Bilateral Upper Limb Prostheses

Jack E. Uellendahl CPO

Jack E. Uellendahl or an immediate family member serves as a paid consultant to or is an employee of Hanger Clinic and has stock or stock options held in Hanger Clinic.

ABSTRACT

After a bilateral upper limb amputation, the ability to perform basic and routine tasks, such as eating and self-care, becomes difficult or impossible without assistance. The goal of prosthetic rehabilitation for a patient with a bilateral arm amputation is to enable the individual to achieve functional independence and to successfully participate in vocational and recreational pursuits. Subtle details of socket fit, control system configuration, and suspension can sometimes mean the difference between success and failure. Success relies on selecting the most appropriate components, matching those components with optimal control sources, and interfacing them with the human body in a comfortable and functional manner. Equally important is the user’s dedication and motivation to succeed in the face of adversity.

Introduction

Bilateral upper limb amputation is a profound loss for an individual. The ability to perform basic and routine tasks, such as eating and self-care, becomes difficult or impossible without assistance. Prostheses and other assistive devices can enable the users to regain a measure of their lost ability to manipulate objects and allow them to successfully accomplish a variety of tasks. However, replacement of the many exquisite features of the physiologic hand is not yet possible. Even simple tasks require an amazing amount of complex manipulation. For example, these words were typed using 10 fingers working in concert. Each finger performs both independent and coordinated simultaneous functions, relying on sensation and precise positioning to accurately produce the intended result. These abilities often are taken for granted until they are lost.

The goal of prosthetic rehabilitation for the bilateral arm amputee is to enable them to achieve functional independence and successfully participate in vocational and recreational pursuits. Although bilateral arm prostheses restore only a small amount of the lost functionality, users are able to perform many activities that otherwise would be impossible.¹^,² Recent data have confirmed the earlier observations that individuals with bilateral upper limb amputation are more likely to use one or more prostheses than their peers with a single upper limb amputation, with more hours of daily use. Subtle details of socket fit, control system configuration, and suspension can sometimes mean the difference between success and failure. Unlike a patient with a unilateral arm amputation, a patient with a bilateral arm amputation does not have the option of compensating for the inadequacies of a prosthesis by using their intact physiologic arm.³ Every detail of prosthetic design should be optimally accomplished. Because of the inability to duplicate the diverse and complex functions of the human arm, prosthetic systems should be viewed as tools with different components best suited for different applications. Success relies on selecting the most appropriate components, matching those components with optimal control sources, and interfacing them with the human body in a comfortable and functional manner. Equally important is the user’s dedication and motivation to succeed in the face of adversity.

Patient Evaluation

Because of the complexity of bilateral upper limb loss and the fluid nature of the early rehabilitation period, a thorough evaluation of the new bilateral arm amputee should take place over a period of time. Most individuals who sustain bilateral upper limb amputations have experienced a traumatic injury and have additional medical comorbidities beyond limb loss. Ideally, a team of experienced professionals should work together to address the many challenges facing the new amputee. The treating or consulting professionals may include an orthopaedic surgeon, a physiatrist, a prosthetist, an occupational therapist, a physical therapist, a psychologist, a nurse, and a social worker. In addition, the access to peer support is an invaluable adjunct to the care and treatment provided by medical professionals. The
patient, as the center of the team, will ultimately determine several aspects of their own care, including which type of prosthesis is preferred.

FIGURE 1 A, Photograph of an individual with a bilateral congenital upper limb absence who has developed remarkable dexterity and manipulative foot function. B, Photograph of a man with acquired bilateral upper limb loss. Adults usually do not develop remarkable foot function but may find foot use an efficient alternative to prosthetic function for tasks away from the body.

Factors that affect the selection of the prosthetic component and control scheme include cognitive level, mechanical aptitude, family life, occupation, hobbies, and self-image. Residual limb length, strength, and range of motion of the upper limbs, including scapulothoracic motion, should be evaluated. These factors have direct implications regarding the method of fitting the prosthesis. The general strength and flexibility of the lower limbs should be assessed. With more proximal amputations, foot use should be encouraged, with training dedicated to exploring and developing the manipulative capabilities of the feet (Figure 1). Alternatively, individuals with comorbid lower limb involvement may need to use their upper limb prostheses to hold and transfer weight through an assistive device (Figure 2). At the conclusion of the initial evaluation process, a defined plan should be in place regarding the prosthetic component selection and control. However, the team should also be flexible and open to change throughout the rehabilitation process. It should be expected that the prosthesis configuration will change over time in response to the changing needs and abilities of the user.

