Prosthetics

David Patrick

Introduction

The elderly make up the largest group of patients requiring lower extremity (LE) amputations. Review of the literature has determined that significant variation exists internationally in the incidence of LE amputation. The incidence of all forms of LE amputation ranges from 46.1–96 per million in the population of amputees with diabetes compared with 5.8–31 per million in the total population of amputees without diabetes (Moxey et al., 2011). Diabetes and its complications are identified as having the most profound influence while the role of ethnicity and social deprivation are also important factors. Globally, a wide variation also exists in the access to high-quality prosthetic and orthotic care for those in need, a major focus of the International Society for Prosthetics and Orthotics (ISPO). Differences in prosthetic and orthotic education have been identified worldwide ranging from no formal education to advanced university-based degrees, such as in the United States of America where the graduate Masters degree has been adopted as the entry level standard by the American Board for Certification. The advancement of global prosthetic and orthotic education utilizing creative educational models and concepts such as distance learning is being pursued in an effort to meet the needs of the underserved in developing countries and improving the standards and consistency of care throughout the world (Ferrendelli, 2012).

Evaluating the patient

The physical therapy program starts with a comprehensive evaluation of the patient. This is particularly important with the elderly amputee, who commonly presents with a number of comorbid conditions that can impact his/her functional outcome. The following elements represent important considerations in evaluation and treatment of the geriatric amputee.

Age

Consider overall wellness and conditioning, functional abilities and motivation as being more important than chronological age.

Secondary Diagnosis

Investigate the presence of comorbid conditions. Elderly vascular amputees can demonstrate multiple secondary conditions in addition to the amputation. The presence of cardiac disease is common, as the same factors that increase the incidence of peripheral vascular disease (PVD) in diabetics also increase the incidence of atherosclerotic coronary artery disease. This leads to an increased death rate (there is an estimated 25–50% 3-year survival for a person with diabetes, with a major amputation) (Schofield et al., 2006) and an increase in the symptoms of angina, congestive heart failure (CHF) and arrhythmias.

Cognitive Status

Determine the patient’s ability to understand and remember instructions. Provide instructions in writing that clearly state the wearing schedule of the shrinker, socks and prosthesis. Review the instructions with the patient frequently. Direct the patient to maintain a written diary of sock-ply use and color-code the various sock plys to assist the patient in maintaining proper socket fit.

Wheelchair

Recommend availability of a lightweight, easily transportable wheelchair for long-distance transportation, limited ambulation endurance, discontinued prosthetic use (because of skin breakdown) and prosthetic breakdown. Bilateral LE geriatric amputees commonly depend on wheelchairs or powered mobility as an option to walking with prostheses, particularly for long distances.

Transfers and Mobility

Train patients to change positions slowly to avoid episodes of syncope that could result in loss of balance. Reduced proprioceptive feedback through the prosthetic extremity, and the predisposition of the elderly for postural hypotension, increase the risk of balance loss when changing positions.

Ambulation

Prioritize the maintenance of skin integrity, the prevention of falls and the control of energy expenditure. Assess the patient’s ability to ambulate (post amputation) with an assistive device without a prosthesis.

Skin Integrity

The loss of elements of the connective tissue, the thinning of the dermis and alterations in the content of elastin and collagen represent characteristic skin changes that occur with aging and predispose the amputee to skin breakdown during prosthetic use (see Chapter 50, Skin Disorders). Particularly with the transtibial (below-knee) amputee, use a conservative, methodical progression of weight-bearing and ambulation distance and continue to monitor the skin of the residual limb (in the past, it was referred to as the stump) on a frequent basis. Consider shear-force-absorbing socket interfaces and prosthetic componentry to reduce forces on the residual limb.

Fall Prevention

Conservative advancement of assistive devices is recommended, prioritizing safety over progression. In the author’s experience, the transfemoral (above-knee) geriatric amputee is less prone to skin breakdown than is the transtibial amputee, but the transfemoral amputee is at greater risk for falls.

Energy Expenditure

The geriatric amputee should not be encouraged to walk at a ‘normal’ walking speed. Allowing the patient to self-select ambulation velocity results in a more normal rate of metabolic energy expenditure, decreasing perceived exertion and potential cardiac difficulties. A slower self-selected walking velocity should be expected at higher amputation levels.

Prosthetic Donning and Doffing

Difficulty in donning and doffing the prosthetic may result from limitations in manual dexterity as well as visual dysfunction. Self-suspending systems, Velcro closures versus buckles, and oversized extensions on belts and socket inserts should be considered.

Range of Motion (ROM)

Adequate ROM is required for successful prosthetic outcome. Degenerative joint disease predisposes elderly amputees to contractures. Common areas of LE contractures include:

• the partial foot level: plantar flexors (due primarily to muscle imbalance)

• the transtibial level: knee flexors and hip flexors

• the transfemoral level: hip flexors, hip abductors, hip external rotators.

Strength and Endurance

Deconditioning, common with aging, may limit ability to participate in the rehabilitation program. Initiate a strengthening and endurance program as soon after surgery as possible.

