You are in: eMedicine Specialties > Physical Medicine and Rehabilitation > PROSTHETICS Upper Limb ProstheticsArticle Last Updated: Oct 10, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 10
 
Author: Brian M Kelly, DO, Assistant Professor, Department of Physical Medicine and Rehabilitation, University of Michigan Medical School; Assistant Program Director, Residency Training Program, Consulting Staff , Service Chief 6A, Inpatient Rehabilitation Services, University of Michigan Health System Brian M Kelly is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Osteopathic Association, American Osteopathic College of Physical Medicine and Rehabilitation, and Association of Academic Physiatrists Coauthor(s): Percival H Pangilinan Jr, MD, Clinical Instructor and Consulting Staff, Department of Physical Medicine and Rehabilitation, University of Michigan Health System; Consulting Staff, Veterans Affairs Ann Arbor Healthcare System; Gianna M Rodriguez, MD, Instructor, Department of Physical Medicine and Rehabilitation, University of Michigan Health Systems; Kevin Martinez, MD, Staff Physician, Section of Physical Medicine and Rehabilitation, Louisiana State University Health Sciences Center; Robert C Mipro, Jr, MD, Assistant Professor, Program Director, Department of Medicine, Section of Physical Medicine and Rehabilitation, Louisiana State University Medical Center; Chief, Department of Physical Medicine and Rehabilitation, VAMC of New Orleans; Valerie S Bodeau, MD, Acting Assistant Professor, Consulting Staff, Medical Director of Outpatient Clinics, Department of Rehabilitation, University of Washington/Harborview Medical Center Editors: Elizabeth A Moberg-Wolff, MD, Associate Professor, Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin; Consulting Staff, Children's Hospital of Wisconsin; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Patrick M Foye, MD, FAAPMR, FAAEM, Associate Professor of Physical Medicine and Rehabilitation, Co-Director of Musculoskeletal Fellowship, Co-Director of Back Pain Clinic, Director of Coccyx Pain (Tailbone Pain, Coccydynia) Service, UMDNJ-New Jersey Medical School; Kelly L Allen, MD, Consulting Staff, Department of Physical Medicine and Rehabilitation, Lourdes Regional Rehabilitation Center, Our Lady of Lourdes Medical Center; Robert H Meier III, MD, Director, Amputee Services of America, Presbyterian St Luke's Hospital; Consulting Staff, North Valley Rehabilitation Hospital, Kindred Hospital, North Suburban Hospital Author and Editor Disclosure Synonyms and related keywords: upper limb prosthetics, upper extremity prostheses, prosthesis, upper-extremity prosthesis, upper-limb prosthesis, amputation, arm amputation, upper limb amputation, upper extremity amputation, myoelectric prosthesis, body-powered prosthesis, above-elbow prosthesis, below-elbow prosthesis INTRODUCTION AND DEFINITIONSSection 2 of 10
 
Prosthesis and orthosis A prosthesis is a device that is designed to replace, as much as possible, the function or appearance of a missing limb or body part. An orthosis is a device that is designed to support, supplement, or augment the function of an existing limb or body part. (Also, see the eMedicine article Upper Limb Orthotics.) Characteristics of a successful prosthesis Ideally, a prosthesis must be comfortable to wear, easy to put on and remove, lightweight, durable, and cosmetically pleasing. Furthermore, a prosthesis must function well mechanically and require only reasonable maintenance. Finally, prosthetic use largely depends on the motivation of the individual, as none of the above characteristics matter if the patient will not wear the prosthesis. Considerations when choosing a prosthesis
Most common reasons for an upper extremity amputation Reasons for amputation vary but can be correlated by age range. Correction of a congenital deformity or tumor is commonly seen in individuals aged 0-15 years. Trauma is the most common reason for amputation in patients aged 15-45 years, with tumors being a distant second. Upper extremity amputations tend to be rare in patients who are older than 60 years, but they may be required secondary to tumor or medical disease. Amputation levels
See Image 1. Definitions of relevant terminology
DIFFERENT TYPES OF PROSTHESESSection 3 of 10
The continuum of prostheses ranges from mostly passive or cosmetic types on one end to primarily functional types on the other. The purpose of most prostheses falls somewhere in the middle. Cosmetic prostheses can look extremely natural, but they often are more difficult to keep clean, can be expensive, and usually sacrifice some function for increased cosmetic appearance. Functional prostheses generally can be divided into the following 2 categories:
