Viscosity of synovial fluid (SF) from 29 clinically normal horses was determined by use of a rotational cone and plate microviscosimeter. Total protein concentration in the SF of the 29 horses, as measured with a refractometer, was < 2.5 g/dl. When the Coomassie brilliant blue test was used to determine total protein concentration in SF for 15 horses, the mean value was 1,088 mg/dl. Viscosity values at 60, 30, 12, 6, 3, and 1.5 revolutions/min (rpm) spindle speed were 4.41 +/- 1.54 centipoise (cp), 5.29 +/- 1.94 cp, 6.76 +/- 2.76 cp, 8.52 +/- 4.27 cp, 10.41 +/- 6.30 cp, and 13.07 +/- 9.05 cp, respectively. Synovial fluid viscosity increased with decreasing rpm and shear rate, but the shape of the curve for each horse fitted the asymptotic curve. The rotational cone and plate microviscosimeter was an accurate instrument in measuring SF viscosity at multiple rpm or shear rates in horses. The values obtained on clinically normal horses in this study will serve as a baseline for comparison in the evaluation of horses with joint disease.

Keratan sulfate (KS) is a glycosaminoglycan, distribution of which is confined mostly to hyaline cartilage. As such, it is a putative marker of hyaline cartilage catabolism. In experiment 1, a focal osteochondral defect was made arthroscopically in 1 radial carpal bone of 2 ponies, and in 2 other ponies, chymopapain was injected into the radiocarpal joint to induce cartilage catabolism. Sequential and concurrent plasma and synovial fluid concentrations of KS were measured, up to 13 months after induction of cartilage injury, to determine whether changes in KS concentrations reflected cartilage catabolism. In experiment 2, a large, bilateral osteochondral defect was made in the radial carpal bones of 18 ponies, which were subsequently given postoperative exercise and/or injected intra-articularly with 250 mg of polysulfated glycosaminoglycan (PSGAG). Medication was given at surgery, then weekly for 4 weeks. Blood samples were collected and synovial fluid was aspirated before surgery, when medication was given, and at postmortem examination (postoperative week 17). The KS concentration was measured in these fluids to determine whether changes in KS concentration indicated an effect of joint treatment. In experiment 1, the concentration of KS in synovial fluid was highest 1 day after joint injury, and the concentration in plasma peaked 2 days after joint injury. For ponies receiving chymopapain intra-articularly (generalized cartilage catabolism), a fivefold increase over baseline was observed in the concentration of KS in plasma (peak mean, 1.2 microgram/ml), and a tenfold increase over baseline in synovial fluid (peak mean, 2.0 mg/ml) was observed. On average, these maxima were threefold higher than values in fluids of ponies with osteochondral defects (focal cartilage disease). In experiment 2, nonexercised ponies had lower KS concentration (as a percentage of the preoperative concentration) in synovial fluid than did exercised ponies at all postoperative times, and.

peer reviewed | OBJECTIVE: To compare the extent of inflammation and catabolic collagen response in the middle carpal joints (MCJs) of healthy horses following intra-articular injection of 2% lidocaine, 2% mepivacaine, lactated Ringer solution (LRS), or 0.1% methyl parahydroxybenzoate. ANIMALS: 17 adult horses. PROCEDURES: In the first of 2 experiments, the left middle carpal joint (MCJ) of each of 12 horses was injected with 10 mL of 2% lidocaine (n = 3), 2% mepivacaine (3), or LRS (control; 6). After a 4-week washout period, the right MCJ of the horses that received lidocaine or mepivacaine was injected with 10 mL of LRS, and the right MCJ of horses that received LRS was injected with 10 mL of 2% lidocaine (n = 3) or 2% mepivacaine (3). In experiment 2, the left MCJ of each of 5 horses was injected with 10 mL of 0.1% methyl parahydroxybenzoate. After a 48-hour washout period, the right MCJ of each horse was injected with 10 mL of LRS. Synovial fluid (SF) samples were aseptically collected before and at predetermined times after each injection. Synovial fluid WBC count, neutrophil percentage, and total protein, neutrophil myeloperoxidase, neutrophil elastase, and Coll2-1 concentrations were compared among treatments. RESULTS: Both lidocaine and mepivacaine induced SF changes indicative of inflammation and a catabolic collagen response, but the magnitude of those changes was more pronounced for lidocaine. Methyl parahydroxybenzoate did not cause any SF changes indicative of inflammation. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that mepivacaine was safer than lidocaine for intra-articular injection in horses.

OBJECTIVE To evaluate lameness and morphological changes associated with an osteochondral fragment–groove procedure as a means of experimental induction of metacarpophalangeal (MCP) joint osteoarthritis within an 11-week period in horses. ANIMALS 6 nonlame adult warmbloods. PROCEDURES The right MCP joint of each horse underwent an osteochondral fragment–groove procedure (day 0). After 1 week of stall rest (ie, starting day 7), each horse was trained daily on a treadmill. Weekly, horses underwent visual and inertial sensor-based assessments of lameness. Both MCP joints were assessed radiographically on days 0 (before surgery), 1, 35, and 77. A synovial fluid sample was collected from the right MCP joint on days 0 (before surgery), 35, 36, 49, 63, and 77 for cytologic and biomarker analyses. On day 77, each horse was euthanized; both MCP joints were evaluated macroscopically and histologically. RESULTS Right forelimb lameness was detected visually and by the inertial sensor system when horses were moving on a straight line after distal forelimb flexion or circling left on days 14 to 77. Compared with presurgical values, synovial fluid interleukin-6, prostaglandin E2, hyaluronic acid, and interleukin-1 receptor antagonist protein concentrations were increased at 2 or 3 time points, whereas tumor necrosis factor-α and interleukin-10 concentrations were decreased at 1 time point. Gross examination of all right MCP joints revealed synovitis and wear lines; synovitis was confirmed histologically. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a combined osteochondral fragment–groove procedure can be used to induce clinically and grossly observable early MCP joint osteoarthritis during an 11-week period in horses.

