[The measurement of nerve root tensile stress]

In the majority of the cases sciatica is caused by an intervertebral disc herniation compressing the nerve root. The compression determines an increased tension in the nerve root. We believe that the magnitude of this stress offers more information about the root impairment that the disc displacement measured on MRI images.

We present in this paper an original device which allows for intraoperative root stress analysis. The device consists of a force transducer composed of an elastic element and a displacement limitation.

The initial measurements were performed on silicon catheters and human cadavers in two different situations: 1. free nerve root; 2. blocked nerve root. Next step was intraoperative nerve roots tensile stress recording during lumbar disc surgery. Different force values were obtained for the same displacement (3 mm perpendicular on nervous root): F1 = 0.21 N; F2 = 0.78 N. Considering experimental values, the tensile stress inside of a nervous root is determined by using specific mechanical calculations presented in this paper. This is a simple and useful device for rapid intraoperative recording of nerve root mechanical stress.