Progression of Hip Dysplasia in German Shepherd Dogs After Unilateral Pectineal Myotomy

Abstract

SUMMARY Four dogs, offspring of purebred, dysplastic German Shepherd Dogs, were subjected to unilateral pectineal myotomy at 1 month of age. Radiographic examinations were made on the dogs over the ensuing 12 months. Three of the dogs developed dysplasia. At 12 months of age, operated sides were 1 grade less dysplastic than unoperated sides in 2 dogs; both sides were grade IV dysplastic in the third dog. The effect of pectineal myotomy was clearly not dramatic in reducing the severity of the disease and did not alter its progression. Structural abnormalities of the coxofemoral joints directly associated with surgery rather than dysplasia were not observed. Anatomic examination revealed that the muscle vestiges on the operated sides were much smaller than the intact muscles and that the distal end of each vestige had adhered to the cranial border of the adductor muscle. Electromyographic examinations of the intact muscle and the muscle vestige revealed an active stretch reflex (pectineal reflex) because electrical activity of motor units was evoked by lateral displacement of the stifles while the dogs were under light surgical anesthesia. The level of electrical activity and the presence of spasms in the intact muscle or the muscle vestige could not be correlated with the presence or grade of dysplasia during the study. It was suggested that the hyperactive stretch reflex of the pectineus muscle contributes to the pain associated with dysplasia in older dogs.