Spine. 34(14):1470-1475, June 15, 2009.

Biomechanical Analysis of a Disc Prosthesis Distal to a Scoliosis Model.

Quirno, Martin MD *; Kamerlink, Jonathan R. MD *; Valdevit, Antonio MSc *; Kang, Matthew MD *; Yaszay, Burt MD +; Duncan, Naphysah ME *; Boachie-Adjei, Oheneba MD ++; Lonner, Baron S. MD *; Errico, Thomas J. MD *
Institution From the *NYU Hospital for Joint Diseases, New York, NY; +Rady Children's Hospital, San Diego, CA; and ++Hospital for Special Surgery, New York, NY.

Study Design. Biomechanical study of bovine spines.

Objective. The purpose of this study was to perform a biomechanical test to analyze intervertebral deflections following placement of both 1 and 2 semiconstrained TDRs in the subjacent segments of a long fusion.

Summary of Background Data. Long-term sequela of long lumbar fusion for scoliosis include adjacent segment disease and flatback syndrome. Total disc replacement (TDR) is a viable option for the treatment of these conditions. Little data has been published regarding the placement of a TDR distal to a scoliosis fusion.

Methods. Six thoracolumbar bovine spines (T12-S1) were instrumented from T12 to L5, with bilateral pedicle screw fixation at each level. L5-L6 and L6-S1 served as the test levels. One TDR (FlexiCore, Stryker Spine, Allendale, NJ) was initially performed adjacent to the fusion, followed by a subsequent TDR insertion at the last spinal segment. The applied load, total specimen deflection, and local transducer deflections were recorded before and after a TDR at both levels. The results were expressed as a percentage of the intact specimen. Flexion, extension, lateral bending, and torsional deflections were recorded.

Results. There were no significant differences (P > 0.05) in sensor deflection observed at the L5-L6 and L6-S1 levels in the anterior and lateral transducers when compared to intact spines specimens. A similar effect was observed at the L5-L6 and L6-S1 levels in the anterior and lateral transducers when compared to intact or prior L5-L6 and intact L6-S1 constructs.

Conclusion. This study has shown that using the FlexiCore system at 1 and/or 2 intervertebral disc spaces caudal to a scoliosis fusion model did not significantly change the sensor deflection at the 2 segments adjacent to a scoliosis fusion construct. Future research will continue to define the clinical setting and patients best suited for management by TDR systems.

(C) 2009 Lippincott Williams & Wilkins, Inc.