An individual with a lower extremity amputation must bear his or her full body weight on soft tissues that are not designed for that function. Therefore, the socket must be designed to distribute these forces over as large a surface area as possible and as evenly as possible over pressure-tolerant areas. For a transtibial limb, the following areas are important :
* Pressure-tolerant areas
o Patellar tendon
o Pretibial muscles
o Posterior aspect of the residual limb over the upper portion of the gastroc-soleus muscles
o Lateral shaft of fibula
o Medial tibial flare
* Pressure-sensitive (relief) areas
o Tibial crest, tubercle, and condyles
o Fibular head
o Distal tibia and fibula
o Hamstring tendons
The same considerations must be taken into account for a transfemoral limb. Weight bearing is concentrated in the medial aspect of the ischium and the ischial ramus. The ischial tuberosity is contained inside the socket, providing a bony lock between the ischium and the greater trochanter. The femoral shaft will distribute some force, and relief is provided to bony prominences.
Sources of pain in the residual limb that are difficult to manage may include the following:
* Bony osteophytes or spurs from trauma or from periosteum that was incorrectly stripped during surgery
* A hypermobile fibula that is longer than the tibia
* An unbalanced myodesis for transfemoral amputation, which can cause the femur to extrude through the muscle and skin
* The failure of a myoplasty or myodesis
There is an increased chance that the presence of osteoarthritis in a patient's sound limbs and/ or back will become a factor over time. There are greater stressors on the remaining joints after an amputation, and the patient tries to adapt to this. Poor socket fit or suspension may be another source of pain. The presence of ongoing pain, skin breakdown, a change in the ability to put on and remove the prosthesis, and a change in the number of sock plies indicate that the prosthesis needs to be modified. Erythema normally appears within a few minutes after the prosthesis is removed and should fade quickly. Erythema that is present upon removal of the prosthesis or that does not completely resolve within 20 minutes is particularly worrisome.
Contractures
Hip and knee flexion contractures affect prosthetic fitting and function. A knee flexion contracture of 10º or less can be treated conservatively with stretching, ambulation, and ultrasound, if desired. A knee flexion contracture of 25º or more may require hamstring lengthening with posterior knee capsule release or a bent-knee prosthesis. The ability to accommodate a hip flexion contracture depends on residual limb length. A long transfemoral residual limb with a contracture of 15º or more leads to compensatory lumbar lordosis. A short transfemoral limb can accommodate up to 25º of hip flexion contracture with resultant loss of hip extension power. For the patient with a transfemoral amputation, a hip contracture results in knee instability and may require the use of a lockable knee. Knee and hip contractures also decrease cosmesis and efficiency of ambulation.
Phantom sensation and phantom pain
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 part of the amputated limb is still present. Phantom sensation is not painful, and the patient usually needs only to be reassured that this sensation is common and not an indication of a mental disturbance. The phenomenon of telescoping—the sensation that the amputated limb has shrunk (eg, the toes are at the ankle, the foot is at the knee)—can accompany phantom sensation. 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 describe a burning, stinging, or cramping pain or report the feeling that the missing body part is "positioned awkwardly or painfully." The pain usually develops in the first month after amputation. It is most likely to appear in individuals who experienced a lot of pain before amputation. Phantom pain is constant and most intense right after the amputation. The pain becomes more intermittent over time before ultimately resolving, although some patients still experience phantom pain years after the amputation. Patients who have undergone amputation commonly report intermittent phantom pain symptoms, but these individuals are able to ignore the pain and require no medication for treatment. Phantom pain usually is worse at night, after the extremity has been in a dependent position, and can be exacerbated by anxiety and stress.
Unlike postsurgical pain, which responds well to opioid medications, such as acetaminophen plus oxycodone (Percocet) and acetaminophen plus hydrocodone (Lortab), phantom pain is best treated with low doses of tricyclic antidepressants (ie, nortriptyline or amitriptyline, 10-25 mgPO qhs) that can improve sleep. Phantom pain may respond well to medications such as carbamazepine (Tegretol), amitriptyline (Elavil), pregabalin (Lyrica), and gabapentin (Neurontin; titrate to at least 300 mg tid; serum gabapentin levels can be monitored); these stabilize the nerve's ability to depolarize and can decrease dysesthetic symptoms.
