Original Research 157 © 2006 Schattauer GmbH Received September 2, 2005 Accepted October 12, 2005 Vet Comp Orthop Traumatol 3/2006 The role of negative intra-articular pressure in the maintenance of shoulder joint stability in dogs B. K. Sidaway 1 , R. M. McLaughlin 2 , S. H. Elder 4 , C. R. Boyle 3 , E. B. Silverman 2 1 Southwest Veterinary Surgery Service, Glendale, Arizona, USA 2 Departments of Clinical Sciences and 3 Basic Sciences, College of Veterinary Medicine; and the 4 Department of Agricultural and Biological Engineering, College of Agriculture and Life Sciences, Mississippi State University, Mississippi State, MS, USA Summary The objective of this study was to evaluate the effect of negative intra-articular pressure on shoulder joint sta- bility in canine cadavers. Cadaver forelimbs from 12 mature dogs were used. The forelimbs were placed in a testing frame and axially preloaded with 4 kg of weight. Shoulder joint stability was tested in flexion, extension, and neutral position before and after venting of the joint capsule. Humeral translation relative to the glenoid was induced by applying a 3 kg load in three different directions (cranial, lateral, and medial) and quantitatively measured by use of an electromagnetic motion tracking system. Peak translational data were compared in each joint position before and after vent- ing of the joint capsule. After venting the shoulder joint capsule, a significant increase in translation was ob- served in the cranial direction with the joint in neutral position and in the medial direction with the joint in extension. The horizontal translations measured after venting of the joint capsule were likely not clinically relevant. Negative intra-articular pressure is not a major contributor to shoulder stability in dogs during weight-bearing. Keywords Shoulder joint, biomechanics, instability, intra-articular pressure, canine Vet Comp Orthop Traumatol 2006; 19: 157–61 Introduction Shoulder stability in dogs is dependent on both active and passive stabilizing mechan- isms. Primarily, the joint capsule and gleno- humeral ligaments prevent excessive trans- lation and rotation of the glenoid and hum- eral head (1, 2). In addition, the biceps ten- don is an important passive stabilizer in sev- eral joint positions (1). Numerous other shoulder joint stabilizing mechanisms have been investigated by researchers in human orthopaedics, including the phenomenon of negative intra-articular pressure. In the nor- mal shoulder joint, a slight negative intra-ar- ticular pressure is present and is created by the synovium as it removes free fluid via os- mosis (3, 4). Several researchers have inves- tigated the effects of this negative intra- articular pressure on the stability of the human shoulder joint (5–8). This negative pressure contributes to shoulder stability in all directions by adding a slight resistance to distraction when the humerus and scapula are separated. The amount of resistance is about 431 N/m 2 (3). Violation of the joint can negate this stabilizing effect because of the equilibration of the intra-articular press- ure with atmospheric pressure. Venting of the joint capsule in human shoulders re- duces the force necessary to displace the humeral head by an average of 50% (5). In veterinary literature, the authors know of only one study that has evaluated the role of negative intra-articular pressure as a stabi- lizer of the dog shoulder (9). In that study, negative intra-articular pressure did not ap- pear to be a major contributor to shoulder stabilization. The goal of this study was to provide additional objective, biomechanical data regarding the effect of negative intra-ar- ticular pressure on shoulder stability in dogs. Material and methods Testing frame The testing frame has been described and used in a previous biomechanical study of shoulder joint stability (1) (Figs. 1, 2). To summarize, the frame consisted of a foun- dation, a locking plate, a loading platform, and three horizontal loading bars. The lock- ing plate anchors the antebrachium during mechanical testing. Four stainless steel verti- cal posts (height, 91.4 cm) were fixed to the corners of the foundation (25.4 cm apart). A 4 kg loading platform was positioned on the four posts and was used to axially load the shoulder joints once they were positioned in the frame. A braking device placed on one of the vertical posts prevented loading of the limbs during mounting of the specimens. A metal brace projected from the loading plat- form to rigidly fix the scapula during testing. The scapular brace allowed for easy angular adjustment of the shoulder joints. On three sides of the testing frame, adjustable loading bars were present that permitted loading of the proximal portion of the humerus in the cranial, lateral, and medial directions. Data collection An electromagnetic motion tracking system (Fastrak, Polhemus, Inc., Colchester, VT) For personal or educational use only. No other uses without permission. All rights reserved. Downloaded from www.vcot-online.com on 2018-04-07 | ID: 1000333563 | IP: 54.70.40.11