Ultrasonographic and Electrophysiological Evaluation of Ulnar Nerve Instability and Snapping of the Triceps Medial Head in Healthy Subjects

Abstract

Ulnar nerve instability increased with elbow flexion and correlated with snapping of the triceps medial head. Ultrasonography of the ulnar nerve is an important tool in ulnar nerve instability assessment.

Is triceps hypertrophy associated with ulnar nerve luxation?

“…When investigating the interaction between the TBM and the position of the ulnar nerve in its sulcus, we found a relatively high prevalence (50%) of ulnar nerve (sub)luxation among our controls. Earlier studies using clinical testing, particularly palpation, estimated the prevalence of ulnar nerve (sub)luxation at about 30%; however, recent studies using sonography showed a prevalence of about 50%, which is in accordance with the results in our control group. This indicates a higher sensitivity of sonography in assessing ulnar nerve (sub)luxation, as suggested earlier by Okamoto and colleagues …”

“…Accordingly, asymptomatic cases of ulnar luxation should not be regarded as pathologic . Finally, other studies failed to establish an association between ulnar dislocation and damage by demonstrating that dislocation did not occur more frequently in patients with ulnar neuropathy, and electrodiagnostic abnormalities did not occur more frequently in subjects with ulnar nerve dislocation . In cases of asymptomatic luxation (the great majority), any therapeutic action is inappropriate .…”

“…13 Finally, other studies failed to establish an association between ulnar dislocation and damage by demonstrating that dislocation did not occur more frequently in patients with ulnar neuropathy, 14 and electrodiagnostic abnormalities did not occur more frequently in subjects with ulnar nerve dislocation. 5 In cases of asymptomatic luxation (the great majority), any therapeutic action is inappropriate. 13 Nevertheless, in cases with symptomatic ulnar dislocation and the frequently concurrent "snapping triceps" (painful dislocation of the TBM over the epicondyle), 15 surgery is recommended as the most appropriate therapy.…”

“…The thickness of the TBM, as well as the subcutis, was determined in B-mode at three-fifths the arm length between the acromion and the lateral epicondyle, 7 with the transducer in a strict dorsal and orthogonal position to the humerus exerting as little pressure as possible. 8 The ulnar nerve and adjacent structures were imaged in 3 positions according to Kang et al 5 on a level with the tip of the ME, using the method described by Jacobson et al 9 In this position, the ulnar nerve is orthogonally, instead of obliquely, depicted in its cross-section. Hence, a cross-section image in extension, 90 flexion, maximal flexion, and also in maximal flexion with isometric tension of the triceps was saved and the following measurements obtained: the distance between the middle of the ulnar nerve and the middle of the ME in the plane perpendicular and parallel to the tip of the ME; the distance between the TBM and the epicondyle in those 2 planes; and the maximal diameter of the ulnar nerve and the diameter orthogonal to this.…”

“…Earlier studies (e.g., Spinner et al ) pointed out the important role of the triceps brachii muscle (TBM) in the pathophysiology of ulnar dislocation. Recently, Kang et al demonstrated a high prevalence of (sub)luxation, and in this context observed that the distance between the ulnar nerve and the medial epicondyle (ME) was correlated with the distance between the margin of the triceps and the ME. However, the mechanism of luxation is not yet fully understood.…”