Principles of amputation in Children

Chinmay S. Paranjape MD, MHSc

Anna D. Vergun MD, FAAOS

Dr. Paranjape or an immediate family member has stock or stock options held in Alphatec Spine, OrthoPediatrics, and Stryker. Dr. Vergun or an immediate family member serves as a board member, owner, officer, or committee member of Association of Children’s Prosthetic and Orthotic Clinics.

ABSTRACT

Amputations in children and adults require different considerations. In children, remaining growth, other potential deficiencies, healing and remodeling potential, and familial needs and expectations drive the principles outlined herein. A collaborative, multidisciplinary approach is needed between surgeons, physiatrists, prosthetists, physical and occupational therapists, and families to achieve a good outcome.

Introduction

Limb deficiencies in children and adults are different owing to differences in etiology and physiology. In children, limb deficiencies most commonly result from errors in formation rather than from trauma or vascular insufficiency.¹ Remaining growth lends to variability in limb size and motor development and creates a potential for terminal overgrowth. Many physiologic differences exist between children and adults and must be considered by the treating team. Children have improved healing potential and, when associated with congenital limb deficiency, less commonly experience phantom pain, though they may experience phantom sensations.²^,³ Painful sensations may be more prevalent when associated with oncologic or traumatic etiologies of limb loss.⁴^,⁵ They are more likely than their adult counterparts to have multiple extremity involvement in addition to cognitive or behavioral challenges because of comorbid conditions.⁶^,⁷ Finally, children are more likely to place increased physical demands on their residual limbs and prostheses, requiring replacement every 12 to 24 months compared with every 3 to 5 years.⁸ These factors must be considered when planning for amputation or salvage to improve the use of prostheses in children. As a result, pediatric limb deficiencies may be best managed at specialized centers with experience and a multidisciplinary team composed of therapists, prosthetists, physiatrists, and orthopedic surgeons. In this chapter, the authors present several guiding principles for the treating surgeon.

Goals of Care

When addressing pediatric limb deficiency, the treating team should attempt to (1) optimize function during childhood while (2) optimizing future function in adulthood and (3) minimizing the total number of procedures required. Typically, optimal management during growth yields optimal final adult outcome. However, there are situations in which those two goals must be separately considered. In these instances, optimal function in adulthood (most of the individual’s life) must be prioritized. All the same, management during growth must be palatable to both the child and the family.

Consider the case of a 3-year-old child with unilateral localized gigantism of a foot undergoing a foot amputation. A foot amputation now would create a residuum that is too long in adulthood to accommodate a foot prosthesis. Addressing that problem with a transtibial amputation in childhood would create a secondary issue with recurrent terminal overgrowth. As a result, a resection of the distal tibia combined with a Boyd amputation addresses both issues. If the length of the tibia is adequate for an adult transtibial residuum at the time of the Boyd amputation in childhood, then a proximal tibial epiphysiodesis can be performed concurrently. Immediately following the surgery, the length of the residuum will still be too long. However, several years later, the growth of the contralateral limb should provide a sufficient difference to accommodate a standard transtibial prosthesis.

Surgical Principles

Several general principles are useful in optimizing eventual function following amputation in children:

Maximize length of the residual limb.
- Preserve epiphyseal plates when possible and consider limb length inequalities.
- Use soft-tissue rearrangements/grafting when needed to increase the available limb length.
Amputate through joints (disarticulation) rather than through bone (transosseous) when possible.
When transosseous amputation is necessary, consider a primary osteochondral capping procedure to prevent terminal bony overgrowth.
Preserve joint function (especially in the knee).
Address proximal limb abnormalities (ie, stability, morphology) if coincident with distal pathology.
Prepare to address other health concerns:
- Associated genetic syndromes.
- Associated organ/structural abnormalities (cardiac, renal, spine).
- Upper extremity and multiple limb deficiencies: consider the goal of function rather than simply normalizing anatomy—children may function better with native sensation and adaptations using residual limbs more efficiently than through limb replacement by means of prostheses. For many children, having more than one prosthesis is cumbersome. Meta-analyses of data available since the 1980s demonstrates a 20% nonwear rate of prosthesis for a variety of reasons.
- Consider additional challenges posed by cognitive and/or motor delay.

Principles 1 and 2: Maximizing Limb Length and Considering Growth

The treating surgeon must consider final limb length at skeletal maturity. At the time of initial consultation, the current and projected limb length discrepancies, both with and without treatment, should be mapped out. Several prior publications discuss different methods of accurately predicting limb length discrepancies and are beyond the scope of this chapter.⁹^,¹⁰^,¹¹ However, some heuristics exist to provide rough estimates of limb lengths at maturity as assessed on initial physical examination.

