Fibular Hemimelia 

Fibular hemimelia was described initially as a condition that is related to aplasia or hypoplasia of the fibula.^[1] 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.

A constellation of lower-extremity features accompanies fibular hemimelia. These should be evaluated and treated when appropriate. The association of these features has led to a recent recommendation that the name postaxial hypoplasia of the lower extremity may be more appropriate and a better description of the entire pattern of abnormalities seen with this syndrome.^[4]

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]

Then, the need arose to establish criteria for the indications for amputation. The first recommendations used a projected limb-length discrepancy of 3 inches 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.

As is evidenced by its historic name, a primary feature of fibular hemimelia is the fibular abnormality. This may range from a minimal shortening of the fibula to its complete absence. See Clinical for other related features.

Frequency

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

Although a number of causes have been suggested for postaxial hypoplasia of the lower extremity (fibular hemimelia), recent 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.

See Etiology.

Presentations of postaxial hypoplasia of the lower extremity (fibular hemimelia) vary widely, ranging from what appears to be merely an absent fifth toe in a newborn or a minimal difference in limb lengths, to severe fibular deformities that are immediately apparent.^[12] The clinician must also look for associated abnormalities, including problems with alignment and stability, and must realize that the clinical picture may evolve with growth and development.

Clinical findings may include the following:

• Fibular abnormality, ranging from minimal shortening to complete absence of the fibulaFibular hemimelia. The radiographic appearance of a 4-month-old girl. The fibula is absent, and the proximal tibial ossification center is absent. Two metatarsals are associated with 3 phalanges, 2 of which are fused to form only 2 toes. Image courtesy of Dennis P. Grogan, MD.
• Proximal femoral focal deficiency (PFFD)
• Coxa vara
• Femoral hypoplasia with external rotation
• Lateral patellar subluxation
• Hypoplastic lateral femoral condyle
• Genu valgus with lateral mechanical axis displacement
• Flattened tibial eminence with absent cruciate and a positive Lachman sign
• Short and/or bowed tibiaType 2 fibular hemimelia and a significant anterior bow to the tibia in a 9-month-old boy. Image courtesy of Dennis P. Grogan, MD.
• Ankle valgus
• Ball-and-socket ankleFibular hemimelia. A ball-and-socket ankle joint is a common finding in patients with fibular hemimelia. In and of itself, this is usually not problematic, but it is commonly associated with limb-length discrepancy and tarsal coalition. Image courtesy of Dennis P. Grogan, MD.
• Absent tarsal bonesFibular hemimelia. The radiographic appearance of a 4-month-old girl. The fibula is absent, and the proximal tibial ossification center is absent. Two metatarsals are associated with 3 phalanges, 2 of which are fused to form only 2 toes. Image courtesy of Dennis P. Grogan, MD.
• Tarsal coalitions
• Absent foot rays

Evaluate the entire limb in patients presenting with postaxial hypoplasia of the lower extremity (fibular hemimelia), specifically examining for all of the previously mentioned clinical features. This is important and helpful for developing a treatment plan, both to guide the physician's treatment decisions and to inform the family of what they might expect.

The ultimate goal is to enable the child to gain maximal function by achieving adequate lower-extremity alignment, length, and stability. If this is not possible, the goal is an appropriately timed amputation to allow the child's development with the use of a functional prosthesis. Goals and expectations must be realistic. When treatment alternatives are discussed, the social and psychological state of the child and the child's family must be considered, especially if multiple surgeries are anticipated.

Fibular hemimelia cannot be characterized fully by any single anatomic feature. The condition encompasses a constellation of features that are best addressed individually to obtain optimal limb length, alignment, and function.

As with any surgical procedure, the potential benefits must outweigh the risks. Although a number of abnormalities are related to postaxial hypoplasia of the lower extremity (fibular hemimelia), limb-length discrepancy is one of the more difficult to address. If the difference is minimal or if it is large and accompanied by a nonfunctional foot, the decision is relatively straightforward. However, in many situations, several relative contraindications to limb-lengthening salvage operations may be present.

The recommended maximum to be corrected is 7.5-15 cm. Other relative contraindications include a nonfunctional foot, a limb that may have severe cosmetic problems, or a patient who may not tolerate multiple surgeries over an extended period.

Each patient's situation is unique, however. Most patients and parents want the limb to be as normal as possible, and they may wish to undergo the long-term treatment necessary to achieve this goal despite relative contraindications.