Transcutaneous electrical nerve stimulation, topical anesthetics (ie, capsaicin cream), and anxiolytics may be useful against phantom limb pain. Decreasing residual limb edema is helpful, and the use of prostheses has been found to result in fewer reports of phantom limb pain.
Theories exist as to why patients experience phantom limb pain and phantom sensation. For example, it may be 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. Still another theory is that altered signal transmission and modulation occur within the somatosensory cortex. Other possible causes include abnormal sympathetic function and psychological factors.
Choke syndrome
When the proximal part of the socket fits too snugly on the residual limb, venous outflow can be obstructed. When this is problem is combined with an empty space more distally in the socket, swelling can occur until that empty space is filled. In an acute choke situation, the skin is red and indurated and may have an orange-peel appearance, with prominent skin pores. If the constriction is not resolved, then chronic skin changes can occur with hemosiderin deposits (verrucose hyperplasia), and venous stasis ulcers can develop (see image below and Image 16 ). Choke syndrome and verrucose hyperplasia are treated by restoring total contact and eliminating the void between residual limb and socket. This is achieved by relieving a tight proximal constriction, adding distal padding inside the socket, improving suspension to eliminate pistoning or a loss of suspension that may be creating the void, using compression on the residual limb when the patient is out of the prosthesis, or constructing a new socket.
Verrucose hyperplasia that has developed after choke syndrome. Choke syndrome develops when a tight proximal socket impairs venous return and a lack of total contact occurs between the residual limb and the prosthetic socket. Acutely, significant edema leads to weeping and blistering skin. As the choke becomes chronic, the tissues become thickened and indurated. Hemosiderin deposition causes hyperpigmentation of the skin.
Dermatologic problems
Common skin management issues include the development of contact dermatitis or sebaceous cysts, excessive sweating, and scar management.
* Contact dermatitis frequently appears as a macular, papular, erythematous rash that is often pruritic. The liner, socks, and suspension mechanism are the usual culprits for contact dermatitis. The socket is a less likely cause. Treatment consists of identification and removal of the offending item and symptomatic treatment with topical diphenhydramine (Benadryl) or cortisone creams.
* Cysts and sweating can be signs of excessive shear forces and components that are improperly fitted. Sweating can also result from the loss of surface area (following amputation and the covering of the skin surface area with a prosthesis) needed for thermoregulation.
* Skin maceration is caused by excess moisture next to the skin. Treatment may include frequently changing prosthetic socks, applying cornstarch or talc power to the limb, and using specially formulated antiperspirants.
* Tinea infections are caused by excessive moisture, with or without poor hygiene.
* Folliculitis is an infection of the hair follicles. It is caused by poor hygiene, sweating, and poor socket fit. Treatment includes use of antiseptic cleaner and topical ointments. Socket modification may be required to avoid high-pressure areas.
* An epidermoid cyst is a sebaceous gland that is plugged with keratin. Treatment includes the use of topical or oral antibiotics, as well as incision and drainage or excision.
* Scar management is focused on massaging and lubricating the scar to obtain a well-healed result without the appearance of "dog ears" or adhesions. Skin adherence may result from scar tissue.
Energy Consumption in Lower Extremity Prostheses
The increased energy requirements of prosthetic ambulation can limit the use of a prosthesis. An individual who has a lower extremity amputation and requires a walker or crutches to ambulate (with or without a prosthesis) uses 65% more energy than does someone with a normal gait. Energy consumption (percentage above normal, according to amputation level) for ambulation with a prosthesis is as follows 15, 16 :
* Below-knee, unilateral amputation - 10-20%
* Below-knee, bilateral amputation - 20-40%
* Above-knee, unilateral amputation - 60-70%
* Above-knee, bilateral amputation - >200%
BKA actually requires less energy consumption than does ambulation with crutches. However, ambulating with an AKA requires more energy than ambulating with crutches does, which makes the cardiopulmonary status of the patient more significant.
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