Congenital Anterolateral Tibial Angulation: Navigating a Unique Bone Deformity

Introduction:

Congenital orthopedics deformities form a major part of deformities that usually go unnoticed or untreated even with diagnosis. The congenital deformities of the tibia may be posterior or anterior, along with medial or lateral deviation of bone. The anterolateral bowing of the tibia is usually linked with pseudarthrosis, which can disable a child from the initial developmental phase of standing and walking.

What Is the Tibia?

The tibia is also known as the shin bone, which is the second longest bone in the human body. It is one of the important bones in the body that helps to stand and move. Moreover, it is one of the strongest bones, which requires a lot of force to fracture it.

The tibia is present in the lower leg and runs from just under the knee to the ankle. The fibula is the other bone in the lower leg along with the tibia and is smaller than the tibia. The tibia is located closer to the inside of the body, and the fibula is on the outside (lateral) of the body. The tibia is the main weight-bearing bone in the lower leg and supports the body when a person stands and helps in movement.

What Is Congenital Pseudarthrosis of the Tibia?

Congenital pseudoarthrosis of the tibia (CPT) means nonunion of a tibial fracture after minor trauma. Pseudoarthrosis means a false joint and a bone gap that fails to heal on its own. This condition is commonly seen within the first two years of life. However, some cases have been reported in the later stage of life. This is often associated with anterolateral bowing of the tibia and plays an essential role in the disability or ability status of a child.

What Is the Pathophysiology of Tibial Bowing?

The posteromedial bowing of the tibia is defined by the apex of the tibial curve being directed medially and posteriorly. The bowing of the tibia is usually associated with different disorders. The change in limb length inequality also occurs due to the bowing of the tibia. However, in some cases, it has been found that bowing of the tibia gets resolved with age, usually by eight years of age. In cases where the bone does not heal correctly, it leads to instability and mobility at the false joint. As a result, the leg becomes unstable and causes difficulty in functioning.

What Is the Classification of Tibial Angulation or Bowing?

There are three types of tibial bowing that exist in children, which include -

• Anterolateral bowing.

• Posteromedial bowing.

• Aanteromedial bowing.

Anterolateral bowing can be further divided into -

• Anterolateral bowing of the tibia.
• Congenital pseudarthrosis of the tibia.

There are various classifications, which include -

I. Boyd Classification of Pseudarthrosis Tibia -

1. Associated with anterior bowing with a defect in the tibia.
2. Associated with anterior bowing and hourglass constriction of the tibia. This is the most common type, with a tapered, rounded, and sclerotic tibia with an obliterated medullary canal. It is often associated with neurofibromatosis and has the poorest prognosis.
3. This develops in a congenital cyst near the junction of the distal and middle third of the tibia. In this case, there may be a fracture or anterior bowing of the tibia.
4. This develops in a sclerotic part of the bone and does not involve narrowing the tibia.
5. Associated with a dysplastic fibula.
6. Occurs as an intra-osseous neuro fibroma resulting in pseudarthrosis.

II. Crawford Classification -

1. Anterolateral bowing with cortical thickening at the apex and with open medullary canal.
2. Has narrowed medullary canal and cortical thickening.
3. Has a cystic lesion.
4. Fractured ends of the tibia are tapered.

III. Anderson Classification -

1. Narrow tibia with segmental dysplasia.
2. Presence of cystic tibia with pseudocysts.
3. Sclerotic and pseudarthrosis appear at five years of age.
4. Anterior tibial bowing with a club foot.

What Is the Etiology of Tibial Angulation?

The actual causes of tibial angulation are unknown. However, factors like pseudarthrosis and neurofibromatosis play an important role. Other than that, intrauterine trauma and generalized metabolic disturbances may also lead to tibial angulation. Other conditions include neurofibromatosis type I, which is characterized by a change in skin pigmentation and the growth of tumors along nerves in the brain and other body parts. Neurofibromatosis type I is commonly found in 50 to 55 percent of patients with anterolateral bowing, and only 6 to 10 percent of patients with neurofibromatosis will have anterolateral tibial bowing.

How Is Congenital Tibial Angulation Diagnosed?

The tibial bowing or angulation can be diagnosed best with a radiographic or physical examination. During this, the length of the tibia from the midpoint to the distal epiphysial plate is done using picture archiving and communication systems (PACS). This helps in measuring the angle between the anatomical axis of the tibia and the lining of the proximal axis.

Conventional radiographs can show thin, atrophic, or hypertrophic tibial bone, usually with a cupped proximal and pointed distal fragment. Moreover, the false joint is often seen in the distal third of the shaft, and the fibula is not that commonly affected. Any discontinuity in the bone cortex in the radiograph indicates that the refracture has occurred.

MRI (magnetic resonance imaging) and CT (computed tomography) scans can be done along with conventional radiographs to diagnose and follow up.

What Is the Treatment of Tibial Angulation?

The treatment of tibial angulation has an uncertain prognosis. The treatment usually involves correcting the angulation with cast application or doing surgical procedures like grafting or excision of local fibrous tissue-bone grafting with stabilization and correction of the deformity using a fixator. The success of the surgical procedures is uncertain due to the idiopathic nature of this condition.

The patient has to use splints or braces till they mature and have to go for regular clinical and radiological follow-ups. Some of the treatment procedures include -

I. Non-operative -

1. Using splints or braces in cases -
2. Where children are of weight-bearing age.
3. Bowing without fracture.
4. Spontaneous remodeling is not expected.
5. The goal is to prevent further fractures or bowing, and the braces are maintained until the patient's skeletal maturity.

II. Operative -

1. Surgical fixation in cases where there is fracture or pseudarthrosis.
2. Amputation is usually indicated in cases with severe limb length discrepancy, multiple failed surgical attempts, and dysfunctional angular deformity.

Conclusion:

Congenital anterolateral tibial angulation is a serious and rare condition that requires regularfollow-up, preventive splint, and necessary treatment after the detection of pseudarthrosis. Early diagnosis and appropriate interventions, including orthotic devices and surgery, can significantly improve outcomes. Continued research and medical advancements offer hope for enhanced treatment options and better quality of life for affected individuals.