Materials and Methods
The primary objective of this study was to establish the reliability of using USI to measure longitudinal radial nerve excursion. Our main finding indicates that the USI technique used in the present study had a moderate to high level of reliability (ICC = 0.63–0.86) for quantifying longitudinal radial nerve excursion. This finding is similar to many studies that have examined longitudinal nerve movement using the same techniques. Reliability for assessing in vivo longitudinal nerve movement using USI has been reported as high for the sciatic (Ellis et al. 2008) and tibial (Boyd and Dilley 2014; Shum et al. 2013) faah inhibitor and very high for the median (Coppieters et al. 2009), sciatic (Coppieters et al. 2015; Ellis et al. 2012; Ridehalgh et al. 2012), tibial (Boyd et al. 2012) and posterior tibial (Carroll et al. 2012) nerves. The present study is the first to present findings for in vivo assessment of radial nerve excursion using USI.
With respect to the forearm position, there was significantly greater radial nerve excursion induced by movements performed in supination compared to pronation. These differences may be partly explained by greater tension imposed on the radial nerve when the forearm is pronated. Although the present study did not examine radial nerve tension or strain, cadaver research has shown that the radial nerve is exposed to greater strain when the forearm is pronated (Wright et al. 2005). Furthermore, in vivo studies of other peripheral nerves have reported a reduction in nerve excursion when nerve tracts are exposed to greater strain (Coppieters and Butler 2008; Dilley et al. 2003; Dilley et al. 2007). Therefore, it was not an unexpected finding that the lowest levels of radial nerve excursion occurred when the forearm was pronated.
No difference was seen in radial nerve excursion when induced via wrist flexion compared to wrist ulnar deviation despite the fact that there was a significant difference in wrist ROM between the different movements. These findings are in agreement with Wright et al. (2005), who demonstrated similar levels of radial nerve excursion during wrist flexion and ulnar deviation proximal to the elbow joint in vitro.
The findings in regard to the amount of radial nerve excursion seen between the different conditions may have important clinical implications. For example, neural mobilisation exercises have been advocated for conditions where impaired nerve movement is perceived (Coppieters et al. 2009; Ellis et al. 2012). For neural mobilisation exercises that clinicians prescribe to induce or encourage radial nerve excursion, decisions could be made in regard to the design of exercises based on the findings of this study. For example, if radial nerve excursion was to be maximised, the clinician should consider performing passive movements of the wrist in a supinated forearm position. Selection of which wrist movement to utilise (i.e., wrist flexion or ulnar deviation) could be made based on the functional limitation of the patient as radial nerve movement induced appears to be similar. Although relevant to consider, it must be noted that this study was conducted within a healthy cohort. The possibility remains that these interpretations may not be consistent in a clinical population. This warrants further investigation.
A number of steps were implemented to improve methodological quality while reducing potential sources of bias. First, randomisation of tasks was utilised, which is believed to reduce the learning effect of improved scanning that has been shown to occur in USI studies (Ridehalgh et al. 2012). Following completion of each condition, the shoulder and elbow positions were reassessed, with goniometry, to ensure consistent participant set-up. The sonographer was blinded to all USI measurements, thereby reducing error bias (Ellis and Hing 2008). Data analysis was performed with the assessor blinded to participant and testing conditions to reduce the level of confounders related to assessor recollection (Ellis et al. 2008, 2012).
Materials and Methods