Archives of Physical Medicine and Rehabilitation
Volume 87, Issue 3, Supplement , Pages 34-43, March 2006

Advances in Amputee Care

  • Paul F. Pasquina, MD

      Affiliations

    • Physical Medicine and Rehabilitation Service, Walter Reed Army Medical Center, Washington, DC
    • Corresponding Author InformationReprint requests to Paul F. Pasquina, MD, Physical Medicine & Rehabilitation, Bldg 2, Section 3J, Walter Reed Army Medical Center, 6900 Georgia Ave, Washington, DC 20307
    • ,
  • Phillip R. Bryant, DO

      Affiliations

    • Good Shepherd Rehabilitation Hospitals, Allentown, PA
    • ,
  • Mark E. Huang, MD

      Affiliations

    • Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL
    • ,
  • Toni L. Roberts, DO

      Affiliations

    • Physical Medicine and Rehabilitation, George E. Wahlen Department of Veterans Affairs Medical Center, Salt Lake City, UT
    • ,
  • Virginia S. Nelson, MD, MPH

      Affiliations

    • Department of Physical Medicine and Rehabilitation, University of Michigan Medical School, Ann Arbor, MI
    • ,
  • Katherine M. Flood, MD

      Affiliations

    • Physical Medicine and Rehabilitation Program, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, PA

Article Outline

Abstract 

Pasquina PF, Bryant PR, Huang ME, Roberts TL, Nelson VS, Flood KM. Advances in amputee care.

This self-directed learning module highlights the recent innovations in amputee care. It is part of the study guide on limb deficiency in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. This focused review article describes the key elements of a successful comprehensive amputee program, the basic surgical considerations for upper- and lower-extremity amputation, and some of the more recent advances in prosthetic components. Further, an update is given on issues such as hand transplantation and the integration of robotics and artificial muscles for people with limb loss.

Overall Article Objective

(a) To discuss current issues and advances in the care of patients with amputation, (b) to describe the key elements in designing a comprehensive amputee care program, and (c) to discuss surgical considerations of limb preservation and amputation levels.

Key Words:  Amputation , Prosthetics and implants , Rehabilitation , Review [publication type]

 

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Key elements of a comprehensive amputee care program 

Teamwork 

OPTIMIZING CARE FOR A PERSON with limb loss is complex. Whether providing inpatient or outpatient care, the key to success is teamwork. Medical, surgical, and rehabilitative care have become subspecialized. Further, the varieties of prosthetic components available on the market make prosthetic prescribing and fitting a complicated process. Although little has been written in the medical literature to define the key elements of a successful program, experts agree that formulating a multidisciplinary—or newly termed transdisciplinary or interdisciplinary—team is an essential feature. The argument for using these new terms is centered on the idea that medical providers from different disciplines and specialties should work together to formulate an integrated and coordinated treatment plan as opposed to multiple independent plans.

Experience from each major military conflict has underscored the value of forming Centers of Excellence for amputee care.1 These centers espouse the need for interaction of multiple specialties and incorporating basic rehabilitation principles to provide holistic care to amputees. Critical specialties involved in caring for amputees include physiatry, surgery, medicine, physical therapy, occupational therapy, nursing, mental health, social work, and prosthetics. This type of teamwork has shown to improve short- and long-term outcomes.2, 3 Additionally, incorporating peer support, vocational rehabilitation, community reintegration, and sports and recreational activities greatly enhances a comprehensive program and improves amputees’ quality of life (QOL) and ability to reintegrate into the community.4 Finally, for a program to be successful, team members must recognize the important role that patients and family members have in the entire treatment process, including the establishment of short- and long-term goals.

Pain Management 

An essential component of any successful inpatient or outpatient amputee program is expertise in pain management. Residual limb and phantom limb pain occur in 55% to 85% of amputees and have a significant negative impact on long-term functional outcomes and QOL.5, 6 Because the incidence of chronic pain may be reduced by aggressive preoperative and perioperative pain management, the entire medical and rehabilitation staff should be sensitive to an amputee’s pain perception and should make pain assessment part of routine evaluation. Team members who have subspecialty training in pain management contribute greatly to a successful outcome. Cutting-edge programs should consider the use of topical agents, regional anesthesia, and multimodal pharmacologic management; they will also consider complementary, integrative, or alternative measures such as biofeedback, hypnosis, relaxation techniques, and/or acupuncture. Therapists should be knowledgeable about the indications for and contraindications against applying modalities such as heat and cold, electric stimulation, and desensitization techniques. Although the literature does not support clear evidence of a single agent as the treatment of choice for phantom or residual limb pain, medications such as opioids, anticonvulsants, tricyclic antidepressants, botulinum toxin, and topical agents (lidocaine, capsaicin) may work synergistically to provide optimal pain relief. It is also generally accepted that the use of an appropriately fitting prosthetic socket helps to reduce pain.

