Postaxial Hypoplasia of Lower Extremity (Fibular Hemimelia)


Fibular hemimelia was described initially as a condition that is related to aplasia or hypoplasia of the fibula. [1As 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. [23These 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. [4This 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. [56 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.


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. [8During 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. [91011Therefore, postaxial hypoplasia of the lower extremity is a descriptive term that encompasses this constellation of abnormalities.


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.


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. 

History and Physical Examination

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. [15 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 fibula (see the first and second images below)
  • Femoral hypoplasia with external rotation
  • Lateral patellar subluxation
  • Hypoplastic lateral femoral condyle
  • Genu valgum with lateral mechanical axis displacement
  • Flattened tibial eminence with absent cruciate and a positive Lachman sign
  • Short or  bowed tibia (see the third image below)
  • Ankle valgus
  • Ball-and-socket ankle (see the fourth image below)
  • Absent tarsal bones (see the fifth image below)
  • Absent foot rays [16]
Type II fibular hemimelia (complete absence) in 4-Type II fibular hemimelia (complete absence) in 4-month-old girl. Note skin dimple in midtibial area and 2-ray foot. Image courtesy of Dennis P Grogan, MD.
Type II fibular hemimelia (complete absence) in 1-Type II fibular hemimelia (complete absence) in 1-year-old girl. Note that foot is in significant valgus position. Image courtesy of Dennis P Grogan, MD.
Type II fibular hemimelia and significant anteriorType II fibular hemimelia and significant anterior bowing of tibia in 9-month-old boy. Image courtesy of Dennis P Grogan, MD.
Fibular hemimelia. Ball-and-socket ankle joint is Fibular hemimelia. Ball-and-socket ankle joint is common finding in fibular hemimelia. In and of itself, it is usually not problematic, but it is commonly associated with limb-length discrepancy and tarsal coalition. Image courtesy of Dennis P Grogan, MD.
Fibular hemimelia in 4-month-old girl. Fibula is aFibular hemimelia in 4-month-old girl. Fibula is absent, as is proximal tibial ossification center. Two metatarsals are associated with 3 phalanges, 2 of which are fused to form only 2 toes. Image courtesy of Dennis P Grogan, MD.

Imaging Studies

Judicious use of appropriate imaging studies is necessary for full evaluation and appropriate treatment of postaxial hypoplasia of the lower extremity (fibular hemimelia). Some of the more pertinent radiographic studies are listed below.

A long-leg standing series shows the overall picture of the affected lower extremity and permits use of the contralateral side as a control. Limb-length discrepancies and alignment can be measured. Abnormalities in specific parts of the lower extremity can be seen and, if necessary, imaged further with specific views.

A pelvis and/or hip series is useful in evaluating acetabular dysplasiaproximal femoral focal deficiency (PFFD), and the location and amount of any varus deformity. Changing the rotation of the femur can sometimes show version and varus/valgus deformity more clearly.

A knee series is useful for evaluating distal femur valgus, hypoplasia of the lateral femoral condyle, and flattening of the tibial eminence. [17The patella may be small and/or high riding, and the femoral sulcus may be shallow.

A tibia/fibula series provides information about the tibia. In several studies, a small percentage of patients showed anteromedial bowing of the tibia. This imaging series is also useful for classifying the disorder. The Achterman and Kalamchi classification system is based on fibular morphology as follows [3:

  • Type IA - The proximal fibular epiphysis is distal to the level of the tibial growth plate with the distal fibular epiphysis proximal to the talar dome (see the first image below)
  • Type IB - The proximal fibula is absent for 30-50% of its length; the distal fibula is present but does not adequately support the ankle (see the second and third images below)
  • Type II - The fibula is completely absent (see the fourth and fifth images below)
Type IA fibular hemimelia in 8-year-old boy. SigniType IA fibular hemimelia in 8-year-old boy. Significant valgus hindfoot is due to shortened fibula. Image courtesy of Dennis P Grogan, MD.
Type IB fibular hemimelia in 3-year-old boy. FibulType IB fibular hemimelia in 3-year-old boy. Fibula is short relative to tibia, and tibia is shorter on affected side. Note that tibia is also mildly bowed. Image courtesy of Dennis P Grogan, MD.
Type IB fibular hemimelia in same patient as in prType IB fibular hemimelia in same patient as in preceding image. By age 5 years, limb-length discrepancy is progressive and significant. Image courtesy of Dennis P Grogan, MD.
Type II fibular hemimelia and significant anteriorType II fibular hemimelia and significant anterior bowing of tibia in 9-month-old boy. Image courtesy of Dennis P Grogan, MD.
Fibular hemimelia in same patient as in preceding Fibular hemimelia in same patient as in preceding image. Because tibial bowing caused prosthetic fitting problems, corrective osteotomy was performed. Image courtesy of Dennis P Grogan, MD.

