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COMPARISON OF LONGITUDINAL SCIATIC NERVE MOVEMENT WITH DIFFERENT MOBILIZATION EXERCISES: AN IN VIVO STUDY UTILIZING ULTRASOUND IMAGING

Ellis RF, Hing WA, McNair PJ. JOSPT. 2012;42:667-675.

Abstracted by Karla Endicott, SPT, from Missouri State University,  Springfield, Missouri

This research study compared the effect of four different neural mobilization exercises on longitudinal sciatic nerve excursion. The single-group design involved 31 healthy adults (22 women, 9 men) with no symptoms of sciatic nerve dysfunction. Participants sat in a consistently managed slumped position while performing exercises using different combinations of passive knee extension and active cervical spine flexion and extension. During each exercise, the longitudinal sciatic nerve excursion was measured in vivo at the posterior mid-thigh region using ultrasound imaging. The four neural mobilization exercises used were the following:

  1.     A) Slider Mobilization – Passive knee extension loaded the sciatic nerve caudally while the participant simultaneously performed active cervical spine extension.
  2.     B) Single Joint Mobilization (Knee) – Passive knee extension loaded the sciatic nerve caudally while the participant maintained a neutral cervical spine position.
  3.     C) Single-Joint Mobilization (Cervical Spine) – The participant performed active cervical flexion loading the nervous system cranially while the knee remained stationary.
  4.     D) Tensioner Mobilization – Passive knee extension loaded the sciatic nerve caudally while the participant simultaneously performed active cervical flexion loading the nervous system cranially.

In general, “slider” techniques combine joint movements to create tension in the nerve at one end while releasing tension at the other end. In contrast, “tensioner” techniques combine joint movements to stretch the neural tissue from both ends. The authors cite research which has shown different types of neural mobilization exercises result in different amounts of neural excursion in the upper limbs.1  Similar research has been lacking concerning the lower extremities, and the authors conducted this study to help fill this gap. The authors hypothesized that the slider mobilization exercises would induce greater longitudinal sciatic nerve excursion compared to the tensioner and single-joint nerve-gliding exercises.

The hypothesis was supported because statistically, the slider mobilization generated significantly more sciatic nerve excursion (3.2 mm) compared to the other techniques. The tensioner mobilization and single-joint mobilization of the knee resulted in nerve excursion that was not significantly different from each other (2.6 mm), and the single joint mobilization of the cervical spine resulted in the least amount of nerve excursion (-0.1 ± 0.1 mm).  The authors report that similar levels of sciatic nerve excursion were found in a previous study. While the slider mobilization generated significantly more sciatic nerve excursion, the actual difference between it and the tensioner mobilization technique was only 0.6 mm. The authors acknowledge that this difference as well as the total excursion distance of 3.2 mm may or may not be clinically meaningful.

The authors report notable factors in this study. First, these findings in the lower limb are consistent with previous findings in the upper limb which may help support a general theoretical construct of nerve excursion during joint movement. Second, the cervical spine flexion used in the tensioner mobilization did not result in significantly more sciatic nerve excursion than the single joint mobilization of the knee.  If cervical spine flexion does not add to neural tension, then the question may be raised concerning its usefulness as part of the slump test. The authors report a similar issue in a previous study that found cervical flexion did not significantly change hip flexion during the straight leg raise test. However this study also noted the use of cervical extension during the slump slider resulted in the largest amount of excursion at this level. Third, sciatic nerve excursion as measured at the posterior mid-thigh region probably does not reflect what is occurring elsewhere along the nerve tract.

IAOM Comment:

The authors are to be commended in providing further information of sciatic neurodynamic mobility specifically at the posterior midthigh in vivo. Especially noteworthy is the demonstration of 4 specific patterns of movement in the seated slump position resulted in a consistent predictable amounts of sciatic nerve excursion at the midthigh. This is consistent with previous upper extremity studies specific to the median nerve, and should contribute to building a theoretical framework concerning how specific combinations of joint movement effects neural mobility. The IAOM was already appreciating the importance of a systematic progression of neural mobilization of the lower extremities targeting specific portions of the sciatic nerve in 1996.4 Since pain free motion helps tissues heal, it is important to continue to refine the most effective techniques to mobilize neural tissue and assist with the healing process.

Although the evidence appears to demonstrate there is very little sciatic nerve excursion in the seated slump position with cervical flexion or knee extension alone, or in combination with each other as a tensioner, the IAOM challenges the authors’ suggestion questioning its usefulness in the seated slump test. This appears to be premature and contradictive, especially in light that this study also supports cervical extension as relieving tension on the sciatic nerve.  A slight change in tension with these movements (with or without a change in excursion) that results in a change in the patient’s symptoms is certainly significant diagnostic information for us.

Also of interest to us is the authors did not include in this study the most distal component of the sciatic neuromobility chain…changes with the ankle in prepositioned dorsiflexion as practiced by the IAOM. Our IAOM colleagues, Gilbert and et al in 2007 demonstrated the significance of this component in the SLR position with and without dorsiflexion altering the displacement and possibly the strain of the lumbosacral nerve roots in the lateral recess.5

References

  1. Coppieters MW, Butler DS. Do ‘sliders’ slide and ‘tensioners’ tension? An analysis of neurodynamic techniques and considerations regarding their application. Manual Therapy. 2008;13:213-221. http://dx.doi.org/10.1016/j.math.2006.12.008.
  2. Ellis R, Hing W, Dilley A, McNair P. Reliability of measuring sciatic and tibial nerve movement with diagnostic ultrasound during a neural mobilisation technique. Ultrasound Med Biol. 2008;34:1209-1216. http://dx.doi.org/10.1016/j.ultrasmedbio.2008.01.003.
  3. Hall T, Zusman M, Elvey R. Adverse mechanical tension in the nervous system? Analysis of straight leg raise. Manual Therapy. 1998;3:140-146.
  4. Matthijs O, Van Paridon D, Phelps V. Clinical Application: Neural flossing with the lower extremity. The AAOM Quarterly. 1996.
  5. Gilbert KK, Brismee JM,  Collins DL, James CR, Shah RV, Sawyer SF, Sizer SS. 2006 Young Investigator Award Winner: Lumbosacral nerve root displacement and strain. Part 2. A comparison of 2 straight leg raise conditions in unembalmed cadavers. Spine. 2007;32(4):1521-1525

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