Weinstein Lovell and Winters Pediatric Orthopaedics 7e

1567

CHAPTER 30  |  The Child with a Limb Deficiency

Both of these procedures have had limited use. There are significant problems in achieving an arthrodesis, and the distal femoral segment cannot be allowed to grow too long. Additional surgical procedures are to be expected. As yet, there are only very limited reports on the functional advantages (190, 191). Prosthetic Management.  Initial prosthetic management of the child with PFFD begins with fabrication of an extension or nonstandard prosthesis, with or without an activated knee joint (Fig. 30-33). With the foot positioned in plantar flexion, the limb is cast proximal to the hip joint, and the prosthesis fab- ricated with a prosthetic foot positioned under the shortened limb. The ischial containment socket has been called a “ship’s funnel” because of the resemblance to the engine air intake funnels of ocean vessels. This drastic socket design is neces- sary because of the flexed hip and knee that must be contained within the socket while attempting to gain ischial support. The purpose of the extension-type prosthesis is to equal- ize limb length, in preparation for early ambulation, while ­affording time for surgical decisions. There are four indications that have been identified relating to the fitting of nonstandard prostheses (192): 1. When the patient is still too young for surgical conversion. 2. When the patient or parent refuses surgical intervention, and a prosthesis is necessary for ambulation. 3. In bilateral cases, when extra height or better balance is the goal. 4. When there is lower extremity involvement, combined with bilateral upper extremity absence, requiring the feet for ADL. When foot ablation with knee fusion option is chosen, the prosthesis resembles a knee disarticulation prosthesis, except for the need for ischial weight bearing and high lateral brim containment to aid in hip stability. Weight bearing is divided between the ischium and the distal heel pad. Full distal weight bearing could severely compromise hip function over a period of time, because of the inherent instability of the hip with pos- sible proximal migration of the femur. Prosthetically, fusion of the knee with correction of the angular deformities results in improved gait and ease of fitting because of the single skeletal lever arm (193). During growth, the child should be evaluated periodically for the relative length of the two limbs so that, if needed, distal femoral epiphysiodesis can be performed. This will allow fitting of an optimal knee joint when the patient is fully grown while maintaining the knees at the same level. In the small child, and when the residual limb is longer than the opposite femoral segment, external knee joints may be used. As the child grows, an internal four-bar knee can be used. More about the indications and selection of knee joints is discussed later in this chapter. A foot amputation without knee fusion results in dif- ficulty with prosthetic management. Movement within the prosthesis, at the level of the anatomic knee, and the increased need for an intimately fitted socket, foster a decreased stride length and increased pelvic movement. However, in the child

with an Aitken class D PFFD and only a remnant of distal femoral epiphysis in which knee fusion will have little to offer, this may be a suitable choice. The Van Nes rotationplasty requires a nonconventional prosthesis with the ankle functioning as the new knee. This is a very difficult prosthesis to align and fit, although it gives excellent function (177, 194). The prosthesis has a lower padded foot socket that contains the rotated foot in full plan- tar flexion. Lateral and medial external joints are attached to the upper thigh section to increase stability and to prevent hyperextension of the lower shank (194). The original design incorporated a laminated thigh section with ischial weight bearing. For patients with good hip stability, for example, in those who had a tumor and trauma, the laminated section is often replaced with a leather thigh lacer and no ischial weight bearing. It is imperative for proper function that the external joints be aligned with the axis of rotation of the ankle/subtalar complex while maintaining the line of pro- gression. Failure to ensure this alignment, regardless of the anatomic joint, will result in a poor gait pattern and skin breakdown. The prosthetist should incorporate mechanical joint placement with slight external rotation on a new pros- thesis, in anticipation of the mild internal derotation inevi- table during growth. Author’s Preferred Recommendations.  Children with more severe forms of femoral deficiency are initially fit with an extension-type prosthesis until the age of approximately 3 years. For children with a congenitally short femur with <20 cm of anticipated limb-length discrepancy at skeletal maturity, an arc of motion of the knee of 60 degrees without flexion contrac- ture, and a foot that is plantigrade or can be made plantigrade with surgery, the authors suggest limb lengthening. Hip and proximal femoral stability are achieved first by redirecting or augmenting the acetabulum as necessary and repairing a proxi- mal femoral pseudarthrosis and/or varus if it exists. For patients where the foot falls at the level of the contralat- eral knee, the authors suggest Van Nes rotationplasty and knee fusion if the family is accepting the idea and the ankle/subtalar joint complex has at least a 60 degrees arc of dorsi/plantar flex- ion and no equinus contracture. If the family is unaccepting of rotationplasty, or if the foot and ankle are not well-aligned and/ or lack sufficient range of motion, then knee fusion with Boyd amputation is undertaken. Careful prediction of the ultimate length of the tibial and femoral segments guides the decision of which epiphyses and physes to remove at the time of knee fusion. In the majority of cases, both physes will be removed. The authors do not have sufficient experience with ilio- femoral arthrodesis with or without rotation to recommend either procedure. Pearls and Pitfalls.  In evaluating these patients, it is important to accurately predict the ultimate limb-length dis- crepancy as early as possible. This is essential in formulating an early treatment plan. Because of the flexion, abduction, and external rotation deformity of the proximal femoral ­segment,