An ankle/foot series is useful for determining ankle morphology, the fibular contribution to the mortise, distal tibial epiphyseal morphology, the presence of tibiotalar valgus, the presence of a ball-and-socket ankle, the presence of a tarsal coalition, and the number of rays. [18]

These factors can be used to classify the fibular hemimelia by employing the system introduced by Stanitski and Stanitski, [19in which a pattern type is constructed to describe the condition. This system includes the following components:

  • Fibula - I (nearly normal fibula), II (small or miniature fibula, regardless of its position in the limb), or III (complete absence of the fibula)
  • Tibiotalar joint and distal tibial epiphyseal morphology - H (horizontal), V (valgus; triangular distal tibial epiphysis), or S (spherical; ball-and-socket ankle)
  • Presence of a tarsal coalition - Denoted with a lowercase c
  • Number of foot rays, medial to lateral - Denoted numerically, from 1 to 5

Thus, for example, a patient with a hypoplastic fibula, a horizontal ankle, tarsal coalition, and a five-ray foot would be classified as having a type IIHc5 fibular hemimelia.

Magnetic resonance imaging (MRI) has been used to assess bone and soft-tissue abnormalities of the knee joint in patients with fibular hemimelia. [20Routine ultrasonography (US) can detect congenital femoral deficiency and fibular hemimelia prenatally, and many mothers may prefer antenatal diagnosis of such conditions because it enables antenatal counseling.

Approach Considerations

In patients presenting with postaxial hypoplasia of the lower extremity (fibular hemimelia), it is essential to evaluate the entire limb, 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 members 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 goal is not achievable, the goal should be 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 surgical procedures are anticipated.

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, 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. In many situations, however, 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 surgical procedures over an extended period.

It must always be kept in mind, however, that each patient's situation is unique. 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.

Medical Therapy

No specific medical therapies can correct the underlying abnormalities for postaxial hypoplasia of the lower extremity. For mild deformities, however, observation or nonoperative management may be useful.

As with limb-length discrepancies resulting from other causes, no treatment may be necessary or the use of heel lifts may be adequate, particularly for discrepancies smaller than 2 cm. However, although the percentage of shortening generally remains constant at 10-20% relative to the contralateral side, the absolute discrepancy may progress with growth and must be followed until skeletal maturity. [22]

Similarly, observation may be adequate for hip varus, genu valgum, tibial kyphosis, and patellar instability. Although an absent anterior cruciate ligament (ACL) with a positive Lachman test result is observed frequently, clinical signs of instability are rare, and nonoperative management is appropriate. [23In mild cases, ankle valgus may be managed with a University of California-Berkeley (UCB) orthosis, but as with limb-length discrepancy, the patient must be monitored throughout growth because the fibular portion of the mortise may be progressively compromised.

Surgical Therapy

Several issues must be addressed before any procedure is performed for postaxial hypoplasia of the lower extremity (fibular hemimelia). The most important part of preoperative planning is thorough evaluation of the entire limb to identify all of the associated abnormalities that may be present as a part of fibular hemimelia. The mechanical and anatomic axes should be determined and corrected when possible.

The ultimate goal is to achieve symmetrical, stable, and well-aligned joints with the minimal number of surgical procedures. Accordingly, there is no single set of operations that should always be performed; instead, individual procedures should be planned that address the specific abnormalities in each patient. (See the images below.)

Type IB fibular hemimelia in 8-year-old boy. Limb-Type IB fibular hemimelia in 8-year-old boy. Limb-length discrepancy is 6 cm. Patient is undergoing tibial lengthening with unilateral external fixation device. Image courtesy of Dennis P Grogan, MD.
Fibular hemimelia in 10-year-old girl. Patient is Fibular hemimelia in 10-year-old girl. Patient is undergoing lengthening of tibia with Ilizarov device, which incorporates foot so as to maintain foot position during lengthening with lift. Device can be adjusted as lengthening proceeds and discrepancy decreases. Image courtesy of Dennis P Grogan, MD.
Fibular hemimelia. Specimen was removed at time ofFibular hemimelia. Specimen was removed at time of Syme amputation in patient with fibular hemimelia and significant limb-length discrepancy, prior to prosthetic fitting. Note separate ossification centers for the talus and calcaneus, but no joint space is evident. Image courtesy of and copyright held by Grogan DP, Holt GR, Ogden JA. Talocalcaneal coalition in patients who have fibular hemimelia or proximal femoral focal deficiency: a comparison of the radiographic and pathological findings. J Bone Joint Surg Am 1994;Sep 76(9):1363-70.
Fibular hemimelia. Clinical photograph of specimenFibular hemimelia. Clinical photograph of specimen shown in preceding image. Note that ossification centers are actually part of single solid cartilaginous anlage; 2 separate ossification centers fuse during adolescence, and only then is tarsal coalition radiographically evident. Image courtesy of and copyright held by Grogan DP, Holt GR, Ogden JA. Talocalcaneal coalition in patients who have fibular hemimelia or proximal femoral focal deficiency: a comparison of the radiographic and pathological findings. J Bone Joint Surg Am 1994;Sep 76(9):1363-70.