Throughout the evaluation process, the prosthetist should consider the advantages and disadvantages of various component and control options as they relate to the specific individual. To give structure to this evaluation process, it is useful to understand the attributes of the ideal prosthesis and then compare those attributes with available technologies.

The ideal prosthesis would restore the appearance and function of the lost limbs and control would be intuitive and subconscious. The ideal prosthetic prehensile device would be a lightweight, durable hand that is capable of manipulating a wide variety of objects that differ in size, shape, and texture. The characteristics of the objects would be related back to the user through a sensory feedback system. Proprioception regarding the speed of prosthetic movement, the force exerted, and the position of the prosthetic device would be inherent.

Currently available, state-of-the-art prostheses and prosthetic prehensile devices fail to meet all of these criteria. However, considering the needs and priorities of each individual and comparing these against the attributes of each prosthetic component and control scheme will help achieve optimal use of current technology.

Although this chapter primarily focuses on the treatment of adult amputees, many of the concepts may have application for the treatment of children. However, because of their small size and often immature cognitive ability, children cannot be treated as small adults. Pediatric cases are characterized by decreased force and excursion and a lower tolerance for weight and prosthesis complexity. Congenital bilateral limb deficiency is very rare, and the issues regarding prosthetic fitting can be quite different from those of adults. Children will often learn to use their feet with remarkable dexterity to augment their manipulative capabilities⁴ (Figure 3).

FIGURE 2 Photograph of a patient who needs an assistive device for ambulation. The design of the upper limb prosthesis should take into consideration how to best hold the assistive device and comfortably distribute the pressure of partial weight bearing through the upper limbs.

FIGURE 3 Photograph of a young boy with acquired bilateral very short transhumeral amputations demonstrating the superior manipulative function provided by his sensate feet as he stabilizes the object with his prosthesis.

Staging of Care

In all patients with an arm amputation, whether unilateral or bilateral, it is advisable to fit the prosthesis as soon as possible, preferably within the first 30 to 90 days. The period of 30 days after amputation has been referred to as the golden fitting period for upper limb prosthetic devices, leading to optimal acceptance and usage.⁵ There are many advantages to early postoperative fitting, including decreased edema and pain, accelerated wound healing, improved patient rehabilitation, decreased length of hospital stay, increased prosthetic use, maintenance of some continuous type of proprioception input through the residual limb, and improved patient psychological adaptation to amputation.⁵ In patients in whom other injuries or other complicating factors make fitting within the golden period infeasible, it may be necessary to delay prosthetic use. In many patients, one side may be ready to fit before the other, and it is advisable to do so. Initially, providing a prosthesis on one side only is often desirable.

Prosthetic training should begin using a component configuration and control scheme that is as simple as possible to prevent the patient from experiencing gadget overload. This is especially true at higher levels of amputation where the possibility exists for multiple dynamically positioned components on each limb. In these cases, it is advisable to introduce new components sequentially, allowing time for the user to become accustomed to each new device before increasing the overall complexity of the prosthesis.

Given the dynamic nature of prosthetic rehabilitation of the bilateral arm amputee, it is useful to develop short-term and long-term goals. As the skills of an amputee develop, their medical condition stabilizes and priorities change in response to the challenges of daily life. The optimal prosthetic device, usage pattern, and individual preferences also may change. It is reasonable to expect that this process will take 6 to 12 months, depending on the level of limb loss, the extent of other complicating factors, and the speed at which an individual adapts. A prototype prosthesis is valuable during this period because it will allow the amputee and the rehabilitation team to evaluate various prosthetic systems before deciding on a definitive prescription (Figure 4).

Short-term goals will generally focus on mastering use of the prosthesis for basic daily functions, including donning the prosthesis, eating, and toileting. Long-term goals may include dressing, vocational skills, and avocational pursuits. During this period of experimentation, it is recommended that the amputee spends most of their time at home, returning to the rehabilitation facility periodically for prosthetic modifications and additional training. This allows the user to determine which prosthetic configurations work best in real-life situations and identify specific problems that need attention during the next consultation with the rehabilitation team. It is reasonable to expect that complete independence will be achieved by nearly all patients, except those with the loss of both limbs at or above the transhumeral level or in patients with other limiting factors. However, even some bilateral transhumeral amputees are able to attain complete independence in accomplishing daily tasks.

FIGURE 4 Photograph of a patient with prototype prostheses that allow her to experience the use of various components before implementation in the final design. Prosthesis alignment, length, and other parameters can be evaluated and optimized during this stage of the fitting.

