Summary The medical records of 192 horses with septic arthritis/tenosynovitis 1979–1989 were reviewed. Forty‐three horses developed infection after an intra‐articular injection, 46 following a penetrating wound, 25 following surgery, 66 were foals less than 6 months old, and 12 were adult horses without a known aetiology. Haematogenous infection of a joint occurs in adult horses and should be considered as a differential diagnosis in horses with an acute onset of severe lameness. The aetiology of the infection had a significant effect on the type of bacteria identified by culture. Staphylococcus was cultured from most of the horses that developed infection following a joint injection or surgery, 69% of the horses from which an organism was identified. Horses that developed infection secondary to a penetrating wound frequently provided cultures of more than one organism; Enterobacteriaceae and anaerobes were more frequently isolated in this group. The most common organisms isolated from foals were Enterobacteriaceae; E. coli was identified in more than 27% of the foals. The hock was the most frequently involved joint. Multiple treatments were used over the 10‐year period of study. Survival rates were lowest in foals; only 45% survived to be released from the hospital. Survival was greater in adult horses; 85% of the horses that were treated were released from the hospital. Survival was significantly greater in horses with septic tenosynovitis; all 14 of the horses that were treated survived. Survival was not significantly affected by the joint involved or by the type of bacteria cultured from the synovial fluid. Follow‐up racing data were obtained for all horses of racing age that were released from the hospital; 56.5% of these horses returned to racing and over 45% of these horses were able to make at least 5 starts. We suggest that if the infection can be eliminated before irreversible damage to the articular cartilage occurs, horses can return to athletic function.

Summary Open drainage was used to treat 26 horses with persistent or severe septic arthritis/tenosynovitis. Infected synovial structures were drained through a small (3 cm) arthrotomy incision that was left open and protected by a sterile bandage. Joint lavage was performed in all 26 horses. In addition to systemic antibiotics, 23 of these horses were also treated with intra‐articular antibiotics; amikacin (17 horses), gentamycin (2 horses), cefazolin (2 horses), and 2 horses were injected at different times with gentamycin and amikacin. The infection was eliminated from the involved synovial structures in 25 of 26 horses; 24 survived and were released from the hospital. The arthrotomy incisions healed by granulation in 16 horses; in 9 horses the arthrotomy incision was sutured closed once the infection was eliminated. Seventeen horses returned to soundness and resumed athletic function. Open drainage was an effective method of achieving chronic drainage from a joint or tendon sheath. It is indicated in horses that have established intra‐synovial infections or in horses that do not respond to joint lavage through needles.

Summary Infectious arthritis was induced experimentally in one tarsocrural joint of six horses by intra‐articular injection of 1 ml Staphylococcus‐saline suspension containing 9 times 104 to 3 times 106 organisms. The corresponding contralateral joint was injected with 1 ml of saline and served as a control. The progression of the induced infectious arthritis was assessed over a nine‐day period by clinical examination and sequential synovial fluid analysis with pH and lactate measurements. Changes in synovial fluid were present before clinical signs of infectious arthritis were manifested. The diagnostic value of different synovial fluid parameters at various stages of infection was determined. Cellular changes initially preceded the biochemical changes. Total leucocyte counts showed a significant increase within 24 h (up to 100 times 109/litre) with great variability in subsequent measurements. Neutrophilia over 90 per cent and pH under 6.9 were the most consistent findings in the infected synovia. Increased total protein was also significant and was progressive throughout the experiment. Serum and synovial glucose difference and synovial lactate had more diagnostic value in the acute stages than in the chronic stages. The control joints elicited an inflammatory response manifested by increased leucocyte count, moderate neutrophilia, slightly increased total protein concentration, and slightly decreased pH, but all reactions were minor in comparison to those in the infected joints.

Summary The medical records and radiographs of all horses with a third carpal bone fracture admitted to The Ohio State University Veterinary Hospital from 1979 to 1987 were reviewed. Three hundred and seventy‐one fractures were found in 313 horses; 57 per cent were Standardbreds, 41 per cent were Thoroughbreds, and only 1.6 per cent were Quarterhorses. All were young racehorses (average age = 3.1 years). Third carpal fractures occurred more frequently in the right limb (60 per cent) than the left limb (40 per cent); Thoroughbreds had a greater right‐left disparity (67.5 per cent R, 27.1 per cent L). Fractures were classified according to their size and anatomical location within the third carpal bone: incomplete fractures of the radial facet (type 1, N = 39), large proximal chip fractures of the radial facet (type 2, N = 140), small proximal chip fractures of the radial facet (type 3, N = 18), medial corner fractures (type 4, N = 13), frontal plane slab fractures of the radial facet (type 5, N = 93), large frontal plane slab fractures involving both the radial and intermediate facets (type 6, N = 35), fractures of the intermediate facet (type 7 N = 13), and sagittal slab fractures (type 8, N = 20). The incidence of each fracture type was significantly different between Standardbreds and Thoroughbreds. Type 1 and 2 fractures were more common in Standardbreds; type 5 and 6 fractures were more common in Thoroughbreds. Differences between these two breeds are related to the different gaits at which they race. The classification more accurately describes the extent of injury and the variation in fractures observed in this study than the traditional division as chips or slabs. A high quality skyline projection is important in correctly identifying these fractures; over 10 per cent of the fractures were detected only on this view.

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