Prevention Programs 

Preventive programs can help reduce the risk of both traumatic and nontraumatic amputation. Safety education and training have contributed to a significant decrease in trauma-related amputations.7 Additionally, The Department of Veterans Affairs (VA) Preservation-Amputation Care and Treatment program has contributed to an almost 40% reduction in nontraumatic amputations performed each year at VA medical centers. The program incorporates the interdisciplinary coordination of a surgeon, rehabilitation physician, therapist, nurse, podiatrist, social worker, prosthetic and/or orthotic personnel, and the primary care medical/diabetes team to track every patient with an amputation or those at risk of limb loss who enter the VA health care system.8

Organizational Structure 

Standardizing medical care across different medical systems and geographic regions depends on multiple factors. Issues such as patient demographics, provider expertise and experience, and availability of resources greatly influence outcomes. To provide best practice, it is essential to have a well-organized system in place. A model program should have adequate resources, support ongoing education and research, and incorporate continuous process improvement. Strong leadership is essential in implementing and sustaining such a program. Physiatrists are uniquely skilled to coordinate care for amputees and to ensure that a system is established to provide comprehensive, holistic care. Regularly scheduled interdisciplinary meetings to discuss patient care and programmatic meetings to discuss systems processes are critical to the success of a program. Flowcharts to clarify patient movement within the system may improve communication and enhance continuity of care. One such flowchart, which addresses the care of a combat amputee at Walter Reed Army Medical Center, a major tertiary hospital for the military, is presented in figure 1.

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  • Fig 1. 

    Flowchart to ensure consistent, systematic handling of patients with limb amputations. Abbreviations: Duty, military occupation; Gen, general; MEB, medical evaluation board; MICU, medical intensive care unit; OT, occupational therapy; Pain, pain management service; PEB, physical evaluation board; PM&R, physical medicine and rehabilitation; Psych, psychiatry/psychology; PT, physical therapy; RTN, return; SICU, surgical intensive care unit; Svc, Service; TRICARE, Network of civilian providers contracted with Department of Defense; WRAMC, Walter Reed Army Medical Center.

Outcome Measures 

An essential element in developing a program that focuses on best practices is a mechanism for collecting and analyzing outcomes. Guidelines from the Joint Commission on Accreditation of Healthcare Organizations and from the Accreditation Council for Graduate Medical Education emphasize the importance of outcomes-based practices. A multitude of outcome measures are available for the amputee population. Although many reliable and validated measurement tools have been reported in the literature, considerable debate continues as to which tool is best for the various patient populations. Further, the success or failure of a particular intervention in the care of an amputee is often the result of multiple factors. Several tools may be required to adequately assess a particular patient population.

Some of the most common outcome domains pertinent to amputee populations include mobility, function, and QOL. Tools used to measure these domains are generally by self-report (survey) or observational based. Several examples of measurement tools are listed in appendix 1.

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Surgical considerations 

Limb Salvage Versus Amputation 

Proper surgical technique is essential to the success in treating amputees. Trauma accounts for over 3500 major amputations per year in the United States.7 Evidence suggests that there is no significant difference in outcomes at 2 years when comparing limb reconstruction versus amputation, although “reconstruction is associated with a higher risk of complications, additional surgeries, and rehospitalization.”9(1930) Therefore, decision making, such as limb salvage and preservation versus amputation, remains complex and is best made by the consensus of surgical and rehabilitation subspecialties. Today’s experienced surgical teams are able to incorporate advanced techniques in skin grafting, soft-tissue flaps, and microvascular repair to not only save limbs but also to preserve critical length. Care must be taken to provide optimal skin and soft-tissue coverage of the residual limb to meet the demands of future socket wear and weight bearing. Further, for upper-extremity amputees, scar lines should be avoided in areas where myoelectric signals will be used to operate an externally powered prosthesis, so as not to impair electrode contact.

