Tibial Hemimelia

A rare congenital limb formation characterized by partial or complete absence of the tibia with a relatively intact fibula.

Epidemiology

Tibial hemimelia incidence is reported to be 1/1,000,000.

Clinical description

The disorder presents with a shortened lower limb and deformities at the knee, foot and ankle. The fibula is always present and may be quite normally formed or dysplastic, might be migrated proximally or can be hypertrophied to match a hypoplastic tibia. The tibia can be shortened, partially absent or completely absent. The quadriceps muscle and patella may be normally formed, deficient or absent, which is an important factor regarding reconstruction. Similarly, the cruciate and collateral ligaments may be present or absent. The knee may fully extend or have a flexion contracture or dislocation. The foot can show duplication or deficiency of the medial rays and can be in equinus or equino-varus. Tibial hemimelia is found bilateral in approximately 30%. The degree of dysplasia and type may vary significantly between sides. Unilateral cases have a leg length discrepancy. Various classifications are published, with early classification based on radiographic appearance, while later included the status of knee motion and also the cartilaginous anlage. The most recent classification additionally focuses on prognosis and treatment. Associated anomalies include congenital femoral deficiency, bifid femur, radial dysplasia, lobster claw deformity, hand syndactyly, polydactyly, triphalagism, missing fingers or toes, hip dysplasia, hip dislocation, hemivertebrae and myelomeningocele. The disorder is associated with several syndromes. Werner's syndrome, Gollop-Wolfgang, chromosome 8q deletion, Langer-Giedion syndrome or type II tricho-rhino-phalangeal syndrome (TRPS II) may also be responsible for the disorder.

Etiology

The etiology is unknown.

Diagnostic methods

Diagnosis is based on clinical and radiological findings.

Antenatal diagnosis

Prenatal diagnosis using ultrasound is possible.

Genetic counseling

Although the majority of cases with tibial hemimelia are sporadic, affected families with possible autosomal dominant or autosomal recessive inheritance have been reported.

Management and treatment

Surgical correction is generally possible for most subtypes. However, in cases with absent patella and/or no quadriceps function a through-knee amputation is usually recommended. The functional result after reconstruction mostly depends on knee stability and the position of the foot. Reconstruction of more severe types includes multiple surgeries and residual knee-instability requiring bracing might persist. Reconstruction versus amputation must be discussed with the family. Associated ray duplications on the foot need to be addressed.