Sclerosing Bone Dysplasias (Osteopetrosis, Pycnodysostosis, Osteopathia Striata, Sclerosteosis/Van Buchem)

Diffusely dense bones with a bone-in-bone appearance and a low-energy transverse, chalk-stick fracture is the classic picture of osteopetrosis, the prototype sclerosing bone dysplasia, caused by defective osteoclast resorption. The bone is dense and sclerotic, often with Erlenmeyer-flask metaphyses, but it is paradoxically brittle, hence the transverse fractures. I would classify the sclerosing dysplasias by target site - osteopetrosis sits in the endochondral group with pycnodysostosis, osteopoikilosis and osteopathia striata - and I would look for features distinguishing pycnodysostosis, which adds short stature and acro-osteolysis. The management challenges are considerable. The fracture is hard to fix because dense bone is difficult to drill, generates heat, and the hardware tends to fail, with high rates of nonunion and infection, so I would plan carefully, use sharp instruments and pre-drill, and anticipate problems. I would also consider the systemic dimensions: the severe infantile autosomal-recessive form causes marrow failure with anaemia and pancytopenia, hepatosplenomegaly, cranial-nerve compression and a tendency to osteomyelitis, classically of the mandible, and may need haematopoietic stem-cell transplant to restore osteoclast function, whereas the adult dominant form is milder. Cranial-nerve compression and raised intracranial pressure may need decompression. Finally, I would be careful not to confuse benign incidental dysplasias such as osteopoikilosis or a bone island with osteoblastic metastases.