Upper Limb Prostheses for Children

Robert D. Lipschutz CPO, BSME

Robert D. Lipschutz or an immediate family member serves as a board member, owner, officer, or committee member of the Association of Children’s Prosthetic and the Orthotic Clinics.

ABSTRACT

Fitting children with upper limb prostheses has many similarities to and many differences from adult prosthetic fittings. The components used in adult and pediatric devices are somewhat analogous in design, shape, and function. However, differences are present in the size of the components, the etiology of the deficiency or amputation, the level of family involvement, and the required accommodations for future growth and component designs. Most adults with upper limb amputations are young men who have sustained traumatic injuries, while congenital limb differences are the most common reason for fitting a child with an upper limb prosthesis. All prosthetic fittings are unique to the situation and the individual. Common factors for choosing the timing, components, and complexity of upper limb prostheses to children are dependent on residual limb length, age at the time of fitting, and current functional needs.

Introduction

The decision to fit an individual with a limb prosthesis, regardless of the etiology or cause of the limb difference, seems to be obvious. Strange as it may seem, fitting upper limb prostheses to some children with upper limb differences has been a topic of controversy for many years. Most parents will pursue fitting of prostheses to their child if their child has had a traumatic amputation or one because of disease or illness. However, fitting a child with a congenital limb difference is not an absolute. Many factors weigh into the decision of whether to fit children with prostheses including level of limb difference, prosthesis options, aesthetics of the device, and experiences of the prosthetist and doctor. Compounding this dilemma are the current approaches and design foci of new prosthetic options for children and young adults.¹^,²^,³^,⁴^,⁵^,⁶^,⁷ Several of these fitting approaches, that is, 3-D printed kits and sharing of scanned files, remotely to fabricate a prosthesis for the child, eliminate the prosthetist (and entire healthcare team) from the clinical evaluation and fitting process. This direction is somewhat concerning to clinicians, but the families and healthcare professionals need to be aware of these options to insure appropriate safety and provisions for children/families seeking prosthetic care.

The development of new components for children has been almost nonexistent for the past decade. Manufacturing of mechanical digits and some designs of externally powered hands are being made in smaller sizes. Additionally, newer methods of electromyogram (EMG) acquisition and processing referred to as pattern recognition are being introduced to younger individuals with limb differences and amputations. Currently, because of the size and weight, the hardware for these systems along with the smaller hands are not applicable to younger children, but may be beneficial for some adolescents or young adults.

Although some studies have alluded to the minimal benefits of fitting children with upper limb prostheses, others have demonstrated their usefulness in improving self-esteem, acceptance among peers, and efficiency in manual activities.⁸^,⁹^,¹⁰^,¹¹^,¹² Regardless of these conclusions, each child and family is unique and has its own reasons and desires when considering prosthetic fitting. Success in fitting a child with an upper limb prosthesis is also subject to a multitude of variables, and requires educating the family and providing the appropriate resources from the community and dedicated healthcare team.

General Considerations

When a family is considering fitting their child with a prosthesis, they should have a thorough understanding and acceptance of the influence of amputation/limb difference etiology, component options, functional benefits, cyclic wearing patterns, the child’s motivation level, and the challenges
associated with prosthetic use. At first, the parents will make the decision for their child; later in life, the child will be encouraged to become involved in the process of selecting a prosthesis that they feel will be most beneficial to them, along with the corresponding components.

The primary etiology for upper limb amputations in children is congenital anomalies. In such patients, it is essential that the parents understand and accept the differences in their child’s upper limb. In a child with an acquired amputation caused by trauma, infection, tumor, or other injury, it may be even more difficult for the child and family to accept the amputation, and greater demands may be expected of both the prosthesis and prosthetist.

Education should be provided about the associated benefits and limitations of various prosthetic fittings and components, such as terminal devices, wrists, and elbows. The child and family also need to be able to clearly express their goals and desires for the prosthetic fitting (whether the device will be aesthetic, prehensile, or have some combination of aesthetic and prehensile attributes) and recognize that such preferences may change throughout the child’s life. Periodically, through their growing years, children may express a reluctance to wear an upper limb prosthesis. This reluctance will often begin with nonverbal cues when the child is quite young and progress to complete rejection when the child has the ability to verbally communicate. Children and young adults have the ability to change their minds and often go through a cyclic pattern of use and rejection of upper limb prostheses. Throughout childhood and adolescence, children will have the ability to try a variety of styles and components, allowing them to make a more educated decision on the prosthetic design of choice and use as they become adults.

The commitment of the family, the child, and the clinical team to the prosthetic fitting process is paramount in achieving success.¹³^,¹⁴ Over the past few decades, the approaches of clinical teams and families toward the fitting and use of upper limb prostheses have changed¹⁵—with fewer absolutes and more gray zones. The clinical team should discuss the pros and cons of prosthetic fitting, including voluntary nonuse by the child. If the child is fit with a prosthesis, a thorough effort must be made to train the child to use it and to incorporate the prosthesis into their daily activities. Parents often express that they are too busy, or do not want to spend the few moments that they have together with their child struggling over donning and practicing with the prosthesis. Unfortunately, unless the family is willing to invest adequate time in the training process, it is unlikely that the child will accept the prosthesis without constant assistance in donning the device and reminders of how and when to use their prosthesis.

