It is a genetic disease characterized by fragility of bones, deafness, blue sclera, laxity of joints and a bent to enhance with age. Osteogenesis imperfecta is a disease of the mesodermal tissues with the deposition of normal collagen in bone, skin, sclera and dentine.
Pathogenesis and Pathology
Primary defect is failure of osteoblast formation during enchondral ossification; osteoid formation does not take place. Features of bones are:
• Periosteum is thick but the cambium layer is thin.
• Bone is short and thin and the epiphysis is bulbous.
• Cortex is thin and medullary contents are fatty and fibrous.
• Bones break easily but heal well with abundant callus. Fracture is usually subperiosteal and heals by periosteal bone formation.
• Deformity results from bending and fractures.
• Vertebral bodies are biconcave.
• Skull is thin and globular.
Osteogenesis imperfecta tarda type I: This type has presence of bowing at long bones.
Osteogenesis imperfecta tarda type II: bowing of long bones is absent.
Fractures could also be present in both the kinds but rare in type II.
The patient presents with blue sclera, dentinogenesis imperfecta and generalized osteoporosis. Blue sclera is seen only in 92 percent of cases, while the other two features are seen in almost all cases. Osteoporosis gives rise to bowing and multiple fractures. Fractures are usually due to trivial trauma but surprisingly heal well. Other features include: Deafness due to otosclerosis, laxity of joints, dwarfism, broad skull, poorly calcified decidual teeth, but permanent teeth are normal and the blood chemistry is normal.
The mnemonic BLOOD in osteogenosis imperfecta.
Quick facts Do you know the 4 O’s responsible for easy fractures?
• Osteogenesis imperfecta.
Remember 3F’s in osteogenosis imperfecta
• Fragile bones
• Fractures—multiple and frequent
• Fetal variety is fatal.
Thick bone type
• Seen only in congenital cases.
• Shafts of long bones are thicker than normal. Thin bone type
• The long bones are thinner and ends are bulbous.
• Vertebral bones are thin and biconcave.
• Cortex is thin. Osteogenesis imperfecta cystica Fracture unites promptly with large callus.
Laboratory tests, there’s no specific laboratory test for this disease. Prenatal determination of the probability of autosomal dominant disease on the fetus are often achieved by amniocentesis and estimation of inorganic pyrophosphate. This compound is elevated 3-4 times the normal value.
X-ray of the affected limbs helps to make a diagnosis. Three varieties are described—the thick bone type thin bone type and cystic types. DNA blood testing of gene defect has an accuracy of 60-94%.
Protect the child until the tendency of the fracture lessens as age advances.
Administer vitamins, estrogens and androgens. Operate in infantile type as the tendency to fracture is much higher and hence the treatment of choice is multiple osteotomies with intramedullary nailing. Physiotherapy, rehabilition, and orthopedic surgery are the treatment for patient with osteogenesis imperfecta.
Sofield’s method consists of multiple osteotomies and realignment and IM nail fixation. It is useful for long bones and is indicated for fresh fractures and correction of bowing. There are no growth disturbances in this technique.
Bailey and Duboy’s here, telescopic medullary rod is used which elongates as growth occurs.
William’s here, retrograde nailing is done by fixing an extension to the distal end of the rod and driving the nail through the heel.