An estimated 82% of all amputations performed in the United States result from complications of vascular disease or diabetes.10 Surgical decisions regarding residual limb length depend on tissue viability. Instruments to improve this determination include preoperative angiograms and tissue oxygenation studies; however, nothing can replace the experience of a well-qualified surgeon, who at the time of operation is able to directly assess tissue integrity and health.

Surgical Techniques 

Multiple surgical techniques have been described for primary and reconstructive amputation procedures. The same technique does not work for all amputees. For example, at the transtibial level closure may be achieved with a long posterior myofasciocutaneous flap, equal anterior and posterior flaps, equal medial and lateral (sagittal) flaps, or skewed sagittal flaps. Success in any amputation surgery depends on proper attention to existing vasculature and nerves, on providing adequate soft-tissue and skin coverage of the residual limb, and on achieving proper muscular balance. Myoplasty is the technique in which antagonistic muscles are sewn together over the distal end of the amputated bone. Myodesis is the attachment of transected muscles directly to the periosteum of the amputated bone. It is common to use both techniques during amputation, whereby the deep muscle layers are affixed to the bone (myodesis) and the superficial layers are attached through myoplasty. Muscle stabilization is achieved by applying adequate tension when securing the residual musculature. Excessive tension or muscle imbalance may lead to excessive pain and poor residual limb function.11

The Ertl procedure is a commonly promoted reconstructive surgical technique for transtibial amputees. In this technique the surgeon creates an osteoperiosteal bridge between the distal tibia and fibula. The Ertl procedure is primarily indicated for amputees with fibula instability. It has also been advocated for improving tolerance to distal end weight bearing, especially in active patients. Like other accepted and effective techniques, this procedure addresses appropriate nerve and vessel treatment, muscle stabilization, bone beveling, and skin management. Most data supporting the benefits of this procedure come from reported series using it as a reconstructive procedure, not as a technique of primary amputation.12, 13 Modifications to this technique have been reported to reduce terminal overgrowth in childhood limb deficiencies.14

Optimizing Limb Length 

Considerable debate continues regarding the optimal length for an amputated limb. Although experts agree that preservation of a functioning joint such as the knee or elbow greatly improves prosthetic function and energy consumption, no consensus exists regarding the controversial sites of amputation discussed below.

Knee disarticulation versus transfemoral amputation 

The controversy here primarily stems from the bulbous nature of the distal residual limb after a knee disarticulation, which may complicate prosthetic fitting. The additional length of the limb may also negatively affect appearance and limit the choice of prosthetic knee options, potentially excluding newer, more advanced knee joint designs. Benefits of the knee disarticulation procedure may include greater tolerance to distal limb weight bearing, a longer lever arm to create power during ambulation or running, and improved sitting balance, particularly for wheelchair users. Preservation of the entire femur has particular advantages for pediatric amputees because it allows continued longitudinal bone growth while limiting distal bony overgrowth at the amputation site.15 A recent study published by MacKenzie et al16 examined the functional outcomes of trauma-related lower-extremity amputees and concluded that those with through-knee amputations had significantly poorer outcomes. The poorer outcomes were attributed to complications arising from soft-tissue failure within the zone of injury, emphasizing the need to observe caution when performing knee disarticulations in the face of extensive soft-tissue trauma, especially when adequate soft-tissue coverage of the residual limb may not be possible.

Syme’s versus transtibial amputation 

With the advancement of current options for prosthetic feet, many now consider a transtibial level amputation to be preferred over a Syme’s amputation. A general rule of thumb when determining the optimal length for a transtibial amputation is for every 30cm of overall patient height, 2.5cm of the distal tibia should be preserved. For an adult male of average height, this would result in approximately 15 to 20cm of residual limb length. This same formula should not, however, be used in a skeletally immature person, in whom as much length as possible should be preserved to accommodate growth. When performing a transtibial amputation, the distal tibia should be beveled anteriorly and the fibula should be 1 to 2cm shorter than the tibia. Despite existing opinions regarding the benefits of the transtibial amputation level, distinct advantages to a Syme’s amputation continue to exist. Its most notable advantages are (1) the ability to perform end weight bearing and limited ambulation without a prosthesis, (2) the preservation of the malleoli to aid in suspension, and (3) the preservation of an intact tibia to allow growth in pediatric patients.

Wrist disarticulation versus long transradial amputation 

To accommodate a myoelectric wrist rotation device, surgeons and rehabilitation professionals must consider amputation at the long transradial level instead of disarticulation at the wrist. Whenever possible, the patient should have the final decision, based on ample education from the medical team. A wrist rotation device occupies several centimeters of space and therefore necessitates removal of the distal ulna and radius to have a final prosthesis equal to the limb length of the intact side. The postulated functional benefits of these wrist units are currently under investigation.

