Upper limb prosthetics

Author(s): Alberto Esquenazi, MD, Daniel Moon, MD

Originally published:09/20/2014

Last updated:09/20/2014

A. Overview and description:

In 2005, an estimated 540,000 individuals in the United States were living with an upper limb loss, of which approximately 40,000 were amputations above the wrist.1The most frequent causes are trauma, vascular complications of disease, and cancer. Upper limb amputations can occur at the forequarter (interscapulothoracic), shoulder, transhumeral, elbow, transradial, wrist, transcarpal, transmetacarpal, and transphalangeal level. The most common major upper limb amputation is at the transradial level, which accounts for over half of all major arm amputations.2,3 Prosthesis is the primary treatment of disability as a result of amputation in an effort to restore functional independence and improve quality of life.

Time is of the essence when dealing with upper limb amputation and prosthetic restoration. Delay in initial prosthetic fitting and training is a major factor for prosthetic rejection/abandonment.4 Therefore, the amputee rehabilitation program should ideally begin prior to amputation.5

B. Relevance to clinical practice:

Prosthetic prescription

Factors to consider when selecting prosthetic components are amputation level, residual limb geometry, sensation, range of motion, strength, cognition, vocation, hobbies, importance of cosmesis, financial resources available, and environment and weather. Collaboration between the patient and physiatrist-led rehabilitation team should be in place at the time of prescription. Major components of upper limb prostheses include the terminal device (TD), interposing joints, socket, suspension, and control system.

Control system

Prostheses can be controlled using body-powered, externally powered, or hybrid control systems. Body powered systems use body movements to control a TD and/or elbow. Advantages include durability, reduced cost, and weight compared with other systems. They also offer some proprioceptive feedback to the user.

Externally battery-powered systems may use electric switches or myoelectric signals for control. Electric switches can be activated by residual limb movements within the socket or by other body parts. Myoelectric systems use electromyographic (EMG) signals generated during muscle contractions. They provide digital or proportional control. With digital control, the system triggers an on/off signal regardless of the intensity of the electromyography. With proportional control, the motor action is proportion to the EMG signal amplitude allowing for variable speed and force. Externally powered systems reduce the need for harnessing and require less movement for activation, but they are heavier, expensive, and require more maintenance than body-powered devices.

Hybrid control systems combine body and external power control in an effort to balance weight, cost, and cosmesis and accommodate different anatomic levels.

Terminal device

The current level of prosthetic technology is far from replacing the versatility and coordination of the human hand. Prosthetic TDs include passive, body-powered, and externally powered hooks and hands. Passive TDs are used primarily for cosmesis.

Prosthetic hands provide 3-jaw chuck pinch, and hooks provide the equivalent of lateral or tip pinch. Body-powered control allows for voluntary opening (VO) or voluntary closing (VC) of the TD, but not both. VO devices are maintained in the closed position by rubber bands or springs. VC devices are maintained in the open position and close when tension is applied through a cable connected to a harness. VC TDs are capable of applying more force, but VO TDs are more practical because tension does not need to be maintained when holding objects.

Externally powered TDs can have digital or proportional control and can open or close as desired and offer the advantage of higher grip force. Newer devices have individual multijoint finger articulation.

Prosthetic wrist

The lightest and simplest prosthetic wrist is a friction control unit, which permits passive pronosupination of the TD but can rotate when lifting heavier objects (eg, a plate of food). A locking, quick disconnect wrist allows locking in the desired pronation/supination position and rapid interchange between different TDs. Spring-assisted wrist flexion is helpful to bilateral amputees to permit midline reach for activities of daily living (ADLs). They may also benefit from spring-assisted wrist rotation.

Externally powered wrist units are prescribed primarily for bilateral transhumeral or higher levels of amputation. Some wrists are capable of 360˚ rotation, which can be used for key turning or operating a screwdriver.

Prosthetic elbow

Body-powered elbows can have spring-assisted flexion. External mounted elbows are indicated for elbow disarticulations in attempts to maintain optimal proportional arm length. Passive and body-powered elbows have a locking mechanism that can be activated with the contralateral hand, chin, or ipsilateral shoulder. When used with a body-powered TD, the elbow must be locked in order to operate the TD.

Externally powered elbows can be controlled with a switch or myoelectric control. Internal and external rotation can be provided with a rotating turn table, which enables midline reach.

Prosthetic shoulder

Most shoulder joints allow passive abduction and flexion through a bulkhead or universal joints with the desired position maintained by friction, chin control, or electric lock. However, there is increased risk of nonuse because of a combination of weight, diminished overall control across multiple joints, and increased effort with shoulder or forequarter amputations. Powered shoulders with electronic controls are in development.

Prosthetic socket

Most upper limb prosthetic sockets are double layered and composed of external carbon graphite or rigid plastic materials to which the necessary prosthetic components are attached. The inner socket is fabricated from a cast of the patient’s residual limb and can be constructed of a flexible plastic. Windows can be cut in the outer socket to allow for inner socket expansion. Although more costly to fabricate, the frame design allows for inner socket replacement to accommodate residual limb volumetric changes.

Suspension system

The major suspension types are harness, anatomic, friction, and suction suspension. Socks can be used in most suspension systems as an interface between the residual limb and socket to accommodate for physiologic volume changes that occur during the day and protect the skin and improve hygiene. Socks cannot be used in suction suspension because these require direct skin to socket contact.

