Neurodynamics is the science of the relationships between mechanics and physiology of the nervous system. Simply put – it is the assessment and treatment of the physical health of the nervous system. Just as a joint moves and a muscle stretches, the nervous system also has physical properties that are essential for movement. You can examine these properties via nerve palpation and neurodynamic tests.
The nervous system is a continuum. A mechanical, electrical and chemical continuum exists in the nervous system. This is the basis of tests such as the slump test, where for example, the position of the neck will influence neural responses in the leg.
The neural continuum allows a differentiation between neural and non-neural tissues. For example, in the case of the slump test (see below), if neck extension which takes load off the nervous system eases evoked symptoms in the leg, then this provides some clinical data to suggest that there is a physical health issue in the nervous system.
The nervous system is usually behind, in front, or to the side of joint axes of movement. This means that the physical loading on the nervous system will be dictated by joint position. In the example shown of the Upper Limb Neurodynamic Test (ULNT), wrist extension, elbow extension, and shoulder abduction would be examples of movements which challenge the median nerve and the brachial plexus. If you know your anatomy, you could make up neurodynamic tests yourself.
Most neurodynamic tests are tests of the ability of the nervous system to elongate. The neighbouring structures (e.g. joint and muscle) which ‘contain’ the nervous system can sometimes pinch it. Wrist flexion is a test of the neural container around the median nerve at the carpal tunnel, and the Spurling’s test is an example of a cinch test for lower cervical nerve roots.
The strain and movement of the nervous system will be affected by the order in which the movement is taken up. For example, as illustrated, if you add ankle dorsiflexion and eversion and then perform a Straight Leg Raise (SLR) , a neurogenic problem in the tibial nerve at the ankle is more likely to be exposed than with other combinations.
There are probably two reasons for this: a more mechanical reason where the neural tissues are ‘borrowed’ from other areas and thus given more of a chance to be challenged, or perhaps the first movement is the one which takes priority in the patient’s consciousness.
A tensioner can be a vigorous technique which ‘pulls from both ends’ of the nervous system. A slider is a ‘flossing’ movement where tension is placed at one end of the system and slack at the other. Sliders provide a large amount of neural movement and are a neurally nonaggressive movement for anxious patients.
Remember that responses to these tests may not always be due to physical health issues in the nervous system. In some patients the sensitivity evoked during testing may be due to changes in the central nervous system.