Body-powered prostheses Body-powered prostheses (cables) usually are of moderate cost and weight. They are the most durable prostheses and have higher sensory feedback. However, a body-powered prosthesis is more often less cosmetically pleasing than a myoelectrically controlled type is, and it requires more gross limb movement. Externally powered prostheses Prostheses powered by electric motors may provide more proximal function and greater grip strength, along with improved cosmesis, but they can be heavy and expensive. Patient-controlled batteries and motors are used to operate these prostheses. Currently available designs generally have less sensory feedback and require more maintenance than do body-powered prostheses. Externally powered prostheses require a control system. The two types of commonly available control systems are myoelectric and switch control. A myoelectrically controlled prosthesis uses muscle contractions as a signal to activate the prosthesis. It functions by detecting electrical activity from select residual limb muscles, with surface electrodes used to control electric motors. Different types of myoelectric control systems exist.
Many contemporary myoelectric control systems allow for the use of proportional control so that the speed of the component or terminal device activation varies with the intensity of the muscle contraction. Table 1. Various Upper Limb Prostheses1
*TD=terminal device †THA=transhumeral amputation TYPICAL COMPONENTS OF AN UPPER EXTREMITY, BODY-POWERED PROSTHESISSection 4 of 10
A typical example of a transradial (below-elbow) prosthesis includes a voluntary opening split hook; a friction wrist; a double-walled, plastic-laminate socket; a flexible elbow hinge; a single–control-cable system; a triceps cuff; and a figure-8 harness. A transhumeral (above-elbow) prosthesis is similar but includes an internal-locking elbow with a turntable for the missing anatomic elbow, uses a dual–control-cable system instead of a single-control cable, and does not require a triceps cuff. All conventional body-powered, upper extremity prostheses have the following components:
Socket The socket of an upper extremity prosthesis typically has a dual-wall design fabricated from lightweight plastic or graphite composite materials. In this design, a rigid inner socket is fabricated to fit the patient's residual limb and the second, outer wall is added, designed to be the same length and contour as the opposite, sound limb. Comfort and function are directly tied to the fit of the inner socket. An alternative approach parallels the rigid frame, flexible liner approach sometimes used in lower extremity socket fabrication. The inner socket is fabricated from flexible plastic materials to provide appropriate contact and fit. Surrounding the flexible liner, a rigid frame is utilized for structural support and for attaching the necessary cables and joints as needed. The windows in the outer socket allow movement, permit relief over bony prominences, and enhance comfort. Suspension The suspension system must hold the prosthesis securely to the residual limb, as well as accommodate and distribute the forces associated with the weight of the prosthesis and any superimposed lifting loads. Suspension systems can be classified as follows:
Harnessed-based systems and their variants are the most commonly used systems. For the figure-8 strap, a harness loops around the axilla on the sound side. This anchors the harness and provides the counterforce for suspension and control-cable forces. On the prosthetic side, the anterior (superior) strap carries the major suspending forces to the prosthesis by attaching directly to the socket in a transhumeral prosthesis or indirectly to a transradial socket through an intermediate Y-strap and triceps cuff. The posterior (inferior) strap on the prosthetic side attaches to the control cable. For heavier lifting or as an alternative to the figure-8 harness, a shoulder saddle with a chest-strap suspension can be used with a transradial prosthesis. A chest strap alone is sometimes used to suspend a transhumeral prosthesis. The figure-9 harness is an alternative for a patient with a long transradial amputation or a wrist disarticulation, in order to provide the control cable's necessary attachment point and counterforce. Although the figure-9 harness provides minimal suspension and requires a self-suspending socket, it is more comfortable than a figure-8 harness. (See Image 2.) Self-suspending and suction sockets are capable of providing adequate prosthetic suspension without the use of a harness. However, either design can also be used with a harness suspension to provide for a more secure suspension of the prosthesis. Self-suspending sockets are largely limited to wrist or elbow disarticulations and to transradial amputations. This socket design is most commonly utilized with an externally powered, myoelectrically controlled transradial prosthesis. An example of this type is the Suction suspension is similar to lower extremity options. These sockets use an external, elastic suspension sleeve; a one-way air valve; or roll-on gel suspension liner with a pin-locking mechanism. Upper limb suction sockets (unlike nonsuction sockets) require a total contact socket design and ideally a residual limb with no skin invagination, scarring, and stable volume to avoid skin problems, such as a choke syndrome. Suction socket designs are most commonly used for the patient with a transhumeral amputation.
