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Surface-EMG

 

Surface electromyography for the evaluation of muscular co-ordination of patients with obstetric plexus lesion

 

Introduction

Patients with a lesion of the n. plexus brachialis frequently suffer from functional impairment of motion in the upper extremities. Causes for this can be the lesion of a specific muscle, the co-activation of antagonistic muscles or a mechanical blockage in the corresponding joint. Surface electromyography offers the opportunity of gathering information about the muscular co-ordination of single muscle groups beyond the pure visual assessment which is usual in clinical routine.

The EMG is derived from bipolar surface electrodes. The signals are normally preamplified at its site of attachment (Fig. 1). Sample signals for flexion/extension of the elbow joint are shown in Fig. 2. The motion of the arm and the EMG signals of the m. biceps brachii and m. triceps brachii are recorded.

 

Results

Figure 2 clearly shows the substantial changes between the healthy and the affected side. The recorded motion of the elbow joint reveals the degree of impairment. The cause for the restriction can be determined objectively and quantitatively by utilising the EMG recordings.

On the healthy side a clear alternation in activation can be observed between agonist and antagonist. In contrast, co-contractions of m. biceps brachii and m. triceps brachii are present on the affected side. Although the biceps of the impaired side shows a normal activation pattern, the EMG curve of the triceps shows, compared with the healthy side, a constant activation during the complete motion. This results in co-contractions and thus in restricted movement.

 

Discussion

Measuring muscular co-ordination thus provides the opportunity for an objective interpretation of motion beyond the possibilities of either a simple 2D-video analysis or a purely visual clinical examination. The presented procedure may have a major influence on therapy planning and the strategy used in surgical intervention. The approach is not limited to specific motions and can therefore be extended to various arbitrary movements in the upper extremity. Moreover this method can be applied to the treatment of other dysfunctions. This implies that patients with other types of impairments in motion could benefit from the presented procedure.

Fig. 1: Derivative of the action potentials of individual groups of muscles by means of preamplified bipolar EMG.

Fig. 2: Joint angle process and synchronously measured surface EMG with repeated inflection of the elbow joint.

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