Along with family and peer support, professional training by a skilled occupational therapist is also beneficial. Although many occupational therapists have limited training in working with upper limb prostheses, there are many centers that specialize in the care of children and have therapists with the required experience. If the therapist does not have the experience working with upper limb prostheses, they should seek the assistance of the prosthetist or an experienced therapist to provide training and support.

The clinical characteristics of children with upper limb deficiencies vary widely. Longitudinal limb deficiencies are less common than transverse deficiencies; therefore, prosthetic fittings are more common in patients with transverse deficiencies.¹⁶^,¹⁷ A discussion of the principles of prosthetic fitting must begin with the distal-most amputations and deficiencies and progress through more proximal amputation levels. The components appropriate for different levels of limb absence in specific age groups are to be discussed.

Digital Absence

Congenital deficiencies are rarely the cause of isolated absences of a digit or digits. Syndromes such as Streeter dysplasia (often referred to as amniotic band syndrome), Möbius syndrome, or Poland syndrome may infrequently cause digital absence, but these disorders are uncommon, and prosthetic restoration of individual fingers is rare in affected patients. In the pediatric cohort, trauma is more likely the cause of digital amputations. Potential causes include injuries sustained from paper shredders, farming equipment, and fireworks.

Historically, the main prosthetic intervention for digit amputation has been an aesthetic replacement of the finger for functional and psychological reasons. The function of these digits is limited and often interferes with the child’s ability to perform manual tasks. Prostheses for this level of amputation that meet the aesthetic needs of the child and family often are very expensive and do not last for long periods of time because of the child’s continued growth and active lifestyle. However, this may prove beneficial as an option, especially for older children and those with an acquired digital amputation.

Newly developed designs of mechanical digits may also be of benefit to the adolescent and younger adult. Manufacturers of individual articulated fingers have made options available for the pediatric cohort. These designs can be cable driven via movement of proximal joints such as the wrist, or passively positional using the contralateral hand, leg, or other surface to preposition the digit in the desired amount of proximal-interphalangeal and distal-interphalangeal (DIP) flexion (Figure 1). The passively positional designs are quite strong and incorporate ratcheting mechanisms to prevent extension of the digit once the prepositioning force is removed. To extend the finger, it is either fully flexed and released or a trigger on the dorsum of the finger is pressed to release the finger (extension) lock, permitting the finger to spring back into full extension.

Partial Hand With No Digits Remaining and Wrist Disarticulation

Partial hand amputations with no digits remaining (eg, transverse deficiency of the carpals, partial) are much more common in children than adults. When an adult sustains a traumatic partial
hand amputation, it is rare to have all five rays completely absent, with a single row of carpal bones remaining. In children with these and other congenital limb differences, the limbs often have small finger-like remnants on the distal end of their limb, referred to as nubbins (Figure 2). Associated with a row or rows of carpal bones may be the presence of movement (ie, wrist flexion and extension). Despite the differences between such amputations and wrist disarticulations, the prosthetic fitting principles are to be addressed together because of the similar limb lengths and overlapping prosthetic interventions, particularly when residual wrist and hand motion is limited.

FIGURE 1 Photograph of point digit on a model. (Courtesy of Point Designs, LLC, Lafayette, CO.)

A residual limb of this length allows the child to perform many tasks without a prosthesis in a physiologic position that is close to normal. The manipulation of objects and the performance of bimanual tasks are only minimally affected because the end of the affected limb is nearly at the level of the contralateral hand (Figure 3).

Prosthetic fitting at this amputation level has both advantages and disadvantages. Encouraging wear of the prosthesis allows the child to become accustomed to its use and emphasizes the benefits of incorporating the prosthesis into daily activities. However, covering the end of the residual limb decreases tactile feedback, which is an important aspect of manual dexterity and development. Some retention of tactile feedback may be accomplished by leaving an opening at the end of the forearm of the prosthesis so that the distal residual limb is exposed (Figure 4). However, it is unclear whether this provision benefits long-term prosthetic use and acceptance.

FIGURE 2 Clinical photograph of a transcarpal congenital limb deficiency with nubbins and physiologic wrist motion. (Courtesy of the Shirley Ryan AbilityLab, Chicago, IL.)

FIGURE 3 Clinical photograph of an approximately 5-year-old girl with a longer residual limb and minimal functional impairment. (Courtesy of the Shirley Ryan AbilityLab, Chicago, IL.)

As with any long residual limb, there are challenges of fitting components and maintaining prosthetic limb-length equality with the contralateral side. Epiphysiodeses of the radial and ulnar styloids have been suggested as a potential means of creating space for prosthetic components. However, opponents of this surgical approach cite the disadvantage of the exaggerated limb-length discrepancy if the individual chooses not to wear a prosthesis.

