Ultrasound Scanning Protocol in the Assessment of Ulnar Neuropathy at the Elbow

Summary

This is a standardized protocol for evaluating the ulnar nerve at the elbow using ultrasound.

Abstract

Ulnar neuropathy at the elbow is commonly encountered in clinical practice and is the second most common entrapment neuropathy. Left untreated, ulnar neuropathy at the elbow can result in significant disability due to loss of dexterity and grip strength secondary to the weakness of intrinsic hand muscles. Precisely localizing a lesion in ulnar neuropathy can be challenging with electrodiagnostic testing alone. Ultrasound is a relatively quick and useful adjunctive diagnostic modality in overcoming this limitation, as an increase in the cross-sectional area (CSA) of the nerve is a common and validated finding in ulnar neuropathies at the elbow. Sonographic assessment of the nerve’s echotexture and vascularity can provide additional diagnostic clues. Ultrasound also offers the unique benefit of detecting ulnar nerve subluxation or dislocation out of the retroepicondylar groove during dynamic assessment, although the clinical significance of this is controversial. Finally, ultrasound can also identify structural abnormalities leading to nerve compressions, such as the presence of bony abnormalities, scar tissue, and space-occupying lesions. These findings may influence management strategies and surgical planning. This protocol aims to illustrate the technique of static and dynamic sonographic imaging of the ulnar nerve around the elbow as a complement to electrodiagnostic testing in the assessment of ulnar neuropathy at the elbow.

Introduction

Ulnar neuropathy at the elbow (UNE) is the second most common entrapment neuropathy¹. Electrodiagnostic testing is an important diagnostic modality but has low sensitivity and specificity in diagnosing UNE in the setting of mild pathology and pure axonal injury². There are several different sites of entrapment that may occur at or near the elbow. The most common locations of entrapment around the elbow are at the retroepicondylar groove and under the humeroulnar aponeurotic arcade (in the true cubital tunnel). However, more proximal locations, such as the Arcade of Struthers and medial intermuscular septum, are also possible³. In the last several years, ultrasound has emerged as a useful tool in identifying the location of ulnar nerve lesions in the setting of abnormal but non-localizing electrodiagnostic findings⁴. In fact, an expert consensus published in Clinical Neurophysiology in 2021 recommended using both ultrasound and electrodiagnostics in evaluating UNE⁵. This protocol is therefore intended to be used as an adjunctive diagnostic modality to electrodiagnostic studies rather than a replacement.

We find it easiest to perform ultrasound and electrodiagnostics together because the results of both modalities provide more information than either modality alone. Furthermore, ultrasound can be performed in a matter of minutes by a proficient sonographer. It is therefore feasible for patients to complete both types of testing in the same encounter. Given this, electrodiagnosticians may find the most benefit in this technique. However, it may also be useful in other settings, such as outpatient sports medicine clinics, during the comprehensive musculoskeletal assessment of elbow complaints. This protocol outlines the steps of the sonographic evaluation of the ulnar nerve with the patient positioned at 90°of elbow flexion. Various techniques are described in the literature about scanning and patient position. Some sonographers choose to examine the patient with the elbow in full extension¹. The advantage of the technique described in this protocol is related to changes in the cross-sectional area (CSA) of the ulnar nerve at the elbow in a flexed versus extended position. A systematic review and meta-analysis of sonographic normal values of the ulnar nerve demonstrated that most studies obtained their measurements with the elbow in 90° of flexion⁶.

The goal of this method is to (1) provide an accurate and specific location of ulnar nerve lesions at or near the elbow, if possible; (2) identify structural variations or abnormalities such as space-occupying masses, accessory muscles, scar tissue, or osseous changes that may be contributing to ulnar nerve compression; and (3) identify nerve hypermobility in the form of subluxation or dislocation out of the retroepicondylar groove during dynamic assessment. Please note that while this protocol focuses on the location of the elbow, we include instructions for scanning the entire length of the nerve per expert consensus guidelines⁵. Reporting these findings may guide management and aid in surgical planning. Overall, ultrasound is noninvasive, well-tolerated, and less expensive than other imaging modalities, such as magnetic resonance imaging.

Protocol

The protocol follows the guidelines of the Wake Forest School of Medicine Research and Ethics Committee, and informed written consent was obtained from patients before deidentifying and including the ultrasound images in this document. 1. Patient positioning, knobology, and basic tools of assessment (Figure 1) Patient positioning Ask the patient to lie supine with the affected arm abducted and externally ro…

Representative Results

Normal appearance of the ulnar nerve at the elbow Nerves are classically described as having a "honeycomb" appearance on ultrasound in the short axis. This appearance is due to the fact that each individual fascicle is hypoechoic (dark) appearingand the surrounding perineurium is hyperechoic (light) appearing. The result is a circular structure with speckled appearance. Note that the normal ulnar nerve often appears slightly hypoechoic at the medial epicondyle due to anisotropy from its arc…

Discussion

Ulnar neuropathy is commonly encountered as entrapment neuropathy in clinical practice. Correct diagnosis and localization aid surgical planning and treatment outcome¹⁰. It is recognized by expert consensus that ultrasound and electrodiagnostics together are more informative than either modality on its own. This expert consensus also maintains that ultrasound assessment should include measurement of CSA in regions where a lesion is suspected and an evaluation of nerve mobility at the medial epico…

Materials

Transducer	GE	H48062AB	L4-12T
Ultrasound	GE	H8041EG	LOGIQ e
Ultrasound gel	Aquasonic	E8365BA	250 mL bottles