BACKGROUND
The US Food and Drug Administration approved the Charité artificial disc on October 26, 2004. This approval was based on an extensive analysis and review process; 20 years of disc usage worldwide; and the results of a prospective, randomized, controlled clinical trial that compared lumbar artificial disc replacement to fusion. The results of the investigational device exemption (IDE) study led to a conclusion that clinical outcomes following lumbar arthroplasty were at least as good as outcomes from fusion.

METHODS
The author performed a new analysis of the Visual Analog Scale pain scores and the Oswestry Disability Index scores from the Charité artificial disc IDE study and used a nonparametric statistical test, because observed data distributions were not normal. The analysis included all of the enrolled subjects in both the nonrandomized and randomized phases of the study.

RESULTS
Subjects from both the treatment and control groups improved from the baseline situation (P < .001) at all follow-up times (6 weeks to 24 months). Additionally, these pain and disability levels with artificial disc replacement were superior (P < .05) to the fusion treatment at all follow-up times including 2 years.

CONCLUSIONS
The a priori statistical plan for an IDE study may not adequately address the final distribution of the data. Therefore, statistical analyses more appropriate to the distribution may be necessary to develop meaningful statistical conclusions from the study. A nonparametric statistical analysis of the Charité artificial disc IDE outcomes scores demonstrates superiority for lumbar arthroplasty versus fusion at all follow-up time points to 24 months.

Key Words lumbar arthroplasty, total disc replacement, clinical trial, statistical analysis. SAS Journal. Winter 2007; 1; 12–19.
DOI: SASJ-2006-0002-RR

From the Illinois Neuro-Spine Center at Rush-Copley Medical Center, Aurora.

The author acknowledges consulting and research relationships with the manufacturer of the Charité artificial disc (DePuy Spine, Raynham, Mass), and has received funding in excess of $500.

Address correspondence and reprint requests to Fred H. Geisler, MD, PhD, Illinois Neuro-Spine Center at Rush-Copley Medical Center, 2020 Ogden Ave, Suite 335, Aurora, IL 60504 (e-mail: fgeisler@concentric.net)

This submission was received December 7, 2006, and accepted for publication February 26, 2007.

Presented at the 6th Annual Meeting of the Spine Arthroplasty Society, May 9–13, 2006, in Montreal, Québec.

Institutional Review Board approval was obtained at the 14 hospital sites that participated in the original IDE study, in accordance with FDA regulations.