Lumbar stabilizer performed better than posterolateral fusion in reducing leg pain

TORONTO — More than 50% of patients with lumbar spondylolisthesis or stenosis treated with a dynamic posterior spine stabilization system achieved clinical success that was maintained through 24 months postop, according to results of a prospective, randomized, controlled investigational device exemption trial.

The U.S. multicenter study sought to determine efficacy and safety of the Dynesys spine stabilization system (Zimmer), by comparing outcomes and complications to those in similar patients randomized for instrumented posterolateral fusion (PLF).

“The 24-month data were very successful for both the Dynesys and the fusion cohort with statistically significant improvement being demonstrated in several components of the Dynesys study,” Reginald J. Davis, MD, said in a presentation at the North American Spine Society 23rd Annual Meeting, here.

Dominant leg pain

The Dynesys device has not been approved for use by the FDA.

Davis reported results for 367 patients randomized 2:1 to the stabilization and fusion control groups (253 vs. 114 patients). Inclusion criteria were “spinal stenosis lesions with or without degenerative spondylolisthesis or retrolisthesis less than or equal to grade 1, with or without decompression as indicated,” he said.

All patients were 20 to 80 years old with one or two contiguous affected levels at L1-S1. All were candidates for PLF with more severe leg than back pain and failed 3 months of conservative care. Preoperative Visual Analog Scale (VAS) leg pain scores were more than40 with Oswestry low back disability index (ODI) scores at or above 30.

Discogenic back pain, greater than 30· degenerative scoliosis, osteoporosis and previous fusion attempts were among the exclusion criteria.

Disability improves

At the 24-month follow-up, the stabilization group met the primary end points of improved VAS leg pain and ODI scores vs. preoperative scores, a successful five-point neurological assessment and lack of major complications.

Their VAS leg pain improved by 54.7 mm compared to 47.3 mm for the controls.

“For the ODI, [there was] significant disability of greater than 50 in both cohorts with significant improvement maintained postoperatively for over 24 months,” Davis said. Disability changed in a positive direction in both groups with ODI scores decreasing 29.7 points in the stabilization and 24.3 points in the fusion control groups.

Low complication rates

VAS back pain scores also improved at 24 months by 26.0 mm in the stabilizations group and 20.0 mm in the fusion controls.

Postoperative neurological deficits were absent in both groups, Davis said.

Overall complication rates were 0.4% and 0.9% for the stabilization and fusion control groups, respectively. Their revision rates were similar at 10% and 11% with a 0.88% screw loosening rate for stabilization-treated patients.

During the discussion period Dilip K. Sengupta, MD, inquired why screw loosening was reduced compared to the 17% rate European surgeons reported.

Davis said he felt this trial was designed with more stringent implantation criteria: “We had larger screws … in terms of diameter and length,” and used a technique for placing screws oblique along the axis of the pedicle.

Sengupta further asked why discogenic back pain patients, who constitute the main indication for spine stabilization, were excluded from the study. Davis explained that the stabilization device was not intended to be studied in this patient group.

For more information:
Reginald J. Davis, MD, can be reached at Baltimore Neurological Associates, 6569 N. Charles St., Suite 403, Towson, MD 21204; 410-828-4621; e-mail: rjdavismd@aol.com. He is a paid consultant to and is on the scientific advisory board of Zimmer.
Dilip K. Sengupta, MD, can be reached at Department of Orthopaedics, Dartmouth-Hitchcock Medical Center, One Medical Centre Drive, Lebanon, NH 03756-0001; 603-650-5113; dksg@hotmail.com. He owns stock in, is on the scientific advisory board of, is a paid consultant to and receives research support from Globus Medical.
Reference:
David RJ, Delamarter RB, Wingate JK, et al. Twenty-four month results from a prospective, randomized, controlled IDE study of the Dynesys dynamic stabilization system. #11. Presented at the North American Spine Society 23rd Annual Meeting. Oct. 15-18, 2008. Toronto.