A 1-year-old Bernese Mountain dog presented with an acute onset of left thoracic limb lameness. Magnetic resonance imaging (MRI) of the left shoulder was performed, showing a subchondral bone defect in the caudomedial aspect of the humeral head. In addition, several round hypointense structures were visible in the biceps tendon sheath. A left shoulder arthroscopy was performed, which confirmed an osteochondritic lesion. Exploration of the biceps tendon sheath via a small open approach allowed retrieval of the fragments, which likely migrated from the joint. Histopathology confirmed the structures to be multiple osteochondritic fragments.