A Prospective Randomized FDA Study of the Charité Disc Replacement-A Correlation of Surgically Accurate Technique with Clinical Outcomes in 276 Consecutive Patients**

• a, d, e - DePuy Spine

Introduction: A prospective randomized study was completed according to an FDA protocol with 2 year minimum follow up for one level disc pathology.

Materials and Methods: One third of patients were randomized with anterior interbody BAK instrumentation and fusion (N= 99). Two thirds of patients were randomized with the Charité mobile bearing disk replacement (N = 205) and an additional group of 71 patients had received the Charité disc as “training cases” in a total of 15 United States investigational sites.

Results: The Charité prosthesis was significantly more effective than the BAK in restoring the height of the collapsed disk space (P <0 .001)—

The initial disk space height at the L5-S1 operative level started at 5.2 mm (mean) +/- 1.44 (Std Dev) and increased to 13.5 mm (mean) +/- 1.18 (Std Dev) for the Charité cases whereas the BAK patients at L5-S1 started at an initial disk space height of 5.9.mm +/- 1.74 and increased to an immediate post-operative disk space height = 11.9 mm +/- 2.07.

There was less subsidence with the Charite disk replacement than the BAK controls over the 24 months follow up (p <0 .001).

The surgical technical accuracy of Charité disk placement correlated with the clinical outcome measures at two years follow up. The 276 disc replacement patients were allocated into one of three groups based on radiographic technical paramenters—

Group I -Ideal. This is defined by Charite disk insertion within 3 mm of ideal in both planes. Coronal plane = AP radiograph = midline or within 3 mm of midline. Mid-Sagittal plane= Lateral radiograph = 2mm posterior to middle of vertebral body or within 3mm of this axis. 83 % of the 276 Charité patients fell into this category.

Group II-Suboptimal (11 %); and Group III - Poor (6 %).

The Oswestry Disability index improved as the technical accuracy of prosthesis placement improved-Group I, 24.1; Group II, 30.3; and Group III, 36.3 (p <.05).

The VAS at 2 years follow up also improved as the prosthesis placement became closer to the ideal parameters- Group I, 28.3; Group II, 35.4; and Group III, 48.4 (p = 0.016).

The flexion-extension range of motion and prosthesis function was also highly correlated with the surgical technical accuracy of radiographic placement-Group I, 7.12 +/- 4.06 degrees; Group II, 7.47 +/- 4.41 degrees; and Group III only 3.15 +/- 3.51 degrees (p = 0.003).

A comparison between the 71 “Training Cases” (Group 1) and the 205 “Enrolled Cases” (Group 2) showed that disk replacement is a technique benefiting from surgical experience as the surgical time improved from mean 142 to 110 minutes and EBL decreased from mean 228 cc to 205 cc. There was a higher rate of complications for the training cases compared to the randomized cases (p<0 .012). Device failure requiring revision or removal was 7 % for the training and 4 randomized cases.

In conclusion, the Charité lumbar disk replacement is a fairly exacting technique-there is a learning curve associated with operative time and major complications which improves after 5 cases. The clinical outcomes (VAS and Oswestry) correlate with the technical accuracy of prosthesis placement within 3 mm of ideal. The flexion-extension range of motion also correlates with the accuracy of restoring the normal axis of rotation.

** Hibbs Clinical Award Nominated Paper

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