Assessment of two novel surgical positions for the reduction of scoliotic deformities: lateral leg displacement and hip torsion

Cobb angles and apical vertebral rotations (AVR) are two of the main scoliosis deformity parameters which spinal instrumentation and fusion techniques aim to reduce. Despite this importance, current surgical positioning techniques do not allow the reduction of these parameters. Two new surgical frame accessory prototypes have been developed: (1) a lateral leg displacer (LLD) allows lateral bending of a patient’s legs up to 75° in either direction and (2) a pelvic torsion device (PTD) which allows transverse plane twisting of a patient’s pelvis at 30° in either direction while raising the thoracic cushion, opposite to the raised side of the pelvis, by 5 cm. The objective of this study was to evaluate the ability of the LLD and PTD to reduce Cobb angles and AVR. Experimental testing was performed pre-operatively on 12 surgical scoliosis patients prone on an experimental surgical frame. Postero-anterior radiographs of their spines were taken in the neutral prone position on a surgical frame, and then again for 6 with their legs bent towards the convexity of their lowest structural curve, 4 with their pelvis raised on the convex side of their lowest structural curve and one each in opposite LLD and PTD intended use. Use of the LLD allowed for an average supplementary reduction of 16° (39%) for Cobb angle and 9° (33%) for AVR in the lowest structural curve. Use of the PTD allowed for an average supplementary reduction of 9° (19%) for Cobb angle and 17° (48%) for AVR in the lowest structural curve. Both devices were most efficient on thoraco-lumbar/lumbar curves. Opposite of intended use resulted in an increase in both Cobb angle and AVR. The LLD and PTD provide interesting novel methods to reduce Cobb angles and AVR through surgical positioning which can be used to facilitate instrumentation procedures by offering an improved intra-operative geometry of the spine.