Mixed results for X-stop in spinal stenosis


An award-winning paper presented at the annual meeting of the British Association of Spine Surgeons found that the short-term benefits conferred by the X-stop implants for lumbar radiculopathy were maintained at two-year follow-up.

Researchers have concluded that the provisional data from their study, despite the small cohort, provide increasing evidence to suggest that the X-stop device may suit people with radiculopathy secondary to foraminal stenosis. They said the interspinous distraction device was found to be safe and did not jeopardise future surgery in the event of failure.

Catherine Gilkes, et al, reported that they followed all patients of one neurosurgeon (Tim Germon, Nuffield Health Plymouth Hospital, UK) treated with X-stop implants.

Investigators measured patient-reported pain and disability outcomes (Oswestry disability index [ODI]; Short Form 36 bodily pain scale [SF36BP]) immediately preoperatively and approximately two years postoperatively. Changes were examined in terms of statistical significance (Wilcoxon signed ranks test) and clinical significance (effect sizes – mean change divided by SD change).

Two-year follow-up data were available for 13 of the 15 people who had the surgery. Researchers said one patient had died of an unrelated condition before follow-up, the other had further lumbar surgery, thus affecting the interpretation of the data, reported Gilkes. Mean duration of follow-up was 30.5 months.

Both ODI and SF-36BP detected sustained improvements two years after surgery. Results for both scales were statistically significant (z=-3.059 & -3.062; p=.002). Mean change scores for both scales were substantial (ODI=31.7; SF36BP=47.4), and effect sizes were very large (ODI=1.35; SF-36BP=1.37) indicating clinically significant improvement. There have been no complications.

Sell says X-stop should be withdrawn

However, two other papers presented at the same meeting raised concerns regarding the X-stop device.

The papers were both from Phillip Sell, a consultant spinal surgeon, who runs a general spinal clinic in Nottingham and special spinal clinics in Leicester, UK. The first paper he presented sought to determine the clinical effectiveness of the device, and the second described its clinical, biomechanical and radiological features.

“What surprises me,” Sell told Spinal News International, “is how many hospitals have been using the device without audit. The NICE guidance IPG165 recommends audit by anyone using the device. All we did was what any user of a new device should do.”

From a cohort of 69 patients with clinical and radiological evidence of spinal stenosis, across five hospital sites, 66 were followed up for between six months and two years after having the X-stop device implanted. Outcome measures were ODI, visual analog score for leg and back, and implant failure, determined by removal and revision.

A small number (17 patients, or 25%) had a dramatic improvement of greater than 24 points, which significantly skews the average change from baseline. “It may be that this represents a subgroup that benefit from the procedure,” said Sell. But he said that what exactly defines this subgroup has not been established. “Surgeons should wait until they are identified before continuing the widespread use of this implant.”
Sell reported 17 cases where reintervention was necessary, representing a failure rate of 24%.

The second paper looked at 45 patients over a two-year period. This group had an average preoperative walking distance of 120 metres, which, at six months follow-up, had risen to 1,430 metres.

Again, Sell reported that a subgroup of patients had exhibited dramatic improvements. However, he also found a failure rate of 24%.

There were two modes of failure: Early, with a failure to improve after the procedure; and late, with an initial improvement and subsequent deterioration.

Bone resorption around the implant was found to be a consistent feature of late failure. Scalloping and erosion of bone was recorded at revision surgery with the implant within a fibrous capsule. Late spinous process fracture occurred in one two-level implant as a result of erosion.

Scouring of the polyetheretherketone surface was evident on retrieved implants.

Sell concludes that long-term surveillance of patients treated with the X-stop implant should be mandatory, and that the implant should be withdrawn from clinical use until trials establish long-term efficacy and safety.

“The design and material used changed from the original used in clinical trials. This change occurred for a reason,” Sell said, “but this reason has not been made clear. The current device and material has not been subjected to any independent prospective studies.

“The high-profile marketing of these devices is a concern with such little scrutiny of them.”