Hand Transplantation 

As of 2004, 24 hand transplants were reported in the world. Most of these procedures were performed in France and Italy. Although considered experimental in the United States, experienced European surgeons have reported modestly successful outcomes.17, 18 The surgical procedure is similar to that of hand reattachment. From a surgical perspective, transplantation has technical advantages, because the donated limb may be harvested at a more controlled length to optimize anastomosis and mechanical functioning. With reattachment of a traumatized limb, the surgical team is often challenged with the need to compensate for significant tissue damage or loss. Return of “good” motor and sensory function has been reported after 24 months of rehabilitation; however, “good” has not been clearly defined. Reasonable results have only been reported in distal transradial amputations or wrist disarticulations. Rejection reactions occur in all cases but generally can be controlled with life-long immunosuppressive medications. Several differences exist between organ transplantation and limb transplantation. First, unlike solid organs, limbs are composed of multiple tissue types (bones, soft tissue, nerve, vessel), which increases the immunogenicity. Further, hand transplantation is not a life-saving procedure, so the risk-to-benefit ratio of performing it creates an ethical dilemma. Ethical guidelines regarding surgical procedures suggest that the procedure be considered only in patients who have lost both their hands or who are already on immunosuppressive medications for other reasons.19, 20

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Advancements in prosthetic components 

Prosthetic prescriptions should be individualized based on the functional capacity and goals of each amputee. Choice of prosthetic components historically has been based on empirical knowledge; however, with the increasing costs of current highly technical components, third-party payers are increasingly demanding scientific evidence to support one component over another. The health care community is challenged to establish benchmarks for assessing prosthetic components and to develop evidence-based guidelines for prosthetic prescription.21

Lower-Extremity Prostheses 

Although a thorough review of lower-extremity prosthetic components is beyond the scope of this focused review, the reader is referred to an excellent review by Harmen van der Linde et al,22 which reports the effect of various lower-limb prosthetic components on function. To date, no clear consensus exists regarding precise prescription criteria. Future studies are needed to evaluate the relative value of different prosthetic components in more real world activities such as performing activities of daily living, negotiating stairs and ramps, and adapting to variable walking speeds and direction. Further, studies examining the late effects of prosthetic components may give insight into relational effects of complications such as back pain, arthritis, overuse injuries, and/or cardiovascular disease in the amputee population.23, 24, 25, 26, 27

Prosthetic feet 

Although studies support evidence that energy storing and return (ESAR) prosthetic components have high subjective satisfaction rates with patients, there is limited biomechanical evidence that these feet have any significant functional benefit.28 Trends suggest that an increase in walking velocity, greater stride length, a decrease in sound side vertical acceptance force, and a slight decrease in metabolic energy expenditure at high speeds may be achieved with an ESAR foot.29, 30, 31

Today, many types of prosthetic feet are available. It is becoming increasingly difficult for clinicians and prosthetists to keep abreast of the various components and their unique characteristics. Current terminology incorporates ESAR prosthetic feet into a broader category called dynamic response feet (DRF). Many of the new generation DRF devices have flexible/recoiling keels configured to provide energy-storing capabilities in multiple planes and provide some vertical and rotational force damping. Six examples of dynamic response feet are shown in figure 2, showing the variability of existing design features.

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  • Fig 2. 

    Examples of dynamic response feet. (A) Ossur Ceterus, c (B) College Park TruStep,g (C) Freedoms Innovations Renegade,h (D) Ohio Willow Wood Pathfinder,i (E) Ossur Re-Flex Vertical Shock Prosthesis, c and (F) Otto Bock LuXon Journey.a

Prosthetic knees 

Over the past decade significant advances have been made in prosthetic knee designs. Today, a multitude of knee components are available for lower-extremity amputees.32 Although a thorough review of the various prosthetic knees is beyond the scope of this focused review, a discussion is provided regarding the current advancements in microprocessor knees.

The mechanical characteristics of the human knee help to control postural stability and to vary step cadence and also enhance the ability to walk on rough or uneven surfaces. Microprocessor knees attempt to simulate normal biologic knee function by offering variable resistance control to the swing and/or stance phases of the gait cycle. The microprocessor incorporated within the prosthetic device reacts to strain gauges and velocity sensors within the prosthesis to vary knee stiffness. Currently, 3 different microprocessor knees are available for commercial use in the United States.

