To develop and to assess a simple, inexpensive method for ascertaining, without any imaging procedure, the intra-articular placement of the needle in the knee for intra-articular injections.
Outpatients referred for intra-articular treatment with "dry" symptomatic knee osteoarthritis were included in this prospective study. "Dry" knee disease was defined as a knee without any clinically detectable effusion. Once intra-articular positioning of the needle considered adequate using the backflow technique, contrast solution was injected using the same needle without changing its position and immediately afterwards lateral and anterior-posterior X-rays were taken to assess the needle position.
Of the 32 of 33 cases with obtained backflow, the needle was correctly placed in all cases. In the remaining case, the needle was extra-articularly positioned. The concordance between the two techniques using the Cohen's Kappa was 1 [CI 95%: 0.22-1].
The backflow technique allows to accurate the intra-articular placement of the needle for "dry" knee joints injection. This technique can be proposed as a learning tool as well as a daily practice technique to ascertaining intra-articular knee injections without using fluoroscopy with injection of contrast material. Further studies are needed to assess the technique for other joint injections.