Date of Award

January 2014

Document Type


Degree Name

Medical Doctor (MD)



First Advisor

Peter G. Whang

Subject Area(s)



Interspinous spacers represent a potentially less invasive treatment for patients with intermittent neurogenic claudication, secondary to lumbar spinal stenosis. Previous anatomic studies have suggested that these devices may bring about an "indirect decompression" of the neural elements by increasing the dimensions of the spinal canal and foramina. However, the mechanism of failure associated with the development of recurrent claudication has not been fully elucidated. The purpose of this investigation is to quantify the changes in these parameters at the stenotic and adjacent levels by comparing the pre- and follow-up magnetic resonance imaging studies of a series of patients who developed recurrent symptoms following the implantation of interspinous spacers.

A cohort of ten subjects, who had been evaluated with follow-up MRI studies for complaints of recurrent neurogenic claudication following placement of interspinous spacers (X-STOP, Medtronic, Memphis, TN) at one or two levels of the lumbar spine, were prospectively identified. Using a PACS system, various anatomic parameters were measured from the preoperative and follow-up MRI studies including cross-sectional area and anterior/posterior diameter of the central canal, subarticular diameter (bilaterally), foraminal area, height, and width (bilaterally), anterior and posterior disc height, and intervertebral angle. For each patient, these values were recorded at both the operative and adjacent levels. Whenever applicable, the left- and right-sided values were pooled and the preoperative and follow-up values were compared using the Welch two-sample t-test.

The placement of interspinous devices resulted in significant increases in the dimensions of the central canal, lateral recesses, and foramina at the levels of implantation. However, there were no statistically significant changes observed in these parameters at adjacent levels.

The anatomic parameters measured in this study were significantly improved at the levels at which interspinous implants had been placed. Thus, even in patients with recurrent claudication, the interspinous spacer appears to increase the dimensions of the spinal canal and foramina at the stenotic levels with no significant effects on adjacent segments.

Findings from this study suggest that the failure of these devices is not necessarily related to an inability to bring about improvements in spinal anatomy. Further research is necessary to elucidate this mechanism of failure, an understanding of which will be instrumental for refining the appropriate surgical indications for these devices.