Posteromedial Tibial Bowing

DISCUSSION: The picture and radiograph demonstrate posteromedial tibial bowing which is thought to be a result of intrauterine positioning. While the tibial bowing deformity usually improves, a progressive leg length discrepancy develops which (like other types of congenital limb length inequality) remains proportional throughout growth. The ultimate difference ranges from 3 to 8 cm.

Pappas et al looked at the patterns of growth in 33 patients with congenital posteromedial bowing of the tibia and fibula. They found the bowing is accompanied by shortening of the tibia and fibula, an initial calcaneovalgus deformity of the foot, and a decrease in ankle motion that does not improve with age. They found the greater the initial bowing, the greater the ultimate extremity length discrepancy.

Incorrect Answers:
Answer 1: Knee instability is not associated with posteromedial tibial bowing but can be associated with other congenital femur, tibia, or fibula deficiencies.
Answer 3: Pseudoarthrosis is associated with anterolateral bowing which is often seen with neurofibromatosis.
Answer 4: Scoliosis is not associated with posteromedial tibial bowing.
Answer 5: Tarsal coalition is associated with fibular hemimelia.

DISCUSSION: The radiographs show posteromedial bowing of the tibia and fibula, which is commonly associated with a calcaneovalgus foot deformity.

Posteromedial tibial bowing is a form of physiologic bowing of tibia thought to be the result of intrauterine positioning. Treatment of this condition involves observation of the tibial deformity, which usually resolves at age 5 to 7. These patient often have a residual leg length discrepancy that may require treatment with an age-appropriate epiphysiodesis of long limb.

Calcaneovalgus is a separate condition, also caused from intrauterine packaging, that may occur independently or in associateion with posteromedial bowing. The "classic" presentation consists of deformity where the dorsal surface of the foot rests against the anterior shin. This condition usually resolves spontaneously, although correction may be expedited with parental stretching. It should be differentiated from vertical talus with a dorsiflexion lateral.

Pappas et al looked at the patterns of growth in 33 patients with congenital posteromedial bowing of the tibia and fibula. They found the bowing is accompanied by shortening of the tibia and fibula, an initial calcaneovalgus deformity of the foot, and a decrease in ankle motion that does not improve with age. They found the greater the initial bowing, the greater the ultimate extremity length discrepancy.

Lincoln et al reviews different rotational deformities found in children. They report in-toeing is usually attributable to metatarsus adductus in the infant, internal tibial torsion in the toddler, and femoral anteversion in children younger than 10 years. Out-toeing patterns largely result from external rotation hip contracture, external tibial torsion, and external femoral torsion. They emphasize that most of these conditions are benign and resolve spontaneously.

Illustration A shows a side-by-side comparison of calcaneovalgus foot (left) and posteromedial tibial bowing (right). In calcaneovalgus foot, the apex of deformity is in the ankle joint, whereas in posteromedial bowing the apex of the deformity is in the distal tibia. Illustration B shows an example of calcaneovalgus foot, as evidenced by the apex of the deformity being in the ankle. Illustration C shows an example of posteromedial bowing, as evidenced by the apex of the deformity being in the distal tibia.