Muscle Activation Patterns in Snapping Triceps Syndrome

Boon AJ, Spinner RJ, Bernhardt KA, Ross SR, Kaufman KR. Muscle activation patterns in snapping triceps syndrome. Objective: To compare the muscle activation pattern in subjects with and without "snapping triceps syndrome" (dislocation of the medial head of the triceps and ulnar nerve over the medial epicondyle). Design: Controlled study. Setting: Biomechanics laboratory. Participants: Eight male subjects (9 elbows), with symptomatic snapping triceps and 9 male controls. Interventions: Not applicable. Main Outcome Measures: Activation pattern of the 3 triceps heads during active elbow extension at 0°, 45°, 70°, 90°, and 115° of flexion, recorded by fine-wire electromyography. Results: There were no significant differences between subjects and controls in the firing pattern of the triceps heads. The medial head fired first in 6 of 9 symptomatic elbows and in 7 of 9 controls at 90° of flexion, and in 6 of 9 elbows of both subjects and controls at 115° of flexion, positions where snapping typically occurs. There was no significant difference between the groups as to how often the medial head fired maximally. Conclusions: This study suggests the firing pattern of the triceps heads may not contribute to the pathogenesis of this syndrome. Rather, the authors believe the anatomic position of the medial head causes it to dislocate over the medial epicondyle, often resulting in ulnar neuritis.