Ultrasonographical Evaluation of the Median Nerve Mobility in Carpal Tunnel Syndrome: A Systematic Review and Meta-Analysis

Abstract

Diagnostic ultrasound is widely used for evaluating carpal tunnel syndrome (CTS), an entrapment neuropathy of the median nerve (MN). Decreased mobility of the MN inside the carpal tunnel has been reported in CTS, and various methods have been used to evaluate MN mobility; however, there is still no conclusive understanding of its connection with CTS. The purpose of this study is to conduct a systematic review and meta-analysis of the current published literature on ultrasonographic evaluations of transverse and longitudinal MN displacement and to identify the relationship between MN mobility and CTS. This study was conducted in accordance with the 2020 PRISMA statement and the Cochrane Collaboration Handbook. Comparative studies that investigated differences in MN displacement between CTS patients and healthy controls were retrieved by searching the Cochrane Library, Embase and PubMed. A total of 15 case-control studies were included. Nine of 12 studies evaluating transverse MN displacement and 4 of 5 studies evaluating longitudinal MN gliding showed that the MN was less mobile in CTS patients than in healthy subjects. Despite the large heterogeneity among the 15 included studies, this systematic review and meta-analysis provide evidence that the mobility of the MN is significantly reduced in both transverse and longitudinal planes in CTS patients compared to healthy controls. Five of the 15 included studies reported that a decrease in transverse or longitudinal MN displacement in CTS was correlated with clinical symptoms or with severity as measured by a nerve conduction study (NCS).

Keywords: carpal tunnel syndrome; median nerve; meta-analysis; nerve displacement; systematic review; ultrasound images.

Figure 1

Ultrasonograms captured at the distal wrist crease level. (a) MN (structure enclosed by the upper dotted line) and FDS tendon (structure enclosed by the lower dotted line) in the carpal tunnel on the transverse plane. (b) MN and FDS tendon on the longitudinal plane. Abbreviations: P = pisiform bone; S = scaphoid bone; MN = median nerve; FDS = flexor digitorum superficialis; L = lunate bone; C = capitate bone.

Figure 2

Doppler waveforms for measuring longitudinal MN gliding during active flexion and the extension cycle of the index finger at a speed of one time per second. (This figure was adapted from Liu et al. [33]).

Figure 3

Study selection flow chart.

Figure 4

The algorithm for measuring the motion area of the MN was adopted from Hara et al. [54] Images were captured frame by frame from a video file (Step 1), and the cross-sectional area (CSA) of the MN was marked in red (Step 2). The CSAs of the MN from the first to the final images were overlaid to form the motion area of the MN (MAMn) (in pink, Step 3). The real motion area of the MN (RMMn) was defined by subtracting the CSA of the MN from the MAMn, while the mobile ratio (MR) was defined by dividing the MAMn by the CSA of the MN (Step 4).

Figure 5

The overall transverse MN displacement during index finger flexion or hand grasping in the CTS group compared with the control group.

Figure 6

The overall transverse MN displacement at the dorsopalmar axis (graph on the upper) and at the radioulnar axis (graph on the lower) during the index finger flexion or hand grasping in the CTS group compared with the control group.

Figure 6

The overall transverse MN displacement at the dorsopalmar axis (graph on the upper) and at the radioulnar axis (graph on the lower) during the index finger flexion or hand grasping in the CTS group compared with the control group.

Figure 7

The overall longitudinal gliding of the MN in the CTS group compared with the control group. Pooled result of studies using speckle tracking method (graph on the upper). Pooled results of studies using duplex Doppler waveform method (graph on the lower).