The harness suspends the prosthetic device to the body while providing body-powered control. A figure 8 harness is commonly used for transradial and transhumeral amputees. A harness loops around the contralateral axilla to anchor the suspension and control cables. A chest strap is an alternative for those who find the axillary pressure uncomfortable. A shoulder saddle with a chest strap can be used in more proximal amputations and for those who do heavier lifting.

A cable connected to the harness allows transmission of body power for prosthetic control. A cable used to activate a single prosthetic component is called a single-control cable or Bowden cable system. A dual-control cable system uses one cable to control two prosthetic functions (eg, flexion of the elbow, activation of the TD). This is accomplished by passing a single cable through two separate sections of cable housings (fair lead cable system). In transradial and transhumeral amputations, biscapular abduction and/or humeral flexion control elbow flexion and/or the TD. However, the elbow must be locked for activation of the TD in transhumeral amputations. In order to lock or unlock the elbow, shoulder depression, humeral abduction, and humeral extension are performed simultaneously. Patients with shoulder disarticulation perform biscapular abduction to control the elbow and TD with scapular elevation to lock the elbow.

Anatomic (self-suspension) systems use bony prominences for suspension encasing the medial and lateral epicondyles, with some loss in terminal elbow range of motion. The supracondylar (Müenster or Northwestern) suspension is used with transradial amputations and some wrist disarticulations. A figure 9 harness can be incorporated for TD control only. This suspension works well with externally powered prostheses and is less restricting when flexible materials are incorporated in the design.

Silicone sleeves provide suspension by creating negative atmospheric pressure and an adhesive bond to the skin. The sleeve also protects the skin by reducing shear forces and cushioning. Therefore, it is useful when the skin is delicate because of scars or injury. It is easily donned with one hand and allows for some residual limb volume change accommodation. There is often a distal attachment pin that interfaces with a shuttle lock mechanism built into the socket. After spraying the external surface with lubricating fluid, the patient rolls the sleeve directly over the skin. Once in place, socks can be applied to improve fit. Disadvantages to this suspension are that excessive perspiration and skin irritation can occur, which limit their use in warm and humid weather.

Suction suspension is preferred for transhumeral amputees with externally controlled devices. The patient dons the socket using a pull sock or lubricant fluid with a 1-way valve to allow for expulsion of air to create negative pressure. For this system to work well, it requires intimate fit between the residual limb and socket to create a tight seal; therefore, the limb volume should be stable with minimal surface irregularities.

Expected functional outcomes Realistic goals for most unilateral transradial and transhumeral amputees are independence in all ADLs, household activities, and driving. Some limitations regarding work and household chores may be necessary, especially when dealing with the handling of delicate, heavy, or voluminous objects. Bilateral amputees should be able to perform most ADLs and household activities after assisted donning of the prosthesis. They may also drive with a spin ring and perform some sedentary work with environmental modifications.

C. Cutting Edge/Unique Concepts/Emerging Issues:

Concepts being developed are prosthetic hands with independently powered finger movements, targeted muscle reinnervation, osseointegration, neural prosthesis interfaces, and incorporation of tactile feedback.6,7 Improvement in power supply, sensors, and newer materials and reduction in the size and weight of motors should allow for further improvement in prosthetic manufacturing. The advent of 3-dimensional printers should result in potential customization of prostheses. Direct brain computer interface in the near future should improve the control strategies for these devices. Cost and limited number of potential users remain a major limiting obstacle.

D. Gaps in Knowledge/Evidence Base

Most upper limb amputees have the potential to return to work. However, the evidence describing the incidence of return to work and vocational modifications after amputation is sparse. In addition, studies measuring functional outcome of upper limb amputees are limited.8,9Overuse injuries and phantom pain in amputees are other areas that warrant further investigation.10

REFERENCES

1. Ziegler-Graham K, Mackenzie E, Ephraim P, et al. Estimating the prevalence of limb loss in the United States: 2005 to 2050.Arch Phys Med Rehabil.2008;89:422-429.

2. Glattly H. A statistical study of 12,000 new amputees.South Med J.1964;57:1373-1378.

3. Kay H, Newman J. Relative incidence of new amputations: statistical comparisons of 6,000 new amputees.Orthot Prosthet.1975;29:3-16.

4. Malone J, Fleming LL, Roberson J, et al. Immediate, early, and late postsurgical management of upper-limb amputation.J Rehabil Res Dev.1984;21:33-41.

5. Esquenazi A. Amputation rehabilitation and prosthetic restoration. From surgery to community reintegration.Disabil Rehabil.2004;26:831-836.

6. Behrend C, Reizner W, Marchessault J, Hammert W. Update on advances in upper extremity prosthetics.J Hand Surg Am.2011;36:1711-1717.

7. O’Doherty J, Lebedev M, Ifft P, et al. Active tactile exploration using a brain-machine-brain interface.Nature. 2011;479:228-231.

8. Kohler F, Cieza A, Stucki G, et al. Developing core sets for persons following amputation based on the International Classification of Functioning, Disability and Health as a way to specify functioning.Prosthet Orthot Int.2009;33:117-129.

9. McFarland L, Winkler S, Jones M, Heinemann A, Reiber G, Esquenazi A. Unilateral upper limb loss: satisfaction and prosthetic device use in service members from Vietnam and OIF/OEF conflicts.J Rehabil Res Dev.2010;47:275-298.

10. Hanley M, Ehde D, Jensen M, Czerniecki J, Smith D, Robinson L. Chronic pain associated with upper-limb loss.Am J Phys Med Rehabil.2009;88:742-751.

Author Disclosure

Alberto Esquenazi, MD
Nothing to Disclose

Daniel Moon, MD
Nothing to Disclose

Related Articles