Linda Saboe, B.P.T., M.C.P.A.
Judy Chepeha, BSc.P.T., M.C.P.A.
David Reid, M.D.,M.Ch.H., F.R.C.S.
Gary Okamura, M.D.
Michael Grace, Ph.D.,P. Eng.
The Glen Sather Sports Medicine Clinic, and the Division of Orthopaedics. The University of Alberta

Biofeedback training of the external rotators to centralize the humeral head in patients with anterior shoulder instability and/or pain.

Anterior shoulder instability and impingement are common athletic complaints associated with overuse, joint laxity, post-traumatic dislocation and muscle imbalance. While traditionally treated as clinically discrete entities, it is now accepted that considerable overlap exists between functional instability and anterior impingement. (1-3)

Until recently, rehabilitation programs have emphasized subscapularis strengthening on the assumption that this muscle provided an anterior buttress preventing anterior humeral head subluxation.(4-6) Turkel (1981) has demonstrated inability of the subscapularis to cover the anterior humeral head in abduction and external rotation(7), and Garth reports that internal rotation forces actually contribute to anterior displacement .(2) These findings provide an explanation for high failure rates of traditional rehabilitation programs.(8-11)

Jobe and Perrys' electromyographic work identifies the external rotators, and in particular, the infraspinatus, to be the primary dynamic anterior shoulder stabilizers in abduction and overhead motions. (12-14) This dynamic stability is provided by preventing forward motion of the humeral head in the glenoid fossa.

In 1988, a treatment protocol, utilizing single channel electromyographic biofeedback was developed; it has been continuously tested and enhanced through controlled clinical trials at the University of Alberta. This program utilizes targeted muscle feedback to perfect motor skills. By electronically monitoring and amplifying activity of the external rotators during an apprehensive motion, with immediate visual and auditory feedback to the subject, the performance is changed or shaped. This program which emphasizes muscle control rather than strength, requires motivation, training, and lifelong routines to maintain the established engram and control shoulder stability.

Using the MyoTracTM EMG Biofeedback System

The MyoTrac EMG single channel biofeedback unit is valuable in reinforcement of appropriate external rotator activity. Patients are provided with visual and auditory feedback of appropriate muscle activity. The unique MyoTrac probe amplifies the muscle signals at the pickup site thereby providing excellent sensitivity with no electrical interference.

Single Channel Biofeedback Treatment Program

1. Electrode placement is critical. Attach the sensor using the disposable triode electrodes below the scapular spine. DO NOT place it over the posterior deltoid as increased activity in this muscle would drive the humeral head anteriorly. The patient remains connected to the biofeedback unit during training, and must practice at home both with and without the unit. For home practice the therapist might wish to place an indelible mark on the skin for electrode placement.

2. To determine threshold and gain settings, have the patient flex the shoulder forward to 70º with the gain switch at x1, and turn the threshold control until the yellow LED illuminates. If the activity is greater than 10uV at 70º, set the gain setting to x10. Again have the patient flex the shoulder forward to 70º while turning the threshold control until the yellow LED illuminates.

3. Ensure the shoulder is in a pain-free neutral position, the switch is set to CONT, the volume is set at a pleasant level (with or without the earphone), and the threshold control and scale reading switch remain in the positions set previously in step 2. Instruct the patient to use visual and audio EMG biofeedback to increase EMG activity well above the yellow LED. This is done by tightening rotator cuff muscles in the neutral position in order to glide and hold the humeral head posteriorly (figure 3). This is a key component and must be successfully performed 100 times (ten sets of 10) prior to progressing to active movement. The use of many repetitions builds endurance. This procedure is quite fatiguing; it may require several sessions before the patient can progress to step 4.

4. With the threshold set at twice the value achieved in Step 2, instruct the patient to forward flex the adducted and neutral rotated shoulder to 90-100º, with elbow in flexion (figure 4). As the shoulder is flexed, have the patient tighten the rotator cuff and achieve the threshold setting between 70 and 90º trying to go as far towards the red LED as possible. If pain or a sense of subluxation is experienced, stop, rest and start again through a smaller arc of movement and/or with altered threshold settings. When the patient can successfully perform 100 consecutive repetitions, progress by altering the threshold and/or movement as outlined in (figure 6).

As the patient masters each level, progress through the following exercises:

a) Forward flexion with a straight elbow.

b) Forward flexion with increasing external rotation.

c) Abduction with flexion, progressing to elbow extension.

d) Abduction with elbow extension with increasing external rotation.

e) Abduction from flexion.

f) Abduction from flexion with increasing external rotation.

g) Reach for objects behind back or overhead.

When the above progression of increasingly difficult tasks have been completed, progress to the activities specific to the sport or position that caused difficulty. Break the movement down into component parts, and introduce catching or throwing activities in preparation for a gradual return to the sport (figures 7,8).

If general weakness exists, instruct the patient in appropriate progressive resistance exercises. Include pushups for serratus anterior with the arms adducted, and external rotation exercises resisted with surgical tubing or dental dam. AVOID resisted exercises which load in an impingement position (figure 5). All pain-free activities are allowed and encouraged. The patient will require two to three weeks of supervised physiotherapy, but must do a lifelong home program to maintain the engram. It might be desirable for patients to return for occasional brief refresher courses.

This program emphasizes muscle control. Strength acquisition is important, but secondary. Electrode placement is critical. The biofeedback program is physically and mentally demanding, therefore appropriate rest periods and encouragement must be provided. Slow and careful progression is usually necessary. Commitment by the therapist and client are required for the program's success.

References

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