Interspinous process device versus standard conventional surgical decompression for lumbar spinal stenosis: randomized controlled trial

I would like to congratulate Dr Moojen and colleagues on making an important contribution to the practice of spinal surgery. It is disappointing that the spinal surgical community, of which I am a member, did not manage to organise such an investigation before so many of these devices were implanted.

However, I think it is worth pointing out that there is a small minority of patients who present with symptoms of spinal stenosis in whom interspinous spacers are likely to be more efficacious. These patients have foraminal stenosis rather than stenosis in the subarticular or central zone of the spinal canal.

The majority of people with spinal stenosis have nerve root compression in the subarticular zone, other wise known as the lateral recess. In these patients the transiting nerve roots are compressed between hypertrophied facet joints dorsally and the disc ventrally. However, the small minority who have foraminal stenosis have compression of the exiting nerve roots as they leave the spine between the facet joint posteriorly, the disc ventrally and the pedicles rostrally and caudally. Management of this condition is generally much more complicated, mainly because it is difficult to achieve a satisfactory decompression of the affected nerve roots without removing so much of the facet joint that the vertebral column is rendered unstable. Therefore, decompression is generally performed in combination with some form of reconstructive surgery. This is a much greater undertaking than direct decompression alone. In these patients indirect decompression using an interspinous spacer is a particularly attractive proposition. At the same time, empirical observation of the movement of the articulated spine suggests that interspinous distraction should increase both cranio-caudal and dorso-ventral diameters of the foramen more effectively than the cross sectional area of the spinal canal. We have published a cohort study which supports the potential efficacy of interspinous spacers in the treatment of lumbar foraminal stenosis.1 I would like to take this opportunity to emphasise that the distinct subgroup of patients with foraminal stenosis need to be recognised and that the results of this trial do not apply to them.

Yours sincerely,

Tim Germon
tim.germon@nhs.net

1. Hobart J, Gilkes C, Adams W, Germon T. Interspinous Spacers for Lumbar Foraminal Stenosis: formal trials are justified. European Spine Journal 2013;22(1):47-53.