Snapping Triceps

Principal Investigator: Andrea Boon, M.D.
Project Coordinator: Kathie Bernhardt— bernhardt.kathie@mayo.edu

Figure 1: Snapping triceps testing utilizes an isometric elbow strength dynamometer, and EMG system, and a uniaxial accelerometer (right medial elbow under white tape).

Dislocation (snapping) of the medial head of the triceps is usually seen in association with ulnar nerve dislocation but is often misdiagnosed, as only the ulnar nerve dislocation is recognized in the majority of cases. Transposition of the ulnar nerve alone in symptomatic elbow snapping does not result in resolution of symptoms if coexisting dislocation of the medial head of the triceps is not recognized and treated as well. We hypothesize that patients with snapping triceps have a pattern of muscle firing during elbow motion that differs from that of the normal population. It is our impression that this abnormal muscle firing pattern leads to hypertrophy of the medial head of the triceps.

The information from this study will be utilized to determine if there are abnormal patterns of muscle firing that can be recognized and used to treat snapping triceps. In turn, muscle retraining techniques may then be used to establish normal muscle firing patterns, restore muscle balance, and prevent future muscle dislocation and snapping. Using custom computerized isometric strength assessment equipment, the EMG activity of the major elbow flexor and extensor muscles will be assessed (Fig. 1). These seven muscles will be tested in resisted isometric elbow flexion and resisted isometric extension and flexion at five different positions.

A uniaxial accelerometer placed on the medial side of the elbow is used as an indicator to aid in determining when snapping occurred under test conditions. EMG data is collected simultaneously with accelerometer data to mark if, and when, muscle firing activity changes. The equipment for collecting the data along with a subject is shown in Figure 1.

Data has been collected on 8 symptomatic patients (9 elbows) and 9 asymptomatic controls. Data analysis is ongoing