Safety and efficacy of a new percutaneously implantable interspinous process device

Abstract

Background: Lumbar spinal stenosis is a degenerative disease of the elderly population. Although microsurgical decompression has shown good long-term results, percutaneous techniques could provide an alternative in the presence of significant comorbidities.

Method: Eighty-seven interspinous process decompression devices (In-space; Synthes, Umkirch, Germany) were implanted percutaneously in up to three segments of 50 patients. Outcome was assessed directly after surgery, at 6-8 weeks, and at average follow-up of 1 year (11.8 ± 6 months). Assessment included complications, pain and spinal claudication, neurodeficit, time to recurrence of symptoms, and time to second surgery. Subgroups with additional low back pain at presentation and mild spondylolisthesis were analyzed separately.

Findings: Intraoperative complications were rare (one misplacement and two cases of failed implantation); average operation time was 16.4 ± 12.2 min per segment. Initial response was very good with 72% good or excellent relief of symptoms. After a 1-year follow-up, 42% reported of lasting relief from spinal claudication. Thirteen percent of these complained about lasting or new-onset low back pain. A second surgery had been performed in 22%. Subgroup analysis was performed for patients presenting with additional low back pain and spondylolisthesis patients. No significant differences could be noted between subgroups.

Conclusions: The In-space is a percutaneous treatment option of claudication in patients with lumbar spinal stenosis. Compared with microsurgical decompression surgery, recurrence rate within 1 year is, however, high and the device seems not suitable for the treatment of low back pain. Therefore, the authors suggest that the device should presently be used primarily in controlled clinical trials in order to get more information concerning the optimal indication.

Fig. 1

Percutaneous implantation of the In-space device. a–c Insertion of a guiding wire and dilatation of the approach. Finally, the implant is inserted (d), and its wings were deployed (e)

Fig. 2

X-ray (a coronary plain and b sagittal plain) of implanted In-space devices in the levels L3/4, L4/5, and L5/S1. The device in level L3/4 is the only dislocated device observed in our cohort (white arrow)

Fig. 3

Follow-up of patients who received an In-space device for lumbar spinal stenosis. At 3 months after surgery, the curve representing patients with recurrent symptoms rises above that of those with lasting relief from claudication. Afterward, both curves seem to parallel each other, suggesting a comparably stable ratio of patients with lasting relive/patients with progradient claudication always from 3 months onward. The sum of all curves decreases to the right of the diagram, because patients fall out of follow-up. A second surgery was first performed 4 months after In-space implantation. The second surgery curve breaks off after 11 months, when the last of so far 10 patients underwent second surgery

Fig. 4

Kaplan–Meier estimator for the time to progression/recurrence of symptoms after implantation of an In-space device in our cohort

Fig. 5

a Results of a subgroup analysis directly after surgery. All groups [all patients, patients with spondylolisthesis only, and patients with (additional) low back pain at first presentation only] show a comparatively good response to surgery, with about 70% good or excellent results. b Situation at last follow-up (in average about 1 year later). Both subgroups do fairly similar concerning lasting relief from claudication. However, a significant number of these patients suffer from lasting or new-onset low back pain (last column in the diagram)