The Role of the Antebrachiocarpal Ligaments in the Prevention of Hyperextension of the Antebrachiocarpal Joint Joshua Milgram, BVSc, Diplomate ECVS, Tomer Milshtein, DVM, and Yaron Meiner, BSc ME The Laboratory for Biomechanics and Applied Anatomy, Koret School of Veterinary Medicine, The Hebrew University of Jerusalem, Israel Corresponding Author Joshua Milgram, BVSc, Diplomate ECVS, Veterinary Teaching Hospital, Koret School of Veterinary Medicine, Hebrew University of Jerusalem, PO Box 12, Rehovot 76100, Israel E-mail: milgram@agri.huji.ac.il Submitted August 2010 Accepted July 2011 DOI:10.1111/j.1532-950X.2011.00908.x Objective: To evaluate the role of the medial collateral ligament, lateral collateral ligament, and the palmar carpal ligaments in the prevention of hyperextension of the antebrachiocarpal (AC) joint. Study Design: In vitro experiment. Animals: Cadaveric canine thoracic limbs (n = 12 pair). Methods: Thoracic limbs from 12 healthy mixed breed dogs, free of carpal joint pathology, were assigned to 1 of 6 groups, defined by the order in which the liga- ments stabilizing the AC joint were cut. The antebrachium, carpus, and proximal metacarpal (MC) bones were stripped of all muscle tissue, preserving the carpal joint capsule. After specimens were prepared for biomechanical testing, the manus was loaded using a system of weights and pulleys to extend the carpus. Exten- sion was measured using a single motion tracking sensor fixed to the MC bones. All specimens were tested with all ligaments intact and after cutting each of the ligaments. Results: Cutting each of the ligaments resulted in a significant change in the angle of extension of the carpus when compared with carpal extension with the ligaments intact. Cutting the palmar AC ligaments resulted in a significantly larger change in extension angle than occurred after cutting the medial and lateral collateral ligaments. Conclusion: Each of the ligaments tested contribute to the prevention of hyper- extension of the AC joint. The carpus, a compound weight bearing joint of the tho- racic limb of dogs, is a complex joint that consists of 7 carpal bones connected to each other by short carpal ligaments and the palmar fibrocartilage. 1 The bones of the carpus are arranged to form 3 joints. The proximal, antebrachiocarpal (AC) joint formed between the distal aspects of the radius and ulna and the proximal row of carpal bones permits the greatest amount of flexion and extension of the carpus. 2 Short medial and lateral collateral ligaments as well as the palmar carpal ligaments and the palmar interosseous liga- ment are the main stabilizers of the AC joint. 1 The collateral ligaments function to prevent medial and lateral opening of the AC joint, whereas the palmar carpal ligaments and the palmar interosseous ligament prevent hyperextension of the AC joint. 1 A normal carpal joint is crucial to canine locomotion; however, little is known about how pathology of individual structures influences the normal kinematics of this joint. Disruption of the structures that stabilize the palmar as- pect of the carpus is generally due to trauma, and results in hyperextension of the carpal joint during weight bearing. 3–5 The location of the injury within the carpal joint is diag- nosed by radiographic projections of the joint under stress. 2 The recommended treatment for hyperextension injury lo- calized to the AC joint is pancarpal arthrodesis. 3–5 No at- tempt is made to identify the individual structures damaged in hyperextension injury because this information is not of clinical importance. Hyperextension injury at the level of the AC joint is thought to occur when the structures stabilizing the palmar aspect of this joint are ruptured. We propose that the short collateral ligaments, in addition to their role in stabilizing the lateral and medial aspects of the AC joint, play a role in prevention of hyperextension of the AC joint and are likely damaged in hyperextension injury. Our purpose was to evaluate the role of the medial collateral ligament, lateral collateral ligament, and the palmar carpal ligaments in the prevention of hyperextension of the AC joint. MATERIALS AND METHODS Thoracic Limb Specimens Paired thoracic limb specimens were obtained from 12 skeletally mature, mixed breed dogs (weighing, 20–25 kg), Veterinary Surgery 41 (2012) 191–199 C  Copyright 2011 by The American College of Veterinary Surgeons 191