Classification OF OI

Since the 1970’s a list of numbered types has been used to describe the different forms of OI. The original list featured 4 Types. Today, as a result of recent research 15 Types of OI have been identified. Many people with OI do not fit clearly into one of the identified types and not all characteristics are seen in each person. A description of the more common OI Types follows. Understanding the individual’s OI Type provides a starting point for understanding the person’s health care needs. But due to all of the variable features, care for each person needs to be individualized.


People with Type I OI, the mildest and most common form, may have only a handful of fractures or as many as several dozen fractures in a lifetime. They may have few obvious signs of the disorder. There usually is little or no bone deformity. Height is less affected than in other types of OI. People with Type I OI are often similar in height to other family members. Muscle weakness, joint laxity and flat feet are common. Dislocations and sprains may occur as well as fractures. Life expectancy appears to be average.


Type II OI is the most severe form. Infants are quite small and are usually born with multiple fractures, an unusually soft skull and an unstable neck. Limbs may be disproportionately small and legs may fall into a frog-like position. The head may be large for the size of the body. Almost all infants with Type II OI die at or shortly after birth, often due to respiratory problems. In the newborn period, it can be difficult to distinguish between Type II and severe Type III OI. This means that some children diagnosed clinically as Type II at birth may actually have Type III OI and have a longer life expectancy.


People with Type III OI are born with fractures. X-rays may reveal healed fractures that occurred before birth. Common signs include short stature, progressive long bone deformities, spinal curvature, and a barrel-shaped rib cage. People with Type III OI may have anywhere from several dozen to several hundred fractures in a lifetime. Surgical correction of long bone bowing and scoliosis is common. Life expectancy varies. Some people with Type III OI have severe, sometimes fatal, respiratory problems in infancy or childhood. Some children and adults with severe Type III OI may require supplemental oxygen. Some individuals succumb to respiratory problems in adulthood due to progressive rib cage and spine deformities. Other people with Type III OI will have a near-average life span.


Type IV OI is the moderate type of OI. The clinical picture can be similar to Type I OI or more like Type III OI. People with this form of OI may be somewhat shorter than others in their family, have frequent fractures that decrease after puberty, and have mild to moderate bone deformity. Life expectancy appears to be average.


Type V is moderate in severity and is similar to Type IV in appearance and symptoms. Identifying features include hypertrophic calluses that may form at fracture or surgical procedure sites and restricted forearm rotation due to calcification of the membrane between the radius and ulna. expectancy.


Type VI is another moderate form and is similar to Type IV in appearance. This is an extremely rare form. It is distinguished by a characteristic mineralization defect that can be seen in biopsied bone.