It is Erlenmayer flask deformity.

Differential diagnosis include

  •  Osteopetrosis
  •  Caniometaphyseal dysplasias
  •  Haemoglobinopathies
    • Thalassemia
    • Sickle cell disease
  •  Niemann-Pick disease
  •  Gaucher disease
  • Leadpoisoning
  • Gaucher disease
  • Metaphyseal dysplasia (Pyle disease)
  • Achondroplasia
  • Fibrous dysplasia

Erlenmeyer flask bone deformity (EFD) is a long-standing term used to describe a specific abnormality of the distal femora. The deformity consists of lack of modeling of the di-metaphysis with abnormal cortical thinning and lack of the concave di-metaphyseal curve resulting in an Erlenmeyer flask-like appearance. The term Erlenmeyer flask is derived from a type of laboratory flask which has a conical base and a cylindrical narrow neck joined by uncurved edges and was named after the German chemist Richard Erlenmeyer, who created it in 1861. The term, Erlenmeyer flask bone deformity (EFD), has been commonly used to describe an abnormality in the distal aspect of the femora. However, similar deformities had been observed in other long bones including the proximal ends of the humeri and tibiae, and the distal ends of ulnae and radii. The deformity can occur bilaterally or unilaterally. This deformity results from defective bone modeling (under-modeling) at the meta-diaphyseal [di-metaphyseal] region leading to straight uncurved [or even laterally bowed] di-metaphyseal borders and cortical thinning giving the appearance of EFD.


It refers to group of disorders caused by severe impairment of osteoclast mediaterd bone resorption. It is also known a marble bone disease due to its solid X-ray appearance, and Albers-Schonberg disease refers to a milder variant. The major type of osteopetrosis include malignant (severe, infantile, autosomal recessive) osteopetrosis and benign (adult, autosomal dominant) osteopetrosis. Osteopetrosis tarda, the benign form, presents in adulthood, while the two more malignant variants, osteopetrosis congenita and marble bone disease, present in infancy and childhood, respectively. In all three forms, the main features are pathologic alteration of osteoclastic bone resorption and thickening of cortical and lamellar bones. Osteopetrosis tarda is usually discovered accidentally on routine radiographs and is often asymptomatic; however, patients may present because of related degenerative joint disease. Osteopetrosis congenita results in bone marrow failure and is almost always fatal. Marble bone disease causes short stature, cerebral calcification and mental retardation. Bone marrow transplant is the only chance for survival in patients with osteopetrosis congenita.

Etiology and genetics

The primary defect in osteopetrosis is loss of ossteoclastic bone resorptionand preservation of normal osteoblastic bone function. There may be mutations of majorly OPG (Osteoprotegrin), RANKL(Receptor activator of nuclear factor kappa-B), CA-2 (Carbonic anhydrase 2), TCIRG1(Osteoclast specific subunit of vacuolar proton pump),CICN7(Chloride channel gene-7).



Osteopetrosis tarda is usually detected by a family history of bone disease or as an incidental radiologic finding, and is asymptomatic in about 50 percent of cases. About 40 percent of patients present with fractures related to brittle osteopetrotic bones or with osteomyelitis, especially of the mandible. There is sufficient retention of marrow cavity for normal hematopoiesis to occur in patients with osteopetrosis tarda. In some cases, there is an elevated acid phosphatase level. Although patients with osteopetrosis tarda have an increased susceptibility to fractures, healing appears to proceed normally.


Osteopetrosis congenita (malignant osteopetrosis) presents in infancy and is associated with failure to thrive and growth retardation. This form of osteopetrosis is very severe and usually results in death by age two years. Proptosis, blindness, deafness and hydrocephalus occur in these patients as bone encroaches on the cranial foramina. A critical feature of osteopetrosis congenita is severe bone marrow failure, resulting in pancytopenia. Extramedullary hematopoiesis, resulting in hepatosplenomegaly and hypersplenism, may occur but cannot compensate for bone marrow failure. Thrombocytopenia, leukoerythroblastic anemia and elevated serum acid and alkaline phosphatase levels are also usually present. Hypocalcemia may or may not be present. Death from osteopetrosis congenita occurs as a result of severe anemia, bleeding and/or infection.

In rare instances patients survive into adulthood. They present with severe anemia, recurrent fractures, growth retardation, deafness, blindness and massive hepatosplenomegaly.


Marble bone disease, the other infantile form of osteopetrosis, is not characterized by bone marrow failure. Although survival rates are better for patients with marble bone disease than for patients with osteopetrosis congenita, the consequences of renal tubular acidosis may shorten life expectancy. Patients with marble bone disease are usually of short stature and present with intracranial calcifications, sensorineural hearing loss and psychomotor retardation.


Allogenic HLA identical bone marrow transplantation before the age of 4 years has been successful in some children. Transplanted marrow cells contain progenitor cells and normally functioning osteoclasts.

Other limited treatments include INF-gamma-1beta, 1,25-DHCC, Methylprednisolone and low calcium high phosphate diet.