By taking into account the spectral power at the frequency band of 500-1500 hertz, the superolateral empty syringe air injection approach having a vibration sensor on the medial collateral ligament at the mid-patellar level was found to effectively discriminate between intra-articular and extra-articular needle placement in the cadaveric knee joint.

This vibration sensor approach can be an alternative approach for detecting the accurate location of needle placement, says a proof-of-concept study published in BMC Musculoskeletal Disorders.

Researchers aimed to determine the usage of vibration sensor for detecting the correct location of needle tip placement for knee intra-articular injection.

With the aid of needles, 2 millilitres of air were injected supero-laterally at and intra-articular and extra-articular positions of a knee joint. For confirming the positions of the needle tip, ultrasonography was utilized. For collecting the vibration signals, a piezoelectric accelerometer was medially mounted on the knee joint. Analysis of signals was done for characterizing the frequency components of the vibration signals during injections.

Visual observation of vibration frequency band power in the range of 500–1500 hertz was done. This was done for localizing the placement of needle tips during air injection. For the needle size  24 gauge,  21 gauge, and 18 gauge, the differences of frequency band power between intra-articular and extra-articular positions were reported to be 39.2 dB, 26.4 dB, and 18.1 dB respectively.

Notably, the largest difference in spectral power was noted in 24G, the smallest needle diameter.

This analysis showed a possible application of an alternative electronic device for detecting the intra-articular knee injection when an ultrasound machine is unavailable.