Revision strategies for single- and two-level total disc arthroplasty procedures: a biomechanical perspective

• Published in: The spine journal 2009-09, Vol.9 (9), p.735-743
• Main Authors: Cunningham, Bryan W., MSc, Hu, Nianbin, MD, Beatson, Helen J., BS, Serhan, Hassan, PhD, Sefter, John C., DO, McAfee, Paul C., MD
• Format: Article
• Language: English
• Subjects: Arthroplasty, Replacement - instrumentation; Arthroplasty, Replacement - methods; Biomechanical Phenomena; Bone Screws; Cadaver; Humans; Lumbosacral Region - surgery; Motion preservation; Multilevel total disc arthroplasty; Orthopedics; Reoperation - instrumentation; Reoperation - methods; Revision strategies; Spinal Fusion - instrumentation; Spinal Fusion - methods
• ISSN: 1529-9430; 1878-1632
• DOI: 10.1016/j.spinee.2009.03.011

Abstract Background context The utilization of motion-preserving implants versus conventional instrumentation systems, which stabilize the operative segments, necessitates improved understanding of their comparative biomechanical properties and optimal biomechanical method for surgical revision. Purpose Using an in vitro human cadaveric model, the primary objective was to compare the multidirectional flexibility properties of single- versus two-level total disc arthroplasty procedures and determine the acute in vitro biomechanical characteristics of two methods of surgical revision—posterior transpedicular instrumentation alone or circumferential spinal arthrodesis. Study design This in vitro biomechanical study was undertaken to compare the multidirectional flexibility kinematics of single- versus two-level lumbar total disc arthroplasty reconstructions using an in vitro model. Methods A total of seven human cadaveric lumbosacral spines (L1-sacrum) were biomechanically evaluated under the following L4–L5 reconstruction conditions: intact spine; discectomy alone; Charité total disc replacement; Charité with pedicle screws; two-level Charité (L4–S1); two-level Charité with pedicle screws (L4–S1); Charité L4–L5 with pedicle screws and femoral ring allograft (FRA) (L5–S1); and pedicle screws with FRA (L4–S1). Multidirectional flexibility testing used the Panjabi Hybrid Testing protocol, which includes pure moments for the intact condition with the overall spinal motion replicated under displacement control for subsequent reconstructions. Hence, changes in adjacent level kinematics can be obtained compared with pure moment testing strategies. Unconstrained intact moments of ±7.5 Nm were used for axial rotation, flexion-extension, and lateral bending testing with quantification of the operative- and adjacent-level range of motion (ROM). All data were normalized to the intact spine condition (intact=100%). Results In axial rotation, single- and two-level Charité reconstructions produced significantly more motion than pedicle screw constructs combined with the Charité or FRA (p.05). The two-level annulus lumbar resection required for multilevel Charité implantation had an added destabilizing effect, resulting in a 140% to 160% ROM increase over the intact condition. Under two-level reconstructions, rotational motion at the L4–L5 level increased from 16