Biomechanical evaluation of a posterolateral lumbar disc arthroplasty device: an in vitro human cadaveric model

Study Design. This in vitro analysis defines biomechanical properties of the Triumph Lumbar Disc (TLD) for posterolateral lumbar disc arthroplasty. Objectives. To quantify segmental kinematics afforded by the TLD, determine whether intervertebral positional changes of the device affect spinal kinematics, and compare kinematics following TLD reconstruction with historical CHARITE data. Summary of Background Data. As an alternative to arthrodesis, total disc arthroplasty serves to restore the biomechanical properties of the spine. However, there are kinematic and clinical concerns regarding posterior lumbar column destabilization and reconstruction using motion-preserving technology. Methods. Seven human lumbosacral spines were biomechanically evaluated under the following conditions: (1) Intact; (2) Unilateral facetectomy; (3) Facetectomy and discectomy; (4) TLD-posterior; (5) TLD-central; (6) TLD-anterior. Centers of intervertebral rotation (COR) and intradiscal pressures were compared at the operative/adjacent levels. Results. In axial rotation, L4-L5 range of motion (ROM) increased to 110% ± 15.3% following unilateral facetectomy and 134.3% ± 26.9% following facet/discectomy. Implanting the TLD in 3 positions—posterior, central, and anterior-demonstrated no significant differences in ROM (P > 0.05). Trends were similar in flexion/extension and lateral bending. The neutral zone increased under the facet/discectomy condition and TLD reconstructions compared to the intact condition (P < 0.05). CORs were dispersed at the operative level following destabilization. TLD in posterior and central positions restored loci to near the intact condition, whereas the anterior position produced more diffuse CORs. Adjacent level intradiscal pressures decreased in flexion-extension following destabilization and reconstruction. Conclusion. Axial rotation ROM following TLD reconstruction (central position) was 131.5% of intact, compared to historical controls for the CHARITE device (162.0%). This indicates that lumbar disc arthroplasty performed using a posterolateral approach may offer biomechanical advantages over the anterior approach. Moreover, this approach may minimize surgical complications and allow simultaneous decompression of the neural elements. Intervertebral positional changes of the TLD were not shown to affect spinal kinematics.