Otto Bock C-Leg 

The Otto Bock C-Lega was first introduced in 1999.33 Sensors located within the pylon take measurements 50 times each second. This information is transmitted to the microprocessor and servomotor within the knee to adjust valves of small hydraulic pistons to provide swing- and stance-phase variable resistance. Also incorporated within this unit is a stance control feature designed to recognize a stumble and react to stiffen the knee to prevent a fall. Parameters within different phases of the gait cycle are adjusted by a trained prosthetist, who connects a computer to the knee electronics to customize it to the individual user. The C-Leg’s rechargeable battery lasts from 25 to 30 hours, necessitating charging on a daily basis.34 An additional safety feature of this knee is the stiffening of knee extension during battery drainage or failure.

Endolite Adaptive Prosthesis 

The Endolite Adaptive Prosthesisb was developed in the United Kingdom. The onboard microprocessor takes measurements at 62.5 times per second to control both hydraulic and pneumatic valves. The hydraulic part of the system controls stance, flexion, and terminal impact, whereas the pneumatic component controls swing-phase and extension assistance. Another feature of this prosthesis is a voluntary locking mechanism for extended standing periods. It also has a stumble control mechanism. The system is programmed by a wireless radio-linked computer program, which allows 3 settings: basic, standard, and advanced levels of control. The rechargeable batteries will last for 3 to 10 days depending on the setting.35 Uncharged, the knee mechanism functions on the hydraulic controller.

Ossur Rheo Knee 

The Ossur Rheo Knee, cdeveloped at the Massachusetts Institute of Technology for Ossur, only became available in the United States in 2005. The microprocessor controls swing- and stance-phase resistance at 1000 times a second through the use of magnetorheologic fluid. This fluid is composed of charged particles that change viscosity when passed through variable adjustable magnetic fields, thereby increasing or decreasing knee stiffness. The knee’s rechargeable lithium battery holds a charge for 24 to 48 hours.36 During power failure or battery drainage the knee converts to free motion.

Like all prosthetic components, prescriptions for prosthetic knees should reflect the activity level and functional goals of each amputee. For high-cost items, physicians are often required to show medical necessity when ordering certain components. Currently, most third-party payers will approve a microprocessor knee only for those patients whose activity level is K3 or higher (see Study Guide, chapter 1, table 137).38 Although multiple preliminary studies have been conducted reporting the positive effects of microprocessor knees, more research is needed to determine appropriate patient selection and to prove their proposed short- and long-term benefits.

There is a paucity of published data on the microprocessor-controlled knee prostheses. Most of the literature focuses on the intelligent prosthesis (IP), which, although similar to the microprocessor knees, is not distributed in the United States. Chin et al39 reported that young IP users were able to walk at normal speeds with only about a 24% increase in energy expenditure. This finding was significant because it showed a dramatic decrease in the traditionally reported 68% increased energy expenditure for transfemoral amputees when walking at speeds comparable to able-bodied people.39 Additionally, it suggests that transfemoral amputees who use an IP are able to walk at energy expenditures similar to those traditionally noted in transtibial prosthetic users.40, 41 Chin’s findings are consistent with previous studies showing evidence of lower energy cost for IP users.42, 43

Datta and Howitt44 surveyed 22 conventional prosthesis users who were given an IP that had a microprocessor-controlled knee prosthesis. All respondents considered the IP to be an improvement over their conventional pneumatic swing phase control knee, especially with respect to walking at different speeds, walking greater distances, and perceived energy consumption.44 A study by Stinus45 found similar results in 15 patients using the C-Leg over a period of 6 to 14 months. Both the treating prosthetist and patients described the microprocessor knee as better than their previous conventional prosthesis. Despite these noted improvements, there is no evidence that walking with a microprocessor-controlled knee requires less cognitive demand than a conventional prosthesis.46 Further research is needed to determine the benefits of microprocessor knees on amputee outcomes. Issues such as patient satisfaction, comfortable walking speed, energy consumption, and falls reduction remain areas of potential benefit.

