LETTER TO THE EDITOR Letter to the Editor concerning ‘‘Relationship between sedimentation sign and morphological grade in symptomatic lumbar spinal stenosis’’ (by Laudato PA, Kulik G, Schizas C (2015) Eur Spine J; 24(10):2264–2268) Markus Melloh 1,2 • Lukas P. Staub 3 • Sarah J. Lord 4,5 • Thomas Barz 6 Received: 6 July 2015 / Accepted: 21 August 2016 / Published online: 26 August 2016 Ó Springer-Verlag Berlin Heidelberg 2016 We were interested to read the recent publication by Laudato et al. [1]. The authors evaluate the value of the Sedimentation Sign (SedSign) [2] and the morphological grading [3] as predictors of treatment modality in patients with symptomatic lumbar spinal stenosis (LSS). However, in LSS the appropriate diagnostic criteria to recommend treatment are not yet well defined. Thus the more central question is if and how these tests can help improve treatment decisions. To address this question we need prognostic information as reported in two recent publi- cations on the clinical validity of the SedSign—one from the SPORT trial [4, 5]. These studies found no significant difference between the patient group with a positive SedSign and the group with a negative sign undergoing decompression surgery in functional limitation nor in pain at baseline and at 24-month follow-up. Both groups demonstrated a comparable improvement after surgery. Conversely, in patients undergoing conservative treatment the ones with a positive SedSign did not show any improvement at follow-up whereas the group with a negative sign did. Unfortunately, clinical outcomes of LSS patients undergoing decompression surgery are not reported by Laudato et al. in their study. However, these clinical outcomes are necessary to understand the down- stream consequences of different treatment modalities for LSS. In this respect previous studies went further in the evaluation of the SedSign than the present paper [4, 5]. And this is where the SedSign may add value as surgery decider in SedSign-positive LSS patients currently undergoing conservative treatment who might benefit from decompression surgery. As a simple binary measure, the SedSign has the practical advantage of being easier to implement in clinical practice where the decision to operate is binary too. A study to investigate the potential role of the morphological grade in clinical decision- making would be valuable. Compliance with ethical standards Conflict of interest None. References 1. Laudato PA, Kulik G, Schizas C (2015) Relationship between sedimentation sign and morphological grade in symptomatic lumbar spinal stenosis. Eur Spine J 24:2264–2268 2. Barz T, Melloh M, Staub LP et al (2010) Nerve root sedimentation sign: evaluation of a new radiological sign in lumbar spinal stenosis. Spine 35(8):892–897 3. Schizas C, Theumann N, Burn A, Tansey R, Wardlaw D, Smith FW, Kulik G (2010) Qualitative grading of severity of lumbar spinal stenosis based on the morphology of the dural sac on magnetic resonance images. Spine 35(21):1919–1924 & Markus Melloh markus.melloh@zhaw.ch 1 Centre for Health Sciences, School of Health Professions, Zurich University of Applied Sciences, Winterthur, Switzerland 2 Centre for Medical Research, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth, Australia 3 Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland 4 NHMRC Clinical Trials Centre, University of Sydney, Sydney, Australia 5 School of Medicine, University of Notre Dame, Notre Dame, USA 6 Department of Orthopaedic Surgery, Asklepios Klinikum Uckermark, Schwedt/Oder, Germany 123 Eur Spine J (2016) 25:3768–3769 DOI 10.1007/s00586-016-4752-5