Review Article - Archives of Orthopaedics (2020) Volume 1, Issue 2
The Role of the Sciatic Nerve Ultrasound Elastography in the Clinical Pathway: A Meta-analysis
Stajic Sava*, Misic Miroslav
Academy of Professional studies, High medical School, Belgrade, Serbia
- *Corresponding Author:
- Stajic Sava
Received date: June 10, 2020; Accepted date: July 14, 2020
Citation: Sava S, Miroslav M. The Role of the Sciatic Nerve Ultrasound Elastography in the Clinical Pathway: A Meta-analysis.
Arch Orthop. 2020; 1(2): 55-60.
Copyright: © 2020 Sava S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Over the last few years, more papers were published related to the usefulness of sciatic nerve ultrasound elastography in clinical
practice. Ultrasound elastography is a diagnostic method, to measure elasticity and strain in tissues and organs. The aim of
this review was to highlight the usefulness of sciatic nerve ultrasound elastography in clinical practice, strictly compared with
electromyography and MRI findings. Sonoelastographic evaluation was performed predominantly in patients with deep gluteal
syndrome (DGS). The results were processed by meta-analysis. In this review, in the final processing, 16 studies were identified, 4
with strain ratio, 12 with shear wave elastography. The data was collected in a timeframe of 2013 to 2019. Looking at the reviewed
studies, different techniques were applied (quasi-static, ARFI and shear wave elastography), with various joint movements, several
“region of interest”, non-standardized measurement units and patients with dissimilar pathologies. The review summary leads to
conclude that sciatic nerve ultrasound elastography test is not well clinically standardized. The nerve and surrounding muscles have
to be assessed by color scale and B mode. Determining strain index may be useful, on particular equipment and within the same
institution. The shear wave technique provides us with more secure and direct results, comparable to those of other institutions
and researchers. This method is the most proven for deep gluteal syndrome with a wide range of manifestations, unilateral lumbar
disc hernia, the assessment of sports injuries, to study musculoskeletal activity, monitoring the course of rehabilitation and in
monitoring postoperative recovery.
Sciatic nerve elastography, Shear wave, ARFI, Strain elastography, Deep gluteal syndrome
DGS: Deep Gluteal Syndrome; MRI: Magnetic Resonance Imaging; ARFI: Acustic Radio Force Impulse
Ultrasound elastography is a diagnostic method, to measure elasticity and strain in tissues and organs. The aim of this review was to highlight the usefulness of sciatic nerve ultrasound elastography in clinical practice. Different changes affect the sciatic nerves through various diseases and conditions. The impingement, the pressure of the surrounding structures, the damage of the nerve sheath and altered nerve structure, influence the nerve resistances. It can be effectively ascertained by ultrasound elastography. In the last few years, there were more papers about sciatic nerve elastography with controversial messages. “It`s interesting, but not very useful” is very often the clinician`s statement. The sciatic nerve stretches and slide during normal joint movement. In case of entrapped or compressed conditions, it causes pain with a change in its elasticity . The sciatic nerve roots descend
from the lumbar plexus, passes through the pelvis with an
exit on the sciatic notch inferior to the piriformis muscle
[2-4]. Some authors believe that it is connected with deep
gluteal syndrome (DGS) [5-7]. The clinical decision making
depends on neurological examination, electromyography
(EMG), and very often on pelvic and lumbar MRI [2,6].
Last few years, authors considered ultrasound elastography
techniques in clinical decision making, strictly compared
with MRI findings. The first announcement was based
on strain elastography features [8,9], later acoustic force
impulse (ARFI) data were involved [10,11], and at last, the
experiences were surrounded with shear wave elastography [12-17]. The pain generated by a sciatic nerve lesion can be
connected with ischiofemoral impingement and hamstring
dysfunction, by a combination of hip extension, adduction
and external rotation, by abnormal contact between the
lesser trochanter of the femur and the ischium, and in
those with the DGS [1-4]. DGS may manifest as a specific
entrapment within the subgluteal space, including fibrous
and fibrovascular bands, piriformis syndrome, obturator
internus syndrome, quadratus femoris and ischiofemoral
pathology, hamstring conditions, gluteal disorders or other
orthopaedic causes [1-4,18]. Sonoelastographic evaluation
of the sciatic nerve was also performed in patients with
unilateral lumbar disc herniation [19,20].
