Retained Cartilage Cores
Also known as: Retained endochondral cartilage cores — Retained cartilagenous cores
Introduction
At the physis, if the blood supply is deficient, there is a failure of endochondral ossification and the cartilage matrix does not become mineralised or replaced by bone. This is regarded as a form of osteochondrosis.
In the distal ulna, the metaphysis is flared and is of a large diameter. This may influence the blood supply to the cartilage that is normally found on the metaphyseal side of the physis and may cause a large core of cartilage to accumulate within the metaphysis.
The failure to convert to bone results in an altered growth rate of the distal ulna. The shortened ulna causes bowing of the adjacent radius or a failure of normal development of the elbow joint.
Retained cartilage cores occur more frequently in giant breeds such as the Great Dane and Wolfhound, generally causing first clinical signs between 4 and 7 months of age.
The condition is usually bilateral.
The most common site is the distal ulna, but RCC can also occur at the distal tibia and femur.
Clinical Signs
Many affected dogs are asymptomatic, and RCC may be an incidental finding.
In some dogs, there may be limb deformities such as valgus deviation and external rotation of the carpus in the forelimb. Cranial bowing of the radius may also be present.
There may be pain and lameness if the decrease in growth rate of the ulna is severe.
Diagnosis
Radiography is the best method of diagnosing the condition.
There will be a radiolucent cone of cartilage extending proximally into the ulnar metaphysis from the distal ulnar physis. The cone usually has a dense fine line indicating the interface between the cartilage core and the surrounding cancellous bone.
The cone may occupy a small area or may be large enough to involve a greater portion of the physis. The diameter of the core may be consistent throughout, or it may vary with a broadened lollipop appearance with a narrow stick or base.
Secondary changes include a slight bowing of the radius and there may be elbow subluxation as the styloid process is displaced proximally, reflecting the shortened length of the ulna.
Treatment
Animals showing no limb deformities do not need treatment.
In mild cases, delaying the growth rate of the affected dog by altering the feeding regimen may provide the opportunity for conversion of the RCC to bone tissue and for straightening of the radius to occur.
If the deformity is still progressive and the cartilage core of moderate size in animals at the age of 6 months, surgery can be contemplated.
Distal ostectomy of the ulna can be performed to remove the effect of the shortened ulna on the radius. This may also relieve the subluxation forces on the elbow joint.
Severe deformity may require corrective osteotomy and straightening of the limb. Ostectomy of the ulna and osteotomy of the radius are necessary to realign the weight-bearing planes of the elbow and carpal joints. Surgery should be performed prior to the dog becoming fully grown.
Prognosis
Any deformity, if present, will probably be a permenant feature.
If deformity has developped rapidly in a giant breed, the prognosis for correction is poor and the limb will most likely not touch the ground when the dog reaches maturity.
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References
Pasquini, C. (1999) Tschauner's Guide to Small Animal Clinics Sudz Publishing
Hosgood, G. (1998) Small animal paediatric medicine and surgery Elsevier Health Sciences
Morgan, J. (2000) Hereditary bone and joint diseases in the dog: osteochondroses, hip dysplasia, elbow dysplasia Schlütersche