Power-Driven Lower-Extremity Prostheses 

Despite the advances in lower-extremity prostheses, currently every component on the market works primarily by force damping or energy damping. Although energy storing feet are designed with “recoiling” materials to store energy, these prostheses are unable to generate functional power like that produced by the lower-extremity muscles of an intact limb during ambulation. Therefore, ambulation with a prosthetic limb requires greater energy expenditure than that of an intact limb at the same walking speed. Through a partnership between Ossur and a Canadian company, Victhom, the world’s first powered lower-extremity prosthesis is currently being developed. The Power Knee prosthesis is able to replicate concentric muscle power through electromechanical actuation. The system works by combining an electromechanical power source with a sound-side sensory control (SSSC). The SSSC incorporates the input from sensors on the sound leg shoe to communicate action of the prosthetic contralateral knee. The company reports that although the system is generally heavier than conventional lower-extremity prostheses, users do not complain of the increased weight because of the reported decreased effort they have with walking, particularly over longer distances and on muddy or rocky surfaces. Additionally, this is the first knee that allows walking upstairs with a reciprocating (step-over-step) gait pattern.47

Prostheses that restore power to the lower extremity are also being developed for transtibial amputees. Researchers in the field are hoping to restore active plantarflexion and dorsiflexion. Current limitations include adequate control mechanisms and power sources, size and weight of existing actuators, and the challenge of creating enough power to lift a human’s body weight during pushoff. The development of such a system may have a significant impact on reduced energy consumption for amputees, particular those with cardiovascular disease.

Upper-Extremity Prostheses 

Prosthetic prescription for upper-extremity amputees should be tailored to help meet each patient’s functional goals. Each prescription should include a terminal device, wrist, socket, suspension system, and, if needed, an elbow and/or shoulder mechanism. Selecting among a body-powered, externally powered, and/or passive (cosmetic) prosthesis is often difficult. Considerations include each patient’s functional and vocational goals, geographic location, expected environmental exposures, type of health insurance coverage, and access to prosthetic professionals to provide technical maintenance. It is also important to fit each upper-extremity amputee with a prosthetic device as soon as possible, because early fitting is associated with a greater rate of acceptance.48

Although a comprehensive review of upper-extremity prosthetic management is beyond the scope of this review, the following summary gives an overview of some of the recent advances in components. For a more detailed review the reader is referred to other sources.11, 49, 50, 51, 52

Terminal devices 

The human hand provides 2 primary functions: prehension (eg, pinch, grip, key grip) and tactile sensation (eg, touch, temperature, position sense). Current prosthetic terminal devices are usually grouped by hands and hooks. Both may be either externally or body-power controlled. Electric hooks are commonly referred to as electronic terminal devices or ETDsd (brand name of Motion Control Inc). Hook devices, although not as cosmetic, offer the user more customized prehension, especially for specific vocational and avocational tasks. They also provide better visualization of objects held by the hook. Many upper-extremity prostheses allow the user to interchange various terminal devices for specific tasks.

The Motion Control Handd (fig 3) is an electronic hand that provides a wide grip and up to 97.9N (22lb) of pinch force. The Greifer devicea (fig 4) is a motorized hook that offers an even wider grip and pinch forces up to 266.9N (60lb). The SensorHand Speeda (fig 5) is an electric hand that is 250% faster than other electric hands, which not only makes it more responsive to the user, but also enhances function. Additionally, slip detection technology can now be incorporated into its terminal device. Sensors within the fingertips provide feedback signals to a microprocessor within the device to control constant grip force so that the user does not need to concentrate on holding an object such as a plastic cup without crushing, spilling, or dropping it.

Wrist units 

Wrist rotation and flexion units may be added to the upper-extremity prosthesis to enhance function. Wrist rotators may be either electric or passive, whereas flexion and extension units are currently only available with passive control. The same myoelectric sensors are typically used to control both the wrist unit and terminal device. The user is able to switch between modes (wrist or terminal device) by using proportional control (fast vs slow muscle contraction) or simultaneous co-contraction of myoelectric control sites. Electric wrist units add both weight and length to the prosthesis. It is best to consider the value of these units before definitive surgery, because the prosthetic device selection may affect limb-length decisions.

Elbow units 

The Boston Digital Arm System,e Utah Arm 3,d and Dynamic Arma are examples of the latest technology in upper-extremity motorized prostheses for transhumeral amputees.53, 54, 55 To allow a more natural movement, these arm systems have dual microprocessors that permit simultaneous operation of the elbow unit and the terminal device. This control is typically achieved through the use of a servo unit, which is a proportionally controlled sensor unit incorporated into a simple lightweight harness strap. It is activated similarly as a body-powered cable by a simple pull through the shoulder apparatus. As an added benefit, these devices offer greater force of elbow flexion and can be locked into place either by active user input or by automatic locking at a preset time.

