Functional and topographic anatomy of the shoulder joint of the alpaca (Vicugna pacos)

Introduction: Since the 1980s, the population of South American Camelids (SAC) in Europe is growing constantly. Because of this, practicing veterinarians are more and more confronted with the necessity to treat these animals. The objective of this investigation is to expand the anatomical knowledge about the shoulder joint of the alpaca. The focus is put on the topographic relations between blood vessels, nerves and the joint. Materials and Methods: Thoracic limbs of three alpacas were examined. They were euthanized for medical reasons that did not affect the locomotor apparatus. The thoracic limbs were isolated, and latex milk injections of blood vessels and the joint were performed. Results: The shoulder joint is a ball-and- socket- joint. Notable is the dominant coracoid process, where the m. coracobrachialis arises. This muscle originates with a prominent tendon stabilizing the joint medially as an additional “collateral ligament”. Together with the m. infraspinatus and m. subscapularis, the movement is limited to flexion and extension. On the cranial aspect, there is a coracohumeral ligament that reinforces the capsule and runs between the tuberculum supraglenoidale and the greater tubercle as well as the caudal part of the lesser tubercle. There are pouches of the synovial membrane of the joint capsule below the tendon of the m. infraspinatus, below the tendon of the m. subscapularis and the furthermost on the caudal aspect of the joint. The a. and v. circumflexa humeri caudalis and the n. axillaris are surrounding the joint on the caudal aspect. Conclusion: To diagnose and treat diseases of the joint correctly, the knowledge of the species-specific anatomy is an important prerequisite. The m. coracobrachialis seems to be an important stabilizer of the joint. The knowledge about the structures surrounding the joint is important, if getting an access to it is necessary.