Congenital and acquired limb loss is a disabling condition that can significantly affect a person’s quality of life. There are additional considerations when managing amputation in the pediatric patient that have implications for residual limb length (RLL), including the preference for transarticular rather than transosseous amputation, when possible, due to the problem of bone overgrowth; and the moving target of limb length difference in the growing patient, both pertaining to the amputated extremity as well as the contralateral limb. The presence or absence as well as the function and expected remaining growth of physes in both limbs must be considered. Congenital and developmental etiologies are overrepresented in this population compared with adult amputees, each bringing with it unique bone and soft-tissue difference in the limb that must be considered as a part of surgical and prosthetic intervention, to achieve the best function.

When an amputation residual limb is short, functional prosthetic fitting is challenging to achieve and hence a prosthesis may require anchorage more proximally. This may condemn the limb to function as an amputation of a more proximal level, increasing energy consumption during gait in the lower extremity, and reducing comfort and dexterity in the upper extremity. An overview of considerations and treatment strategies with regard to limb length management in the childhood amputee is presented.

RLL can be measured in absolute or proportional terms. Absolute length may be quantified in centimeters or inches as bone length radiographically, or bone length relative to a soft-tissue point (such as a flexion crease), or the RLL difference relative to the other limb (known as clearance from a prosthetic fitting perspective).¹

Proportional methods may also be used; for example, a residual limb may be 70% the length of the contralateral limb, or described in terms of anatomic landmarks (the residual limb ends at the level of the contralateral distal tibial metaphysis). Additionally, in the patient with bilateral amputation, proportionality may be considered in relation to torso length, arm span, or other anatomic considerations.

When considering pediatric patients or implications for gait, a proportional method may be more informative. The physician should be aware, however, that prosthetic componentry is usually measured in absolute terms.

Bone lengthening was first described by Codivilla in 1905; however, it was Ilizarov who developed the modern methods of distraction osteogenesis, commonly known as the Ilizarov method.²

The factors Ilizarov viewed to be important for osteogenesis at an osteotomy site are:

The techniques of distraction osteogenesis as well as distraction histogenesis are useful not only for limb lengthening but also for the management of nonunions, bone deficits, and angular deformity.^3,4

Such techniques were traditionally achieved using fine wire fixation, eponymously referred to as an Ilizarov apparatus or ring fixator. The innovation of hexapod style frames, commonly referred to as Taylor spatial frames, was a significant technologic advancement, but retained the disadvantages of earlier fixators of being cumbersome, uncomfortable, difficult to apply, and association with high complication rates.⁵

The introduction of the intramedullary skeletal kinetic distractor (Orthofix) intramedullary lengthening nail hailed the arrival of all-internal solutions for distraction osteogenesis, and these ratchet-based devices were driven by patient movement. The Fitbone (Orthofix) motorized intramedullary nail is activated by external remote control, and this was rapidly followed by the development of a second remote controlled nail, the PRECICE (NuVasive). Both implants are activated by an external signal, radiofrequency and magnetic, respectively.

These devices are useful in the context of residual limb lengthening, and both companies have developed modified devices specifically for short amputation residual limb lengthening (Figure 1).

Although motorized internal lengthening nails are less cumbersome and have been demonstrated to have lower rates of certain complications compared with their external fixation predecessors, some difficulties remain, and new problems have been introduced. The same limits of soft-tissue tolerance are present. New problems exist with the size limitations of the devices, particularly when trying to fit them within short residual limbs.

A residual limb should be long enough to allow comfortable and functional fitting of a prosthesis that does not impede the function or motion of more proximal joints, and be able to act as a functional lever arm within that prosthesis. A residual limb should not be so long, however, such that there is insufficient longitudinal space for prosthetic componentry to gain maximal achievable function. Preserving length is crucial in pediatric patients; for example, because the distal epiphyseal plate contributes 75% of longitudinal femoral growth, transfemoral amputation results in a very short final residual limb.⁶

Because of the type of amputations often performed in children, excessive length thought initially to be of advantage in retaining as much of the limb as possible may indeed hinder performance. Adolescents with Syme amputations were found to have higher self-reported function and satisfaction when their residual limb ended at the level of their contralateral tibial middiaphysis; a longer residual limb resulted in a limb with insufficient clearance space for the fitting of an energy return prosthesis and more prosthetic complications.⁷ In both this setting as well as amputations performed for vascular overgrowth syndromes, well-timed epiphysiodesis or even acute intercalary shortening may be of utility in achieving ideal limb lengths at skeletal maturity.

Additionally, the local soft-tissue envelope (most evident in amputation posttrauma), as well as proximal joint stability and function (most important in congenital and developmental etiologies), needs be considered in a pediatric population.

If indeed the residual limb is so short that more proximal prosthetic fitting is required, and the patient possesses a soft-tissue envelope that will tolerate it, residual limb lengthening may be of benefit. It is also unknown how much length will be necessary to benefit an individual patient.

The minimum RLL for adequate prosthetic fitting is highly variable, although studies have suggested bone length for a successful transtibial prosthesis should be 15 cm and for a transfemoral prosthesis 25 cm.^8,9,10

The paucity of English language literature on residual limb lengthenings consists of brief case reports and small series.^8,11,12 Limb lengthening via distraction osteogenesis is an involved process even in complete limbs, requiring impeccable surgical technique, regular follow-up, and a nuanced and proactive approach to arising complications. Limb lengthening in the residual amputated limb adds further considerations, and should only be embarked upon by a surgeon and team confident in the technique, and a patient who has provided consent informed by comprehensive discussion.