[Basic principles of successful implantation of the SB Charité model LINK intervertebral disk endoprosthesis]

The scope of the LINK SB Charité Artificial Disc is to replace degeneratively changed, symptomatic intervertebral discs and to restitute the fundamental functions of the lumbar mobile segment. Biomechanical static- and dynamic test results as well as postoperative controls of a patient-group with uniform indications are presented. The options of an intervertebral disc replacement with the SB Charité Artificial Disc are discussed. For the evaluation of segmental stability, comparative static examinations of the range of motion of cadaveric lumbar segments prior to and after the implantation of the artificial disc were carried out. The stress-dependent mechanical response to directional static load on implanted SB Charité Discs in neutral position, extension and flexion was examined under different testing-conditions in order to gain results on changes of surfaces, durability and sustain of functionality. Restitutable changes to the UHMWPE sliding core, prognosed definite deformations of the sliding core after 5 and 10 years, and the functionality of the UHMWPE sliding cores after stress were examined using dynamic compression tests. Our clinical results refer to 20 patients, who received a mono- (n = 14) or bisegmental (n = 6) implantation of a SB Charité Artificial Disc following a postnucleotomy-syndrome. Comparison of the ranges of motion in cadaveric segments with and without a SB Charité Artificial Disc reflected a significantly higher mobility in cases with an implanted prosthesis only in axial rotation. Other movements showed similar ranges of motion in native segments and in segments with prosthesis. The UHMWPE sliding cores showed tolerable changes during maximal static compression in neutral position and extension. The 7.5 mm sliding cores showed changes beyond normal deformations on compression in maximal flexion. None the less it may be concluded that in vivo these sliding cores also retain their mechanical integrity. Most of the 7.5 mm and 9.5 mm high sliding cores showed a regeneration of 50% compared to maximal deformation. All the tested UHMWPE sliding cores reflected continued articulation despite plastic deformation. Predictions for a period of 5 and 10 years state that extreme loads of 4.5 kN would lead to a reduction in the height of the sliding cores of less than 8%. There was no failure of the sliding cores due to delamination or extreme coldflow. The Oswestry-Score amounted to 24% (0-56) in the postoperative controls 46 months (6 months-13 years) postoperatively. In pain analysis 5 patients (25%) were pain free, 14 patients (70%) reported a pain reduction and 1 patient (5%) had no pain relief compared to preoperatively. 15 (83%) of 18 patients had no leg pain anymore after implantation of the SB Charité Artificial Disc. 14 (93%) of 15 patients had a negative leg raising test. 2 of 5 patients recovered from their motor symptoms. The segmental saggital total range of motion was 6.8 degrees (0-20) and in cases of bisegmental implantation 5.8 degrees (0-14) in the second disc segment. Those neighboring segments with the best function showed a range of motion of 6.8 degrees (2-15). The stated general and specific complications (n = 9) had a definite influence on the results of the postoperative control in one patient and a questionable influence in another patient. Based on biomechanical static and dynamic testing, the SB Charité Artificial Disc is suited to replace the fundamental functions of the lumbar intervertebral disc. Patients suffering from a postnucleotomy-syndrome can be rendered pain free with the implantation of this prosthesis.