Fibular Hemimelia

Fibular hemimelia (longitudinal fibular deficiency) is a congenital absence or hypoplasia of the fibula, with shortening and deformity of the tibia, ankle and foot, and sometimes of the femur and the knee. It is the commonest congenital long bone deficiency, with an incidence of about 1 in 40 000 to 50 000 live births.

It is usually sporadic and unilateral (about 70%), with a male predominance and slightly more often on the right side.

Associated findings are:

• shortening of the tibia with anterior or anteromedial bowing and a skin dimple over the apex
• hypoplasia of the lateral femoral condyle with a shallow trochlear groove
• cruciate ligament deficiency
• ankle valgus with a ball-and-socket joint
• tarsal coalition
• absent lateral rays of the foot
• in some, a short femur (proximal femoral focal deficiency) or a limb deficiency in the other leg

The Achterman and Kalamchi classification divides the condition into three types:

• type IA: hypoplastic fibula with a proximal growth plate distal to the tibial growth plate
• type IB: partial absence, with the proximal 30 to 50% absent
• type II: complete absence of the fibula

Paley classification adds foot involvement and limb length. Complications are limb length difference (growing with age), progressive deformity, ankle and knee instability, foot stiffness, and need for amputation or multiple reconstructions.

Pathophysiology.

The cause is unknown; a disturbance of limb bud development in the 6th to 8th weeks of gestation is proposed. Rarely, a gene variant or a genetic syndrome is found.

Growth inhibition of the tibia and femur is constant (about 6 to 8% of limb length at birth increasing to 15 to 20% at maturity). The discrepancy is predicted from the ratio of the short limb to the normal limb, which stays about constant during growth.

A short leg at birth, with the foot in equinovalgus, absent lateral toes, a tibial skin dimple, and a prominent anteromedial tibial bow. Unilateral cases are noted by limb length difference. Knee laxity (anterior cruciate ligament deficiency) and ankle instability appear with growth. Children walk with an abnormal gait, with the foot unable to stay plantigrade in severe cases.

Examine the limb length (femur and tibia separately), knee stability (anterior drawer, Lachman), hindfoot position and flexibility, foot rays, hips (the femur), the other limb, and the spine, heart, kidneys and hands for associated anomalies.

• Radiographs: long leg standing films with blocks (scanogram), foot and ankle views, and knee views. Features include an absent fibula or a fibular remnant, shortened and bowed tibia, tarsal coalition, absent lateral rays, a valgus or ball-and-socket ankle, and femoral hypoplasia.
• MRI of the knee for cruciate ligament deficiency and fibrous remnants (the fibular anlage), which tether growth and deformity.
• Prediction of the leg length difference at maturity (multiplier method or growth percentile chart) to plan treatment.
• Prenatal ultrasound often shows it at 18 to 20 weeks, and the baby needs a full postnatal check for other anomalies. Genetic testing when syndromic features exist.

Differential diagnosis.

• Tibial hemimelia and proximal femoral focal deficiency.
• Congenital pseudarthrosis of the tibia and posteromedial tibial bowing.
• Congenital short femur and amniotic band syndrome.
• Clubfoot with limb length difference.

The choice is between amputation (Syme or Boyd) with prosthesis, and limb reconstruction with lengthening. The decision follows the predicted limb length difference, foot function, and family wishes, and is made early.

Amputation (favoured for severe cases).

• Indications: a non-functional or severely deformed foot (fewer than 3 rays, rigid equinovalgus), a predicted limb length difference at maturity over 10 to 15 cm (over about 30% of the other leg), or an unstable, hypoplastic knee with a short femur.
• Syme or Boyd amputation at 9 to 18 months of age (before the child walks), with removal of the fibular anlage, followed by a prosthesis, gives good function with fewer operations.
• The heel pad is kept and the tibia is shortened when needed. Epiphysiodesis of the opposite limb adds to the equalisation.

Limb reconstruction (for a functional, plantigrade foot with 3 or more rays and a predicted discrepancy under 10 to 15 cm).

• Fibular anlage resection, tibial osteotomy to correct bowing, and ankle stabilisation (the Paley procedure: Achilles lengthening, ankle realignment and subtalar coalition resection) in early childhood.
• Staged tibial and femoral lengthening (external fixator or intramedullary lengthening nail) to correct 5 to 10 cm, with contralateral epiphysiodesis near maturity.
• Foot and ankle: supramalleolar osteotomy for valgus, fusion for ankle instability.
• Multiple operations are needed, with a risk of knee and ankle stiffness, subluxation, nerve injury and recurrence.

Orthoses and prostheses. Shoe lifts for small discrepancies (under 2 cm), an extension prosthesis for severe discrepancy, and a knee-ankle-foot orthosis for reconstructed limbs.

Operative antibiotic prophylaxis. Cefazolin 30 mg/kg to a maximum of 2 g intravenously (2 g in adolescents; 3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL).

With severe penicillin allergy, give clindamycin 10 mg/kg (maximum 900 mg) intravenously or vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.

Pin site care and infection (external fixation). Daily pin site cleaning with saline and dry dressing.

For pin site infection, give flucloxacillin 25 mg/kg orally every 6 hours (maximum 1 g a dose; 500 mg to 1 g every 6 hours in adults) on an empty stomach for 5 to 7 days (avoid with penicillin allergy and with a history of flucloxacillin cholestatic jaundice). In penicillin allergy, give clarithromycin 7.5 mg/kg orally every 12 hours (maximum 500 mg a dose) (check QT interval and interactions).

Analgesia.

• Children: paracetamol 15 mg/kg orally every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily) and ibuprofen 10 mg/kg orally every 6 to 8 hours with food (maximum 40 mg/kg daily and not exceeding 2400 mg daily), for up to 5 days.
• Avoid ibuprofen with kidney impairment, dehydration or active bleeding, and while bone lengthening is under way.
• After major surgery, oral morphine 0.1 to 0.2 mg/kg every 4 hours as needed for severe pain for up to 3 days (maximum 10 mg a dose); monitor sedation and respiration, and prescribe a laxative.

Monitoring. Limb length, alignment, knee stability, and prosthesis or orthosis fit every 6 months in childhood, with long leg radiographs yearly. During lengthening, weekly review with radiographs every 2 weeks, and nerve and joint checks. Psychological and school support. Growth until maturity.

Referral and escalation. Refer every child with suspected fibular hemimelia to a paediatric limb reconstruction centre before 6 months of age, with early counselling of the family on the options. Urgent referral for neurovascular compromise or signs of infection in an external fixator.

Special groups.

• Infants: plan early decisions on amputation or reconstruction.
• Bilateral or syndromic disease: assess the hands, heart, kidneys and spine; genetic counselling.
• Families: meet prosthetic users and the team before choosing, with psychological support.
• Adolescents: contralateral epiphysiodesis timing; assess for pain and arthritis.