For some conditions, the most direct and predictable pathway to a high level of function and the least interruption to the life of a child may include an amputation/prosthesis strategy.1 Indications for amputations in children include management of both congenital and acquired deformities. Long bone deficiencies of the femur, tibia, and/or fibula are commonly managed with amputation strategies.2–4 Congenital malformations such as those in early amnion rupture sequence may require ablation procedures. Trauma remains a leading cause of acquired amputations in children, often secondary to lawn mower injuries or motor vehicle accidents. Definitive care of severe infections such as meningococcemia, and management of certain malignant conditions may require amputation. In addition, prolonged pain, compromised function, or poor cosmesis in an extremity that failed multiple attempts at reconstruction can often be effectively managed with an appropriate amputation and a well-fitting prosthesis.
An adequate residual limb is one that can properly power a prosthesis, is end-bearing, and is tolerant of the prosthesis. Surgical planning and surgical decision-making must provide an optimal residual limb that fits well in a prosthesis and tolerates the stresses of the prosthetic environment. Insensate limbs and limbs with extensive skin grafts or scars may be prone to skin breakdown from the contact pressure of a prosthesis.5 The residual limb must also have adequate proximal muscle function and joint mobility to maneuver and control a prosthesis. Short residual limbs may be difficult to suspend resulting in poor stability of the prosthetic device.
APPOSITIONAL BONE OVERGROWTH
Appositional overgrowth of the residual limb or juvenile amputee overgrowth is a common problem in growing children who have an amputation. Overgrowth may be avoided by amputation through the joint (disarticulation), or preservation of the end of the bone covered by normal cartilage (ie, Boyd procedure).6 Occurrence is reported from 4% to 35% and is dependent on the age of the patient and the location of the amputation.7 It is most commonly seen in below knee amputations affecting the tibia and fibula, and in the upper extremity with transhumeral amputations. It occurs after amputations through the diaphyseal level of long bones in both congenital and acquired conditions, is rarely seen in the femur, and seldom occurs after skeletal maturity.
Multiple theories regarding the etiology of juvenile amputee overgrowth exist. Originally, growth of the bone, due to an open physis and contraction of the soft tissue envelope, was thought to lead to prominence at the end of the residual limb, formation of a bony spike, and eventual compromise and perforation of the overlying skin. As studies have demonstrated that abnormal growth occurs at the distal aspect of the bone as a consequence of a local biological phenomenon. The current accepted explanation is that this process represents a malfunction in normal bone healing mechanisms due to stimulation of pleuripotential medullary cells by mechanical, chemical, electrical, and other forces.8
When a patient presents with end-bearing pain or bursa formation, initial management should include conservative measures to reduce inflammation and further irritation to the limb. Radiographs should be reviewed to characterize the morphology of the residual limb for possible overgrowth or spike formation (Fig. 1). Modification of the prosthesis or cessation of use for a limited time may be helpful. If a bony spike is present, conservative measures are likely to fail and surgical treatment is usually required.
Surgical resection of the prominent bony spike is often necessary. Resection alone leads to frequent recurrence and often requires repeated surgical events to shorten the residual limb. Capping of the medullary canal, along with resection of the bony spike, has been shown to reduce recurrence of overgrowth. Multiple agents including autograft, allograft, silicone sleeves, and polyethylene caps have been utilized. The biological cap had superior results when compared with other materials.9
RESIDUAL LIMB DEFORMITIES
A residual limb must be of optimal length to provide stability and allow for customization of prosthetic devices. In some cases the residual limb may be too long, precluding the use of certain prosthetic components.10 This is commonly seen in traumatic amputations of the foot, especially in older children. It can also occur in congenital deficiencies when a foot ablation procedure is performed leaving a relatively normal length residual tibia. In most cases, a shorter residual limb is favored over a longer residual limb. Many of the foot and ankle components, especially the dynamic response feet, are larger and require a longer build height. These devices allow for energy absorption and are commonly used in high demand or sporting activities. A very long residual limb precludes the use of these devices.
Guided growth strategies may be utilized to modify the length of the residual limb. An appropriately timed epiphysiodesis of the proximal tibia and fibula may result in improved differential of leg lengths between the intact and the prosthetic side. If the distal tibial epiphysis is present and active, ablation of this physis may be performed as well. Similarly, children who have undergone a knee disarticulation may experience mismatch of the knee level if the femoral lengths are similar. In these cases, the prosthetic knee joint is set slightly lower than the biological or sound-sided knee. A distal femoral epiphysiodesis of the residual limb allows for a more natural appearance at the knee levels.
