Force measurement of the "derotation maneuver"

Currently surgeons are unable to determine how much force is applied during scoliosis correction. The Gripper is a modified Moss Miami rod rotator wit h an instrumented sleeve that slips over the handle. This system is able to measure the force and resulting moment applied by the surgeon during the d erotation maneuver of scoliosis surgery. The rigid frame of the hand grip i s insensitive to the squeezing force and thus only the net forces and torqu e transmitted by the surgeon are recorded. The strain gauge data was sample d with a data acquisition system (DAQ 1200, National Instruments) and the v oltage output was interpreted by MATLAB to calculate the forces and moments . Calibration showed that die system could calculate the forces accurately (R-2=0.96) and to within +/- 3 N. For scoliosis surgery, data were collecte d during the derotation of the rod, prior to fixation. Forces and moments w ere recorded for about 30 seconds at 10 samples per second. This system was tested on 4 subjects. The maximum forces applied by the surgeon ranged fro m 20 to 50 N with a torque of 4-11 Nm.