Study finds Dynesys dynamic stabilization ineffective against disc degeneration

Investigators also found evidence contrary to the theoretical advantages of Dynesys treatment.

Dynesys dynamic stabilization does little to halt the progress of disc degeneration in patients suffering from lower back pain, researchers have found.

The findings are the result of a study by Alexandru Mertic, Medic, MSc, and others at the Center for Spinal Research, Woodland Hospital in Aberdeen, Scotland.

Mertic summarized the findings at the North American Spine Society 23rd Annual Meeting in Toronto.

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“Disc degeneration at the bridge segments remains the same despite Dynesys dynamic stabilization, and it is difficult to determine if this continued degeneration is due to the normal progression of the disease or to the Dynesys stabilization,” he said.

Mertic’s study aimed to evaluate disc changes at the segments adjacent to and bridged by Dynesys dynamic stabilization system when used in the management of chronic low back pain.

Study methods

Thirty-eight patients who were unresponsive to conservative measures underwent Dynesys for chronic low back pain between November 2002 and June 2005, then completed a 2-year follow-up MRI scan. Of the 38 patients, 26 underwent Dynesys alone and 12 underwent additional fusion at one or more levels. Surgeons operated on a total of 83 levels, 70 of which were bridged only by Dynesys. Fusion was performed at 13 levels.

Two independent observers evaluated preoperative and 2-year postoperative lumbar MRI scans. The researchers used T2-weighted mid-sagittal images and classified disc degeneration according to the Woodend classification of disc degeneration.

MRIs taken preoperatively (left) and 2 years postoperatively at L3-S1. Images: Wardlaw D

Both observers used their findings to calculate mean pre- and postoperative scores for each patient at each of the five lumbar levels. Those mean preoperative and postoperative scores were then compared using a paired t-test procedure. Inter-observer agreement was measured using the weighted Kappa scores.

Results and conclusions

According to the findings, there was a statistically significant increase in the mean Woodend score for inter-segmental levels bridges only by Dynesys – from 2.20 preoperatively to 2.51 at 2 years postoperatively (P < .001).

For adjacent segments, mean Woodend scores changed from 1.35 preoperatively to 1.51 postoperatively if only the proximal segments were included, Mertic said. When both proximal and distal adjacent segments were included, the mean scores changed from 1.36 to 1.53.

The investigators noted progressive degeneration in eight of 46 adjacent levels, and there was satisfactory interobserver agreement – a weighted Kappa score of 0.819.

The results of the study pointed toward Dynesys dynamic stabilization being ineffective against disc degeneration. Douglas Wardlaw, MB, MhB, ChM, FRCSEd, lead author of the paper, said, “We have previously demonstrated that Dynesys does not increase the range of movement at the cephald adjacent segment (Beastall et al), which is considered to increase the likelihood of degenerative change following fusion. Therefore, the long-term effect of these findings is unknown at present. Longer follow-up is needed."

For more information:

• Douglas Wardlaw, MB, MhB, ChM, FRCSEd, can be reached at Woodend Hospital, Eday Road, Aberdeen AB15 6LX, Scotland; e-mail: Doug.Wardlaw@arh.grampian.scot.nhs.uk or d.wardlaw@nhs.net.

References:

Beastall J, Siddiqui M. Karadimas E. Nicol M. Hughes J, Smith FW. Wardlaw D. The Dynesys Lumbar Spinal Stabilization System. A Preliminary Report On Positional Magnetic Imaging Findings. Spine. 32(6):685-90, 2007 Mar 15.

Mertic A. Radiographic disc changes in the bridged and adjacent segments following Dynesys dynamic stabilization. Presented at the North American Spine Society 23rd Annual Meeting. Oct. 14-18, 2008. Toronto.