Fractures at the distal tibia (ankle) in children pose a special challenge. This is especially true if the fracture goes through the epiphysis (growth plate) or separates the growth plate from the joint. Surgery to hold it all together while it heals may be needed. Metal screws are used that can be removed later.
But transepiphyseal metal implants (through the growth plate) change the way the ankle is loaded during weight-bearing (standing and walking). Over time, the increased pressure leads to breakdown of the joint. Pain and disability can be the final outcome.
One way to avoid this problem is to use bioabsorbable screws. These implants serve the same function as metal screws: to maintain a closed position of the fracture while the bone heals. But the screws dissolve and are absorbed by the body over the next two to four years.
Before anything new of this type can be used in children, they must be proven both safe and effective. In this study, surgeons from two large children’s hospitals in Texas compared the use of metal versus bioabsorbable screws for fractures of the distal tibia. The tibia is the lower leg bone. The distal tibia describes the bottom of the tibia where it forms the upper half of the ankle joint.
An equal number of children were in each group. The groups were matched by age, gender, type and severity of injury, and time between the injury and surgery. The surgical technique used for bioabsorbable screws was slightly different from metal screws. The bioabsorbable screws cannot cut into the bone and screw into place like metal screws. Threaded wires were used and holes drilled before the partially threaded bioabsorbable screws could be placed.
Results were measured using X-rays and patient report of symptoms and function. Operative time (about 80 minutes) was the same for both groups. Children in both groups were back on their feet in about seven weeks’ time. Full activities were resumed by the end of four months.
There were some complications for both groups but a greater number of problems in the metal screw group. Irregularity of the joint line and disruption of the growth plate causing growth to stop were the two main complications. Both of these were more common in the metal group. None of the children with bioabsorbable implants needed further surgery. Half of the children with metal screws had a second operation to remove them.
Bioabsorbable implants have been used in adults with good results. But this is the first report of their use in a number of skeletally immature children (i.e., they are still growing and have not reached full skeletal maturity) with ankle injuries. The surgeons were careful not to cross the growth plate with the screws in order to avoid disturbing growth.
Future studies need to answer some additional questions. For example, is the bioabsorbable screw strong enough to support more severe fractures? Can it be used across the epiphysis/physis without inhibiting growth? And what are the long-term effects (if any) of an implant left in place?
For now, it appears that bioabsorbable screws can be safely used for distal tibial (ankle) fractures. Results are as good, if not better, than results with metal screws. And it eliminates a second surgery (to remove the implants), which is both cost effective and less risky for the patient.