Possible Points of Ulnar Nerve Entrapment in the Arm and Forearm: An Ultrasound, Anatomical, and Histological Study

Abstract

Background: Ulnar nerve entrapment is one of the most common entrapment neuropathies, usually occurring in the cubital tunnel of the elbow and in Guyon’s canal of the wrist. However, it can also occur at other anatomical locations. Purpose: Our aim was to review other possible locations of ulnar nerve entrapment in an ultrasound and anatomical study. Material and Methods: Eleven upper limbs from eight adult corpses were ultrasonographically examined and subsequently dissected in a dissection laboratory. Four specific anatomical points were analysed, and any anatomical variations were documented. Moreover, six samples of the nerve were taken for histological analysis. Results: Distinct anatomical relationships were observed during ultrasound and dissection between the ulnar nerve and the medial intermuscular septum, the triceps aponeurosis, Osborne’s fascia at the elbow, the arcuate ligament of Osborne and the intermuscular aponeurosis between the flexor carpi ulnaris and the flexor digitorum superficialis muscles. A statistical study showed that these locations are potential areas for ulnar nerve compression. In addition, a fourth head of the triceps brachii muscle was found in some specimens. Conclusion: Results demonstrate that ultrasound is a good tool to investigate ulnar nerve entrapment neuropathy and to identify other anatomical points where the nerve can remain compressed.

Ultrasound of the Ulnar Nerve: A Pictorial Review

“…36 Just distal to the cubital tunnel, the passage at the flexor pronator aponeurosis where the nerve enters the forearm is another reported area of compression. [51][52][53] In our experience, this entrapment is uncommon; the UN has a normal appearance at the cubital tunnel whereas it is compressed in proximity to the coronoid tubercle (Figure 23).…”

The Unpredictable Ulnar Nerve—Ulnar Nerve Entrapment from Anatomical, Pathophysiological, and Biopsychosocial Aspects

“…The ulnar nerve can be compressed and affected at various points around the elbow, such as the arcade of Struthers, the medial intermuscular septa, at the level of the medial epicondyle at the ulnar groove, or under the ligament of Osborne, the latter typically the most crucial site-the cubital tunnel, as well as in the forearm where it passes under the flexor carpi ulnaris muscle [32][33][34] (Figure 2). It is important to note that the ulnar nerve may be severely affected due to different types of traumas to the elbow region, including fractures and subsequent closed or open repositioning with various osteosynthesis procedures, including heterotopic ossification around the elbow.…”

Ultrasound of the Ulnar Nerve: A Pictorial Review

“…23 Then, the nerve lies close to the medial head of the triceps muscle together with the superior ulnar collateral artery, which originates from the brachial artery. 24,25 At the distal third of the upper arm, around 8 cm cranial to the medial epicondyle, the UN is reported to pass under the arcade of Struthers (Figure 3D). 26 This anatomical structure is controversial and some authors believe that the UN merely passes beneath the brachial fascia (or its thickening), whereas other confirm the existence of an arch, which Alternative patient positioning to study the UN, with the patient seated in front of the examiner.…”

“…From a practical sonographic point of view, the UN distal to the axilla (Figure 3A) is initially in the same compartment with the median nerve and the brachial artery at the proximal upper arm (Figure 3B), then passes posteriorly (Figure 3C). The passage through the MIMS, which appears as a thin hyperechoic line, 25 may be more or less evident at US. Distally, the UN can be seen close to the medial head of the triceps, deep to the fascia, which can be slightly thicker and which we believe represents what is usually referred to as the arcade of Struthers (Figure 3D).…”

“…The deep flexor pronator aponeurosis is difficult to be clearly delineated at US in normal patients, but is possibly indicated by a hyperechoic area (Figure 9B). 25 Along the forearm, the UN is located deep to the FCU, ulnar to the ulnar artery (UA) (Figure 10). This may be another possible point at which to start the examination, particularly if only the distal part of the nerve has to be studied, because the UN is next to the artery, which is easily identified in the ulnar region of the distal forearm (Figure 11).…”