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Saturday, February 26, 2005

Disc replacement found to restore anatomic, motion parameters better than fusion

Total disc replacement restores and maintains a more normal range of motion and disc space height than anterior interbody fusion with cylindrical cages and iliac crest bone graft, according to the presenters of Paper 189. Researchers were reporting on the results of a prospective, randomized study conducted according to protocols established by the U.S. Food and Drug Administration with two-year minimum follow-up for one level disc pathology.

The study was performed at 14 centers throughout the United States and involved a total of 304 patients. One-third of patients (n=99) were randomized and received anterior lumbar interbody fusion with Bagby and Kuslich (BAK) cages and iliac crest bone graft. The remaining two-thirds of patients (n=205) received the Charité mobile-bearing disk replacement. An additional 71 patients had received the Charité disc as "training cases" before the study began. All preoperative and follow-up radiographs, including flexion-extension x-rays, were digitized in a central core laboratory and corrected for magnification factors.

"Total disc replacement with the Charité artificial disc resulted in significantly better restoration of disk space height and significantly less subsidence than anterior interbody fusion with BAK cages," reported the researchers.

To determine any correlation between technical surgical accuracy and clinical outcome measures, researchers established three groups of patients, based on radiographic technical parameters. Group I was defined as ideal placement, meaning the disc insertion was within 3 mm of exact central placement in both the coronal and mid-sagittal planes. Group II was defined as suboptimal placement, with insertion from 3 mm-5 mm from exact central placement in at least one axis. Group III, or poor placement, was defined as greater than 5 mm from exact central placement in one axis or any patient requiring posterior spinal fixation and arthrodesis secondary to prosthesis placement or component subsidence or migration.

Patients who received the Charité disc replacement had an initial disk space height at the L5-S1 operative level started at 5.2 mm (± 1.44 mm), which increased to 13.5 mm (±1.18 mm) postoperatively. The initial disk space height for patients who received fusion was 5.9 mm (±1.74 mm), which increased to an immediate postoperative disk space height of 11.9 mm (±2.07 mm).

"By restoring the intervertebral space height, an artificial disc should increase the exiting foraminal height and prevent compression on the exiting nerve roots at the stabilized level," note the authors. "In Groups I and II, there was not a single patient with postoperative radiculopathy or an adverse neurologic event."

Researchers also found less subsidence with the Charité disc replacement than with the BAK controls over the 24-month follow-up period (p < 0.001).

At the 24-month follow-up, 83 percent of disc replacement patients were in Group I, with 11 percent in Group II and 6 percent in Group III. Technical accuracy of prosthesis placement correlated with improvements in the Oswestry Disability Index (ODI) and the VAS [AU: Please spell out at first mention Visual Analog Scales] scales. Mean ODI scores were 24.1 for Group I, 30.3 for Group II and 36.3 for Group III (p < .05). Mean VAS scores were 28.3 for Group I, 35.4 for Group II and 48.4 for Group III (p = 0.016).

The flexion-extension range of motion (ROM) and prosthesis function also improved with the surgical technical accuracy. ROM in Group I was 7.12° (±4.06°); in Group II, it was 7.47° (±4.41°); and in Group III, it was only 3.15° (±3.51°) (p = 0.003).

"The mobile, sliding core design allows it to shift dynamically during normal spinal motion, moving posteriorly in flexion and anteriorly in lumbar extension," said the authors. "This provides for unloading of the posterior elements during this normal replication of motion."

Researchers noted that the patients will be followed for many years to track their clinical and functional progress. The research team included Paul C. McAfee, MD; Bryan Cunningham, Mmech Eng; Gwen Hotsapple, BS; Karen Bussard-Adams, BS; and Anton Dmietriev, MS, all of Baltimore, Md.; Scott Blumenthal, MD, and Richard Guyer, MD, of Plano, Texas; Jim Maxwell, MD, of Scottsdale, Ariz.; John Regan, MD, of Los Angeles, and Jorge Isaza, MD, of Baton Rouge, La. All authors except Ms. Hotsapple and Ms.Bussard-Adams are consultants to DePuy Spine, Inc.

Correct placement of the Charité Artificial Disc in the mid-sagittal and coronal planes. In the coronal plane, the ideal position is in the center of the intervertebral spae in the midline.

Lateral radiograph of artificial disc in ideal placement (within 3 mm of ideal in both mid-sagittal and coronal planes).

Same patient as above image, anterposterior view

With Centerline instrumentation, the surgeon lines up the instruments with the vertebral disc midline to achieve ideal prosthesis placement.

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