Muscle and Nerve: Are We Really Caught Between the Devil and the Deep Blue Sea?
It has been thought for a long time that it's not possible to move nerves and muscles differentially. This is completely logical because they're all soft tissues and the body doesn't move in single parts.
But neurodynamic tests do things differently because they're not the usual movements of daily living. Whilst they move limbs generally, they can also emphasize nerves through combining limb movements to: a. produce an effect along the nervous system and b. move a nerve in one area by moving a body part in another, e.g. ankle dorsiflexion moving the sciatic nerve and nerve roots during the straight leg raise, but not the lumbar spine or the hamstrings at their insertion.
This manoeuvre at a different location is called a "Differentiating movement".
Here are our studies on this mechanism to see if it's valid.
Research: The Difference Between Nerve and Muscle Movement in Neurodynamic Tests.
Specificity of nerve movement relative to musculoskeletal tissues is very important because it helps us better understand diagnosis with neurodynamic tests - whether a neurodynamic response is actually nerve mechanics or just a general physical test.
For instance, ankle dorsiflexion is used to differentiate responses to the sciatic nerve and nerve roots in low back pain, deep gluteal syndrome and upper hamstring injury. The straight leg raise moves everything above the knee, so we add dorsifexion to see if the response is neural or musculoskeletal, but the effects of that differentiating movement have not been validated so we never really knew if it was neurodynamic.
We've been studying this for quite some time using highly sensitive electronic strain gauges in fresh cadavers and have now published several experimental studies:
- sciatic nerve movement relative to biceps femoris in the upper thigh - dorsiflexion
- tibial nerve and biceps femoris at the posterior knee - dorsiflexion
- median nerve at the wrist and flexor digitorum superficialis - cervical lateral flexion.
We have consistently found (all studies so far) that, during neurodynamic tests (straight leg raise and ULNT), the sciatic and median nerves move about 0.25-4.0 mm with a differentiating manoeuvre, but the adjacent muscles did not move at all.
So we now have preliminary evidence that nerves can be moved independently from muscles - in certain situations. This does not take into account muscle contraction because it's in cadavers, but on a passive level, the indications are in favour of specificity.
Early evidence supports that we can emphasize nerves mechanically in neurodynamic testing.
Video - our research on nerve and muscle movement.
-- 1. Bueno Gracia E, Pérez-Bellmunt A, Estébanez-de-Miguela E, López-de-Celis C, Shacklock M, Caudevilla-Poloa S, González-Rueda V 2019 Differential movement of the sciatic nerve and hamstrings during the straight leg raise with ankle dorsiflexion: Implications for diagnosis of neural aspect to hamstring disorders. Musculoskeletal Science and Practice 43: 91-95: DOI: 10.1016/j.msksp.2019.07.011
-- 2. Bueno-Gracia E, Estébanez-de-Miguela E, López-de-Celis C, Shacklock M, Caudevilla-Polo S, González-Rueda V, Pérez-Bellmunt A 2020 Effect of ankle dorsiflexion on displacement and strain in the tibial nerve and biceps femoris muscle at the posterior knee during the straight leg raise: investigation of specificity of nerve movement. Clinical Biomechanics May 75: DOI: 10.1016/j.clinbiomech.2020.105003105003
-- 3. Bueno Gracia, Pérez-Bellmunt A, Estébanez-de-Miguela E, López-de-Celis C, Caudevilla-Polo S, Shacklock M, González-Rueda V 2020 Effect of cervical contralateral lateral flexion on displacement and strain in the median nerve and flexor digitorum superficialis at the wrist during the ULNT1 – Cadaveric study. Musculoskeletal Science and Practice 50 (2020): 102244 DOI:10.1016/j.msksp.2020.102244
My compliments and gratitude to the wonderful scientists and clinicians with whom I've worked on this important project..
December 9, 2020