Materials and Methods
In 27 reviewed manuscripts the citations about sciatic nerve ultrasound elastography were identified. The case reports and small series (up to 5 cases), as well as the theoretical studies, non-representative population studies, or studies without clear data were excluded. In the final processing, 16 studies were identified, 4 with strain ratio. 12 with shear wave elastography. The final meta-analysis was done on patient data, elastography data, exercises data, ROC analysis, and by obtained processing. Figure
1 describes the flow chart with step by step processing of selected ultrasound elastography data. The data was collected in a timeframe of 2013 to 2019. The equipment has elastography supply. Looking at the reviewed studies, there were different techniques applied (quasi-static, ARFI and shear wave elastography), with various joint movements (“knee movement”, “limb movement”, “ankle motion”, “plantar or dorsal flexion”), at several positions of the transducer at the “region of interest”, nonstandardized measurement units and diverse pathology [8,10,12,14-17,19,21]. In 2013, Santos and Armada have
tested sciatic nerve by ultrasound elastography . In
healthy people, there were higher percentages of blue
color (hard properties) which conclude that sciatic nerve
can be tested by color elastograms. That statement was confirmed in 2018 by Stajic et al. . They conclude
that it is possible to identify sciatic nerve conversions by
color elastograms. One of the first announcement about
different ultrasound elastography techniques was by
Brandenburg and collaborators in 2014. The discussion
was about the basic principles of ultrasound elastography
techniques, including the strengths and limitations of their
measurement capabilities . Looking at the influence of
elastography on rehabilitation, François Hug et al. ,
noted that there is growing evidence that elastography
may be a useful tool in detecting subtle changes in
muscle, tendon or nerve mechanical properties that occur
early in the course of an injury or disorder. That should
be important as an earlier detection can improve sports
training and rehabilitation strategies. The quantification
of muscle, tendon or nerve stiffness also provides insight
into the mechanisms which may underlie treatment and
rehabilitation programs and could ultimately assess their
efficacy. Neto Tiago Goncalves in his doctoral thesis 
processed the effects of neural tension by the sciatic
nerve stiffness, in healthy people and people with low
back related leg pain. The thesis aimed to determine the
immediate effects of neural tension in the sciatic nerve
stiffness. Andrade et al. reported the potential role of
sciatic nerve stiffness in the limitation of maximal ankle
range of motion (by shear wave elastography) [12,21].
Sciatic nerve stretching induced both, the decrease
in the nerve stiffness and the increase in the maximal
joint dorsiflexion. Greening and Dilley practiced shear
wave elastography to examine the changes in peripheral
nerve stiffness of upper (median nerve) and lower (tibial
nerve) limb position by . Dikici and his team 
evaluated the tibial nerve with shear-wave elastography,
as a potential sonographic method for the diagnosis of
diabetic peripheral neuropathy. The conclusion was that
the tibial nerve stiffness measurements appear to be highly
specific in the diagnosis of established diabetic peripheral
neuropathy. In 2018, Demirel and collaborators 
also have showed that the muscle elasticity and tissue
hardening increased on the problematic side, both on
piriformis muscle and gluteus maximus. According to
them ultrasound elastography may provide early diagnosis
of piriformis muscle syndrome. The study of Ellis et al.
 showed that ultrasound elastography was seen to be
a reliable method for calculating sciatic nerve hamstring
muscle interface by shear strain and sciatic nerve
displacement. Using ultrasound elastography to quantify
sciatic nerve displacement as the body moves, peripheral
nerves are constantly being exposed to mechanical forces
and stress from the surrounding tissues. Stajic et al.