Sockets and Liners 

Advancements to both upper- and lower-extremity prosthetic sockets and liners have been achieved primarily through enhanced materials. Carbon graphite sockets now offer greater durability at a lighter weight. The incorporation of flexible materials within the socket may offer a more adaptable and comfortable socket. Custom fitting can be enhanced by the use of devices featuring computer-aided design and computer-aided manufacturing. This technology has also greatly reduced socket fabrication time, allowing amputees the ability to be trained with a custom prosthesis sooner. Advances in custom-fitting techniques and materials have allowed better suction suspension systems and the ability to use total contact sockets. A vacuum-assist socket systema has been introduced by Tech Harmony and Otto Bock Health Care. The principle behind this design is to create negative pressure within the socket for suspension, particularly during the swing phase of gait. The manufacturers suggest that this system improves residual limb perfusion, reduces limb volume changes, and improves fit and comfort; however, objective clinical trials are lacking.56 The Iceross Seal-In liner chas been introduced by Ossur as a simpler means to achieve suction suspension.57 The system incorporates a membrane lip placed circumferentially around the distal aspect of the liner to cause a plunger effect and create a negative pressure when moving from stance to the swing phase of gait.

Advances in upper-extremity sockets allow self-suspension at the long transradial and wrist disarticulation levels and minimize the restriction of elbow flexion pronation and supination. Additionally, inventive developments incorporate myoelectric sensors and metal connections within silicone and elastomeric liners to improve the consistency of electromyographic signal acquisition and better control of myoelectric prostheses.58, 59

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Innovations in prosthetic research and design 

Osseointegration 

Osseointegration involves the direct skeletal attachment of a prosthesis to bone. This process was first described in the 1950s by Swedish bioengineer Per-Ingvar Brånemark, who realized that titanium cylinders implanted into the femurs of rabbits became integrated within the bone matrix.60 Today, the integration of titanium in bone is widely used in creating dental implants. Furthermore, ongoing studies in Europe are exploring the use of osseointegration for limb prostheses. Successful reports have been described for both thumb and transfemoral amputees.60

The operation is performed in 2 stages. First, a titanium fixture is threaded into the medullary cavity of the bone, and then the skin is closed over the fixture. Once the bone has threaded to the fixture at approximately 6 months, the patient is brought back to the operating room to undergo a second procedure, where a pin-like abutment is placed into the fixture. Then a hole is made through the skin to allow the abutment to protrude through the skin of the residual limb, which serves as the interface with the prosthetic device. A progressive weight-bearing schedule is started postoperatively, although full weight bearing is typically not achieved until 3 months after the second operation. In addition to the extended period of time required for non–weight bearing (≈9mo total) and rehabilitation (recommended for 2y), significant risk of infection exists with this procedure. A report from the United Kingdom cited 2 of 11 patients requiring abutment and internal fixture removal because of infection at 1 year, despite prescribed daily pin site cleaning. Other limitations of the procedure include recommendations to avoid running, jumping, and heavy manual work to minimize loosening or risk of breaking, in addition to avoidance of swimming to reduce the risk of infection.61 The potential benefits of direct skeletal attachment primarily include comfort and the elimination of poor prosthetic socket fit and skin problems. Additionally, recipients report improved sensory feedback from their directly skeletally attached limb through osseoperception. Although currently this procedure is not being performed in the United States because of the relatively high complication rate, the potential benefits have warranted ongoing basic science research.

Robotics 

Numerous robotic hands have been developed for industrial and entertainment purposes; however, none have yet been incorporated into prostheses. These hands are capable of producing both fine and gross motor movements and can also record tactile, proprioceptive, and temperature sensations. The primary limiting factor to their application in prosthetics is the lack of an adequate control interface needed to transmit these signals between the residual limb and the robotic device. Hands, similar to that developed by the CyberHand project, offer hope that a much more sophisticated hand can be developed that will provide a significant improvement over the prosthetic components currently available.62, 63 In addition to requiring multiple degrees of freedom for adequate motor control, robotic limbs are generally very heavy and require considerable power sources. Research is currently underway to develop lighter materials, smaller batteries, fuel cells, and new actuators.

