What exactly is Pars Interarticulares Deficit?, 15yr old grandaughter diagnosed with same following horse accident, said to be congenital, also a compressed fracture of L5 ? old # as no pain,had xray & scan, Neurologist feels MRI would not be of any benefit ???, now returning to horse riding [5 weeks post] will not accept advice to fined alternate sport . Appreciate your opinion & explanation of what Pars etc. is.With thanks, Nan.