Posteromedial Tibial Bowing (PMTB)
What Is Posteromedial Tibial Bowing (PMTB)?
Posteromedial Tibial Bowing (PMTB), also sometimes called congenital posteromedial bowing of the tibia, (shin bone) is a rare condition. When a baby is born with this condition, the foot is bent up on itself to the point where the top of the foot is almost touching the front of the shin bone. This severe angulation is an actual bend in the middle of the tibia. Amazingly, this tends to resolve spontaneously over 5-7 years. However, at the International Center for Limb Lengthening, we advocate a stretching program and splints to stretch out the tight muscles and tendons in front of the tibia. Children with this condition are often left with a residual bow in their shin bone despite the spontaneous improvement. In many affected children, there is a second deformity that develops at the upper end of the tibia, pointed in the opposite direction, as if the body was trying to compensate for the first angulation.
Children with posteromedial tibial bowing also develop a leg length discrepancy where one affected leg is 4 to 10 cm (1.6 to 4 inches) shorter than the normal side. The amount of the final limb length discrepancy can be predicted using the Multiplier App developed at the International Center for Limb Lengthening of the Rubin Institute for Advanced Orthopedics.
Sometimes the ankle and subtalar joints can be negatively affected, because they twist into a configuration that compensates for the bowed deformity in the shin bone. If left untreated, the shin bone will mostly correct itself, but the resulting ankle and subtalar deformity may become rigid due to tightening of the muscles, called a contracture, around the ankle joint.
How is posteromedial tibial bowing treated?
In infancy, we recommend splints and stretching exercises to help speed up the correction of the initially severe angulation. Once the infant becomes a toddler, we often prescribe shoe modifications to keep the hindfoot aligned with the rest of the lower half of the shin bone. These shoe modifications are essentially a shoe lift that also includes a “shim” to account for the angulation and the limb length discrepancy.
For older children, when the limb length discrepancy gets to be more than 4 to 5 cm (1.6 to 2 inches), or if the angulated shin bone is not spontaneously straightening enough, we consider surgery. We perform surgery as early as ages 4-6 in more severe cases.
Surgery for posteromedial bowing of the tibia includes lengthening the Achilles tendon. Then the surgeon performs an osteotomy, making one or two bone cuts, (depending on the severity of the deformity), in the shin bone and applies an external fixator to gradually lengthen the bone and correct the angular deformity. Once the lengthened bone is well healed, the external fixator is removed and a cast is put on for one month. Then the patient continues recovery with physical therapy. A second lengthening may be necessary when the child is a teenager if there will be a significant limb length discrepancy. For some children, these lengthening treatments can be paired with stunting the growth of the longer limb around ages 10-12 years in an effort to minimize the amount of lengthening needed. This minimally invasive procedure is called epiphysiodesis.
The goal of treatment in posteromedial tibial bowing is for the child, when fully mature, to have straight legs of equal length. Treatment must be individualized for each child, taking into account the predicted height and predicted limb length discrepancy. Both of these can be estimated with the Multiplier App.
Why come to the International Center for Limb Lengthening for treatment of posteromedial tibial bowing?
Limb Lengthening and deformity correction are complex processes. Your doctor at the International Center for Limb Lengthening will take the time to make sure you understand all of your options and then will customize your treatment to meet your specific needs. Our patients benefit from our team-centered approach with world-renowned surgeons and specialized physician assistants, nurses and physical therapists. We help patients with posteromedial bowing of the tibia achieve their best possible result.
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