134 - 5-year radiological outcomes post an interlaminar device insertion for symptomatic lumbar spinal stenosis

Introduction
Lumbar spinal stenosis (LSS) is a common spine condition that is frequently encountered especially with an ageing population. A common treatment strategy employed for symptomatic patients is open decompression and fusion. However, that option poses its own unique set of drawbacks which led to the adjunct use of the interlaminar device (ILD) as an increasingly popular alternative instead. There are varying designs available for interlaminar and interspinous devices, all aiming to serve a common goal of limiting extension at the affected index lumbar segment and allowing for increased foraminal height and reduced disc pressure. This in return may translate into a longer symptom free interval with reduced recurrence or need for further procedures.
There is a paucity in the current literature about the radiological parameters that are affected or maintained with the use of an ILD and the implications of those observations. Hence, the objective of our paper was to compare and monitor several radiological indices as a surrogate marker to determine the effectiveness of the ILD insertion up to 5-years postoperatively.

Materials and Methods
A retrospective review of prospectively collected data under a single surgeon cohort study, consisting of 116 patients who underwent spinal decompression with and without an ILD insertion between 2007 - 2015 was performed. Patients who met the study criteria were offered the choice of an ILD device insertion. Those who accepted an ILD insertion were placed in the D+ILD group (n=61); while those opting for decompression alone, were placed in the DA group (n=55). Radiological indices consisting of anterior and posterior disc height, foraminal height at the level of decompression, segmental lordosis and sagittal angle were assessed both preoperatively and up to 5-years postoperatively.

Results
The D+ILD group achieved and maintained significant radiological correction at all time points for posterior disc height, foraminal height, sagittal height and L4 to S1 lordosis measured while the DA group did not attain this; implying good lateral recess restoration and neuroforaminal decompression. This in return is translated into better clinical outcome scores in the postoperative period and improvement in radiological parameters.

Conclusion
The use of an interlaminar device in conjunction with spinal decompression in patients with symptomatic LSS has been shown to offer a sustained correction in radiological parameters.