Can ultrasound propagate in the joint space of a human knee?

A large body of evidence supports the principle that the use of low-intensity pulsed ultrasound with a frequency of 1.5 MHz can reduce fracture healing time. It is hypothesized that similar therapeutic benefits may be achieved in damaged articular cartilage. This study looks specifically at a 22-mm circular ultrasound transducer delivering ultrasound with a frequency of 1.5 MHz. A human cadaver knee was imaged using CT, the resulting images were used to help map a number of hydrophone positions in the joint from which measurements were taken. The experimental results suggest that at best there is a 30-mm window in which to place the ultrasound transducer for ultrasound to propagate through the joint space. In terms of a clinical device delivering an I-SATA of 30 MW cm(-2) to anterior regions of the joint, the I-SATA in posterior regions will at best be in the region of 10 mW cm(-2). The clinical implications of this are not known and require further investigation. (E-mail: d.m.white@ieeds.ac.uk) (C) 2007 World Federation for Ultrasound in Medicine & Biology.