Elsevier

Manual Therapy

Volume 15, Issue 4, August 2010, Pages 376-381
Manual Therapy

Original article
Impact of order of movement on nerve strain and longitudinal excursion:A biomechanical study with implications for neurodynamic test sequencing

https://doi.org/10.1016/j.math.2010.03.001Get rights and content

Abstract

It is assumed that strain in a nerve segment at the end of a neurodynamic test will be greatest if the joint nearest that nerve segment is moved first in the neurodynamic test sequence. To test this assumption, the main movements of the median nerve biased neurodynamic test were applied in three different sequences to seven fresh-frozen human cadavers. Strain and longitudinal excursion were measured in the median nerve at the distal forearm. Strain and relative position of the nerve at the end of a test did not differ between sequences. The nerve was subjected to higher levels of strain for a longer duration during the sequence where wrist extension occurred first. The pattern of excursion was different for each sequence. The results highlight that order of movement does not affect strain or relative position of the nerve at the end of a test when joints are moved through comparable ranges of motion. When used clinically, different neurodynamic sequences may still change the mechanical load applied to a nerve segment. Changes in load may occur because certain sequences apply increased levels of strain to the nerve for a longer time period, or because sequences differ in ranges of joint motions.

Introduction

Upper limb neurodynamic tests (ULNTs) apply mechanical loads to the nervous system by changing the dimensions of the targeted nerve bed (Elvey, 1985, Butler, 1991, Shacklock, 1995). Clinicians are advised to monitor symptoms, range of motion, and resistance during testing in order to assess the nervous system's ability to tolerate these mechanical loads (Elvey, 1997, Butler, 2000). Standardised sequences for neurodynamic tests have been recommended to improve test reproducibility. However, clinicians are also encouraged to adjust the order of movement to match an individual patient's presentation (Maitland, 1979, Elvey, 1997, Butler, 2000).

Zorn et al. (1995) found that different sequences of a median nerve biased test (ULNT1MEDIAN) changed the distribution of sensory responses reported by asymptomatic participants. Sensory responses were more prevalent in the distal part of the upper limb when ULNT1MEDIAN was applied in a distal-to-proximal sequence. One explanation for the more distal responses is that strain in a targeted nerve segment is believed to be greatest when the joint nearest that nerve segment is moved first in the neurodynamic test sequence (Butler, 2000). This belief is based on reports that a nerve does not behave like a uniform cylinder when lengthened. Different segments of a nerve exhibit different amounts of stress and strain when placed under tensile load in situ (Kleinrensink et al., 1995, Wright et al., 1996, Phillips et al., 2004). The potential for a certain order of movement to apply more strain to a nerve segment is thought to increase the sensitivity of a neurodynamic test (Butler, 2000). For example, ULNT1MEDIAN may be more sensitive for detecting carpal tunnel syndrome if it is performed in a distal-to-proximal sequence where wrist extension is the first movement.

Although differences in the location of sensory responses have been reported for different neurodynamic sequences (Zorn et al., 1995), preliminary biomechanical findings do not support the belief that test sequence can change mechanical loading on the median nerve. A cadaver study by Coppieters and Alshami (2007) measured the effects of different combinations of elbow and wrist extension on median nerve biomechanics. Their findings indicated that lengthening the nerve bed through different combinations of movement did not change strain in the median nerve at the distal forearm. Even though their results do not support the assumption that different sequences lead to different levels of nerve strain, it should be recognised that their study did not aim to test the effect of sequencing. They examined the biomechanical impact of moving two adjacent joints and therefore did not intend to reproduce the standard, distal-to-proximal, and proximal-to-distal sequences of ULNT1MEDIAN.

A comprehensive investigation of the effect of sequencing on nerve biomechanics should include movement of all the major joints of the limb. Movement of the shoulder, elbow, and wrist permits simulation of all three sequences for ULNT1MEDIAN. This methodology more closely replicates the clinical application of this neurodynamic test and increases the ability to generalise results. Therefore, the primary aim of this study was to determine whether different orders of movement at the shoulder, elbow, and wrist changed median nerve strain and net longitudinal excursion at the end of ULNT1MEDIAN. The secondary aim was to assess how different orders of movement affected the patterns of median nerve strain and longitudinal excursion during progressive stages of this neurodynamic test.

Section snippets

Methods

Strain and longitudinal excursion of the median nerve were measured proximal to the carpal tunnel during three neurodynamic test sequences. All tests were applied to the right upper extremity of human cadavers.

Elbow and wrist positions at the end of a test

The end positions for the elbow and wrist were not significantly different between the three neurodynamic sequences (elbow: p = 0.71; wrist: p = 0.97). This confirmed that the joints were moved through similar ranges of motion during all sequences (Table 3).

Strain at the end of a test

Neurodynamic sequence did not change strain in the median nerve at the end of a test (p = 0.067) (Table 3). The non-significant result was supported by the small number of differences within individual cadavers that exceeded the SDD95 (Fig. 1

Discussion

It is assumed clinically that different orders of movement can apply different levels of strain to a particular nerve segment at the end of a neurodynamic test. Our data on ULNT1MEDIAN do not support this assumption. The most clinically relevant comparison is between the standard and distal-to-proximal sequences because these are the two most commonly described testing sequences for ULNT1MEDIAN (Elvey, 1997, Butler, 2000). No difference in end position strain was observed between these two

Conclusion

This study assessed the impact of different orders of movement on nerve biomechanics by simulating all three sequences for ULNT1MEDIAN. Even though nerves are not uniform cylinders, the order of joint movements does not have a special effect on the level of end position strain or net longitudinal excursion of the median nerve at the distal forearm. The ability to apply a certain level of strain for a longer or shorter duration may be a plausible reason for using a particular sequence to

Acknowledgements

The authors thank the Silent Mentors for donating their bodies to the simulated surgery program. We also thank the physicians and staff at the Tzu Chi University Medical Simulation Centre for their assistance during data collection. Robert Nee is funded by an Endeavour International Postgraduate Research Scholarship from the Australian Government and a Research Scholarship from The University of Queensland. This study was funded by the National Health and Medical Research Council of Australia

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