Weinstein Lovell and Winters Pediatric Orthopaedics 7e

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CHAPTER 30  |  The Child with a Limb Deficiency

often results in contralateral hip and lower back pain as well as patient frustration. Prosthetic Feet.  Variations in the materials, design, and alignment of the foot can have profound effects on the perfor- mance of the prosthesis. Functionally, prosthetic feet can be categorized into five main groups (226):

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●● Solid ankle cushion heel (SACH)

Single axis Multiaxis Elastic keel

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●● Dynamic response The SACH foot [Therapeutic Recreation Systems, Inc. (TRS)] contains no articulating parts, and foot motion depends on the various compressive properties of the materials used between heel-strike and toe-off (Fig. 30-52A). It is generally considered when amputees require maximum late-stance stability because of weak knee extensors, knee-flexion contractures, or poor mid- to late-stance balance (227). The SACH foot is used in pedi- atrics when the foot size is below 12 cm. The Little Feet is a bolt on type SACH foot designed with unique energy dynamics (Fig. 30-52B). The toes are very flexible because of the use of an elastomer that more closely mimics the child’s foot. A special removable heel core allows the foot to be used “barefoot.” The single-axis foot usually contains rubber bumpers that allow passive dorsi- and plantar flexion. By changing the hard- ness of the bumper, the prosthetist is able to effectively change the properties of the foot. The single-axis foot does not come in a size suitable for the child amputee. This foot is best suited for the transfemoral amputee, in whom full-foot contact with the ground is necessary to increase stability. The multiaxis foot allows passive dorsi- and plantar flexion, inversion, and eversion. The multiaxis foot was once thought best suited for the amputee who because of uneven terrain or a lifestyle that includes golfing or various sports requires flexibility and some rotational control: It has now found its way into the pediat- ric population. The ­multiaxial foot (College Park Truper foot) (Fig. 30-52C) allows controlled resistance in all planes—inver- sion/eversion, dorsiflexion and plantar flexion, and transverse rotation about the ankle joint. This class of foot has gained wide acceptance within the pediatric arena, in part because of its ability to absorb forces at the ankle and reduce transmission of these forces to the socket. This is particularly useful when fitting a very short residual limb. Once the child’s activity level warrants a higher function- ing foot, the prosthetist can move the child into a dynamic- response foot. This group of feet is distinguished by a spring mechanism in the keel that deflects during gait (Fig. 30-52D). The dynamic-response foot has found its way into competi- tive-level sports as well as day-to-day activities. Although the variety of componentry for children is still much less than for adults, there is a wide variety of feet with different perfor- mance characteristics available. It is important to use compo- nents that will maximize performance and at the same time be appropriate for the patient (228).

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knees. Traditionally, an articulating knee would be introduced in a congenital amputee at approximately 3 to 4 years of age. This age was determined, in part, by the limitations in the size and function of the components. In the experience at the authors’ center, as well as others, introduction of a prosthetic knee without a locking feature can be used as the first pros- thesis when the child first pulls to stand. A recent report dem- onstrated the benefits of early fitting with articulated knees in children as young as 17 months. All children learned to walk with an articulated knee, despite their age differences (157). As the child develops and grows, more sophisticated con- trol systems (e.g., hydraulic knees) can be incorporated into the prosthesis. Most components carry specific weight guidelines, and many children reach these ranges well before adulthood. For example, an adult hydraulic polycentric knee is routinely used on 8-year-old boys whose weight has surpassed 100 lb. This does not mean that every child of a certain age and weight should have a particular knee. Placing a sophisticated knee and control system on an individual who has neither the hip range, muscle strength, nor residual limb length to activate the knee FIGURE 30-51.  Four-bar linkage is an internal polycentric knee that provides many advantages to the patient, including increased stabil- ity and better ground clearance during swing phase. As indicated in this illustration, the point of rotation varies with the degree of flexion. With the knee flexed, the leg folds under the thigh segment and there- fore is very useful for longer residual limbs. There is also a hydraulic version of the four-bar linkage for children.