Median nerve deformation and displacement in the carpal tunnel during finger motion

Abstract

The objective of this study was to evaluate the correlations between deformation and displacement of median nerve and flexor tendons during finger motion in the carpal tunnel for both carpal tunnel syndrome (CTS) patients and healthy controls. Sixtytwo wrists of 31 asymptomatic volunteers and fifty-one wrists of 28 idiopathic CTS patients were evaluated by ultrasound. The displacement of the median nerve and the middle finger flexor digitorum superficialis (FDS) tendon, as well as area, perimeter, aspect ratio of a minimum enclosing rectangle, and circularity of the median nerve were measured in finger extension and flexion positions. Deformation indices were defined as the ratios of indices in finger extension and flexion positions. The correlations between displacement and deformation indices were evaluated. There were significant correlations between nerve palmar-dorsal displacement and deformation indices (p < 0.05). The aspect ratio deformation index showed the strongest correlation to palmar-dorsal displacement of the nerve (À0.572, p < 0.01). This study showed that there is a relationship between median nerve deformation indices and nerve palmar-dorsal displacement in the carpal tunnel. Since the highest correlations were between palmar-dorsal nerve displacement direction and aspect ratio deformation index, these parameters may be helpful to understand the pathophysiology of CTS. Keywords: carpal tunnel syndrome; median nerve; displacement; deformation; ultrasound Carpal tunnel syndrome (CTS) is a compression neuropathy of the median nerve at the wrist. The diagnosis of CTS is mostly clinical, and usually confirmed with nerve conduction studies. Recently, cross-sectional ultrasound imaging has been proposed for the diagnosis of CTS. Static ultrasonography can detect pathological changes such as thickening and alteration of the echogenicity of the flexor tendons and flexor retinaculum, synovial proliferation and flattening of the median nerve in the carpal tunnel. 1-7 These findings can distinguish patients with CTS from normal subjects.Peripheral nerve trunks slide over considerable length with movements of the extremity. 8 However, in the case of chronic compression, fibrosis of the perineurium and endoneurial edema 9 may alter the motion and deformation characteristics of the median nerve. Thus, to fully understand the pathophysiology of CTS, to the clinician should consider the deformation and displacement of the nerve and tendons.An ultrasound method to observe the movement of the structures in the carpal tunnel during finger motion has been described, 10 and several ultrasound indices of deformation have been identified which may be helpful in the assessment of patients with CTS. 11 The median nerve shape is affected more by the flexor digitorum superficialis (FDS) tendons than by the flexor digitorum profundus tendons, because the FDS tendons lie closer to the median nerve. There is a changed pattern of median nerve motion in association with middle finger, index, and thumb motion, when co...

Transverse Movement of the Median Nerve in the Carpal Tunnel during Wrist and Finger Motion in Patients with Carpal Tunnel Syndrome

“…Recently, several studies reported that the median nerve moves longitudinally and transversely in response to active tendon motion in the carpal tunnel during finger or wrist movement (Nakamichi and Tachibana 1992;Erel et al 2003;Yoshii et al 2009;van Doesburg et al 2010). Additionally, some authors have used transverse ultrasound to evaluate median nerve motion in the carpal tunnel (Yoshii et al 2009(Yoshii et al , 2013van Doesburg et al 2010van Doesburg et al , 2012Wang et al 2014a, b;Nanno et al 2015). With use of this modality, it has previously been determined that the median nerve becomes displaced palmarly and gets compressed against the TCL in active finger flexion in healthy subjects and in patients with CTS (Yoshii et al 2009(Yoshii et al , 2013van Doesburg et al 2012;Wang et al 2014a, b).…”

“…Additionally, some authors have used transverse ultrasound to evaluate median nerve motion in the carpal tunnel (Yoshii et al 2009(Yoshii et al , 2013van Doesburg et al 2010van Doesburg et al , 2012Wang et al 2014a, b;Nanno et al 2015). With use of this modality, it has previously been determined that the median nerve becomes displaced palmarly and gets compressed against the TCL in active finger flexion in healthy subjects and in patients with CTS (Yoshii et al 2009(Yoshii et al , 2013van Doesburg et al 2012;Wang et al 2014a, b).…”

“…There are a number of studies concerned with transverse displacement patterns of median nerve in the carpal tunnel during finger motion at the wrist neutral position (Yoshii et al 2009(Yoshii et al , 2013van Doesburg et al 2010van Doesburg et al , 2012Wang et al 2014a). However, there has been little research detailing the transverse displacement of the median nerve within the carpal tunnel at various wrist positions during finger motion by ultrasound.…”

“…In recent years, several studies have demonstrated that wrist and finger motion could bring substantial movement of the median nerve and the flexor tendons at the wrist (Yoshii et al 2009(Yoshii et al , 2013van Doesburg et al 2010van Doesburg et al , 2012Wang et al 2014a, b;Nanno et al 2015). Additionally, the transverse displacements of the nerve and the tendons within the carpal tunnel have been evaluated during wrist or finger motion (Nakamichi and Tachibana 1992;Erel et al 2003).…”

“…Comparison between the affected and unaffected sides of the CTS patients could reduce the problem of individual differences. Furthermore, Yoshii et al (2013) have described the detailed location of the median nerve as a coordinate within the carpal tunnel. It is important to describe the position of the median nerve as a coordinate to further understand the accurate nerve location within the carpal tunnel during wrist and finger motions.…”