Positioning device for optimal active kinematic real-time magnetic resonance imaging of the knee joint: a technical note

Objective. A prototype of a positioning device created especially for the diagnostic imaging of the patellofemoral joint was developed in order to achieve reproducible examination conditions. Design. For this purpose a clinical trial on healthy test persons was carried out under real examination conditions. Background. A special real-time MRI technique (Local-Look-technique) makes the analysis of active functional motion images possible. A prerequisite for this technique is accurate reproducible positioning of the knee joint in the MRI unit. Methods. This positioning device was evaluated during a total of 50 examinations of the knee joints of five healthy test persons. The right patellofemoral joint of each test person was examined twice at different time points in order to check the reproducibility of all examination conditions. Comparing two examination series from the same individual, reproducibility of MRI slices was guaranteed by using identical anatomical landmarks. Image quality and test-retest reliability were analyzed on the computer screen. Results. Optimal desired fixation of the leg in the MRI tube using the device was accomplished in all cases. The extent of motion of the knee joints ranged from 38 ° (n = 2) to 40 ° (n = 3) of flexion to full extension, which was satisfactory for the evaluation of the patellofemoral joint. Free movement of the patella and the lower leg was observed. The active functional MRI examination using this device was satisfactory and reproducible as assessed by test-retest reliability. Conclusions. The positioning device is a useful development in achieving active functional real-time MRI evaluation of the knee and patellofemoral joint. Using this diagnostic tool, reproducible quantitative examinations can now be easily performed. The reproducibility and high reliability as well as its simplicity of operation render this diagnostic tool suitable for use in orthopedics and traumatology.