Abnormal Bony Density or Structure
Osteogenesis imperfecta
Osteogenesis imperfecta (OI) is a heritable bone disorder with abnormal bone quality or quantity (326).
Characteristics. Fractures are the hallmark of OI.
The number of fractures in a lifetime vary from a few to several hundred. There are numerous associated clinical findings, but phenotype can vary greatly even within families with the same genotype (327). Short stature is common, as are a relative macrocephaly and triangular facies (328). Cognition is normal. People with OI tend to have a high-pitched voice. In addition to fractures, musculoskeletal findings can include scoliosis, muscle spasms, and hypermobility. Multiple bone microfractures can lead to bowing and increased fracture risk (329). Respiratory failure is the leading cause of death in OI (330). Basilar impression, an abnormality of the skull base, can cause compression and neurologic compromise (331). Skin tends to be fragile, leading to increased bruising (328). With fractures and bruising, some children with mild OI may be difficult to distinguish from those sustaining nonaccidental trauma (326,328). Hypercalcuria and renal calculi can occur, as can aortic dissection and mitral valve prolapse (328). Hearing loss may require amplification or surgery. Dentinogenesis imperfecta can be present.Sillence described four types of OI (326,327,332, 333,334,335), as outlined in Table 14.7. There is overlap in the clinical presentation, particularly Sillence types III and IV. In recent years, new types of OI have been described based on unique structure found on bone biopsies as well as clinically distinguishing features (326). Previously, these patients had been described as having type IV OI, but were found to have normal type I collagen.
Rehabilitation. Infants can be positioned to encourage active movement while decreasing fracture risk (336,337,338).
Improvement of head control can be encouraged by prone lying or lying on a reclining parent's chest or shoulder. Towel rolls can be used to avoid excessive hip abduction while supine or support the infant's back in side-lying. Diaper changes should be done by rolling the infant, not by lifting the legs (339). Lifting the infant should be done with a wide base (eg, hands spread apart), not under the arms.Range-of-motion exercises should be active (337). Aquatic therapy has been recommended to increase strength and mobility (337,340). Weight bearing can improve bone strength. Clamshell bracing may be used to provide support for weight bearing (336,338,341). Long leg bracing may be shortened later (336). There has been a trend for less bracing recently, as infants have been starting early intervention programs and sit in their first year (336).
Sports and recreation activities may be added in the school-age or teen years (342). However, high-impact activities such as gymnastics, aerobics, martial arts, hiking, and contact sports are not recommended (343). The Osteogenesis Imperfecta Foundation published a book that provides detailed therapy recommendations and rates the relative risks and benefits of various sports (344). They also provide excellent resources for patients, families, physicians, nurses, and therapists (345).
Children should stand or walk daily (343). They may benefit from playing a wind instrument or singing to improve pulmonary health (343). Independence with activities of daily living can be gradually increased. Children should avoid staying in their wheelchairs for the entire day. Armrests can be removed from manual wheelchairs to decrease forearm bowing (338). Adolescents can learn to manage their medical care, drive, and transition to college or work (346).
Medical Interventions. Multiple drugs have been tried in OI without success until the bisphosphonates were shown to increase bone density, decrease risk of fractures, increase mobility in some patients, and decrease pain (347,348).
Side effects such as transient fevers and discomfort were relatively mild for most children. Markers of bone turnover decreased. Some studies have shown benefit for infants and toddlers (349,350). There are concerns that prolonged use could cause decreased bone healing (348). Long-term risks are unknown. Some studies (351,352), but not all (353), have shown improved function with bisphosphonates treatment. The optimal drug and dosing has not been determined (354).Surgical Interventions. The risk of fracture has been found to increase significantly when long bone angulation was 40 degrees (341,355). Intramedullary rods can improve fracture risk but can migrate into joints (356). As a child grows, the bone “unprotected” by the now too-short rod can break. Telescoping rods have been used, but still have risks. Some surgeons have found fewer surgical complications in children treated with bisphosphonates (357).
Outcomes. Despite the fractures, surgeries, and mobility impairments common in OI, people with OI rate their quality of life well (358,359). A recent study showed that children with OI rated higher than the reference norms on the psychosocial summary of the Child Health Questionnaire (359). Adults with OI often attend college and have employment similar to the general population without disabilities (358).