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Clinical Application of Roll-on Sleeves for Myoelectrically Controlled Transradial and Transhumeral Prostheses

Wayne Daly, BS, CPO, LPO

ABSTRACT

This article describes six transhumeral and seven transradial prostheses that were successfully fit to patients using electrodes installed in roll-on suspension sleeves. This design maintained consistent electrode contact for all patients, especially those who had volume changes or who experienced difficulty with the traditional suspension methods. To provide improved suspension and electrode contact, metal electrodes and modified wiring systems were developed and tested along with techniques for installing electrodes in roll-on sleeves. This series of patients demonstrated that a roll-on sleeve is an excellent way to achieve superior suspension and greater range of motion.

Key Words: transradial, transhu-meral, myoelectric, roll-on suspension

Introduction

The goal of an upper limb prosthesis is to restore as much function as possible to the amputee. With the use of roll-on suction liners, the suspension and function of a myoelectric prosthesis can be greatly improved over traditional designs (Table 1 ). This article presents preliminary experience fitting six patients with six transhumeral (Table 2 ) and seven transradial prostheses (Table 3 ), all of which have subsequently shown improved suspension and function for these amputees. Ultimately, such increased function will benefit all wearers, but particularly those in high-demand occupations who have shown the lowest usage of conventional and myoelectric prostheses.¹

Much of the difficulty encountered with myoelectric fittings has been how to maintain suspension and yet still provide a consistent position of the electrode sites over the muscles for control of the prosthesis. The electrodes must maintain close contact with the skin and not shift as the person moves the prosthesis or else accurate control will be lost. With traditional suspension systems, fitting requires great care, a very stable limb volume, and sometimes uncomfortably tight areas in the socket. In this series of fittings, a roll-on suspension system was shown to provide a secure and comfortable attachment for the upper-limb prosthesis, just as it had in lower limb² and switch-controlled upper limb fittings.³

The polymer materials from which roll-on suction liners are made provide excellent suspension but will not conduct the myoelectric signal to provide control of the terminal device. Several methods have been proposed for using myoelectric control with roll-on sleeves, including cutting holes in4 and applying conductive posts through the liner.5 However, we found that cutting holes in the liner reduced the suspension capability of the liner proximal to the holes and caused discomfort for some patients because of the increased pulling on the distal end of the limb. We also found that traditional suspension methods had major drawbacks and that these methods were less successful in our facility than the described design. In our experience, the described method provided both enhanced suspension and improved myoelectric control for the prosthesis.

Description of the Roll-on Suspension System

After experimentation with many other liners, the Ohio Willow Wood (Mount Sterling, OH) Alpha liner was chosen for this system. The Alpha liner is different from most other roll-on liners because it is constructed of a thermoplastic material with a fabric covering. This fabric cover eliminates the need for a lubricant to don the liner and is easier for a one-handed individual to apply. The thermoplastic material also allows the shape of the liner to be customized. If an error in electrode placement is made, the holes can be "healed" with a heat gun or an adhesive to eliminate air leakage and loss of suspension. The material is also less likely to tear than other designs when the electrodes pierce the material.

Passing Myoelectric Signals through the Liner

When used with a myoelectric prosthesis, the difficulty with all other liners is how to pass the myoelectric signal from the skin to the electronics. With this system, metal electrodes pass through the liner and are connected to the myoelectric preamplifiers (preamps) with snap connectors and shielded cables (Fig. 1 ). At the present time, we are using two different designs for electrode snap connectors. One design is hand fabricated from modified Liberty Technology (Hopkinton, MA) ES-84 ground reference electrodes; the other design uses stainless steel or gold-plated clothing snaps. With the modified Liberty Technology electrodes, a 2-56 SAE screw is soldered to a male snap head, which then pierces the liner and provides the conductor to the shielded cable. In the second design, the clothing snaps have prongs that pierce through the liner; the heads provide the connection to the wires. Standard, shielded electrocardiogram cables or cables with snap heads (Part #503004) from Motion Control (Salt Lake City, UT) are used to conduct the signal to the preamps (Fig. 2 ). Otto Bock (Minneapolis, MN) is beginning to make available modified preamps (13E-125-60-liner), which will not need to be altered like the prototype designs shown in Figure 3 . Because they require no modification, Motion Control preamps could be used with transradial and transhumeral designs using the ProControl 2 or the U2 elbow system. Additionally, Liberty Technology electronics can be modified to accept the shielded cables used with this system.

Fabrication Method

Casting and electrode placement are determined as with any myoelectric system, then the electrodes are placed in the liner over the selected muscle sites (Fig. 4 ). The wires from the electrodes to the preamps are contained loosely between the liner and the socket, which is bulged out slightly over the electrode area to allow for their bulk. The preamps can be located at any convenient location in the prosthesis between the socket and the outer shell. If there is insufficient length for a shuttle lock, a Velcro lanyard strap will provide secure suspension with the liner (Fig. 5 ). The proximal socket shape is modified as usual to prevent rotation and to allow for a good range of motion. With the improved suspension from the suction liner, a greater range of motion can generally be achieved (without the loss of suspension) by opening up the proximal trim lines (Fig. 6 ). The remaining wiring and fitting procedure is the same as for a typical myoelectric prosthesis.

Possible Design Improvements

One possible evolution of this design would integrate the electrodes and wires by molding them into the liner and a connector, which could be included into the shuttle lock to decrease the wiring bulk and donning problems. Such a design would also allow for more than one distinct signal site per muscle group, allowing extra control functions that could provide optional control of hand or wrist functions using extra electrodes and control systems from more than the usual two control sites.

Conclusion

The described design has been used on 12 patients for periods of time ranging from 3 months to 2 years, and there have been few failures. However, the more active of these patients had wire and electrode failures at about 1 year intervals. Further research and design work need to be done to improve the durability of the electrodes and wiring used. Although the wires and electrodes are easily replaced, better durability would be desirable. The design presented in this article has proven successful for the 12 patients currently fitted with it. Not only has the design increased the comfort and function of these patients, it has also increased their suspension capability and range of motion over more traditional designs, which has lead to universally positive feedback from the wearers.

Acknowledgements

I would like to express my appreciation to T. Walley Williams III, for help in the preparation of this article and for presenting this design at the MEC-99 conference in New Brunswick, and to Harold Sears, for his assistance in reviewing this article.

References:

1. Silcox DH, III, Rooks MD, Vogel RR, Fleming LL. Myoelectric prostheses: A long-term follow-up and a study of the use of alternate prostheses. J Bone Joint Surg (Am). 1993;75:1781-1789.
2. Fillauer K. Experiences with Upper Extremity: 3-S Designs. In Proceedings of the American Orthotics and Prosthetics Association National Assembly, Washington, DC, October 11-15, 1994.
3. Vacek KM. Transition to a switch-activated, 3-S, transhumeral prosthesis: A team approach. J Prosthet Orthot. 1998;10:56-60.
4. Salam Y. The use of silicone suspension sleeves with myoelectric fittings. J Prosthet Orthot. 1994;6:119-120.
5. Laghi A, inventor. Conductive patch for control of prosthetic limbs. US patent 5 443 525, June 27, 1994.