Adapted2 Body-powered prosthetic limbs use cables to link movements of 1 part of the body to the prosthesis in order to control a prosthetic function. This usually is a movement of the humerus, shoulder, or chest, which is transferred via a Bowden cable (a single cable passing through a single housing) to activate the terminal device of the prosthesis. A control cable used to activate a single prosthetic component or function is called a single-control cable, or Bowden cable system. A dual–control-cable system uses the same cable to control 2 prosthetic functions (such as flexion of the elbow and, when the elbow is locked, activation of the terminal device). This latter control cable setup is accomplished with a single cable passing through two separate cable housings known as a fair lead cable system. Body movements that are captured for prosthetic control
TERMINAL DEVICESection 5 of 10
The major function of the hand that a prosthesis tries to replicate is grip (prehension). The 5 different types of grips are as follows:
Terminal devices generally are broken down into 2 categories: passive and active. Passive terminal devices Passive terminal devices fall into two classes, those designed primarily for function and those to provide cosmesis. Examples of the functional passive terminal devices include the child mitt frequently used on an infant's first prosthesis to facilitate crawling or the ball handling terminal devices used by older children and adults for ball sports. The main advantage of most passive terminal devices is their cosmetic appearance. With newer advances in materials and design, some passive hands are virtually indistinguishable from the native hand. However, most of these cosmetic passive terminal devices usually are less functional and more expensive than active terminal devices. Active terminal devices Active terminal devices usually are more functional than cosmetic; however, in the near future, active devices that are equally cosmetic and functional may be available. Active devices can be broken down into 2 main categories: hook (and similarly specialized function) terminal devices and prosthetic hands. There are designs of both of these terminal device groups available to operate with cable or externally powered prostheses. Cable-operated terminal devices (hooks or hands) can be of a voluntary opening design (most commonly used) or a voluntary closing design.
A prosthetic hand usually is bulkier and heavier than a hook, but it is more cosmetically pleasing. A prosthetic hand can be powered by a cable or utilize external power. With a myoelectrically controlled device, it is possible for the patient to initiate palmar tip grasp by contracting residual forearm flexors and to release by contracting residual extensors. Most hook-style terminal devices provide the equivalent of active lateral pinch grip, while active hands provide a 3-point chuck action. Many different options are available for terminal devices that address occupations, hobbies, and sports. WRIST, ELBOW, SHOULDER, AND FOREQUARTER UNITSSection 6 of 10
Wrist unitsThe wrist unit provides orientation of the terminal device in space. It can be positioned manually, by cable operation, or with external power (whether myoelectrically or by switch). Once positioned, the wrist unit is held in place by a friction lock or a mechanical lock. Several different unit designs are available, including a quick-disconnect unit, a locking unit, and a flexion unit. Friction-control wrist units are easy to position but can slip easily when carrying heavier loads. Quick-disconnect wrist unit This style is configured to allow easy swapping of terminal devices that have specialized functions. Locking wrist unit Wrist units with a locking capacity prevent rotation during grasping and lifting. Wrist flexion unit A wrist flexion unit can provide an amputee (especially a bilateral upper extremity amputee) with improved function for midline activities, such as shaving, manipulating buttons, or performing perineal care. A flexion wrist unit usually is employed on only one side, most often the longer of the two residual limbs, but ultimately it should be placed on the side that the amputee prefers. Multifunction wrist units have become available. Elbow unitsElbow units are chosen based on the level of the amputation and the amount of residual function. It is helpful to remember that supination and pronation of the forearm decrease as the site of amputation becomes more proximal. Flexible elbow hinge Flexible elbow hinges are utilized for medium and long transradial amputations and wrist disarticulations. When the patient has sufficient voluntary pronation and supination, as well as