Synovial fluid detection in intra-articular injections using a bioimpedance probe (BIP) needle—a clinical study

Intra-articular glucocorticoid injections are the recommended treatment for active arthritis, but accurate positioning of the needle may be challenging. Inexperienced physicians might decide not to inject because an unsuccessful injection impairs clinical outcome and may lead to complications; however, choosing not to inject may impair or delay the best possible treatment. Here, we address this problem by introducing a novel Bioimpedance Probe (BIP) Needle-guidance method that was tested in a clinical study. The BIP Needle was utilized for detection of synovial fluid. It measures real-time bioimpedance spectra and identifies when the needle tip is in contact with the synovial fluid. Injections into 80 joints with active arthritis were performed by an experienced rheumatologist using the BIP Needle. The location of the BIP Needle was ensured by aspiration of synovial fluid, absence of resistance during injection, and/or using real-time ultrasound imaging. Sensitivity and specificity of the device for synovial fluid detection were 86 % (CI 75–93 %) and 85 % (CI 74–92 %), respectively. The BIP Needles showed high spatial resolution and differentiated the synovial fluid from the surrounding tissues. However, lack of synovial fluid, anatomic variability, and intra-articular structures challenged the technology. The BIP Needles provided adequate results in intra-articular injections. Performance of the device was good even in small joints, which may be the most difficult for inexperienced physicians. Further performance improvement can be expected when more data is collected for mathematical models. Overall, this novel method showed potential to be used in real-time needle guidance.