The stifle joint is the largest and the most complex of all the articulations in a horse and is composed of 2 joints: the femoropatellar and the femorotibial joints.1 The femorotibial joint is subdivided into lateral femorotibial and medial femorotibial compartments. In a study by Reeves et al2 and a study by Vacek et al,3 injection of a gelatin-based dye or latex into the femoropatellar joint demonstrated a direct anatomic communication between that joint and the medial femorotibial compartment alone in both stifle joints of 15 of 23 (65%) horses and of 18 of 30 (60%) horses, respectively. In the study by Reeves et al,2 4 of the 23 (17.4%) horses also had communication between the femoropatellar joint and both compartments of the femorotibial joint. In the study by Vacek et al,3 latex injected into the medial femorotibial compartment entered directly into the femoropatellar joint of 24 of 30 (80%) stifle joints from 14 horses. Conversely, both studies2,3 showed poor communication between the lateral femorotibial compartment and the other 2 compartments of the stifle joint (ie, the femoropatellar joint and the medial femorotibial compartment). Authors of one of those studies2 suggested that chronic effusion of 1 compartment of the stifle joint as a result of inflammation may enable direct communication to develop among all 3 compartments of the stifle joint, whereas others have proposed that inflammation of 1 or more of the compartments could result in obstruction of the anatomic communications.4–6 More recently, in an in vitro study,5 diffusion of local anesthetic solution between compartments of the stifle joint was greater than that previously assumed on the basis of results of anatomic, latex injection, and contrast arthrographic studies.2,3
Frequently, local anesthetic solution is instilled into 1 of the 3 synovial compartments of the stifle joint of lame horses to isolate the site of lameness-causing pain. The uncertainty regarding the anatomic or functional communication among the synovial compartments of the stifle joint has led to a common recommendation to inject all 3 compartments with a local anesthetic solution to isolate the site of lameness-causing pain.2,3,5,7
For research purposes, various techniques have been used to induce lameness localized to a synovial cavity in horses, including intra-articular administration of 1% solution of sterile carrageenan,8 amphotericin B,9 Escherichia coli lipopolysaccharide,10 Freund's complete adjuvant,11 or recombinant equine IL-1β.12 The cytokine IL-1β is known to play a fundamental role in naturally occurring synovial inflammation.13
The objective of the study reported here was to evaluate the effects of sequential anesthesia of the individual compartments of the equine stifle joint on lameness resulting from transient synovitis induced by intra-articular deposition of IL-1β in 1 randomly selected synovial compartment. We hypothesized that deposition of recombinant equine IL-1β into a synovial compartment of the stifle joint would result in clinically apparent lameness and that instillation of local anesthetic solution into any of the 3 compartments would significantly reduce lameness, regardless of which compartment was injected with IL-1β.
Equinosis LLC, Columbia, Mo.
R&D Systems, Minneapolis, Minn.
Omnipaque 240 (iohexol), GE Healthcare Inc, Princeton, NJ.
Carbocaine-V, Pfizer Inc, New York, NY.
Equi-Phar Phenylbutazone Injection 20%, Vedco Inc, St Joseph, Mo.
StatsDirect statistical software, version 2.7.8, StatsDirect Ltd, Altrincham, Cheshire, England.
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