elbow flexion and extension, flexible elbow hinges help translate any residual active pronation and supination to the terminal device. A triceps pad or cuff helps distribute suspension forces and is needed to anchor the control cable. Rigid elbow hinge With short transradial amputations, a patient has no residual, active forearm pronation and supination but does have adequate native elbow flexion. Rigid elbow hinges provide additional stability. Hinges are available in single-axis or polycentric versions. Rigid hinges are important in amputees with short transradial limbs. In patients with very short transradial, residual limbs or limited active elbow flexion, the use of step-up elbow hinges can improve prosthetic function by increasing functional, active elbow motion. This system uses special elbow joints together with a split-socket design permitting the prosthetic forearm and attached terminal device to move 2º of motion for every 1º of actual residual limb and elbow motion. Since movement of the limb and the prosthesis are not directly connected, the proprioceptive feedback is compromised. Internal elbow The standard elbow component for a transhumeral prosthesis is an internal locking elbow joint. This allows for 135º of flexion and can be locked into a number of preset flexed positions. The standard internal elbow joint incorporates a turntable that allows passive internal or external humeral rotation. Elbow spring-lift assists are available and are used to counterbalance the weight of the forearm, making elbow flexion easier. The standard elbow unit requires a length of 8-10 cm to be adequately installed in a transhumeral prosthesis. If the level of amputation is less than 8-10 cm proximal to the distal end of the humerus, then an internal locking elbow unit cannot provide symmetric elbow centers (prosthesis and sound upper extremity). Even if an asymmetric elbow position (compared with the sound side) is acceptable, functional problems will result with the prosthesis from this alignment. Unless the forearm section of the prosthesis is lengthened to accommodate the lengthened arm section, the amputee will not be able to reach the midline or mouth, with the prosthesis compromising function. However, lengthening the forearm to accommodate the added arm length will result in difficulties when the patient tries to perform bimanual activities, and it usually will not be cosmetically acceptable to the patient. For long transhumeral amputations or elbow disarticulations, locking external elbowjointsmay be used, but they are not cosmetic or as durable as internal elbow joints. Shoulder and forequarter unitsWhen an amputation is required at the shoulder or forequarter level, function is very difficult to restore. This is due to a combination of the weight of the prosthetic components and the diminished overall function when combining multiple prosthetic joints, as well as the increased energy expenditure necessary to operate the prosthesis. For this reason, some individuals with a unilateral amputation at this level choose a purely cosmetic prosthesis to improve body image and the fit of their clothes or decide to go without a prosthesis. OVERALL PROCESS/TIMELINE FOR AN AMPUTATION/PROSTHESIS FITTINGSection 7 of 10
Pre-amputation Ideally, a patient who needs an upper extremity amputation should be seen by the rehabilitation team prior to the surgery. This allows a chance to evaluate postoperative needs and desires, to discuss prosthetic restoration, and to begin any needed range-of-motion (ROM) exercises, strengthening, and training in activities of daily living (ADLs). Peer support by another successful amputee at the proposed level has a positive benefit for all amputees and may reduce anxiety for the elective amputee patient. However, since most upper extremity amputations are traumatic in nature, this is not always possible. Surgical procedure During the amputation surgery, several actions can be taken to maximize the function of the residual limb. These actions include the following:
Acute postsurgery The major physical issues in this phase are adequate wound healing, pain management, instruction in the performance of ADLs, mobility, ROM, and strength. During this phase, a program to prepare the residual limb for the prosthesis should be initiated. A skin desensitization program consists of the following:
