STUDY DESIGN: In vitro biomechanical study. OBJECTIVE: To characterize cervical total disc replacement (TDR) kinematics above two-level fusion, and to determine the effect of fusion alignment on TDR response. SUMMARY OF BACKGROUND DATA: Cervical TDR may be a promising alternative for a symptomatic adjacent level after prior multilevel cervical fusion. However, little is known about the TDR kinematics in this setting. METHODS: Eight human cadaveric cervical spines (C2-T1, age: 59 ± 8.6 years) were tested intact, after simulated two-level fusion (C4-C6) in lordotic alignment and then in straight alignment, and after C3-C4 TDR above the C4-C6 fusion in lordotic and straight alignments. Fusion was simulated using an external fixator apparatus, allowing easy adjustment of C4-C6 fusion alignment, and restoration to intact state upon disassembly. Specimens were tested in flexion-extension using hybrid testing protocols. RESULTS: The external fixator device significantly reduced range of motion (ROM) at C4-C6 to 2.0 ± 0.6°, a reduction of 89 ± 3.0% (P < 0.05). Removal of the fusion construct restored the motion response of the spinal segments to their intact state. The C3-C4 TDR resulted in less motion as compared to the intact segment when the disc prosthesis was implanted either as a stand-alone procedure or above a two-level fusion. The decrease in motion of C3-C4 TDR was significant for both lordotic and straight fusions across C4-C6 (P < 0.05). Flexion and extension moments needed to bring the cervical spine to similar C2 motion endpoints significantly increased for the TDR above a two-level fusion compared to TDR alone (P < 0.05). Lordotic fusion required significantly greater flexion moment, whereas straight fusion required significantly greater extension moment (P < 0.05). CONCLUSION: TDR placed adjacent to a two-level fusion is subjected to a more challenging biomechanical environment as compared to a stand-alone TDR. An artificial disc used in such a clinical scenario should be able to accommodate the increased moment loads without causing impingement of its endplates or undue wear during the expected life of the prosthesis.
STUDY DESIGN: In vitro biomechanical study. OBJECTIVE: To characterize cervical total disc replacement (TDR) kinematics above two-level fusion, and to determine the effect of fusion alignment on TDR response. SUMMARY OF BACKGROUND DATA: Cervical TDR may be a promising alternative for a symptomatic adjacent level after prior multilevel cervical fusion. However, little is known about the TDR kinematics in this setting. METHODS: Eight human cadaveric cervical spines (C2-T1, age: 59 ± 8.6 years) were tested intact, after simulated two-level fusion (C4-C6) in lordotic alignment and then in straight alignment, and after C3-C4 TDR above the C4-C6 fusion in lordotic and straight alignments. Fusion was simulated using an external fixator apparatus, allowing easy adjustment of C4-C6 fusion alignment, and restoration to intact state upon disassembly. Specimens were tested in flexion-extension using hybrid testing protocols. RESULTS: The external fixator device significantly reduced range of motion (ROM) at C4-C6 to 2.0 ± 0.6°, a reduction of 89 ± 3.0% (P < 0.05). Removal of the fusion construct restored the motion response of the spinal segments to their intact state. The C3-C4 TDR resulted in less motion as compared to the intact segment when the disc prosthesis was implanted either as a stand-alone procedure or above a two-level fusion. The decrease in motion of C3-C4 TDR was significant for both lordotic and straight fusions across C4-C6 (P < 0.05). Flexion and extension moments needed to bring the cervical spine to similar C2 motion endpoints significantly increased for the TDR above a two-level fusion compared to TDR alone (P < 0.05). Lordotic fusion required significantly greater flexion moment, whereas straight fusion required significantly greater extension moment (P < 0.05). CONCLUSION: TDR placed adjacent to a two-level fusion is subjected to a more challenging biomechanical environment as compared to a stand-alone TDR. An artificial disc used in such a clinical scenario should be able to accommodate the increased moment loads without causing impingement of its endplates or undue wear during the expected life of the prosthesis.
Authors: A G Patwardhan; M N Tzermiadianos; P P Tsitsopoulos; L I Voronov; S M Renner; M L Reo; G Carandang; K Ritter-Lang; R M Havey Journal: Eur Spine J Date: 2010-09-24 Impact factor: 3.134
Authors: Zachary A Smith; Saeed Khayatzadeh; Joshua Bakhsheshian; Michael Harvey; Robert M Havey; Leonard I Voronov; Muturi G Muriuki; Avinash G Patwardhan Journal: Eur Spine J Date: 2016-02-01 Impact factor: 3.134
Authors: Aniruddh N Nayak; Michael C Doarn; Roger B Gaskins; Chris R James; Andres F Cabezas; Antonio E Castellvi; Brandon G Santoni Journal: Int J Spine Surg Date: 2014-12-01
Authors: Richard A Wawrose; Forbes E Howington; Clarissa M LeVasseur; Clair N Smith; Brandon K Couch; Jeremy D Shaw; William F Donaldson; Joon Y Lee; Charity G Patterson; William J Anderst; Kevin M Bell Journal: J Orthop Res Date: 2020-05-04 Impact factor: 3.102