FIGURE 4 Photograph of a forearm prosthesis with a distal opening at the end of the forearm that exposes the distal residual limb to allow tactile feedback. (Courtesy of the Shirley Ryan AbilityLab, Chicago, IL.)

Fitting Infants

The age of a child at the first fitting with an upper limb prosthesis varies from clinic to clinic and according to the level of the limb deficit. At the partial hand and wrist disarticulation levels, it has been widely accepted that infants (younger than 1 year) can be fit with a prosthesis at approximately 6 months of age when they are obtaining sitting balance and are beginning to explore their environment bimanually.⁶^,¹⁴^,¹⁵^,¹⁸ The optimal fitting age varies from child to child and may be affected by many variables, including the effect of having infants sleep on their backs to decrease the risk of sudden infant death syndrome. Limited tummy time may delay upper body development and coordination, thus delaying the benefits gained from using an upper limb prosthesis. For very young children, passive prostheses are the most widely accepted options for decreasing the difference in length between the residual limb and contralateral hand, maintaining sitting balance, directing lines of site for spatial relations when manipulating objects and encouraging bimanual activities. It has been suggested that
the earlier prosthetic fitting begins, the more likely the child and family will be to accept the device; however, this topic is debatable.

In infants, the passive terminal devices may have the appearance of an open hand, a crawling hand, or a mitt. Standard terminal devices and wrist units are discouraged at these levels of limb absence because they make the prosthesis too long. Instead, proximally hollowed terminal devices and/or gloves filled with a flexible material are generally used. These modifications permit the socket to protrude into the proximal aspect of the terminal device to attain limb-length equality.

At this early age, an infant’s limbs have little bony definition and, thus, will not require the prosthetic accommodations for a bulbous distal end. This, however, will become necessary as the child matures. The shape of the socket is very generic, and reliance on sleeves or minimal harnessing for suspension is preferred. Socket construction for an infant’s prosthesis often consists of a thin, lightweight lamination with a removable (onion-skin) layer to accommodate growth. A semiflexible thermoplastic material, such as Surlyn (Dupont), is often used for this removable layer (or inner socket) because it provides a hygienic environment with ease of cleaning and allows direct lamination of the rigid socket without a separator. Laminating directly over the semiflexible thermoplastic material permits the two sockets to temporarily bond together until such time that the prosthetist and the family deem it appropriate to remove the inner socket because of growth. This will become evident, as the child’s limb no longer fits well into the socket. When this transition occurs, the prosthetist should check the trim lines of the remaining laminated socket because the edges most likely will be sharp and require smoothing.

Additional volume management is often necessary because the child grows rapidly during this stage. Limb volume may be managed by initially oversizing the socket and using fitting socks that can be reduced in thickness and ultimately eliminated as the child grows. However, the thickness of the original sock should be limited because it further increases the size and bulk of the forearm, which is already larger because of the addition of the onion-skin layer. Although the preemptive use of an inner socket layer and additional fitting socks will ultimately prolong the useful life of the prosthesis, too large a forearm will be noticeable and unacceptable to the family.

Fitting Toddlers and Preschoolers

Similar components may be used when fitting a toddler (1 year to younger than 3 years) and a preschooler (aged 3 to 5 years). Although no exact age exists at which the child will be fit with a prosthesis that has grasping capabilities, the introduction of a child’s first prehensile terminal device often is accomplished at the toddler stage. The main factors that necessitate the recommendation for most new prosthetic fittings at this developmental stage include anatomic changes to the limb and the child’s capacity to use prosthetic designs with expanded capabilities. If designed appropriately with growth accommodations, the child’s first prosthesis should last approximately 1 year, at which time the child will be approximately 18 months of age—an appropriate age for fitting a prosthesis with a prehensile terminal device.

At 18 months of age, toddlers with transverse deficiencies of the carpals may or may not have sufficient space for a prehensile terminal device in their prosthesis without having a length discrepancy of their forearm and hand. Congenital anomalies are rarely isolated to one structure, and these deficiencies are generally no exception. A discrepancy in the length of the ipsilateral humerus and/or radius and ulna is frequently associated with a transverse deficiency of the carpals. Shortening of these additional structures may be beneficial as standard prosthetic components may be used without resulting in a longer prosthetic arm compared with the noninvolved arm.

Terminal devices for toddlers may be similar to the passive devices previously mentioned or passive devices with prehensile capabilities (Figure 5). They may have flexible, conformable fingers or true articulations with spring-loaded or elastic-loaded closing force. Some may also be designed with the anticipation of adding a cable for body-powered use at a later date. These designs may be of various shapes, including hooks, hands, and the CAPP (Fillauer) terminal device (Figure 6). Arguments have been made for the functional abilities of one design compared with another; however, the most important aspect is
acceptance by the family and actual use of the prescribed prosthesis.

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