What is it?
Tibial Pseudarthrosis refers to a condition in which a child is born with a defect of the shin bone whereby the bone is dense, bent or fractured. If the fracture is not present at birth it often develops over the first few years of life and shows no evidence that it will heal going on to form a false joint or pseudarthrosis.
Who gets it?
Approximately 50% of cases are associated with a condition known as neurofibromatosis which may not be obvious at birth. Neurofibromatosis is a significant condition of nerves that produces benign tumours that can affect the brain, eyes, spine and peripheral nerves. For this reason children with tibial pseudarthrosis require a genetic consultation, gene screening and eye tests to exclude the diagnosis.
What are the associations?
Fifty percent of children will have neurofibromatosis whilst in the other fifty percent there are no associations and the condition is not inheritable.
What is the natural history?
Children with tibial pseudarthrosis may be born with and established non union with thin bone ends and significant bowing of the leg. The fracture is usually in the lower half of the bone and often also involves the smaller out side bone – the fibular. A number of children have a bowing of the tibia out to the front and side without fracture and on x-ray the bone is dense and abnormally shaped. All children will have a degree of leg shortening due to growth inhibition and bowing.
Over time the deformity becomes worse and many of the intact tibia bend and break without every showing any evidence of healing. The skin over the tibia may break down and the leg remains unstable. Generally the knee and foot are normal but due to the deformity and instability walking becomes increasingly difficult if not impossible.
How do you treat it?
In the past tibial pseudarthrosis was either treated by amputation or with a variety of surgical procedures that inevitably compromised the limb producing stiffness and shortening. It was always seen as a condition that had a high failure rate and that good outcomes with acceptable function were difficult to achieve. Greater understanding of the pathology, biology and improved surgical techniques has changed that outlook considerably.
The biological healing response can be changed with the use of certain medications the improve the healing response and the recognition that this is a disease of the tissue that covers bone (periosteum) means that there is a surgical imperative to remove this tissue completely. Perfect alignment of the tibia with the use of growing rods stabilises the limb and ring external fixators are used to promote healing maintaining compression and control rotation. The fibular is also fixed in place and copious amounts of bone graft used to promote union of both bones.
Once union is achieved the fixator is removed and the child wears a plastic splint for a number of years. Regular check ups are required and later exchange of the growing rod is required.
Limb equalisation can be achieved by lengthening the shin either at the time of initial surgery or at a later date once the bone is well healed. Small length differences are managed by slightly slowing down the growth of the opposite leg.