Artificial Muscles 

Electroactive polymers are currently undergoing investigation. Otherwise know as artificial muscles, these polymers bend, twist, stretch, and contract under the influence of an electrical charge. Current limitations, however, include the need for high-voltage stimulation and a low amount of actuation force. Therefore, continued investigation and technologic refinement are needed to better define their role in the future of prosthetics.64

Experimental Interface Systems 

Although the integration of robotics and prosthetics continues to evolve, significant challenges persist in developing improved human-machine interface systems to better control prosthetic devices. Current myoelectric prosthetic devices are controlled by surface electromyographic activity. Surface sensors (electrodes) are dependent on good skin contact, minimal sweating, a well-fitting socket, and good voluntary muscle control by the user. Prosthetic control frequently requires the user to activate muscle groups that previously provided a different motor function than is now needed for operation of the prosthesis, creating an unnatural feeling. An example of this would be using the biceps muscle to activate hand opening or closing.

To improve myoelectric control, researchers are currently experimenting with implanting electrodes within residual limb muscles to increase the number of degrees of freedom for prosthetic device control. Devices such as the Bionf have already shown great promise in this application.65 Myoelectric control has also been facilitated with surgical reinnervation procedures. Kuiken et al66 reported the successful targeted reinnervation of residual brachial plexus nerves to the pectoralis major and minor muscles to increase the amount of voluntary surface myoelectric control sites for an individual with bilateral shoulder disarticulation.

Other potential sources of control include the peripheral and central nervous systems. Researchers at the University of Utah have already demonstrated the ability to implant longitudinal intrafascicular electrodes into chronically severed peripheral nerves of human amputees and record both efferent motor and afferent sensory electric potentials. Although the electrodes were percutaneous and only remained in place for 2 days, the experiment provides proof of the concept that peripheral nerve control of a prosthetic device could be achieved. It also suggests the ability to transmit sensory feedback from the prosthesis to the user.67, 68 Cortical control of both prosthetic and robotic arms has also been shown in both primates and humans. So-called brain-machine interfaces incorporate the placement of electrodes near or within the motor cortex of the brain. These electrodes sense motor thoughts and transmit electrical signals to a computer processor that decodes these impulses and transmits them to a powered robotic arm.69, 70, 71, 72

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Conclusions 

Today marks a unique period in history, in which modern science, advanced technology, and improved material design can be brought together to revolutionize the care for people with amputation. Accomplishing this goal, however, will require significant teamwork and partnership both across and within different disciplines. Modern medical research must reach out to all areas of science, including those not traditionally associated with health care. Clinicians must clearly identify and communicate the functional needs of patients to engineers, biologists, computer scientists, and systems integraters to achieve common goals. Furthermore, a mutual sharing of ideas between public and private universities and industry is necessary to truly advance the field.

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Appendix 1. Instruments to assess amputation outcomes 

Self-Reporting Measures 

•Medical Outcomes Study 36-Item Short Form Health Survey73

•Prosthesis Evaluation Questionnaire74

•Locomotor Capabilities Index75

•Sickness Impact Profile76

•Questionnaire for Persons with a Transfemoral Amputation77

•Trinity Amputation and Prosthetic Experience Scale78

Performance-Based Measurement Tools 

•Get up and go test79, 80

•6-minute walk test81

•Amputee Mobility Predictor82

•Disabilities of the Arm, Shoulder and Hand questionnaire83

•Box and block test84

•Jebsen-Taylor Hand Function Test85

•Step Activity Monitor86

•3-dimensional gait and motion analysis87, 88

•Energy consumption measurements29, 89

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  • a Otto Bock, 2 Carlson Pkwy N, Ste 100, Minneapolis, MN 55447.
  • b Endolite, 105 Westpark Rd, Centerville, OH 45459.
  • c Ossur North America, 27412 Aliso Viejo Pkwy, Aliso Viejo, CA 92656.
  • d Motion Control Inc, 115 N Wright Brothers Dr, Salt Lake City, UT 84116.
  • e Liberating Technologies Inc, 325 Hopping Brook Rd, Ste A, Holliston, MA 01746.
  • f Bion Applications, PO Box 905, Santa Clarita, CA 91380.
  • g College Park Industries, 17505 Helro Dr, Fraser, MI 48026.
  • h Freedom Innovations Inc, 7 Studebaker, Irvine, CA 92618.
  • i Ohio Willow Wood, 15441 Scioto-Darby Rd, PO Box 130, Mt Sterling, OH 43143.

 No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

PII: S0003-9993(05)01462-0

doi:10.1016/j.apmr.2005.11.026

Archives of Physical Medicine and Rehabilitation
Volume 87, Issue 3, Supplement , Pages 34-43, March 2006

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