Coronal plane deformity, such as genu valgum, is also common in congenital deformities including fibular deficiency and postaxial limb bud deficiency. The mechanism is related to hypoplasia of the lateral femoral condyle. Guided growth strategies with a hemiepiphyseodesis strategy may be done before skeletal maturity to improve coronal plane alignment.11
During acute management of a traumatic amputation, the soft tissue envelope of the residual limb may be compromised. Frequently, skin grafts or soft tissue transfers are required to provide adequate coverage and length of a residual limb. The surgeon must recognize that the prosthetic environment is suboptimal with a compromised soft tissue envelope. The residual limb is exposed to significant mechanical and thermal stresses due to prosthetic wear. Limbs that have undergone extensive grafting may be prone to further scarring and skin breakdown, leading to disruption of prosthetic use and ultimately revision surgery (Fig. 2). Focal skin grafts of <25% of the surface area are well tolerated, whereas larger skin grafts especially in distal locations lead to poor functional outcomes.5
A skilled prosthetist plays a vital role in the overall successful management of a child with an amputation. The growing child presents numerous challenges to the prosthetist. In a growing child, the residual limb is not static. Changes in the length and girth of the limb, especially during peak growth years, require frequent adjustments and replacements of the prosthetic device. The developmental capabilities of a child are constantly changing and influence the choice of components and overall design of the prosthesis.12
The choices of prosthetic design and components are determined by many factors. Components should be appropriate for the developmental age of the child. Typically, a simple device for walking is recommended for young children, with gradual transition into more customized devices as the child matures.13 A child who desires to participate in mainstream activities or sports may require higher end components. Children need durable devices that are low maintenance, or simple to repair when broken. Cost must also be considered as a child is going to require multiple devices throughout the growing years.
Significant advances in the prosthetic industry have occurred over the past 2 decades. Government-sponsored research programs have led to advances in the types of components and materials utilized. Millions of dollars each year are appropriated toward prosthetic research. Some of these advances now provide materials that improve fit and suspension, are lighter weight, and have the added option of microprocessor control of the knee and ankle.
Custom devices enable children to participate in mainstream activities including sports such as track, swimming, or rock climbing. Recent advances in prosthetic technology now provide devices that store kinetic energy during loading producing a spring-like effect for running. Swimming can be accomplished with standard devices, or with newer components that facilitate propulsion through the water.
Despite these advances, durable, economic, and basic design prostheses are routinely used in the pediatric population. The exoskeletal design provides a low cost, durable device that can be adjusted in length, and has the advantage that it may be used by children for swimming activities (Fig. 3). The endoskeletal design is popular with older children and teenagers.14 A prosthesis with this design is often lighter weight and can be adjusted for length and/or allow socket replacement when necessary (Fig. 4).
The most common prosthetic feet utilized in the younger population are the solid ankle cushion heel foot and Seattle light foot. Both of these are durable and relatively inexpensive. Energy storing and dynamic response components are made of high-grade material, provide a more natural gait, and are commonly used for sporting activities in older children and teens.15 Single-axis or locking knees are used in the younger population. As the child develops balance skills, polycentric knees may be introduced. Microprocesser knees are available, but have significant cost compared with traditional components.16
The overall cost of a prosthesis is significant. Price is dependent on multiple factors including the type (above knee vs. below knee), method of suspension, choice of materials, and choice of components. For example, a standard below knee prosthesis, with solid ankle cushion heel foot and pelite liner generates a charge of ∼$3500 (2015 South Carolina Medicaid allowable charges). In comparison, a below knee endoskeletal prosthesis with gel liner and flex-foot system increases the charge three-fold. The charge for a basic knee disarticulation prosthesis begins at $7000 (2015 South Carolina Medicaid allowable charges), but with the addition of a microprocessor knee and multiaxial foot, and ankle component, the charge approaches $40,000 (2015 South Carolina Medicaid allowable charges). Patients and families can expect recurring costs which include periodic repairs as well as necessary replacements.
The financial impact of utilizing a prosthetic device over a child’s lifetime must be considered when counseling families regarding treatment options. In conditions where limb salvage is a reasonable alternative strategy, the cost of multiple surgeries, extensive physical therapy, management of complications, and loss of work time must be weighed against the potential costs of a prosthesis that will need replacement every 3 to 5 years.
Significant advances in design and manufacturing processes for prosthetics have led to improvements in efficiency and patient satisfaction. Traditional methods involved manual casting of the extremity and creation of a positive mold of the limb. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology now provides an alternative to the traditional methods of molding and prosthetic manufacturing.17
With this technology, a scanner is utilized to capture the shape of the residual limb. Computer-based software then creates a 3-dimensional image of the limb which can be adjusted, corrected or modified. A 3-dimensional carver then carves foam blanks into positive molds that are ready for lamination or vacuum forming. This technology is applicable to not only prosthetics, but also lower extremity and spinal orthoses.
The benefits of CAD/CAM technology are several. Patient satisfaction is high as the process does not require traditional casting, which can be uncomfortable or embarrassing for a patient. For the practitioner, dedicated space for storage of plaster casts is no longer necessary. The portability of scanners allows networks of providers to utilize fabrication centers with image acquisition from multiple off-site or remote locations. A virtual library documenting a patient’s changing shape and volume over time can easily be created and accessed.
Historically, the high cost and learning curve involved with CAD/CAM systems inhibited widespread use. The cost of the most expensive component, the carver, may be avoided or minimized by using central fabrication facilities. More studies are necessary to demonstrate that CAD/CAM technology produces devices that fit as well, cost less, and are produced more efficiently than traditional hand cast methods.
For children with amputations, successful outcomes are possible with well-done surgical procedures, occasional modifications to the residual limb, and an appropriate prosthesis fit by a skilled prosthetist. These children live regular, mainstream lives and experience a very high level of function.
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Keywords:Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.
amputation; prosthetics; pediatric