The design of instrumentation for force measurement during scoliosis surgery

Scoliosis surgery involves fixation of various hooks, screws and rods to straighten the ‘S’ shaped spine. The procedure is controlled by the surgeons' skill and feel, as they are unaware of the applied forces. The object of this thesis was to design instruments capable of measuring forces and moments applied during scoliosis surgery.

An instrument called the Gripper, housing strain gauges, was fit over a rod rotator to measure the forces and moments. The Gripper was tested on 17 patients where the average maximum force and moments applied were 39 (±14) N and 8 (±1) Nm respectively.

Finite element analysis (FEA) was used to aid in designing a hook capable of measuring the forces at the vertebral level. Preliminary results, from the Plate hook, show the largest moments are applied on insertion and removal of the hook, reaching a maximum of 1.1 Nm. The largest axial force observed was 370 N. Time traces of forces and moments produced by the Gripper and the Plate hook provided insight on scoliosis surgery mechanics.