A current clinical product from Smith and Nephew uses a pulsed 1.5 MHz signal for treating fractures 20 minutes per day. This pulsed 1.5 MHz signal produces radiation force vibration at 1 kHz. It was hypothesized that the radiation force, not the ultrasound, is responsible for the biological effect of the Smith and Nephew system of stimulating chondrocytes. In vitro experiments using the following method indeed showed that treatment with 1 kHz induced chondrogenesis similar to treatment with 1.5 MHz pulsed ultrasound. This study provides the first evidence for 1 kHz activation of chondrocytes and for the potential mechanisms with which this vibration is sensed in the cell.