Dynamic neutralisation of the lumbar spine confirmed on a new lumbar spine simulator in vitro.

A new dynamic neutralisation system for lumbar spine segments has been developed and tested on four cadaveric lumbar spines. Segments L4/5 (3 cases) and L3/4 (1 case) were tested on a new lumbar spine simulator which allowed the simultaneous application of bending moments, compressive and shear loads. The average applied loads were 18.3 Nm flexion moment, 2296 N compressive and 458 N anterior shear load for flexion, and 12.5 Nm extension moment, 667 N compressive and 74 N posterior shear load for extension. The relative motion of the upper vertebra in respect to the lower vertebra was measured with the three-dimensional FASTRAK system, using an advanced computer software. The endplate centres as well as the centre of the screw heads were taken as reference points, identified by orthogonally taken radiographs. The dynamic neutralisation system described reduces bending angles and horizontal translations, but it expands vertical translations. The bulging of the posterior annulus is also reduced.