Finally, realistic expectations of the timing, the duration of recovery, and the ultimate outcome must be communicated to the patient and to his or her family. [24An overall plan is important, and should be discussed in detail with the patient and his or her family.

In patients with a nonfunctional foot, Birch et al recommend amputation, regardless of limb-length discrepancy, unless the upper extremities also are nonfunctional. [25In patients with a functional foot, the surgical recommendations generally fall into one of the following three groups:

  • Patients with a discrepancy smaller than 10% - There is little disagreement that these patients can benefit from lengthening procedures or contralateral epiphysiodesis
  • Patients with a discrepancy larger than 30% - Amputation is recommended for these patients; again, there is little disagreement on management
  • Patients with a discrepancy of 10-30% (the most challenging group) - At maturity, an average lower-extremity length is 80-110 cm, and a 10% discrepancy for such a limb is 8-11 cm; lengthening more than 10 cm in a limb with associated knee, ankle, and foot abnormalities is difficult; hopes for a normal limb notwithstanding, parents must be helped to understand the problems associated with lengthening in severe deficiencies; lengthening with a contralateral epiphysiodesis may be considered as an alternative to multiple lengthening procedures

If amputation is determined to be the most appropriate procedure for an individual, the Syme amputation is generally used. In the past, transtibial amputation was performed more commonly because of cosmetic concerns for a bulky ankle. However, subsequent observations showed that the ankle does not enlarge with growth after the Syme amputation and that the procedure allows weightbearing on the residual limb.

Boyd described a modification to the Syme amputation in which the talus is removed but the retained calcaneus is fused to the tibia to help prevent posterior migration of the heel pad. [2627In this modification, the heel pad grows with the patient. However, the procedure is associated with more wound problems, nonunion, and malpositioning of the calcaneus. Thus, the unmodified Syme amputation is generally recommended. [28]

When a Syme amputation is performed in children, trimming the condyles is not necessary. As opposed to adults, children have small condyles that do not grow to a normal size.

For patients with hip dysplasia, proximal femoral focal deficiency (PFFD), or coxa vara, further details on the various treatment procedures are available elsewhere (see Developmental Dysplasia of the HipProximal Femoral Focal Deficiency, and Congenital Coxa Vara).

Several issues should be addressed. Any necessary operations for acetabular redirection are generally performed before femoral lengthening. Moreover, in the setting of combined coxa vara and limb-length discrepancy, lengthening via callotasis at the subtrochanteric level is not recommended, because of the bending moment and the small cross-sectional area in that portion of the femur. Instead, a more standard valgus intertrochanteric osteotomy should be performed, with any necessary lengthening performed separately at the distal femur.

Genu valgum associated with postaxial hypoplasia of the lower extremity is progressive and can adversely affect lower-limb alignment. It can be treated in several ways. Acute correction can be achieved by performing a distal femur corticotomy during a femoral lengthening procedure or an osteotomy during correction of anteromedial tibial bowing. In patients with a hypoplastic lateral femoral condyle, temporary medial epiphyseal stapling has been recommended because osteotomy has a high recurrence rate unless it is performed near maturity.

Ankle abnormalities can range from complete absence of the fibula to ankle valgus or a ball-and-socket ankle. [2930For the more severe deformities, a Gruca reconstruction has been described. [31This procedure creates a lateral malleolus by using an oblique sliding osteotomy of the distal tibia. In milder cases of fibular hypoplasia and possible valgus, a supramalleolar osteotomy is traditionally used. As a less invasive alternative, a medial malleolar screw epiphysiodesis may provide good results, as Stevens described. [32]

Procedures in the foot include resection of talar coalitions or fusions and addressing any problems with shoe fit that might arise for any deformity. Specific details of these procedures are discussed in other articles.

Postoperative Care

Postoperative care depends on the specific procedures performed. Because the abnormalities associated with postaxial hypoplasia of the lower extremity tend to be relative as opposed to absolute, the patient should continue to be monitored through maturity to ensure that no additional interventions are necessary.


Postaxial hypoplasia of the lower extremity (fibular hemimelia) is a syndrome that involves structures throughout a large anatomic area, and complications of treatment are not infrequent. In addition to the standard surgical complications (eg, infection, bleeding), several complications specific to this disorder have been described. [33]

In the hip, the Hilgenreiner epiphyseal angle must be corrected to less than 38° from the horizontal; repeat valgus intertrochanteric osteotomies may be needed. [34Limb lengthening has a range of complications, from the frequent superficial infections along the pin tract to more significant problems related to fracture, tightening of soft tissues, stiffness, and recurrent deformity.

Stapling is an effective method for correcting angular deformities, but staple displacement or rebound growth may occur. In some situations, however, stapling may be preferable to an osteotomy because of the increased morbidity associated with osteotomy and of the possibility of nonunion and recurrence after an osteotomy.

Finally, amputation may ultimately be necessary despite limb-sparing treatment, a possibility that must be discussed with the parents from the beginning