Psychology should be involved at this phase if possible (ie, elective procedure) or immediately postoperatively. Adjustment and grief reaction are common for new amputees. The patient may struggle with self-image and cosmetic concerns early, as well as later, in the prosthetic restoration process. A simple and organized psychological framework proposed by Van Dorsten delineates the process well.3 The stages address survival, recovery and reintegration. The amputee will have many questions and concerns during each stage. As previously mentioned, peer support visits by another successful amputee can provide a tremendous benefit for the new amputee. Initially, the team should suggest and remind the patient of available peer support, but it is important to allow the patient to indicate when he or she is ready for such a visit. A temporary prosthesis can be fitted during surgery; in this way, when the patient awakens, he or she can visualize a limb in place. This is called an immediate postoperative prosthesis (IPOP). IPOPs are usually fitted in healthy young patients with traumatic amputations. In such cases, rehabilitation physicians work integrally with surgical specialists and prosthetists. Alternatively, in older patients or in those with vascular disease, a prosthesis is not fitted until the suture line has completely healed. The prosthesis must be individually fitted to the patient, since 1 size does not fit all. Fitting an upper extremity amputee with a body-powered preparatory prosthesis within 7-30 days after amputation is advisable. This is referred to by Malone as the "golden period."4 Prosthetic fitting during this time correlates with a higher acceptance and success rate of prosthetic use. Prostheses are either preparatory (nonpermanent) or definitive (permanent). The advantage to using a preparatory prosthesis is that it is fitted while the residual limb is still maturing. A preparatory prosthesis allows the patient to train with the prosthesis several months earlier in the process. Use of a preparatory prosthesis often results in a better fit for the final prosthesis, since the preparatory socket can be used to mold the residual limb into the desired shape. During this period, the patient “test drives” the prosthesis and learns what it can and cannot do. Sometimes a preparatory prosthesis is not feasible because of financial considerations. In this case, a patient can only be fitted for the definitive (final) prosthesis. If a patient is being fitted for a final prosthesis without ever having had a preparatory prosthesis, fitting for the socket should be delayed until the residual limb is fully mature (a process that sometimes can take several months).PHANTOM LIMB SENSATION AND PAINSection 8 of 10
In addition to the usual postoperative pain, most individuals who have undergone an amputation experience phantom sensation. Phantom sensation is the perceived sense that the amputated limb, or at least a part of it, is still present. Phantom sensation is not painful, and the patient usually just needs to be reassured that this sensation is common and that he or she is not suffering from mental instability. The phenomenon of telescoping can accompany phantom sensation. Telescoping is the sensation that the amputated limb has shrunk (eg, the toes are at the ankle, the foot is at the knee). Telescoping is normal and usually fades without sequelae. Phantom pain is the sensation of pain originating in the amputated part. Phantom pain may or may not be dermatomal in nature. Individuals may describe a burning, stinging, or cramping pain, or they may describe a feeling that the missing body part is "positioned awkwardly or painfully." The pain usually develops in the first month after amputation and is most likely to develop in individuals who had a lot of pain before amputation. Phantom pain is constant and is most intense right after the amputation. The pain becomes more intermittent and resolves with time, although some patients can still experience phantom pain years after the amputation. Patients who have undergone amputation commonly report intermittent phantom pain symptoms, but they are able to ignore them and require no medication for treatment. Phantom pain is usually worse at night, after the extremity has been in a dependent position, and can be worsened by anxiety and stress. Theories exist as to why patients experience phantom limb pain and phantom sensation. One theory is that the remaining nerves continue to generate impulses spontaneously or as a result of irritation. A second theory is that the spinal cord nerves begin excessive, spontaneous firing in the absence of expected sensory input from the limb. A third theory is that altered signal transmission and modulation occur within the somatosensory cortex. Other possible causes include abnormal sympathetic function and psychologic factors. MULTIMEDIASection 9 of 10
REFERENCESSection 10 of 10
Upper Limb Prosthetics excerpt Article Last Updated: Oct 10, 2007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
