Pedicle stress fracture: an unusual complication of pycnodysostosis.

Pycnodysostosis is a rare dysplasia characterised by high bone density and susceptibility to long bone fractures caused by cathepsin K deficiency. Spinal abnormalities have rarely been described in this uncommon inherited bone dysplasia. A 28-year-old female, with a past history of pycnodysostosis and spontaneous leg fractures was hospitalized for a 2-month history of spontaneous low back pain.