Nucleus replacement could get a new chance with annulus closure

Purpose Disc herniations are usually treated by decompression of the spinal nerves via a partial nucleotomy. As a consequence of reduced disc height (DH), reduced intradiscal pressure (IDP) and increased range of motion (ROM), accelerated degeneration may occur. Nucleus replacement implants are intended to restore those values, but are associated with the risk of extrusion. Methods In six fresh frozen lumbar spinal segments (L2-3/L3-4/L4-5/L5-S1, age median 64.5 years (57-72), Pfirrmann grade 2-3), a prolapse was provoked through a box defect (6 x 10 mm) in the annulus. The herniated nucleus material was removed and replaced by a novel collagen-based nucleus implant. An annulus closure device sealed the defect. ROM, neutral zone (NZ) and IDP were measured in the (1) intact and (2) defect state, (3) postoperatively and (4) after cyclic loading (n = 100,000 cycles) applying pure moments (+/- 7.5 Nm) in flexion-extension, lateral bending and axial rotation. Additionally, the change in DH was determined. Extrusion of implants or nucleus material was evaluated macroscopically. Results In all specimens, a prolapse could be provoked which decreased DH. Subsequent nucleotomy changed ROM/NZ and IDP considerably. Initial values could be restored by the implantation. Macroscopically, none of the implants nor nucleus material did migrate after cyclic loading. Conclusions In this study, a prolapse followed by a nucleotomy resulted in a biomechanical destabilisation. Implantation of the nucleus replacement combined with an annulus closure restored the intact condition without showing signs of extrusion nor migration after cyclic loading. Hence, nucleus replacements could have a new chance in combination with annulus closure devices.