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Neurodynamic evaluation of the sciatic nerve during neural mobilisation: ultrasound imaging assessment of sciatic nerve movement and the clinical implications for treatment
Ellis, Richard Francis
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Neural mobilisation is a physiotherapeutic tool that is used to directly influence peripheral nerve mechanics, in particular the neurodynamic features of the peripheral nervous system. Neurodynamics refers to the integrated biomechanical and neurophysiological features of the nervous system. It is believed that many common peripheral nerve disorders have underlying features of neurodynamic dysfunction as part of their clinical aetiology, for example a loss of the ability of a nerve to glide and slide against adjacent tissues. Neural mobilisation offers an intervention which aims to restore optimal neurodynamics. The first aim of this thesis was to collate the randomised controlled trials (RCTs) that have assessed neural mobilisation in order to evaluate the methods and strength of evidence of their findings. A systematic review was conducted which also focused on identifying methodological robustness and consistencies. Prior to this systematic review, there has been no previous systematic review published that has examined neural mobilisation. The results showed that there was a lack of RCTs that have assessed the therapeutic efficacy of neural mobilisations, particularly for neural mobilisation employed for lower limb nerve disorders. Secondly, the studies that were identified lacked consistency and had methodological weaknesses. None of these studies directly assessed nerve movement. One of many issues apparent from the review was the lack of research which has utilised a tool that examines and quantifies the biomechanical features of peripheral nerve movement during neural mobilisation. This issue could be resolved through ultrasound imaging (USI) allowing real-time, in-vivo assessment of peripheral nerve mechanics. An initial aim of this thesis was to investigate the intra-rater reliability of using USI to quantify sciatic nerve movement during neural mobilisation. Although the reliability of this technique has been assessed within the upper limb (median nerve), this has not been done for nerves of the lower limb. The findings of the reliability studies of this thesis indicated that there was excellent reliability (Intraclass Correlation Coefficient (ICC) ≥ 0.75) in the assessment of longitudinal sciatic nerve excursion which is consistent with previous studies which examined upper limb nerves. The next study examined whether different types of neural mobilisation resulted in different amounts of sciatic nerve excursion. Theoretically different neural mobilisation exercises will influence nerve excursion differently, and this has been determined for the median nerve. However, this situation has not been explored in the lower limb. It was found that neural mobilisation exercises designed to maximise nerve excursion (‘sliders’) resulted in significantly greater nerve excursion compared to those exercises designed to elongate peripheral nerves (‘tensioners’). This finding was consistent with studies conducted in the upper limb. These findings have important clinical ramifications as identifying which neural mobilisation exercises maximise nerve excursion will guide exercise selection. The final two studies examined the two specific biomechanical features of sciatic nerve excursion during neural mobilisation, namely the influence of added nerve tension and the sequence of nerve excursion. Several key features were observed. Firstly, that sciatic nerve excursion was greatest when closer to the axis of joint rotation which induced the movement. Secondly, that additional neural tension, obtained from adding cervical flexion to the slump-sitting neural mobilisation exercises, was insufficient to alter sciatic nerve excursion consistently. Thirdly, that sciatic nerve excursion shows a specific sigmoidal sequence of excursion. These findings provided a biomechanical perspective to support both theoretical models regarding nerve movement and clinical commentary concerning the use of neural mobilisation. The findings of this thesis are relevant for the future design of clinical trials which will further examine the therapeutic efficacy of neural mobilisation. USI, as a tool to assess nerve movement in-vivo and real-time, is reliable and will enhance assessment of nerve mechanics in nerve disorders. Its use as an outcome measure for clinical trials is warranted. The design and choice of neural mobilisation exercises to influence nerve excursion can now be more specific. Ultimately this will allow more accurate assessment of the therapeutic efficacy of neural mobilisation.