Many studies have focused on the accuracy rate of intraarticular injection. However, sometimes, even when the needle enters the joint cavity accurately, it can be difficult to obtain a sufficient amount of joint fluid. This problem may be attributable to the position of the knee during arthrocentesis. The purpose of this prospective study was to determine which position, supine or sitting, would yield more joint fluid during knee arthrocentesis.
In this study, 40 knees belonging to 30 patients with osteoarthritis were examined. The patients were randomized between the supine position group (20 knees) and the sitting position group (20 knees). A "blind" aspiration was performed on each group. The volume of aspirated joint fluid (in milliliters) (V(1)) was recorded for each knee. Each knee was then checked by ultrasound immediately after aspiration. If there was more than a depth of 2 mm of knee effusion, then a second knee arthrocentesis was performed using ultrasound guidance. The aspirated joint fluid volume (in milliliters) (V(2)) was recorded for each knee. The value V(1)/V(1) + V(2) was calculated for each knee. The data were analyzed using the SPSS 16.0 statistical package program.
In the supine position group, the "dry tap" rate was 10% in the first arthrocentesis, and 30% of the knees needed a second arthrocentesis. In the sitting position group, the dry tap rate was 25% in the first arthrocentesis, and 75% of the knees needed a second arthrocentesis. There was a significant difference in the V(1)/V(1) + V(2) values between the two groups (P = 0.02).
In our study, more joint fluid was aspirated from patients in the supine position than from patients in the sitting position.