=====Sedimentation sign=====
Barz et al.
((Barz T, Melloh M, Staub LP, Lord SJ, Lange J, Röder CP, et al. Nerve root sedimentation sign: evaluation of a new radiological sign in lumbar spinal stenosis. Spine (Phila Pa 1976). 2010;35(8):892-7. ))
demonstrated for the first time in 2010 that in patients without [[lumbar spinal stenosis]] (LSS) a sedimentation of the nerve roots to the dorsal region of the dural sac in magnetic resonance images by gravitational force and defined its absence as a positive sedimentation sign. 

A positive sedimentation sign was defined as the absence of sedimentation of the nerve roots at the level above and below the stenosis in at least one cross-section magnetic resonance image, irrespective of the level of the section and its proximity to the maximum stenosis. As a rule, the nerve roots usually settle into the dorsal region of the dural sac by gravity, which was defined as a negative sedimentation sign. The only exception are the two roots exiting the dural sac one level below the stenosis. If there are nerve roots in the ventral dural sac (apart from the exception mentioned above), the sign is positive.

====Evidence====

===2015===
Current evidence suggests that the sedimentation sign has high sensitivity and specificity for diagnosing severe lumbar spinal stenosis. Its performance in diagnosing moderate and mild spinal stenosis, however, has yet to be corroborated in properly designed studies
((Zhang L, Chen R, Xie P, Zhang W, Yang Y, Rong L. Diagnostic value of the nerve
root sedimentation sign, a radiological sign using magnetic resonance imaging,
for detecting lumbar spinal stenosis: a meta-analysis. Skeletal Radiol. 2015
Apr;44(4):519-27. doi: 10.1007/s00256-014-2064-6. Epub 2014 Nov 28. PubMed PMID: 
25431094.
)).

A positive sedimentation sign was associated with a small but significantly greater surgical treatment effect for [[Oswestry Disability Index]] in patients with symptomatic LSS, after adjusting for other demographic and imaging features. These findings suggest that positive sedimentation sign may potentially be a useful adjunct to help guide an informed treatment choice regarding surgery for LSS
((Moses RA, Zhao W, Staub LP, Melloh M, Barz T, Lurie JD. Is the Sedimentation
Sign Associated With Spinal Stenosis Surgical Treatment Effect in SPORT? Spine
(Phila Pa 1976). 2015 Feb 1;40(3):129-36. doi: 10.1097/BRS.0000000000000672.
PubMed PMID: 25668333; PubMed Central PMCID: PMC4324511.
)).



===2014===
Patients with LSS have an increased epidural pressure at the level of the stenosis and altered pressure wave characteristics below. We argue that the absence of sedimentation of lumbar nerve roots to the dorsal part of the dural sac in supine position may be due to tethering of affected nerve roots at the level of the stenosis
((Barz T, Melloh M, Staub LP, Lord SJ, Lange J, Merk HR. Increased
intraoperative epidural pressure in lumbar spinal stenosis patients with a
positive nerve root sedimentation sign. Eur Spine J. 2014 May;23(5):985-90. doi: 
10.1007/s00586-013-3071-3. Epub 2013 Oct 29. PubMed PMID: 24166020.))

In patients commonly treated with decompression surgery, the sedimentation sign does not appear to predict surgical outcome. In nonsurgically treated patients, a positive sign is associated with more limited improvement. In these cases, surgery might be effective, but this needs investigation in prospective randomized trials (Australian New Zealand Clinical Trial Registry, number ACTRN12610000567022)
((Barz T, Staub LP, Melloh M, Hamann G, Lord SJ, Chatfield MD, Bossuyt PM, Lange
J, Merk HR. Clinical validity of the nerve root sedimentation sign in patients
with suspected lumbar spinal stenosis. Spine J. 2014 Apr;14(4):667-74. doi:
10.1016/j.spinee.2013.06.105. Epub 2013 Sep 20. PubMed PMID: 24055611.)).