Dynamic interspinous process stabilization: review of complications associated with the X-Stop device

The X-Stop interspinous device is designed for the treatment of patients with neurogenic intermittent claudication due to lumbar spinal stenosis. It distracts the posterior elements of adjacent vertebral bodies, unloading the intervertebral disc, limiting spinal extension, and improving central canal and neuroforaminal stenosis. In this paper, the authors reviewed the complications and failure/reoperation rates in a small series of patients and compared their results with other reported complication and failure/reoperation rates.

The medical records of all patients who underwent placement of the X-Stop device for the treatment of NIC at the authors' institution were retrospectively evaluated, and demographic information, diagnosis, and preoperative pain levels were recorded. Postoperatively, patients subjectively graded the percentage (0-100%) of improvement in pain as well as the amount of residual pain and underwent imaging at 1-, 3-, and 6-month intervals. Approximately 4 years after X-Stop placement, information on long-term outcomes was obtained from patient medical records or additional follow-up.

Thirteen patients (8 men and 5 women) underwent placement of the X-Stop device. Central canal stenosis with bilateral foraminal stenosis was diagnosed in all patients: 9 (69%) of 13 had severe stenosis and 4 (31%) of 13 had moderate stenosis. Five patients (38%) also had associated Grade I spondylolisthesis. Nine patients underwent placement of the X-Stop device at the L4-5 interspinous space and 4 at both the L3-4 and L4-5 levels. The average duration of follow-up was 42.9 months (range 3-48 months). Initially, pain improved an average of 72% (range 50-100%) in these patients; however, preoperative pain returned in 77% of the patients (10 of 13). The overall complication rate was 38%, including 3 spinous process fractures (23%) and 2 instances of new-onset radiculopathy (15%). The ultimate failure rate requiring additional spinal surgery was 85% (11 of 13 patients). These complication and failure rates are much higher than those previously reported.

Overdistraction, poor bone density, poor patient selection, and preexistent adjacent foraminal stenosis may all be factors in the development of the aforementioned complications. Thus, careful attention should be paid preoperatively to adjacent-level disease, bone density, appropriate implant size, and optimal patient selection.