Improving the fixation of an artificial intervertebral disc.

The fixation of an artificial intervertebral disc has been studied especially with respect to the dimensions, the convexity of the endplates and the size of the fixation elements. From literature and cadaveric vertebrae, the dimensions and shape of the lumbar vertebral endplates were determined and the dimensions of fixation ribs for the artificial intervertebral disc were calculated. To withstand shear forces and prevent dislocation, two sagittal ribs, each 3.5 mm in height and at least 20 mm in length and four transversal ribs, each 1.5 mm in height and with a total length of 60 mm are sufficient. A range of five different sagittal diameters was selected as sufficient for all patients. At least 72.6 % of the endplate of the vertebrae is covered. A convexity with a radius of 140 mm limits the gap to 0.62 mm.