[10,11,24] concluded that the variation of the sciatic nerve
is challenging for diagnostic and therapeutic procedure
in many clinical and surgical cases. Quick ultrasound
detection of the sciatic nerve makes surgical approaches
more precise and effective, with a better outcome. This procedure could provide crucial information about the
degree of nerve stiffness during the follow up . In
2019, Celebi and collaborators  had shown results of
elastography evaluation in patients with unilateral lumbar
disc herniation. The experience directed to increase of
sciatic nerve stiffness. Wang et al.  established the
relationship of the shear wave elastography findings
with unilateral lumbar disc herniation and clinical
characteristics. According to their findings, ultrasound
imaging can be considered as a very useful tool to detect
changes in the sciatic nerve, due to disc herniation.
Results and Discussion
The significance of sciatic nerve color elastograms by quasi-static method was confirmed by Santos and Armada in 2013  and by Stajic et al. in 2018 , presented in Table 1. Neto et al. and Hug et al. have confirmed the significance of shear-wave color scale [14,15] (Table 1). The correlation coefficient of color elastograms was 0.675. The correlation coefficient with MRI findings was 0.749. The ultrasound equipment upgraded with shear wave elastography gave a new opportunity . It is based on direct measurement of muscle stiffness . In the musculoskeletal field, the quasi-static method was rarely applied . Stajic et al. have presented in 2018 and 2019 [10,11,24], the referent values of relative stiffness in asymptomatic patients, during extension and flexion knee movements (2.78 to 5.75SR) and in patients with DGS (7.32 to 11.97SR). The specificity was 93.5%, sensitivity 88.9%, with the accuracy 90.6%. They continued with follow up sciatic nerve stiffness in patients with the deep gluteal syndrome, who underwent surgery . The neurodynamic sciatic nerve changings were noted by Francois Hug , in exercises of plantar flexion to dorsiflexion (from 1 to 7m/sec and by color scale). The shear wave features were presented in different conditions and diseases, respectively in healthy patients. Neto et al.  presented higher sciatic nerve stiffness compared to the unaffected limb (8.2 to 16.2m/sec and 9 to 13.6m/sec, P=.05) in patients with chronic low back leg pain. The resistance (shear-wave technique) in dynamic and unresisting knee extension was observed by Ellis . The shear-wave resistance in active knee ?exion knee was 73.06%, while in active knee extension 59.84%. The shear wave sciatic nerve stiffness was also tested during human ankle motion . The shear wave velocity of the sciatic nerve significantly increased (p<0.0001) during dorsiflexion, when the knee was extended (knee 180°), but without changes when the knee was flexed (90°). The posture?induced changes by tibial nerve stiffness in different positions were 3.47 to 8.10 m/sec (Greening and Dilley) . Çelebi and his team  assessed the sciatic nerve stiffness in patients with unilateral lumbar disc herniation and reported that on the axial (12.3kPA) and longitudinal (14.3kPA) planes of the involved side the sciatic nerve stiffness was significantly higher than non-involved side (6.8 and 8.3kPA) in the patient group (p<0.001). On the other side, Wang et al.  established sciatic nerve
stiffness on affected side 20.4/27.5kPa (P<0.05), contrary
to unaffected side 12.9/17.3kPa. Demirel and his team 
have tested sciatic nerve in piriformis muscle syndrome by
shear waves. The stiffness in piriformis muscle syndrome
on painful side was 1.59m/sec (mean value), whereas it was
0.5 m/sec on normal side. The sciatic (tibial) nerve was
evaluated by Dikici . Patients with diabetic peripheral neuropathy had much higher stiffness values on both sides. A cutoff value proximal to the medial malleolus was 51.0 kPa, with the sensitivity of 90%. The variations of elastography score by several techniques in flexion and extension movements of painful limb are presented in Table 2. Due to these conditions, the correlation coefficient of elastographic measurements was low, r=0.195. Also, in comparison with other diagnostic findings (MRI, EMG) the correlation coefficient was not highly expected, r=0.465. The variations of elastography score in healthy persons are presented in Table 3. In several techniques involving
flexion and extension limb movements, the correlation
coefficient was significantly high, r=0.795. Looking at the
demographic characteristics of few studies (Table 4), the
average in patients groups was well-balanced, mean 42.4
years (p<0.05), as well as sex distribution.
