Myoelectric Intervention For The Interscapulothoracic Amputee

Matthew Garibaldi, C.P.O.
University of California, San Francisco
San Francisco, California

The loss of upper extremity function following an interscapulothoracic amputation is unquestionably significant. Historically, the prosthetic rejection rate at this level of amputation has been high, due to reasons such as increased energy expenditure, increased weight, increased warmth, decreased socket comfort, poor suspension, and inadequate function. This paper proposes a seven-step prosthetic treatment protocol that has been successfully implemented in several interscapulothoracic cases at the University of California, San Francisco (UCSF). The protocol being introduced includes the initial evaluation, preprosthetic training, component selection, socket design, alignment and construction, customized programming, and initial training with the prosthesis.

Figure 1

The initial evaluation is paramount to a successful prosthetic outcome. A patient's past prosthetic history must be taken into consideration, so not to repeat previously failed prosthetic attempts. Also, if a patient has developed strong proficiency with a particular style of prosthesis it is unlikely that they will adapt easily to a new treatment protocol. During the soft tissue evaluation the clinician can assess the overall presentation of the remaining structures, such as bony prominences, quality of skin coverage, adherent tissue, and skin sensitivity (Fig. 1). This is important when choosing appropriate areas of socket contact and weight bearing. Next, careful palpation of the remaining muscle bellies is accomplished by having the patient move the residual segment through various motions, such as elevation, depression, protraction, and retraction. Any muscle contraction should be noted along with the corresponding motion required to produce the contraction. Myoelectric site testing is then implemented to evaluate muscle strength and electromyographic (EMG) signal potential (1). The main objective during this portion of the evaluation is to isolate two independent EMG signals that can be utilized for functions of opposing nature. When testing, the electrode should be placed in the direction of the muscle fibers. Given the uncertainty of muscle orientation following an interscapulothoracic amputation it may be necessary to alter the position of the electrode several times in order to achieve the most optimal EMG signal. In being cautious to avoid undesirable co-contractions it is recommended that antagonistic muscle groups be utilized. Commonly used opposing muscle groups at the interscapulothoracic level are pectoralis major in combination with either trapezius, levator scapulae, or rhomboid muscles. Occasionally, serratus anterior can be combined with either trapezius or levator scapulae. Finally, an evaluation of the contralateral upper extremity is performed. Adequate range of motion and strength of the sound side extremity is an important factor when considering how a patient will don, doff, and manually manipulate the prosthesis.

Preprosthetic training in many cases can determine what type of long term prosthetic outcomes the patient should expect. For this reason, the final prescription is often not formulated until the completion of the training period. During this time therapeutic intervention is of utmost importance in preparing the patient to use the prosthesis. Therapeutic goals at this stage are aimed at desensitizing the residual segment and performing strength training exercises focused on isolating specific muscle groups (1). The patient should be reassessed by the prosthetist several times during the preprosthetic training period to evaluate progress. This can be accomplished with the aid of a volt meter or myotester (2).

Figure 7

Figure 6

One of the most common reasons of prosthetic rejection is due to the overall lack of function and responsiveness of the device. For this reason, it should be the goal of the prosthetist to supply the patient with the most appropriate, high-functioning, componentry available. Although each interscapulothoracic case at UCSF has a unique clinical presentation, the component selection in all cases is fairly similar. We have found that patients who begin their rehabilitation process with more remedial prosthetic designs, such as body-powered or hybrid systems, become quickly frustrated and have experienced a much delayed rehabilitation compared to those who begin with fully electric systems. This finding is unique to interscapulothoracic amputees because their overall functional envelope is greatly reduced. Thus, component selection for the interscapulothoracic amputee is largely based on but is not exclusive to EMG signal generation of the residual segment and scapular protraction range-of-motion (ROM) of the contralateral upper extremity. The patient should be able to produce two independent and opposing, high to mid-level, EMG signals which are used for terminal device and wrist rotator activation. If they are able to co-contract voluntarily the patient will be able to utilize the elbow and terminal device simultaneously without requiring an external switch. The patient should also have at least 5° degree of sound-side scapular protraction ROM to activate a proportionally controlled linear device. This is used for control of the electric elbow and should be incorporated into the harness (Fig. 6). Finally, a shoulder joint with free motion, and the ability to lock in any desired position is highly indicated to increase the patient's functional envelope (Fig. 7). It also allows the patient to have a natural reciprocation of the arms during gait.

