1586 AJVR, Vol 72, No. 12, December 2011 A number of publications have been about the TMJ of horses. 1–8 These have included anatomic studies, surgical interventions (for condylectomies and septic arthritis), and attempts to correlate dental disease and TMJ abnormalities. 2,4,a However, specific research into diseases of the TMJ in horses is sparse, possibly because disease in this synovial joint is considered rare. However, diseases of the TMJ in humans are com- mon and can have a variety of causes (eg, trauma, sep- sis, degenerative arthropathies, dental malocclusions, and myofacial disorders). These diseases result in myri- ad clinical manifestations, ranging from headaches and jaw and muscle pain to an inability to open or close the mouth. 8,a In addition to clinical, radiographic, and computed tomographic evaluation, arthrocentesis of the TMJ is commonly performed in humans to evaluate Comparison of the response to experimentally induced short-term inflammation in the temporomandibular and metacarpophalangeal joints of horses James L. Carmalt, MA, VetMB, MVSc; Chris D. Bell, DVM, MVSc; Dane M. Tatarniuk; Sarabjeet S. Suri, PhD; Baljit Singh, BVSc&AH, PhD; Cheryl Waldner, DVM, PhD Objective—To investigate the relationship between inflammatory responses of the temporo- mandibular joint (TMJ) and the metacarpophalangeal (MCP) joint in clinically normal horses. Animals—7 mature horses. Procedures—In each horse, 1 TMJ and 1 MCP joint were injected with lipopolysaccharide (LPS; 0.0025 μg). The contralateral TMJ and MCP joint were injected with saline (0.9% NaCl) solution. Synovial fluid samples were collected from all 4 joints over 24 hours af- ter injection. Concentrations of interleukin-6, tumor necrosis factor-α, transforming growth factor-β, and total protein were measured via immunoassay. Horses were assessed for clinical signs of joint inflammation at each time point. Results—Concentrations of interleukin-6 were not significantly different between LPS- injected MCP joints and TMJs at any time point. Transforming growth factor-β concentra- tions were significantly increased in MCP joints, compared with concentrations in TMJs, at 12 and 24 hours after injection. Tumor necrosis factor-α concentrations were significantly higher in LPS-injected TMJs than in LPS-injected MCP joints at 1 and 6 hours after injection. Total protein concentration did not differ significantly between LPS-injected MCP joints and TMJs. Injection of LPS induced clinical inflammation at all time points; additionally, 2 MCP joints (but no TMJs) had an inflammatory response to injection of saline solution. Conclusions and Clinical Relevance—The inflammatory response to LPS appeared to be attenuated more quickly in TMJs than in MCP joints of horses. The difference in response suggested that a lack of clinical osteoarthritis in the TMJ of horses could be attributable to a difference in cytokine response. (Am J Vet Res 2011;72:1586–1591) the joint environment, to assist in reaching a diagnosis, and for use as a treatment modality. 9 There have been several studies 10–13 in humans in which cytokines (IL-1, IL-6, IL-8, TNF-α, and TGF-β) have been evaluated in an effort to categorize and quantify the degree of joint inflammation and to provide a prognosis. The interac- tions of these cytokines are integrally involved in acute inflammation and have been associated with synovial metabolism and the degradation of articular cartilage. A single study 9 in horses in which investigators attempted to correlate dental malocclusions with al- terations in inflammatory cytokine profiles in the TMJ (similar to results reported in studies in humans) found no significant difference in the concentrations of pro- inflammatory (Il-1, IL-6, IL-8, and TNF-α) and anti- Received June 29, 2010. Accepted October 27, 2010. From the Departments of Large Animal Clinical Sciences (Carmalt, Bell, Tatarniuk, Waldner) and Biomedical Sciences (Suri, Singh), Western College of Veterinary Medicine, University of Saskatch- ewan, Saskatoon, SK S7N 5B4, Canada. Supported by the Western College of Veterinary Medicine-Equine Health Research Fund. Address correspondence to Dr. Carmalt (james.carmalt@usask.ca). ABBREVIATIONS IL Interleukin LPS Lipopolysaccharide MCP Metacarpophalangeal TGF Transforming growth factor TMJ Temporomandibular joint TNF Tumor necrosis factor Unauthenticated | Downloaded 08/26/22 05:04 AM UTC