Socket Design

Generally, socket designs for the bilateral amputee do not differ from unilateral designs. However, because of the absence of both hands, it is necessary to consider the donning ease and the positioning flexibility of the prosthesis. Positioning flexibility includes the range of motion of the intact physiologic joints when a prosthesis is worn and, in some instances, the ability to reposition the prosthesis in useful ways at the limb-socket interface to increase the scope of functional use (Figure 5).

Although the socket may not be completely self-suspending, the interface should fit snugly and work with the suspension system to provide a prosthesis that feels firmly connected to the user. This intimate fit will afford optimal positioning control of the prosthesis and minimize its perceived weight. In both body-powered and electronically controlled systems, the socket is the foundation of the prosthetic system; any shortcomings will substantially affect the successful use of the prosthesis. Ineffectual motion
should be minimized so that when the residual limb begins to move, the prosthesis will move.

FIGURE 5 A patient’s functional envelope can sometimes be expanded by repositioning the prosthesis on the limb. Photograph of a man retrieving his wallet from his back pocket, which requires operation of the prosthesis hook behind his back.

The materials used in the construction of a prosthesis are an important consideration. For example, carbon fiber and other composite materials provide a strong and lightweight prosthesis.

Custom-made silicone sockets provide improved comfort for all levels of upper limb prostheses users compared with previous construction materials. These sockets are made of high-consistency rubber (HCR) silicone, which has several advantages over the rigid and flexible plastics previously used for socket construction.⁶ Because HCR silicone is very flexible and elastic, it facilitates greater range of motion as the material bends and stretches with limb movement (Figure 6). However, the tackiness of HCR silicone can complicate donning, and this should be taken into consideration.

Transradial Sockets

Patients with transradial amputations who use body-powered control will often benefit from flexible hinges because they allow the amputee to retain physiologic forearm rotation. When self-suspension is desired, supracondylar sockets such as those typically used for myoelectric control, and to a lesser extent, for body-powered control, are generally best donned by pushing the residual limb into the socket. The Northwestern University self-suspending socket⁷ offers particular advantages for bilateral transradial fittings in which supracondylar suspension is desired because it tends to offer good range of motion at the elbow and is easily donned by pushing in. The Northwestern socket can be modified with a cutout over the olecranon, which reduces heat buildup and improves appearance, especially when the elbow is extended.⁸

FIGURE 6 Clinical photographs of a patient wearing a shoulder saddle. A, A custom, high-consistency rubber silicone socket with an integrated shoulder saddle provides good suspension and socket stability. B, The patient, who has quadriplegia, uses a hybrid myoelectric transhumeral prosthesis with an integrated silicone shoulder saddle.

Socket designs that require the limb to be pulled in are generally avoided because of the obvious difficulties presented by bilateral upper limb loss. However, in rare instances when pulling in is considered necessary, the use of a nylon donning bag has proved an effective tool and can be used independently by some patients.

Transhumeral Sockets

The socket for a transhumeral prosthesis should provide for close coupling of the residual limb and the prosthesis to maximize prosthetic function. Because the ideal socket design should cause little or no restriction of intact joint motion, open shoulder designs are preferred because they allow relatively free range of motion at the shoulder joint, especially when sufficient residual limb length remains.⁹ Another option for transhumeral socket design is the half-and-half socket.¹⁰ This socket uses a flexible silicone proximal section that is fitted over the shoulder region and is fabricated as an integral part of a distal inner flexible socket. The deltoid area is cut out laterally, providing improved flexibility and air circulation within the socket. The rigid external frame of the socket extends from the axilla level distally (Figure 6). Another option similar to the half-and-half socket is the flexible shoulder suspension system in which a strip of spandex-backed neoprene (or similar material) replaces the silicone saddle and is attached to the wings of the standard open shoulder socket.³

In contrast, closed shoulder designs are best used for short residual limbs where insufficient leverage exists to use the full range of physiologic shoulder motion. The closed shoulder socket offers good stabilization of the prosthesis on the user and a convenient and secure anchor point for the lateral suspension strap of the harness.

Shoulder Disarticulation Sockets

Designs for a shoulder disarticulation interface require sufficient surface area to effectively stabilize the prosthesis on the amputee. Because of the length of the lever arm of the prosthesis and the weight of the components, there is a strong tendency for rotation at the prosthesis-user interface, especially as the terminal device is moved away from the body. Therefore, the socket perimeter should extend sufficiently on the torso to resist these forces.¹¹ A frame-type socket allows for stabilization and heat dissipation while minimizing weight. If body-powered control is used, the frame should capture as much body motion as possible, particularly biscapular abduction. Any lost motion will reduce the function of the prosthesis.