OBJECTIVE To evaluate gene transfer of recombinant adeno-associated viral (rAAV) vectors with AAV2 or AAV5 capsid and encoding hyaluronic acid (HA) synthase-2 (HAS2) into joints of healthy dogs. ANIMALS 22 purpose-bred Beagles. PROCEDURES Plasmid expression cassettes encoding canine HAS2 (cHAS2) were assessed in vitro for concentration and molecular size of secreted HA. Thereafter, rAAV2-cHAS2 vectors at 3 concentrations and rAAV5-cHAS2 vectors at 1 concentration were each administered intra-articularly into the left stifle joint of 5 dogs; 2 dogs received PBS solution instead. Synovial fluid HA concentration and serum and synovial fluid titers of neutralizing antibodies against AAV capsids were measured at various points. Dogs were euthanized 28 days after treatment, and cartilage and synovium samples were collected for vector DNA and mRNA quantification and histologic examination. RESULTS Cell transfection with plasmids encoding cHAS2 resulted in an increase in production and secretion of HA in vitro. In vivo, the rAAV5-cHAS2 vector yielded uniform genome transfer and cHAS2 expression in collected synovium and cartilage samples. In contrast, rAAV2-cHAS2 vectors were detected inconsistently in synovium and cartilage samples and failed to produce clear dose-related responses. Histologic examination revealed minimal synovial inflammation in joints injected with rAAV vectors. Neutralizing antibodies against AAV capsids were detected in serum and synovial fluid samples from all vector-treated dogs. CONCLUSIONS AND CLINICAL RELEVANCE rAAV5-mediated transfer of the gene for cHAS2 into healthy joints of dogs by intra-articular injection appeared safe and resulted in vector-derived cHAS2 production by synoviocytes and chondrocytes. Whether this treatment may increase HA production by synoviocytes and chondrocytes in osteoarthritic joints remains to be determined.

The aim of this study was to determine the pharmacokinetics of amikacin and penicillin G sodium when administered in combination as an intravenous regional limb perfusion (IVRLP) to horses. Seven healthy adult horses underwent an IVRLP in the cephalic vein with 2 g of amikacin sulfate and 10 mill IU of penicillin G sodium diluted to 60 mL in 0.9% saline. A pneumatic tourniquet set at 450 mmHg was left in place for 30 min. Synovial fluid was collected from the metacarpophalangeal joint 35 min and 2, 6, 12, and 24 h after infusion of the antimicrobials. Concentrations of amikacin and penicillin in synovial fluid were quantitated by liquid chromatography tandem-mass spectrometry analysis. Therapeutic concentrations of amikacin and penicillin for equine-susceptible pathogens were achieved in the synovial fluid. Maximum synovial concentrations (Cmax) (mean ± SE) for amikacin and penicillin were 132 ± 33 μg/mL and 8474 ± 5710 ng/mL, respectively. Only 3 horses had detectable levels of penicillin at 6 h and 1 at the 12 h sample. The combination of amikacin with penicillin G sodium via IVDLP resulted in reported therapeutic concentrations of both antibiotics in the synovial fluid. The Cmax:MIC (minimum inhibitory concentration) ratio for amikacin was 8:1 and Time > MIC for penicillin was 6 h. At 24 h, the mean concentration of amikacin was still above 4 μg/mL. Terminal elimination rate constants (T1/2 lambdaz) were 13.6 h and 2.8 h for amikacin and penicillin, respectively. The use of IVDLP with penicillin may therefore not be practical as rapid clearance of penicillin from the synovial fluid requires frequent perfusions to maintain acceptable therapeutic concentrations.

OBJECTIVE To evaluate the effect of volume of IV regional limb perfusion (IVRLP) on amikacin concentrations in synovial and interstitial fluid of horses. ANIMALS 8 healthy adult horses. PROCEDURES Each forelimb was randomly assigned to receive IVRLP with 4 mL of amikacin sulfate solution (250 mg/mL) plus 56 mL (total volume, 60 mL) or 6 mL (total volume, 10 mL) of lactated Ringer solution. Horses were anesthetized, and baseline synovial and interstitial fluid samples were collected. A tourniquet was placed, and the assigned treatment was administered via the lateral palmar digital vein. Venous blood pressure in the distal portion of the limb was recorded. Additional synovial fluid samples were collected 30 minutes (just before tourniquet removal) and 24 hours after IVRLP began; additional interstitial fluid samples were collected 6 and 24 hours after IVRLP began. RESULTS 30 minutes after IVRLP began, mean amikacin concentration in synovial fluid was significantly greater for the large-volume (459 μg/mL) versus small-volume (70 μg/mL) treatment. Six hours after IVRLP, mean concentration in interstitial fluid was greater for the large-volume (723 μg/mL) versus small-volume (21 μg/mL) treatment. Peak venous blood pressure after large-volume IVRLP was significantly higher than after small-volume IVRLP, with no difference between treatments in time required for pressure to return to baseline. CONCLUSIONS AND CLINICAL RELEVANCE Study findings suggested that large-volume IVRLP would deliver more amikacin to metacarpophalangeal joints of horses than would small-volume IVRLP, without a clinically relevant effect on local venous blood pressure, potentially increasing treatment efficacy.