Volume Containment

Controlling the volume of the residual limb is an important aspect of preparing it for definitive prosthetic fitting, reducing pain in the limb that is related to edema, and facilitating healing after the amputation surgery. Comorbid conditions such as renal failure and dialysis or CHF predispose the geriatric amputee to significant girth fluctuations. Shrinker socks are recommended instead of elastic wraps because of the relative ease of donning and the greater consistency of fit (they require less frequent reapplication and adjustment). A rigid dressing should be considered when protection of the residual limb is a priority. Premanufactured removeable rigid plastic shells (e.g. Flotector: APOPPS FLO-TECH-TOR products www.1800flo-tech.com/products.html) provide the dual benefits of protection of the residual limb from external trauma and positioning of the knee to prevent flexion contractures. Regular girth measurements of the residual limb are recommended to monitor the effectiveness of the volume-containment program.

Sensation

Sensory examination is important to accurate prediction of the amputee’s ability to detect abnormal forces during prosthetic use and to detect soft-tissue trauma in the remaining limb. Vascular insufficiency and particularly diabetes may result in polyneuropathy involving the sensory nerve fibers, predisposing the elderly amputee to skin problems.

Condition of the Remaining LE

It is essential to examine the remaining LE for evidence of vascular insufficiency or sensory deficits that could lead to further amputation. Unilateral amputees with diabetes have more than a 40% risk over 4 years of having an amputation of the remaining LE (Johannesson et al., 2009). Polyneuropathy associated with diabetes may involve sensory, motor and autonomic nerve fibers. Motor deficits may cause atrophy of the foot intrinsics and muscle imbalances in the foot. These problems result in deformity that predisposes the skin to injury from fitting problems with shoes. Sensory deficits result in the lack of an appropriate avoidance response to abnormal forces. Autonomic involvement may result in dry skin which creates greater susceptibility to breakdown and infection. The importance of this evaluation cannot be overemphasized, as a peripheral neuropathy has been identified as the primary underlying cause of amputation in the elderly with diabetes. Patient education that emphasizes proper footwear and skin management is an essential component of the amputation prevention program. The incidence of LE amputations has been shown to be significantly reduced in specific at risk populations after the introduction of specialist diabetic foot clinics (Moxey et al., 2011).

Prosthetic prescription

Advances in the technology of prosthetic components have improved the possibility of successfully fitting the geriatric amputee with a prosthesis. Innovations in socket designs, lightweight components, improved suspensions and stable knee design options all contribute to improved prosthetic tolerance and better functional outcomes for elderly amputees. The application of advanced prosthetic componentry also results in increased expense, so judgments must be made about the relative costs and benefits of these components to each patient. In the US, the Lower Limb Prosthetics Medical Review Policy (LLPMRP: available from the US Department of Health and Human Services) developed by Medicare, structures financial sponsorship of the various prosthetic ankle, foot and knee components based on the patient’s anticipated functional outcome. The LLPMRP should be considered by the prosthetics team in the process of prescribing prostheses for geriatric amputees as many third party payers follow this policy as a basis for financial sponsorship.

Preparatory vs. definitive prosthesis

A preparatory prosthesis is often recommended over a definitive prosthesis as the first prosthetic device for a geriatric amputee. The preparatory prosthesis includes basic components that are easily adjusted but is not finished cosmetically. The preparatory prosthesis allows earlier prosthetic fitting by avoiding the need to wait until shrinkage of the residual limb is complete (Edelstein, 1992). This may help to prevent secondary complications resulting from immobility that are potentially life-threatening to the elderly patient. The definitive prosthesis is the finished product, with all the appropriate components and cosmetic touches. The definitive prosthesis is fitted when the residual limb size stabilizes. The specific training and skills required for use of certain advanced componentry such as microprocessor knees has led to the debate of using high-tech componentry in the initial prosthesis and replacing only the socket of the prosthesis once the expected shrinkage of the residual limb occurs. The need for training can be reduced as the patient is not required to re-learn how to ambulate with different components. Gait performance, stability and safety may be improved through the earlier use of technology, and bad habits may be avoided in the initial gait training process.

Endoskeletal vs. exoskeletal design

The exoskeleton design has a hard, laminated plastic shell that provides the weight-bearing support. In contrast, the endoskeletal design consists of a tubular structure that constitutes the internal support to which the foot, ankle and knee assemblies are attached. The endoskeleton is covered with a pliable surface that is shaped and colored to match the opposite limb.

Endoskeletal prosthetic design is usually recommended for geriatric amputees because of the ease with which adjustments can be made and components interchanged, the reduced weight and the cosmetic benefits in transfemoral applications. Weight restrictions have been identified by the manufacturers of some endoskeletal components.

Prosthetic sockets

At the level of the transtibial amputation, the patellar tendon-bearing (PTB) socket with a soft insert is commonly utilized. A patient with fragile skin or sensitivity in the residual limb may benefit from soft insert materials such as silicone that are designed to dissipate shock and shear forces. A flexible inner socket supported in a rigid outer frame may result in greater comfort for the elderly amputee by providing relief to pressure-sensitive structures. The flexible inner socket also facilitates necessary socket adjustments (American Academy of Orthotists and Prosthetists, 2004).

After a transfemoral amputation, a geriatric patient can be successfully fitted with either a quadrilateral or an ischial containment socket. A patient with a short residual limb, poor residual limb muscle tone, obesity, or a high activity level would be expected to achieve the greatest benefit from the ischial containment socket design. The elderly amputee may experience more comfort when sitting if he or she has chosen a flexible socket design that is capable of accommodating its shape to the supporting surface.