A new method for continuous intraoperative measurement of Harrington rod loading patterns

A new method has been developed for continuous intra-operative monitoring of bone and implant loading patterns in the operative correction of scoliosis using the Harrington distraction rod. The method incorporates a strain gauge instrumented, distal Harrington hook and similarly equipped Harrington operating instruments (outrigger and distractor). These latter instruments are used to calibrate the hook's response to bone loads under existing operative conditions. Alternative methods of monitoring loading patterns were explored and rejected because they were noncontinuous, more difficult to use, altered the mechanics of the system, or required more expensive components. The method established is being used to avoid bone rupture or rod damage while gaining maximum spinal correction and to determine the effect of auxiliary implant components on loading patterns.