One assumption is that infants with congenital deficiencies will continue to grow proportionally. For example, if the deficient long bone is 60% of the length of the opposite long bone at birth, it will be about 60% of the contralateral unaffected long bone length at skeletal maturity. On examination, with both limbs in full extension, the examiner should see where the distal end of the limb is relative to the longer side. At full maturity, untreated, the deficient limb will end at approximately the same level relative to the other side. With previously described predictions for final limb length, this proportion can be used to provide a rough prediction of final limb length of the deficient limb to enable informed discussion of management options. Conversely, early treatment without consideration of growth can be disastrous. For example, amputation above the level of the distal femoral physis in an infant may initially appear to have an appropriate length. However, because of the missing 70% to 80% of femoral growth from the distal physis, the residuum at maturity will grow only slightly longer, resulting in such a tiny proximal femur that the amputation level will function like an amputee with a hip disarticulation at maturity.¹²

A notable exception to using the aforementioned assumptions is when trauma has caused complete growth arrest in a physis of interest. Instead, the relative contributions of the relevant proximal and distal physes should be referenced and used to provide a prediction. The authors of this chapter reference the proximal femur as contributing to 15%, the distal femur to 35%, proximal tibia 30%, and distal tibia 20% of the final length of the limb. Two additional assumptions are then made: (1) girls stop growing at 14 years of age and boys at 16 years of age, and (2) growth arrest is complete. Next, the average growth in millimeters per year from each contributing femoral or tibial epiphyseal plate can be calculated. Note that infections may cause partial physeal arrest and that this method may not be valid. Instead, the growth inhibition method or Moseley’s straight-line method may be used. For a bit more accurate residual limb length determination, skeletal age combined with either Moseley or Paley method can be employed.

Generally, a longer residuum results in improved function.¹³^,¹⁴^,¹⁵ This is true for both ambulatory and nonambulatory children. In ambulators, the longer lever arm affords greater power and distributes forces within the socket over a larger area. In nonambulators, longer limbs improve balance when seated and with transitional movements.¹⁶ No ideal length for amputated long bones has been identified. The minimum required length is determined by the length required to keep the prosthesis in place. This is a moving target with advancements in liners and with the advent of transosseous integration. Recent studies of osseointegration in adults have demonstrated increased prosthesis use, walking speed, and decreased energy expenditure. The stoma site between the implant and skin requires careful hygiene to prevent infection, but the technology remains promising.¹⁷^,¹⁸ The technique and potential complications related to growth have not yet been studied in children. Short residua can be lengthened distal to tendinous insertions to allow for more appropriate prosthesis wear using limb lengthening techniques (Figure 1). The maximum length is based on the desire for equal joint heights (eg, the knee for transfemoral amputees) and the interposed bulk of soft tissue between the residuum and the mechanical joint. Variable knee heights have similar function when walking on level ground, and studies have demonstrated more normal gait parameters with lowered center of mass and hinge with prostheses.¹⁹ In the experience of the authors, minor problems with variable knee heights include difficulty fitting into stadium seating, pain under the longer thigh when sitting because of a short tibial segment, and increased pressure from chairs on the posterior thigh.

Principle 3: Using Soft-Tissue Grafting to Increase the Available Limb Length

Traumatic amputations and postradiation oncologic resections may affect the soft-tissue envelope, with the temptation to allow for primary closure by resecting more bone. The reconstructive surgery ladder progresses from
local wound care, primary closure, split-thickness skin grafting, local skin flaps, pedicled flaps, and finally to free flaps. Orthoplastic principles may help achieve longer residuum by allowing staged soft-tissue coverage to allow retention of diaphyseal long bone and native joints.²⁰ This in turn may maximize functional outcome. Several case examples of these principles were outlined by Fleming et al²¹ in an adult military cohort suffering traumatic amputations caused by war. Therapies discussed by his group included rotational flaps, free flaps, split-thickness skin grafts, tissue expanders, and biocomposite dermal substitutes. They noted that preservation of residuum length requires management considerations of both the underlying bony segment and its associated soft-tissue envelope.

When following the reconstructive ladder, Fleming et al recommend:

Consideration of split-thickness skin grafting should outweigh conversion to higher functional amputation levels just for skin coverage
Consideration of tissue expanders and negative wound therapies to allow for delayed primary closure
Consideration of atypical local skin flaps, albeit in the zone of injury
Progression through the reconstructive ladder to allow retention of native diaphyseal bone and proximal articulations

In a pediatric traumatic amputation cohort, the benefits of residual length with orthoplastic considerations should be weighed with principles 4 and 5 described next (Figure 2).

Principles 4 and 5: Prevention of Terminal Overgrowth by Disarticulation Versus Cartilage Capping

Nearly 50% of transosseous amputations experience terminal bony overgrowth, likely as a result of periosteal reaction with penciling of the terminal bone. This principle was first noted by Ernst Marquardt, who observed that overgrowth never occurred after amputation through joints.²² Age and location of amputation are the most
influential factors in overgrowth. Overgrowth is not observed in children older than 12 years or in disarticulations.²³ Overgrowth is rare in the forearm but common in the arm and lower extremity amputations.²³

FIGURE 1 AP radiographs of a short femoral residual limb (A) that was associated with poor control of the prosthesis. The femur underwent an osteotomy and lengthening of 9 cm (B) with an external fixator. The amount of length achieved was limited by pain over the distal tip during the lengthening process, but this pain abated during the consolidation phase. The mild hip flexion contracture present before lengthening resolved once the patient was using their new prosthesis.

FIGURE 2 Lateral radiograph (A) and clinical photograph (B) of a 4-year-old boy who was injured by a bomb blast, resulting in a traumatic tibial amputation. The left tibial segment was extremely short with inadequate soft-tissue coverage, but the extensor mechanism remained intact. The full thickness tissue loss over the distal residuum and the tibial periosteum was treated with skin graft. After the grafted tissue hypertrophies and matures, it will function well inside a standard transtibial prostheses. With normal growth, the proximal tibia will increase by an additional 6 to 8 cm at maturity.

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