Dear Editor,

We read with great interest the article by Giannadakis et al., Microsurgical decompression as treatment for central lumbar spinal stenosis [Giannadakis C, Hammersboen LE, Feyling C et al. (2015);157(7):1165-71] [2]. They reported an interesting single-center observational study in which the surgical results of microsurgical decompression were evaluated through data collected at the Norwegian Registry for Spine Surgery (NORspine) from 2007–2012. Demographics and lifestyle issues in addition to primary and secondary outcome measures were assessed using preoperative and postal follow-up questionnaires.

We would like to point out just one observation.

Giannadakis et al. reported the use of microsurgical decompression in a series of patients. Compared to laminectomy, microsurgical decompression is a less invasive procedure in which, via a smaller incision, the decompression of the dural sac and nerve roots is obtained. In microsurgical decompression the spinous processes and supra- and interspinous ligaments are left intact. In their study only patients without radiological instability were included but how the instability was preoperatively assessed was not reported. We consider the flexion/extension radiograph a useful examination in the assessment of lumbar instability, and we recently reported that instability is sometimes not evident at static examinations and the dynamic examination can reveal it. In these cases it is called microinstability [3]. Microinstability has clinical relevance and may be helpful to distinguish patients who require decompression alone from those who require decompression plus fixation [1]. Giannadakis et al. reported low complication rates in microsurgical decompression for central lumbar stenosis in patients without radiological instability; however, an equivalent outcome was previously demonstrated in microsurgical decompression or laminectomy [4]. It would be interesting to assess microsurgical decompression in patients affected by microinstability, since in these patients a standard laminectomy may aggravate the instability, and fixation is probably too aggressive a treatment. Unfortunately, a prospective study in microsurgical decompression for patients affected by radiological microinstability is missing.