Evaluation of different intraarticular injection volumes to assess optimum efficient amount; an experimental study in rat knee joints.

Introduction: The injection amount of solutions differs in wide ranges, from 20 to 200 μL in intraarticular injections experiments that was carried out with rats. The 10-fold difference between applied volumes is not acceptable since injection errors might affect the outcomes of the studies significantly. The excessive amount of solution that was injected into the knee joint of rats might end up with leakage of the solution from injection aperture, and damage the articular structures etc. In our preliminary experiments, we mentioned problems during the injection of excessive amount of solution into the rat knee joint. The main purpose of the present study, which was performed with rat knee joints, was to evaluate the applicability of different amounts of solutions used in experiments and to determine the optimal volume for intraarticular injection in rats.

Methods: The volume of 100 μL water-based stain was administered into knee joints of non-living rats. The legs were dissected to evaluate the possible presence of injected solution outside the knee joint. Then, the decreasing volumes (100 μL, 50 μL, 40 μL and 30 μL) of X-ray contrast solution (lobitridol) were applied into the knees of living rats to investigate whether systemic circulation acts on the leakage outside the joint. The X-ray images of all these joints were also taken to confirm the results.

Results: In nonliving rats, the place where water-based strain overflow from the knee joint was pointed out. The place of leakage is where the tendo musculi extensor digitorum longus leaves outside the joint. In living rats, by using contrast solution, an overflow was noticed in the subdermal place with the intraarticular injection volumes of 100 μL, 50 μL, and 40 μL. No overflow was observed with the intraarticular injection volumes of 30 μL X-ray contrast solution.

Discussion: In conclusion, the injection volume for the knee joints of rats should not exceed the 30 μL for optimum efficiency.