Tibial hemimelia is a rare congenital condition characterized by the partial or complete absence of the tibia, the larger of the two bones in the lower leg. This limb difference affects approximately one in a million live births. It typically results in a disparity in leg length, and while it often affects one leg, it can occur in both limbs in about 30% of cases.
Symptoms and Classification of Tibial Hemimelia
Children born with tibial hemimelia often present with a visibly shortened lower limb. The affected leg may exhibit angular deformities, and the foot commonly turns inward, a condition known as equinovarus deformity. Instability or even dislocation of the knee joint can also be observed due to the lack of proper tibial support. The patella (kneecap) and quadriceps muscles may be underdeveloped or absent, which impacts their function. Foot anomalies are also common, including the duplication of toes or a reduction in the number of medial rays.
The Jones classification system is widely used to categorize tibial hemimelia based on the radiographic appearance of the tibia. This system helps medical professionals plan treatment. Type 1 involves the complete absence of the tibia, subdivided into Type 1A where the distal femoral epiphysis is hypoplastic, and Type 1B where it appears normal, suggesting a cartilaginous tibial anlage that may ossify over time.
Type 2 is characterized by the presence of an ossified proximal tibia but an absent distal tibia. In Type 3, the distal tibia is present and ossified, while the proximal tibia is missing. Type 4 describes a shortened tibia where the distal ends of the tibia and fibula diverge at the ankle, creating a “congenital diastasis of the ankle”.
The Diagnosis Process
The identification of tibial hemimelia can occur at two main stages: prenatal and postnatal. Prenatal diagnosis often involves routine ultrasound scans during pregnancy. Severe cases may be detected as early as 16 weeks of gestation, showing a deficient tibia or other limb abnormalities. Ultrasound can accurately identify these conditions.
Following birth, a physical examination of the newborn is the first step in postnatal diagnosis. Medical professionals observe the shortened limb, foot and ankle deformities, and knee instability. To confirm the diagnosis and determine the specific type and severity, X-rays are performed. These images provide clear views of the bones, indicating which parts of the tibia are present or missing, and help estimate leg length discrepancies. Magnetic resonance imaging (MRI) or ultrasound scans may also be used to gain more detailed information about the knee and ankle joints for treatment planning.
Treatment Pathways
Treatment for tibial hemimelia aims to achieve a functional limb that supports mobility and can eventually match the length of the unaffected leg. The approach is highly individualized, considering the specific type of hemimelia, the condition of the knee and ankle joints, and the family’s preferences. Two primary treatment philosophies guide decision-making: limb reconstruction and amputation with prosthetic fitting.
Limb reconstruction focuses on preserving the limb and creating a functional lower extremity, often involving a series of complex surgical procedures over many years. One common technique is centralizing the fibula under the femur, effectively using the fibula to create a more stable knee joint when the tibia is absent or significantly deficient. Correcting foot deformities, such as clubfoot, and stabilizing the ankle are also frequent components of reconstructive surgery. Limb lengthening procedures, often utilizing external fixators, are then employed to gradually extend the shortened bone. Factors favoring reconstruction include the presence of a functional knee joint, a proximal tibia, and an intact patella and quadriceps mechanism.
Alternatively, amputation with prosthetic fitting is another recognized treatment pathway, often involving a Syme-type amputation to create a stable, weight-bearing stump. The goal is to provide a residual limb well-suited for fitting with a prosthesis, enabling early mobility. Children adapt quickly to prosthetic limbs, and modern prosthetics can offer excellent function, allowing participation in various activities. While reconstruction offers the benefit of preserving the natural limb, amputation can provide a more straightforward and predictable path to achieving functional mobility with fewer surgical procedures and potentially lower overall costs. The choice between reconstruction and amputation is a shared decision made by the medical team and the family, weighing the complexities, recovery times, and functional outcomes of each option.
Associated Health Conditions
Tibial hemimelia can sometimes occur alongside other health conditions, which necessitates a comprehensive medical evaluation for affected individuals. These associated anomalies can involve other parts of the musculoskeletal system or other organ systems. Common co-occurring issues include deformities of the femur (thigh bone), such as congenital femoral deficiency, or a bifid femur.
Hand and foot abnormalities beyond those directly related to the tibia may also be present, such as polydactyly (extra fingers or toes), syndactyly (fused digits), or a “lobster claw” deformity of the hand. Hip dysplasia or dislocation, as well as spinal anomalies like hemivertebrae, have also been reported in association with tibial hemimelia. The condition can also be part of broader genetic syndromes, including Werner’s syndrome or CHARGE syndrome.