Development of an experimental model of septic knee arthritis in rats through intra-articular inoculation of Staphylococcus aureus

Abstract

Haematogenous models of septic arthritis have some inherent disadvantages, such as the manifestation of arthritis relies on chance, the size of the inoculum is unknown and the number of animals to be studied cannot be reduced because the animals cannot serve as their own controls. This study aimed to develop a rat model of knee septic arthritis by injecting a known inoculum of Staphylococcus aureus into the joint. The left knees of 27 Sprague Dawley rats were injected with four different inoculum concentrations of a sensitive strain of S. aureus (30,000 colony-forming units (CFUs), n = 3; 18,550 CFUs, n = 6; 15,500 CFUs, n = 9; and 7700 CFUs, n = 9); the right knees served as controls. Clinical, microbiological and histological variables were assessed two and seven days later. The main criterion for diagnosing septic arthritis was a positive culture of synovial fluid. The rate of microbiologically confirmed septic arthritis was high for all inoculum concentrations (3/3, 6/6, 8/9 and 7/9, respectively), and the rate of bacteraemia was also high. Animal welfare was better for the two lowest inoculum concentrations. No animal reached the pre-established humane end points. Overall, the third inoculum was considered the most suitable. Thus, acute septic arthritis can be caused in rats by inoculating 15,000 CFUs of an ATCC strain of S. aureus directly into the knee joint. Overall, the model seems to be useful for studying the effectiveness of drugs for the treatment of acute septic arthritis.

Clinical and histological safety assessment of repeated intra-articular sevoflurane injections into knee joints of Sprague-Dawley rats

“…The volume for injection (150 μL) was selected to avoid mechanical damage to the articular capsule owing to overdistension. 28 However, the distension produced by this volume could be sufficiently intense to cause a painful sensation, which, in turn, could result in scratching. In this case, the intense analgesic effect of sevoflurane could alleviate this sensation, which, in turn, could prevent scratching of the left knees.…”

“…This safety study lacks a dose-response curve. We selected an initial dose/volume after considering that the joints would not be damaged because of mechanical overdistension 28 while, at the same time, it was deemed to be high enough to be eventually useful for the treatment of arthritis. Based on the absence of definitive histological changes, we discarded to evaluate further lower doses to minimize the number of experimentation animals.…”

“…The needle (30 G ½” BD Microlance TM ) was inserted perpendicular to the leg axis and parallel to the floor until contact with the joint, which was identified by loss of resistance after breaching the articular capsule. 28…”

“…The needle (30 G ½" BD Microlance TM ) was inserted perpendicular to the leg axis and parallel to the floor until contact with the joint, which was identified by loss of resistance after breaching the articular capsule. 28 The left knees (cases) were injected with 150 μL of sevoflurane (Sevorane © , 250 mL bottles containing pure sevoflurane; AbbVie, Camproverde, Italy), with the quantity selected to prevent rupture of the capsule owing to an excess of liquid. 28 The right knees (controls) were injected with 150 μL of saline.…”

“…28 The left knees (cases) were injected with 150 μL of sevoflurane (Sevorane © , 250 mL bottles containing pure sevoflurane; AbbVie, Camproverde, Italy), with the quantity selected to prevent rupture of the capsule owing to an excess of liquid. 28 The right knees (controls) were injected with 150 μL of saline.…”