Postaxial Hypoplasia of Lower Extremity (Fibular Hemimelia)

Updated: May 10, 2018
  • Author: Michael C Holmstrom, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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Overview

Background

Fibular hemimelia was described initially as a condition that is related to aplasia or hypoplasia of the fibula. [1] As is evidenced by its historic name, the fibular abnormality is a primary feature of this condition and may range from a minimal shortening of the fibula to its complete absence. Coventry and Johnson, and later Achterman and Kalamchi, provided early classification systems. [2, 3] These are primarily based on and concerned with treatment of the accompanying limb-length discrepancy.

Fibular hemimelia cannot be characterized fully by any single anatomic feature. It encompasses a constellation of lower-extremity features, which should be evaluated and treated individually when appropriate. Now that more insights have been gained into the constellation of related abnormalities stemming from the embryologic limb bud, the term postaxial hypoplasia of the lower extremity may describe the syndrome more accurately. [4] This term also helps remind the clinician to look for other subtle abnormalities and not to focus solely on the obvious fibular deficiency.

Historically, the recommended treatment for postaxial hypoplasia of the lower extremity (fibular hemimelia) was amputation, but only as a last resort. However, Herring et al showed that patients who undergo amputation after several failed attempts at salvage are at high risk for emotional problems. [5, 6]  Therefore, determining which patients fare better with immediate amputation is important. Generally, these are patients with a nonfunctional foot or a limb-length discrepancy of more than 20-30%. [7]

Subsequently, the need arose to establish criteria for the indications for amputation. The first recommendations used a projected limb-length discrepancy of 3 in. (~7.5 cm) at maturity as an appropriate cutoff. However, as limb-lengthening techniques have improved, this length criterion has increased, and limb salvage is regarded more often as a feasible option. Other features of postaxial hypoplasia have also been investigated, and treatments have been defined.

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Etiology

A number of causes have been suggested for fibular hemimelia. One theory postulates that interference with limb-bud development plays an important role. Widespread pathology throughout the limb has been noted, even in mild cases of fibular deficiency. [8] During the fetal period, the fibular field of the limb bud controls development of the proximal femur, explaining the frequent association of femoral abnormalities.

Other associated abnormalities of the knee, leg, ankle, and foot also are related to the fibular field of the lower limb bud. [9, 10, 11] Therefore, postaxial hypoplasia of the lower extremity is a descriptive term that encompasses this constellation of abnormalities.

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Epidemiology

Postaxial hypoplasia of the lower extremity is rare and has variable expression, ranging from mild deformity (which the patient may never notice) to severe deformity.

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Prognosis

Because postaxial hypoplasia of the lower extremity represents such a wide range of abnormalities with varying degrees of involvement, no simple statement can be made regarding the patient's prognosis. Judiciously chosen, well-timed procedures specifically tailored to the individual patient provide the best prospects for a well-aligned, functional limb of adequate length. [12, 13, 14]

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