Effect of Intrathecal Amikacin Administration and Repeated Centesis on Digital Flexor Tendon Sheath Synovial Fluid in Horses SUSANNE DYKGRAAF, BVSc, MVSc, JULIE E. DECHANT, DVM, MS, Diplomate ACVS, JENNIFER L. JOHNS, DVM, MARY M. CHRISTOPHER, DVM, PhD, Diplomate ACVP, DAVID M. BOLT, Dr Med Vet, MS, Diplomate ACVS, and JACK R. SNYDER, DVM, PhD, Diplomate ACVS Objective—To determine the effect of intrathecal amikacin administration and repeated tenovagi- nocentesis on the total nucleated cell count (TNCC), total protein (TP) concentration and cytologic characteristics of synovial fluid of the equine digital flexor tendon sheath (DFTS). Study Design—Randomized, cross-over experimental design. Animals—Adult horses (n ¼ 8). Methods—Synovial fluid was aseptically collected from the DFTS and either 1 mL amikacin sulfate (250 mg/mL) or lactated Ringer’s solution (LRS) was injected into the DFTS. Serial synovial fluid samples were obtained at 0, 12, 24, 48, and 72 hours. The opposite treatment was administered to the contralateral DFTS after a washout period of 2 weeks. Results—Treatment increased TP concentration, TNCC, percentage of neutrophils, and neutrophil counts from baseline levels. There was no difference between treatment of the DFTS with amikacin or LRS. Values peaked at 12–24 hours after the initial centesis and then declined toward baseline levels. Conclusions—Injection and repeat centesis of the normal DFTS with 250 mg amikacin or an equivalent volume of LRS resulted in mild increases in synovial fluid analytes from baseline. Synovial inflammation in this study was not accompanied by lameness at the walk and measured analytes returned toward baseline levels within 12–24 hours of first injection. Clinical Relevance—The effect of tenovaginocentesis and intrathecal administration of amikacin or LRS on DFTS synovial fluid values are modest in most horses; however, some horses can develop marked increases in synovial fluid values that may be interpreted as sepsis. r Copyright 2007 by The American College of Veterinary Surgeons INTRODUCTION P ENETRATING INJURY to the digital flexor ten- don sheath (DFTS) can lead to performance limiting or life-threatening synovial infection. 1,2 The degree of lameness is usually severe, unless the tendon sheath is open and draining. 3 It can be difficult to determine with certainty if a wound has penetrated the tendon sheath, particularly in small self-closing wounds or in horses examined soon after injury. 4 Tenovaginocentesis is commonly performed during the management of tendon sheath injuries to obtain syn- ovial fluid samples for analysis and to administer intra- thecal antibiotics. 5 Quantifying total nucleated cell count (TNCC), total protein (TP) concentration, percentage of neutrophils and cytologic characteristics of the synovial fluid, in combination with clinical signs, can assist in de- termination of an appropriate treatment plan for wounds involving the DFTS. There may be some overlap between clinicopathologic values in early sepsis, non-septic pro- Funding for this study was provided by the UCDavis Center for Equine Health Dan Evans Memorial Endowment and UCDavis Comparative Gastroenterology Laboratory. Horses were provided by the UCDavis Center for Equine Health. Address reprint request to Dr. Susanne Dykgraaf, BVSc, MVSc, Veterinary Medical Teaching Hospital, University of California, One Shields Ave, Davis, CA 95616. E-mail: sdykgraaf@ucdavis.edu. Submitted April 2006; Accepted September 2006 From the Veterinary Medical Teaching Hospital and the Departments of Surgical and Radiological Sciences and Pathology, Mi- crobiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA. r Copyright 2007 by The American College of Veterinary Surgeons 0161-3499/07 doi:10.1111/j.1532-950X.2007.00235.x 57 Veterinary Surgery 36:57–63, 2007