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This in vivo controlled laboratory
study was performed to evaluate various intra-articular clinical
injection regimes that might be less toxic than some in
vitro studies suggest. We hypothesised that low-concentration,
preservative-free, pH-balanced agents would be less toxic than high-concentration
non-pH-balanced agents with preservatives, and that injections of
individual agents are less toxic than combined injections. The left
knees of 12- to 13-week-old Sprague–Dawley rats were injected once
with eight different single agents, including low and high concentrations of
ropivacaine and triamcinolone, alone and in combination, as well
as negative and positive controls. The rats were killed at one week
or five months, and live–dead staining was performed to quantify
the death of chondrocytes. All injections except pH-balanced 0.2%
ropivacaine combined with preservative-free 1 mg/ml triamcinolone
acetonide resulted in statistically significant decreases in chondrocyte
viability, compared with control knees, after one week and five
months (p <
0.001). After one week there was no significant difference
in viability between 0.2% and 0.5% ropivacaine; however, 4 mg/ml
triamcinolone resulted in a lower viability than 1 mg/ml triamcinolone.
Although many agents commonly injected into joints are chondrotoxic,
in this in vivo study diluting preservative-free
10 mg/ml triamcinolone 1:9 in 0.2% pH-balanced ropivacaine resulted
in low toxicity.