Luiz Pimenta1, Alex Turner2, Leonardo Oliveira1, Luis Marchi1, Bryan Cornwall3. 1. Department of Minimally Invasive Surgery, Instituto de Patologia de Coluna, São Paulo, Brazil. 2. Department of Research and Testing, NuVasive, San Diego, California, United States. 3. Department of Clinical Operations, NuVasive, San Diego, California, United States.
Abstract
OBJECTIVE: Anterior-approach total disk replacement (TDR) devices are thought to retain close to so-called normal range of motion (ROM); however, they are also inherently unstable due to resection of the anterior longitudinal ligament and annulus. This instability/laxity is manifested as increased neutral zone (NZ) motion. The XL-TDR device (NuVasive, Inc., San Diego, California, United States) is implanted through a lateral approach that preserves the anterior ligamentous and annular structures. This potentially makes the XL-TDR device more stable than those delivered anteriorly. This study investigates XL-TDR biomechanical features in a cadaveric model. METHODS: Biomechanical evaluation consisting of nondestructive multidirectional testing was performed with the hybrid protocol on six fresh-frozen cadaveric specimens (L2-S1). Motion segment kinematics were obtained using an optoelectronic system. Test conditions were (1) intact spine, (2) XL-TDR at L4-L5, and (3) XL-TDR at L4-L5 with anterior annulus/ligament resected. ROM and NZ were calculated for each condition in each loading direction (flexion-extension total, flexion alone, extension alone, lateral bending, and axial rotation). RESULTS: Insertion of the XL-TDR device decreased ROM with respect to intact in all directions. NZ in all directions was not statistically different from intact (p < 0.05), although there was a trend toward decreased NZ in flexion (p = 0.078). Removing the anterior ligament/annulus increased ROM significantly with respect to the XL-TDR condition in all directions (p < 0.003). NZ also increased, with the most significant changes in extension, lateral bending, and axial rotation (p < 0.002). CONCLUSIONS: The kinematics of XL-TDR have demonstrated that the retention of the anterior ligament/annulus has a significant stabilizing effect, diminishing ROM to less than intact, with a more controlled motion (more natural NZ). Removing the anterior ligament/annulus illustrated its stabilizing role, with ROM and NZ increasing significantly. Future studies will investigate the potential benefit of controlled XL-TDR motion on facet kinematics that may have clinical implications related to limiting facet degeneration. Georg Thieme Verlag KG Stuttgart · New York.
OBJECTIVE: Anterior-approach total disk replacement (TDR) devices are thought to retain close to so-called normal range of motion (ROM); however, they are also inherently unstable due to resection of the anterior longitudinal ligament and annulus. This instability/laxity is manifested as increased neutral zone (NZ) motion. The XL-TDR device (NuVasive, Inc., San Diego, California, United States) is implanted through a lateral approach that preserves the anterior ligamentous and annular structures. This potentially makes the XL-TDR device more stable than those delivered anteriorly. This study investigates XL-TDR biomechanical features in a cadaveric model. METHODS: Biomechanical evaluation consisting of nondestructive multidirectional testing was performed with the hybrid protocol on six fresh-frozen cadaveric specimens (L2-S1). Motion segment kinematics were obtained using an optoelectronic system. Test conditions were (1) intact spine, (2) XL-TDR at L4-L5, and (3) XL-TDR at L4-L5 with anterior annulus/ligament resected. ROM and NZ were calculated for each condition in each loading direction (flexion-extension total, flexion alone, extension alone, lateral bending, and axial rotation). RESULTS: Insertion of the XL-TDR device decreased ROM with respect to intact in all directions. NZ in all directions was not statistically different from intact (p < 0.05), although there was a trend toward decreased NZ in flexion (p = 0.078). Removing the anterior ligament/annulus increased ROM significantly with respect to the XL-TDR condition in all directions (p < 0.003). NZ also increased, with the most significant changes in extension, lateral bending, and axial rotation (p < 0.002). CONCLUSIONS: The kinematics of XL-TDR have demonstrated that the retention of the anterior ligament/annulus has a significant stabilizing effect, diminishing ROM to less than intact, with a more controlled motion (more natural NZ). Removing the anterior ligament/annulus illustrated its stabilizing role, with ROM and NZ increasing significantly. Future studies will investigate the potential benefit of controlled XL-TDR motion on facet kinematics that may have clinical implications related to limiting facet degeneration. Georg Thieme Verlag KG Stuttgart · New York.
Authors: Ian J Wellington; Cameron Kia; Ergin Coskun; Barrett B Torre; Christopher L Antonacci; Michael R Mancini; John P Connors; Sean M Esmende; Heeren S Makanji Journal: Bioengineering (Basel) Date: 2022-05-23