Imaging appearance following surgical decompression of the ulnar nerve

Abstract

Ulnar neuropathy at the elbow is the second most common entrapment neuropathy of the upper extremity. Yet, there is a paucity of literature focusing on the imaging appearance following surgical decompression of the ulnar nerve at the elbow. Diagnostic imaging studies obtained after surgical decompression at The University of Michigan were reviewed and imaging findings were documented. We aim to describe the various techniques of ulnar nerve decompression and corresponding post-operative appearance on imaging. Potential complications following decompression will also be described with imaging and clinical correlation of recalcitrant ulnar neuropathy. It is important for the radiologist who performs MRI or ultrasound of the elbow to be aware of the various ulnar nerve decompression procedures. This knowledge will facilitate rapid and accurate diagnosis of normal and abnormal appearance of the ulnar nerve in this context.

Figure 1.

Illustration depicts sites of ulnar nerve entrapment about the elbow.

Figure 2.

The intermuscular septum (arrows) separate the anterior (brachialis muscle) and posterior (triceps muscle) compartments of the arm with the ulnar nerve (*) coursing between the septum and medial head triceps muscle (T).

Figure 3.

Intraopearative photo demonstrate the post-condylar groove (elipse), an osteofiberous tunnel between the medial humeral epicondyle and olecranon process through which the ulnar nerve(*) courses. The structure tagged with the band is the MABC nerve. MABC, median antebrachial cutaneous.

Figure 4.

Intraopearative photo demonstates the broad based fascia (arrowheads) superficial to the flexor carpi ulnaris elevated by instrument. Ulnar nerve (*).

Figure 5.

Intraopeartive photo demonstrates an intact osborne's ligament (arrow) following the incision of the superficial fascia and between the two heads of the flexor carpi ulnaris. Ulnar nerve (*) and MABC (tagged, arrowhead).

Figure 6.

In situdecompression. Insert shows transection of the superficial investing fascia and osborne's ligament, releasing the deeper ulnar nerve (yellow). Release from the more proximal sites of compression is also noted.

Figure 7.

Ulnar nerve discompression at the postcondylar groove. (a) Short axis ultrasound depicts a gap (arrows) between the superficial fascia stumps (*) extending between the humeral epicondyle (H) and the olecranon process following simple decompression of the ulnar nerve (u). Axial T₂ weighted images following fat saturation depicts (b) An intact fascia (arrows) superficial to a thickened ulnar nerve (U) and (c) increased T₂ signal (arrowheads) involving the medial aspect of the fascia (arrows) following decompression. [Olecranon process (O)].

Figure 8.

(a) Short axis ultrasound depicts a hypoechoic cleft (*) involving the superficial fascia and deep osborne's ligment between the FCU muscles following decompression. Ulnar nerve (U). (b) Axial T₁ weighted image depicts the more distal division (double arrow) between the FCU (arrows). Ulnar nerve (arrowhead).FCU, flexor carpi ulnaris.

Figure 9.

Anterior subcutaneous ulnar nerve transposition. In subcutaneous transposition, the ulnar nerve is secured in a sling fashioned with the subcutaneous fat (insert).

Figure 10.

Axial T₂ weighted images (a) and long axis ultrasound (b) depict the course of the ulnar nerve (arrow, a; U, b) superficial to the flexor pronator muscle mass (FPM) . (c) more distally, the nerve (arrow) courses between the ulnar (U) and humeral (H) heads of the flexor carpi ulnaris muscles. (Post-traumatic deformity of the humerus -*, a). .

Figure 11.

Anterior submuscular transposition. The ulnar nerve is positioned deep to a lengthened pronator teres muscle via a z-plasty (insert).

Figure 12.

(a) Axial T₂ weighted image with fat saturation and (b). Long axis ultrasound image depict an anterier submuscular transposition with the ulnar nerve (arrow) deep to the FPM mass. Humerus (H). FPM, flexor pronator muscle.

Figure 13.

Entrapment following anterior submuscluar transposition. Saggital T₂ weighted images following fat saturation depict increased signal within the ulnar nerve and focal kinking/angulation of the ulnar nerve (arrows) due to inadequate release of osborne's ligament.

Figure 14.

Axial T₂ weighted image with fat saturation depicts an inadequately positioned ulnar nerve following anterior subcutaneous transposition with the ulnar nerve in a posterier location (arrows) abutting the medial humeral epicondyle (*). FPM, Flexor pronator muscle mass.

Figure 15.

(a) Long axis ultrasound depicts a surgically coinfirmed “belt like” scarring (arrow) with focal narrowing of an ulnar nerve (U) at the level of the medial humeral epicondyle. Humerus (H). (b) short axis ultrasound image depicts a thick irregular IMS (arrows) correlating with surgically confirmed scarring with subluxation of the ulnar nerve (arrowheads) over the IMS. (Brachilias muscle, B; medial head triceps, T; humerus, H). IMS,intermuscular septum.