|Santos et al. 2013 (8)||Blue (hard)||Green/Yellow (soft)||quasi-static estimation|
|Stajic et al. 2018 (10)||Blue (hard)||Yelow/Red (soft)||quasi-static estimation|
|Neto et al. 2019 (14)||Yellow/Red (hard)||Blue (soft)||shear-wave estimation|
|Hug et al. 2016 (15)||Yellow (hard)||Blue (soft)||shear-wave estimation|
The correlation coefficient of color elastograms r=.675
The correlation coefficient with MRI findings r=.749
Table 1: The color elastograms were compared according to tissue elasticity.
|Neto et al. 2017 [14,17]||8.2 m/sec (plantar)||16.2 m/sec (plantar)|
|Greening et al. 2017 ||3.47 m/sec (tibial)||8.10 m/sec (tibial)|
|Celebi et al. 2019 ||12.3kPa (leg)||14.3kPa (leg)|
|Wang et al. 2019 ||20.4kPa (plantar)||27.5kPa (plantar)|
|Stajic et al. 2018 [10,11]||7.32SR (knee)||11.97SR (knee)|
|Ellis et al. 2018 ||59.84% (knee)||73.06% (knee)|
|Andrade et al. 2018 ||1800 (ankle)||900 ( ankle)|
|Demirel et al. 2018 ||1.59 m/sec|| |
|Dikici et al. 2017 ||51.5kPa|| |
|The Elastography Studies||In extension||In flexion|
The correlation coefficient of elastographic measurements r=.195
The correlation coefficient with diagnostic (MRI,EMG) findings r=.465
Table 2:The variations of elastography score by different techniques in flexion and extension movements of painful limb.
|The Elastography Studies||In extension||In flexion|
|Neto et al. 2017 [14,17]||9 m/sec (plantar)||13.6 m/sec (plantar)|
|Celebi et al. 2019 ||8.3 kPa (leg)||9.8 kPa (leg)|
|Wang et al. 2019 ||8 kPa||17.7 kPa|
|Dikici et al. 2017 ||12.9 kPa (leg)||17.3 kPa (leg)|
|Stajic et al. 2018 [10,11]||2.78SR||5.75SR|
|Demirel et al. 2018 ||0.5 m/sec|| |
The correlation coefficient of elastographic measurements r=.795
Table 3: The variations of elastography score by different techniques in flexion and extension movements in healthy
|The Elastography Studies||Age||Gender (M/F)|
|Neto et al. 2017 ||30.8||6/2|
|Stajic et al. 2019 ||43.5||12/12|
|Wang et al. 2019 ||44.5||7/13|
|Celebi et al. 2019 ||43.1||20/20|
Table 4:The demographic characteristics (population with disease).
In this review it was concluded that ultrasound elastography was applied within different projects and studies, but clinical backup was not established. The ultrasound elastography was not involved in clinical and diagnostic pathways. However, the nerve and surrounding muscles must be assessed by color scale and B mode. A strain index may be useful, on particular equipment and within the same institution. The shear wave technique provides much more secure, direct results, comparable within various institutions and researchers, but it has to be standardized (m/sec or kPa). In correlation with MRI findings this method should be applied in deep gluteal syndrome with a wide range of manifestations, in unilateral lumbar disc hernia, in the assessment of sports injuries, to study musculoskeletal activity, in monitoring the course of rehabilitation and in monitoring postoperative recovery. Further investigations must be continued. The orthopedic and the ultrasound community must make agreement about principles in sciatic nerve ultrasound elastography examinations. According to this review the shear wave elastography must be a basic method. The color elastograms must be established (with subgroups). The region of interest (ROI) must be determined (intra or extra-neural or surrounding tissue) and the agreement looking at the validate cut off must be achieved. At last, in clinical practice the Ultrasound Elastography recommendations by European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) must be respected.
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