ONSET OF EPIPHYSEAL MINERALIZATION AND GROWTH-PLATE CLOSURE IN RADIOGRAPHICALLY NORMAL AND DYSPLASTIC LABRADOR RETRIEVERS

Objective--To determine whether onset of mineralization of the femoral and proximal tibial epiphyses and age at closure of the femoral and a cetabular triradiate growth plates was different for Labrador Retrieve rs that were radiographically normal or that had canine hip dysplasia (CHD). Design--Cohort study. Animals--36 Labrador Retriever puppies. P rocedure--Puppies were radiographed every other day from the time they were 8 to 10 days old until ossification of the femoral heads was app arent. Radiographs were then obtained weekly until puppies were 1 mont h old and then monthly until puppies were 8 to 12 months old. Age at w hich mineralization was first observed in the proximal and distal femo ral and proximal tibial epiphyses and at which the femoral capital, tr iradiate acetabular, and distal femoral growth plates were no longer r adiographically visible were recorded. Fifteen dogs were euthanatized and necropsied to determine whether dogs had CHD. Results--There were 26 radiographically normal left and right hip joints and 10 dysplastic left and right hip joints. Onset of mineralization of the proximal fe moral epiphyses and of the right proximal tibial epiphysis was signifi cantly later in dysplastic than in radiographically normal puppies. Th e left femoral capital growth plates closed significantly later in dys plastic than in radiographically normal joints, but other differences in growth plate closure were not detected. Clinical Implications-Endoc hondral ossification may be abnormal in dogs with CHD. The disease app ears to affect multiple joints, even though it is most evident clinica lly in the hip joint.