If the components are controlled myoelectrically, the generation of control signals may create incidental shoulder motion that could displace the socket and
allow electrode movement. In such cases, it may be advantageous to allow the shoulder to move independently within the frame. The weight of the prosthesis can serve to anchor the frame to the user while allowing the use of shoulder motion to activate various electronic inputs.

Several shoulder disarticulation frame designs are currently used. When designing a frame for a particular individual, the prosthetist should consider control sources, harness attachments, and shoulder joint mounting as well as design objectives. These design requirements will dictate the optimal frame geometry for a particular individual.

Harnessing

Conventional harnessing serves the dual role of suspension and control of a body-powered prosthesis. In designing a harness system for the bilateral arm amputee, it may be useful for the prosthetist to consider suspension and control separately. Harness requirements are altered when electrically powered components are used or when the socket design provides suspension. Either or both of these situations can lead to a simpler harness design that can be worn less tightly, potentially making the harness more comfortable.

In situations in which bilateral prostheses are harnessed together, each prosthesis serves as the anchor point for the other. When both prostheses rely on the harness for control, inadvertent cable excursion (sometimes referred to as cross-control) becomes a potential problem. One solution to cross-control is to provide a fully body-powered prosthesis on one side and a fully electrically powered prosthesis on the other side so that the control motions affect only the intended device.

In some instances, a socket may be fitted to provide an anchor for the contralateral prosthesis (Figure 7). For example, in the shoulder disarticulation/transhumeral combination, the side of the shoulder disarticulation might be managed with a frame-type socket or passive prosthesis to provide a firm anchor for suspension and control of the transhumeral prosthesis. These options can be shaped to provide aesthetic shoulder symmetry.

FIGURE 7 Photograph of a patient with a shoulder level and transhumeral limb absence. In some instances, the user may prefer to activate only the more dominant transhumeral prosthesis. The passive shoulder level prosthesis then serves as an anchor for the control harness.

The patient with a bilateral transradial amputation who uses body-powered control will generally be fitted with a standard figure-of-8 harness, which typically incorporates a ring at the cross point for free movement of the straps, with flexible hinges and a triceps pad. Compared with the unilateral figure-of-8 harness, the bilateral version eliminates the axilla loop, which frequently causes discomfort. This type of harness is well tolerated by almost all patients and is easy to don and doff independently. At the transradial level, bilateral myoelectrically controlled prostheses typically require no harness.

Similarly, a bilateral transhumeral amputee wearing body-powered systems will usually be fitted with a figure-of-8 harness with or without a ring. If cable excursion is limited, it is advisable to use a harness design without a ring to limit any loss of motion that may occur when the harness straps rotate on the ring during use. Either a sewn configuration or a leather pad may be beneficial to direct the control attachment straps more inferiorly on the scapulae and increase the available excursion (Figure 8). Alternatively, a cross-back strap can be used to keep the control attachment straps low on the scapulae. This also can be accomplished with a dual-ring type harness, with two rings fixed to each other by a strap, one inferior to the other (Figure 9). Harness configurations for mixed-level fittings must use sound principles for prosthesis stabilization, suspension, and control (Figure 10).

FIGURE 8 Photograph of a patient wearing a harness with a leather pad that is used to replace the cross point of the webbing harness. This design spreads the load over a larger area and helps position the control attachment straps lower on the back.

FIGURE 9 Photograph of a patient with a bilateral transhumeral amputation wearing a prosthesis with a double ring harness that increases available excursion by positioning the control attachment straps lower on the scapulae.

Components

Terminal Devices

The new bilateral upper limb amputee will likely express a preference to be fitted with prosthetic hands because of the assumption that available
technology can replace the function and appearance of the physiologic hand. Unfortunately, most body-powered hands are mechanically inefficient and are not useful to the bilateral amputee. If hands are desired, electrically powered hands are generally indicated, although such hands provide little or no proprioceptive feedback.¹² The advantage of electrically powered prehensile devices is a high grip force that can be sustained without continued control input. Multifunctional hands offer a wider variety of grip patterns and hand postures that some bilateral prosthesis users have found useful (Figure 11). Most bilateral amputees fitted with electrically powered hands will also benefit from the use of interchangeable electric hook prehensile devices (Figure 12). This option allows the amputee to choose which device is best suited to accomplish specific tasks.

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