[Histological studies of a tongue-shaped formation at the intertubercular groove in the shoulder joint of the dog].

Radiologically apparent unilateral changes at the intertubercular groove of the humerus were investigated histologically in three dogs and compared with the findings in an unaltered shoulder joint of a dog. Polymethylmethacrylate embedded, undecalcified sections were cut through the sulcus area at the head of humerus and through the biceps tendon, its synovial sheet and the transverse ligament, and were evaluated by light microscopy. While the tendon and soft tissue features were for the most part typical for a normal "gliding" tendon, the respective groove exhibited an again groove-like, 10-12 mm wide and up to 2 mm high exostosis consisting mainly of lamellar bone, filled with hemopoietic and fatty marrow. The normal fibrocartilaginous lining of the groove showed degenerative arthrotic changes in the altered grooves, pointing to mechanical overloading. The possible mechanisms of these ossifications are discussed.