD of the shoulder is bilateral but can involve one limb with few or no signs in the contralateral limb. On the other hand, both joints can be equally involved and the gait is stiff and uncertain on both limbs, with the dog attempting to move forward ‘galloping’ on both front legs. When there is little sign of lameness, it is almost always possible to observe a partial shifting of body weight off the affected limb when the dog is standing still. In general, the severity of the clinical signs is related to the extent and severity of the osteochondral lesion.
DIAGNOSIS
An orthopaedic examination shows pain on passive movements of the joints. As the condition becomes chronic a variable degree of atrophy of the shoulder muscles can be seen. A diagnostic suspicion of OCD following the clinical examination is confirmed by X-ray of the shoulder joint. A medio-lateral projection of the shoulder is usually sufficient to confirm the diagnosis. Traction should be exerted on the limb to ensure that the joint does not overlap the sternum on the X-ray. Given that OCD of the humeral head is often bilateral, the contralateral limb should also be examined to detect lesions which are still producing few or no symptoms. X-rays show a defect in the profile of the caudal third of the humeral head (Fig. 3). In some cases, the osteochondral flap can be seen to be lifted but still in situ (see Fig. 1). In other cases, only increased radiolucency of the subchondral bone, of variable extension, can be seen. Some initial forms of osteochondrosis, which have still not developed into OCD, can be seen in X-rays as small flattened areas of the rounded humeral head, without any changes in the homogenous density of the subchondral bone (Fig. 4).
Correct diagnosis of these initial forms helps in the decision as to whether a surgical or conservative therapeutic approach should be adopted. In the case of a diagnosis of osteochondrosis, X-ray monitoring of the lesion is recommended with follow-up visits every 2-3 weeks to evaluate the evolution of the disorder: spontaneous healing or the formation and separation of an osteochondral flap. In cases in which the lesion is located medially, a neutral medio-lateral projection may not reveal an osteochondral defect or may lead to its extent being underestimated (Fig. 5a). It is, therefore, advisable to take a medio-lateral projection with external rotation of the leg in order to expose also lesions located in the medial compartment to the X-ray beam (Fig. 5b). The osteochondral flap may also migrate. In the most fortunate cases, the detached flap can be spontaneously reabsorbed; however, it may act as a loose body in the joint (Fig. 6). The most frequent site where the free body tends to lodge is the caudal recess of the joint (see Fig. 2). In less favourable cases, the osteochondral flap can migrate into the cranial compartment, more precisely into the bicipital groove, where it can cause mechanical irritation of the biceps tendon. In this case, symptoms will reflect the development of a bicipital tenosynovitis.
As the lesion becomes chronic, irregular repair of the osteochondral defect can be seen, followed by the formation of osteophytes at the caudal part of the humeral head and the caudal glenoid (Fig. 7).
TREATMENT
Surgery is the usual treatment for OCD of the shoulder and involves removal of the osteochondral flap and treatment of the base of the lesion. This treatment consists in reactivating the base of the lesion, when it is sclerotic, by osteostixis, using a special spike to make holes a few millimetres apart from each other which penetrate the subchondral bone: this promotes vascularisation of the lesion and exposes mesenchymal cells (Figs. 8a and 8b). Any reparative fibrocartilage present should be conserved as this is a manifestation of early healing.
Both arthroscopic treatment and traditional surgery can be used to treat OCD of the shoulder. Recently, transplantation of autologous cartilage and subchondral bone has been proposed for large lesions with a less favourable prognosis. The graft is taken from the troclear lip of the distal femur, an area easily accessed by mini-arthrotomy and, most importantly, not a weight-bearing part of the joint. This method has important applications and can be considered a turning point in the treatment of OCD of the knee (Conservative treatment must be proposed in cases of early osteochondrosis, taking care to monitor the joint until the lesion has healed spontaneously.
PROGNOSIS
As stated above, OCD of the shoulder is the manifestation of osteochondrosis with the best prognosis in dogs. Functional recovery after surgery is usually very good. Unsatisfactory recovery may occur in cases of large lesions treated late or when there are numerous free flaps that are difficult to remove.
Suggested readings
- Fitzpatrick N, van Terheijden C, Yeadon R, Smith TJ.“Osteochondral autograft transfer for treatment of osteochondritis dissecans of the caudocentral humeral head in dogs.”Vet Surg Dec; 39(8): 925-35, 2010
- Mortellaro CM, Petazzoni M, Vezzoni A “Atlante BOA: approccio ortopedico orientato alla razza” Innovet ed, pp 56-57, 2008
- La Fond E. et al “Breed susceptibility for developmental orthopedic diseases in dogs” J Am An Hosp Assoc 38(5): 467-477, 2002
- Olivieri M, Ciliberto E, Hulse DA, Vezzoni A, Ingravalle F, Peirone B.“Arthroscopic treatment of osteochondritis dissecans of the shoulder in 126 dogs.”Vet Comp Orthop Traumatol 20(1): 65-9, 2007
- Martini FM “La spalla” in “Patologie articolari del cane e del gatto” Poletto ed, pp 106-113, 2006
- Person MW.“Arthroscopic treatment of osteochondritis dissecans in the canine shoulder.”Vet Surg May-Jun 18(3): 175-89, 1989
- Berzon JL.“Osteochondritis dissecans in the dog: diagnosis and therapy.”J Am Vet Med Assoc Oct 15;175(8): 796-9, 1979 Review