What Is The Procedure And Membrane Used For Retethering?

my daughter has spina bifida. she is adopted from Ch*na and had her repair surgery at 3 1/2. she is 6 now and has a tethered cord. her surgery is somewhat optional at this time because she is showing no symptoms at all. the neurosurgeon says there is a new membrane being used that reduces the chance of retethering. we would like to do research on this, but we don't know what the procedure/membrane is called. Can you help?