IS SCIATIC NERVE COMPRESSION UNDER PIRIFORMIS A THING?




 

 

Introduction

 

Key questions are whether sciatic neuropathy can come from compression by piriformis AND whether we can test for it with neurodynamics.

 

What does the research say about this?

 

Gold standard: electrophysiology.  The first gold standard for detection of neuropathy is electrophysiology. Fortunately, the rate of false positives in asymptomatic subjects is so low that the evidence is strong when a deficit is detected. 

 

 

Electrodiagnosis Shows It Up

 

Here is what a couple of significant studies found:

  • Reduced motor nerve conduction in the sciatic nerve in the buttock in patients with symptoms of piriformis syndrome. This relates to the common fibular part and is often involved (Chang et al 2006).

  • Impaired H reflexes in the AIF 'pirformis stretch' position (hip Add, IR, Flex) compared to the contralateral side and asymptomatic subjects.  Sustaining the position normally produces a slight reduction in the H reflex but it was much larger in the presence of piriformis syndrome.

SCIATIC NERVE DEFICIT WAS DYNAMIC WITH LOAD (Fishman and Zybert 1992).

 

REMEMBER - electrophysiology can do some things but not others:

  • CAN - detect a deficit.

  • CAN - often show where the problem is.

  • CAN NOT - determine the cause, which could be compression, infection, tumour, demyelination - there are many.

 

THE CAUSE - can be determined by imaging (e.g. MRI) and visualisation at surgery.

 

 

Radiology and Surgical Visualisation Reveals It

 

More good news for validity: Filler et al (2005) showed sciatic nerve compression under piriformis with MR neurography and confirmed it at surgery.  They then decompressed the nerve.

 

So we now have several things:

 

  • Gold standard evidence of neurological deficits in the deep gluteal area.

  • Gold standard establishment of various causes, in these cases:
    • compression by the muscle
    • ischial tunnel entrapment
    • sciatic nerve tumour.

 

 

You Can Find It

 

Remember that this is diagnosis of NEUROPATHY, not necessarily neurodynamic dysfunction, which requires a neurodynamic test because of its capacity to assess sensitivity and movement. The patient might NOT have a neuropathy but they might have a NEURODYNAMIC DISORDER - they're not the same thing.

 

 

 

Piriformis Slump Test

 

Here is the piriformis slump test - SEE PICTURES AND VIDEO

 

 

This variation of the slump test is in the hot seat here (pun intended!) because it uses a piriformis stretch to compress the sciatic nerve during the neurodynamic test. 

 

For those who have done NDS courses, you may remember that this is a level/type 3c technique that emulates the patient's provoking movements.

 

 

Who Is This Aimed At?

 

High performance individuals who tolerate extensive activity. They have:

 

  • Isolated buttock and/or upper thigh pain

  • LITTLE OR NO radiation

  • NO neurological symptoms.

 

We often don't test these people neurodynamically because we are focused on the muscle.

 

 

CONCLUSIONS AND RECOMMENDATIONS

 

Gold standard electrodiagnostic and pathology studies support sciatic nerve compression in some patients with piriformis syndrome.

 

Be sure to test the nerve in a way that emulates the patient mechanisms by using the piriformis slump test.

 

Remember that the test is only suitable for those who function at a high level and whose pain is difficult to reproduce.

 

Make sure the standard slump test is OK first.

 


References

 

Chang C, Shieh S, Li, Wu W, Chang K 2006. Measurement of motor nerve conduction velocity of the sciatic nerve in patients with piriformis syndrome: a magnetic stimulation study. Archives of Physical Medicine and Rehabilitation. DOI: 10.1016/j.apmr.2006.07.258.

 

Filler A, Haynes J, Jordan, Prager J, Villablanca P, Farahani K, Mcbride D, Tsuruda J, Morisoli B, Batzdorf U et al 2005. Sciatica of nondisc origin and piriformis syndrome: diagnosis by magnetic resonance neurography and interventional magnetic resonance imaging with outcome study of resulting treatment. Journal of Neurosurgery Spine. DOI: 10.3171/spi.2005.2.2.0099.

 

Fishman L, Zybert P 1992. Electrophysiologic evidence of piriformis syndrome. Archives of Physical Medicine and Rehabilitation. DOI: 10.1016/0003-9993(92)90010-t.