M. PILAR LAFUENTE, DVM PhD 1 , BOEL A. FRANSSON, DVM, PhD, Diplomate ACVS 1 , JAMES D. LINCOLN, DVM, MS 1 , STEVEN A. MARTINEZ, DVM, MS, Diplomate ACVS 1 , PATRICK R. GAVIN, DVM, PhD, Diplomate ACVR 1 , KEVIN K. LAHMERS, DVM, PhD, Diplomate ACVP 1 , JOHN 1 Department of Veterinary Clinical Sciences, Washington State University, Pullman, WA Vet Surg April 2009 38 3 380-387 Objective—To report and compare the clinical diagnosis, surgical treatment, histopathologic changes, and outcomes of dogs with mineralized and nonmineralized supraspinatus tendinopathy (ST). Study Design—Case series. Animals—Dogs (n=24) with ST. Methods—Medical records (1995–2006) of dogs with ST that had surgical treatment were reviewed. Results of clinical examination, diagnostic imaging, surgery, histopathology of resected tendon tissue, and outcome were compared between dogs with mineralized and nonmineralized ST. Results—There were 15 dogs with mineralized ST and 9 with nonmineralized ST. Chronic, unilateral, intermittent or waxing-waning lameness, and pain elicited on palpation of the cranial aspect of the shoulder were the most consistent findings. On ultrasonographic or magnetic resonance imaging (MRI) of 35 shoulders, enlargement of the supraspinatus tendon (54%), increased fluid content (63%), and medial displacement of the biceps tendon (60%) were observed. Eleven of 12 dogs with bilateral abnormalities only had unilateral lameness. Surgery was performed in 30 shoulders. Resected tendon specimens had myxomatous degeneration and/or cartilaginous metaplasia in 11 of 13 dogs in the mineralized group and all 9 dogs in the nonmineralized group. Functional outcome after surgery was poor in 3 dogs and good-to-excellent in 16. Conclusions—Mineralized and nonmineralized ST have many similarities. Although lameness is usually unilateral, the supraspinatus tendon may be affected bilaterally. Clinical Relevance—Ultrasonography and MRI are good imaging techniques for detection of ST especially the nonmineralized form. Surgical treatment results in good recovery of limb function. Nonmineralized ST is a recently described disorder in dogs and evaluation of more cases is necessary to determine outcome after surgical or medical treatment.