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Asymmetry and Diagnosis: Are We Neurodynamic Mirror Images?
Asymmetry and Diagnosis
One of the great difficulties with neurodynamic testing is how to classify the response - normal or abnormal. My experience is that, in the clinical community, the classification of neurodynamic test responses in patients is in chaos. For instance, if one were to ask a group of therapists the question "What is a positive test?" the answers would be numerous, and only some would be correct. The best forum to discuss and practise neurodynamic testing is at courses and it is not possible to cover this subject comprehensively here. However, in this short commentary, I will discuss one of the important variables in testing for diagnosis - asymmetry.
One of the common beliefs about neurodynamic tests is that, for them to be normal, they should be symmetrical. But this can be incorrect.
An example of the belief that symmetry is necessary for a normal response is in the location, or distribution, of symptoms. It is common for asymptomatic subjects to exhibit asymmetry in this aspect. The median neurodynamic test 1 may produce symptoms in the anterior elbow region on one side whereas, in contrast, symptoms may occur in the ventral aspect of the wrist or thenar eminence on the other side. Technically, this is asymmetrical and has the potential to be considered an abnormal response. However, when reinterpreted, the response on each side is in the area reported by asymptomatic subjects (Kenneally et al 1988), namely the field of the median nerve (Figure 1). Hence 'normal' may be the final classification.
Fig 1: Mirror images of the median neurodynamic test 1
Figure 1. Mirror images of the median neurodynamic test 1. The symptom responses (yellow areas) are not mirror images, although both responses could be normal.
In relation to the parameter range of motion, studies of the median neurodynamic test 1 response in asymptomatic subjects have shown that small asymmetries do in fact occur. When a good number of asymptomatic subjects are tested, in isolation there may be no statistically significant differences between range of elbow extension when the data are only analyzed in terms of left and right sides. However, when limb dominance is taken into account, the results reveal important differences. Approximately one-third of subjects show a significant reduction in ROM of elbow extension and this difference averages 10˚ (Van Hoof et al 2011). Ten degrees could be the difference between a normal and abnormal response and, if omitted from the analysis, could place the patient on the wrong diagnostic and treatment pathway.
With the slump and straight leg raise tests, in relation to the effect of neck flexion/extension movements on limb range of motion in asymptomatic subjects, Herrington et al (2008) showed that the effect of the cervical movements on the range of knee and ankle movements did not differ between limbs in the same subjects when analyzed in terms of gender. However, their observations on asymmetry were described eloquently: "It should be noted though that there was not a statistically significant difference between the limbs, this is not the same as the response between the limbs being identical. In fact, out of the 88 subjects only 10 subjects had a truly identical response between limbs ...".
Clearly statistical analysis placed these variations within the standard error of the mean (SEM). However, it is critical that the therapist be aware of these possible responses in patients.
It is therefore important that the patient's response to neurodynamic testing is interpreted in light of their entire presentation, including limb dominance.
Finally, an abnormal neurodynamic test is NOT a diagnosis. It is an indicator that something may be wrong in the mechanics and/or physiology of the nervous system, the cause of which must be established in the context of a comprehensive biopsychosocial evaluation involving both subjective and physical factors.
Herrington L, Bendix K, Cornwell C, Fielden N, Hankey K 2008 What is the normal response to structural differentiation within the slump and straight leg raise tests? Manual Therapy 13(4): 289-294
Van Hoof T, Vangestel C, Shacklock M, Kerckaert I, D'Herde K 2011 Asymmetry of the ULNT1 elbow extension range-of-motion in a healthy population: Consequences for clinical practice and research. Physical Therapy in Sport/doi:10.1016/j.ptsp.2011.09.003