title: In vitro and in silico investigations of disc nucleus replacement.
abstract: Currently, numerous hydrogels are under examination as potential nucleus replacements. The clinical success, however, depends on how well the mechanical function of the host structure is restored. This study aimed to evaluate the extent to and mechanisms by which surgery for nucleus replacements influence the mechanical behaviour of the disc. The effects of an annulus defect with and without nucleus replacement on disc height and nucleus pressure were measured using 24 ovine motion segments. The following cases were considered: intact; annulus incision repaired by suture and glue; annulus incision with removal and re-implantation of nucleus tissue repaired by suture and glue or plug. To identify the likely mechanisms observed in vitro, a finite-element model of a human disc (L4-L5) was employed. Both studies were subjected to physiological cycles of compression and recovery. A repaired annulus defect did not influence the disc behaviour in vitro, whereas additional nucleus removal and replacement substantially decreased disc stiffness and nucleus pressure. Model predictions demonstrated the substantial effects of reductions in replaced nucleus water content, bulk modulus and osmotic potential on disc height loss and pressure, similar to measurements. In these events, the compression load transfer in the disc markedly altered by substantially increasing the load on the annulus when compared with the nucleus. The success of hydrogels for nucleus replacements is not only dependent on the implant material itself but also on the restoration of the environment perturbed during surgery. The substantial effects on the disc response of disruptions owing to nucleus replacements can be simulated by reduced nucleus water content, elastic modulus and osmotic potential.
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research, University of Ulm, Ulm 89081, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Reitmaier
authors.forename: Aboulfazl
authors.initials: A
authors.lastname: Shirazi-Adl
authors.forename: Maxim
authors.initials: M
authors.lastname: Bashkuev
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wilke
authors.forename: Antonio
authors.initials: A
authors.lastname: Gloria
authors.forename: Hendrik
authors.initials: H
authors.lastname: Schmidt
mesh_terms: D000818:Animals; D055119:Elastic Modulus; D006801:Humans; D020100:Hydrogels; D007403:Intervertebral Disc / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D055959:Intervertebral Disc Degeneration / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D008159:Lumbar Vertebrae / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D008954:Models, Biological; D009997:Osmotic Pressure; D012756:Sheep; D013312:Stress, Physiological; D059145:Total Disc Replacement
chemical_list: D020100:Hydrogels