Having a bad back is no fun, and the corrective measures can be just as unpleasant. So Disc Dynamics, Devicix, and MTS Sensors Div. got together to devise a minimally invasive way to treat degenerative disc disease. The result is the Dascor Disc Arthroplasty System, in which the nucleus of a spinal disc is removed and replaced with an artificial nucleus that restores the correct gap height between the vertebrae.
Initial versions of the surgical tool used to install the artificial nucleus delivered the two-part polymer to the site pneumatically, and proved to have control issues that made it difficult to ensure the desired amount of polymer was injected.
The challenge: Devise an easier way to treat spinal disc disease
Disc Dynamics (www.discdyn.com) and Devicix (www.devicix.com) integrated the procedural requirements into a surgical tool that could be easily operated by physicians and trained technicians. Devicix integrated software, electrical, and mechanical disciplines into a microprocessor-based tool that allows closed-loop control of polymer injection via feedback from linear position and pressure sensors. Instead of pneumatics, the Dascor System now uses a motor driving a ball screw monitored by a Temposonics MTS C-Series magnetostrictive linear position sensor to deliver an accurately measured quantity of the polymer.
The sensor head measures 36 mm dia.; the 4 mm dia. sensor shaft, 18 mm dead zone, and 21 mm null zone improve the overall length-to-active zone ratio. Forward and rearward travel limits are calibrated from the C-Series position feedback, eliminating the need for limit switches. The sensor's absolute output also obviates the need for encoders. The required volume of polymer as determined from a CT scan is compared with filling volume in the artificial nucleus and then calculated from the sensor's feedback to ensure the correct final size.