In this experimental study, 48 Labrador retrievers from seven litters with a high prevalence of canine hip dysplasia were examined throughout their lives for a relationship between a radiographic marker and the development of osteoarthritis in the hip joint. The marker has been described as a caudolateral curvilinear osteophyte (CCO) on the femoral neck and is also known as Morgan's line. Additionally, the authors discovered a less discrete line, termed a puppy line, in the same location that occurs only in animals less than 18 months of age and evaluated its relationship to subsequent osteoarthritis. Radiographic evaluations were performed on anesthetized dogs by using standard ventrodorsal, extended hip projections. Histologic examinations of hip joint tissues were also performed. Dogs were divided into two dietary groups: controls and restricted-fed (75% of the control diet).

Results of this study indicate that 100% of the control dogs with a CCO developed radiographic signs of osteoarthritis while 55% of restricted-fed dogs with a CCO developed osteoarthritis. The CCO was the first radiographic change in 76% of all dogs with osteoarthritis, and 95% of dogs with a CCO had histopathologic lesions of osteoarthritis. The authors concluded that a CCO is an important early radiographic indication of osteoarthritis in dogs with hip dysplasia. Furthermore, the puppy line detected in 81% of dogs less than 1 year old was not related to the development of a CCO or subsequent osteoarthritis.

COMMENTARY

Canine hip dysplasia and degenerative osteoarthritis of the joints are common clinical problems in young and old dogs. Early radiographic markers are helpful in identifying affected dogs and, it is hoped, could be used to reduce the functions of such dogs for breeding or working purposes. The results of this study in Labrador retrievers maintained in a controlled environment suggest that the development of a CCO in dogs greater than 18 months of age is a reliable indicator of subsequent osteoarthritis. As noted by the authors, however, the absence of histologically confirmed normal joints in this study warrants further clinical assessment.

Joseph Harari, MS, DVM, DACVS