Figure 5

Figure 2

Until the advent of Microframe and XFrame socket designs, interscapulothoracic prosthetic wearers complained of the weight of the prosthesis, excessive heat, instability, donning and doffing difficulties, and reduced control of the terminal devices (1). However, due to the complete absence of the shoulder girdle, we have found that slight modifications to these designs have been necessary to improve suspension of the prosthesis. We have utilized the superior slope of the residual segment as a primary weight bearing region (Fig. 5) and extended the distal trimline to 4 cm proximal to the inferior rib margin. What this has afforded our patients is a solid weight bearing region proximally which reduces the need to excessively tighten the harness, and an extended trimline distally to minimize proximal socket gapping and distal-lateral rib pressures. Prior to casting, draw a rough outline of what your socket shape will look like. The chosen areas with the highest EMG signal output should be within your trimlines. The casting procedure is crucial in obtaining the most anatomically accurate representation of the patient's residual segment under load (Fig. 2). This is accomplished by compressing the patient anteriorly, posteriorly, and proximally. It is recommended to have the patient lean into the cast slightly so not to cause them loss of balance when applying force. For more accurate results two clinicians should be used to perform this procedure. Care should be taken not to create an overly compressed anterior-posterior dimension which may impede the patient's ability to don the prosthesis independently. If an accurate cast is taken, very little model rectification is done for this level. The test socket should be fit with a temporary harness system and run through a series of loading exercises; i.e. vertical loading, and anterior-posterior loading. The socket should be evaluated for loss of contact, excessive localized pressure, and overall comfort. Any necessary socket modifications should be made at this time. It is indicated to remove any excessive material from the socket that does not appear to aid in control or weight bearing of the socket on the residual segment. Insert the electrodes into your socket and reevaluate the EMG signal output. This should be done with and without load, and in both sitting and standing. The EMG signal output should be consistent under all conditions, and transient signals should not occur when changing positions.

Figure 4

Figure 3

When approaching the construction of the prosthesis the patient should have the test socket donned using a temporary harness. A final harness can be constructed using soft, durable, and hygienically pleasing materials. The height of the shoulder joint should be aligned with the patient standing and should be no higher than that of the contralateral acromion (Fig. 3). The anterior-posterior dimension of the shoulder alignment apparatus should be shaped with the patient sitting which allows you to sight down the patient and shape the alignment apparatus according to that of the contralateral shoulder girdle (Fig. 4). The final joint position should be abducted and internally rotated approximately 10° to help facilitate midline activities. Once the shoulder joint and alignment apparatus are properly secured to the test socket a humeral section is shaped and fastened to the down bar. The distal end of the humeral section, which connects to the turntable of the elbow unit, should be outset enough to clear the hip during swing. The length of the humeral section is determined by measuring the distance between the acromion and the olecranon on the sound side extremity. This measurement is taken with the elbow bent and replicated on the involved side. The length of the forearm is determined by measuring the distance of the sound side lateral epicondyle to the distal end of the thumb. The forearm section is cut to length to replicate this measurement. Once the terminal device is temporarily fastened into place, the length and alignment of the prosthesis is given a final evaluation.

Programming the prosthesis is accomplished by using software dedicated to the selected components. Initially, it is suggested to set the system in a sequential control format so to familiarize the patient with each of the components independently of one another; i.e. hand, wrist, and elbow. This is accomplished by using the proportionally controlled linear device to switch between each component. The selected component is then activated using the two electrode sites. Once the patient has shown some proficiency with each component the system can then be set to a simultaneous control format. Generally the flexor group is dedicated to closing and pronating the hand, and the extensor group is used for opening and supinating the hand. This setting can be changed at the patient's request. The patient should be able to co-contract between hand and wrist, however, software adjustments may be necessary to help facilitate this. The proportionally controlled linear device is now responsible for flexing and extending the electric elbow which can be done simultaneously with hand or wrist activation.

The initial training period is the final step of this treatment protocol. Following controls training the patient is required to activate the hand, wrist, and elbow at a controlled rate prior to delivering the prosthesis. Should they have any difficulty, changes can be made via the software. They are also instructed how to don and doff the prosthesis, power the device on and off, and how to properly charge the arm. Following the initial training period the patient is ready for postprosthetic training with a qualified therapist which includes functional operation and activity-based training. (2).

References

  1. Meier RH, Atkins DJ. Functional Restoration of Adults and Children with Upper Extremity Amputation. 1st ed. New York: Demos Medical Publishing, 2004: 240-244.

  2. Carroll K, Edelstein JE. Prosthetic and Patient Management: a comprehensive clinical approach. 1st ed. New Jersey: SLACK Incorporated: 164, 170.