Background
Osteopetrosis is a rare inherited bone disorder originally described in 1904 by Albers-Schonberg, a German radiologist; this is a group of sclerosing bone dysplasia due to diminished osteoclast-mediated skeletal resorption. The disorder is characterized by osteosclerosis, obliteration of the medullary cavity and calcified cartilage. Despite the sclerotic radiographic appearance of the thickened cortices and its material hardness, osteopetrotic bone is weak and prone to fracture by minor trauma. The sclerosis of bone is, in fact, the result of increased thickness and disorganization, not an increase in mineralization. Areas of concentrated stress such as the femoral neck and subtrochanteric areas are especially susceptible.
Osteopetrosis has been categorised clinically into three primary types: infantile, or "malignant" osteopetrosis, inherited in an autosomal recessive pattern; "intermediate" autosomal recessive osteopetrosis and "benign" autosomal dominant osteopetrosis. The severe infantile forms of osteopetrosis are associated with diminished life expectancy, with most untreated children dying in the first decade as a complication of bone marrow suppression. Orthopaedic surgeons most commonly encounter patients with the benign autosomal-dominant type of osteopetrosis (Albers-Schönberg disease), previously known as adult osteopetrosis or osteopetrosis tarda. In fact autosomal dominant osteopetrosis typically onsets in late childhood or adolescence and is compatible with a normal life span; blood studies show that acid phosphatase, calcitriol, and creatine phosphokinase BB variant levels are elevated, but as many as 40% of patients with the benign form may remain asymptomatic, while most of them first learn of their diagnosis after a fracture. Life-threatening symptoms include anemia, pancytopenia, osteomyelitis and sepsis due to poorly developed bone marrow and impaired medullary hematopoiesis, associated with secondary hematopoiesis in liver and spleen that causes hepatosplenomegaly.
Fractures typically occur in the appendicular skeleton, most commonly in the proximal femur, as well as in the femoral shaft, tibia, and upper extremities. These fractures may result from minimal trauma due to the pathologic nature of bone. Fracture-healing abnormalities have been noted both histologically and clinically. Because of dysfunctional remodeling, the callus does not attain haversian organization even by one year postfracture. Broad cement lines persist, creating areas of lowered resistance where microfractures may propagate. Some authors report delayed union and nonunion following fractures. In some patients, nonunion of femoral neck fractures may lead to coxa vara. Long-bone deformities are also possible, in particular, lateral bowing of the femur. Coxa vara deformities typically appear during childhood, apparently caused by stress-induced microfractures in the brittle femoral neck. Degenerative osteoarthritis also may develop secondary to coxa vara deformity. When fractures are encountered, fixation is extremely difficult.
Two of these problems, osteoarthritis and certain periarticular nonunions, may be recalcitrant to other treatment options and may be considered for treatment with total joint arthroplasty. It is recognized that the hard brittle bone, often without a normal medullary canal, makes arthroplasty implantation difficult, may compromise the outcome and lead to more frequent complications.
Osteomyelitis is common in patients with osteopetrosis because of a reduced resistance to infection The increased incidence of osteomyelitis has been attributed to the lack of marrow vascularity in osteopetrotic bone and impairment of white cell function. The mandible followed by the maxilla, scapula, and extremities is most frequently involved. The cause of osteomyelitis of the jaws is usually odontogenic infection and polymicrobial in nature, as opposed to long bone osteomyelitis, in which classically Staphylococcus aureus remains the main responsible organism.
To date, only one case of osteomyelitis of the proximal third of the femur has been described and treated successfully with femoral head resection. This is, to our knowledge, the first description of a staged implant of a cementless total hip prosthesis for the treatment of a septic hip in femoral neck nonunion in osteopetrosis