such as chaperone proteins, the wnt signaling pathway, the bril protein, et cetera. in type i the collagen's structure itself is normal, it is just its quantity that is low.: 1516 types ii, iii and iv are usually, but not always, related to a deficiency of type i collagen. one possible deficiency arises from an amino acid substitution of glycine to a bulkier amino acid, such as alanine, in the collagen protein's triple helix structure. the larger amino acid side-chains lead to steric effects that creates a bulge in the collagen complex, which in turn influences both the molecular nanomechanics and the interaction between molecules, which are both compromised. depending on both the location of the substitution and the amino acid being used instead, different effects are seen which account for the type diversity in oi despite the same two collagen genes being responsible for most cases. replacements of glycine with serine or cysteine are seen less often in fatal type ii oi, while replacements with valine, aspartic acid, glutamic acid, or arginine are seen more often. at a larger scale, the relationship between the collagen fibrils and hydroxyapatite crystals to form bone is altered, causing brittleness. bone fractures occur because the stress state within collagen fibrils is altered at the locations of mutations, where locally larger shear forces lead to rapid failure of fibrils even at moderate loads because the homogeneous stress state normally found in healthy collagen fibrils is lost. oi is therefore a multi-scale phenomenon, where defects at the smallest levels of tissues (genetic, nano, micro) domino to affect the macro level of tissues. diagnosis blue sclerae in a patient with osteogenesis imperfecta diagnosis is typically based on medical imaging, including plain x-rays, and symptoms. in severe oi, signs on medical imaging include abnormalities in all extremities and in the spine. as x-rays are often insensitive to the comparatively smaller bone density loss associated with type i oi, dexa scans may be needed.: 1514 an oi diagnosis can be confirmed through dna or collagen protein analysis, but in many cases, the occurrence of bone fractures with little trauma and the presence of other clinical features such as blue sclerae are sufficient for a diagnosis. a skin biopsy can be performed to determine the structure and quantity of type i collagen. while dna testing can confirm the diagnosis, it cannot absolutely exclude it because not all mutations causing oi are yet known and/or tested for.: 491–492 oi type ii is often diagnosed by ultrasound during pregnancy, where already multiple fractures and other characteristic features may be visible. relative to control, oi cortical bone shows increased porosity, canal diameter, and connectivity in micro-computed tomography. oi can also be detected before birth by using an in vitro genetic testing technique such as amniocentresis. genetic testing in order to determine whether osteogenesis imperfecta is present, genetic sequencing of the most common problematic genes, col1a1, col1a2, and ifitm5, may be done; if no mutation is found yet oi is still suspected, the other 10+ genes known to cause oi may be tested. duplication and deletion testing is also suggested to parents who suspect their child has oi. the presence of frameshift mutations caused by duplications and deletions is generally the cause of increased severity of disease. differential diagnosis an important differential diagnosis of oi is child abuse, as both may present to a clinician with multiple fractures in various stages of healing.: 1514 differentiating them can be difficult, especially when no other characteristic features of oi are present.: 391 this can become an issue in court; in the united states, several child abuse cases were resolved with a finding that osteogenesis imperfecta was the true cause of a child's fractures, leading to lawsuits seeking redress such as alice velasquez, et al. v. united states.: 391 other differential diagnoses include rickets and osteomalacia, both caused by malnutrition, as well as rare skeletal syndromes such as bruck syndrome, hypophosphatasia, geroderma osteodysplasticum, and ehlers–danlos syndrome.: 1513 : 253–256 various forms of osteoporosis, such as iatrogenic osteoporosis, idiopathic juvenile osteoporosis, disuse osteoporosis and exercise-related osteoporosis should also be considered as explanations when oi is suspected.: 255–256 treatment there is no cure for osteogenesis imperfecta. maintaining a healthy lifestyle by exercising and avoiding smoking can help prevent fractures. treatment may include care of broken bones, pain medication, physical therapy, mobility aids such as braces or wheelchairs, and surgery. judging the success or failure of treatment can be difficult in oi patients, as decreased bone fracture rates may just be coincidental. while these rates are often used in medical studies to judge treatment efficacy, a norwegian study of fifteen people with oi emphasized that they feel doctors should consider the whole patient and not just fracture rates. acute bone fracture care bone fractures are treated in individuals with osteogenesis imperfecta in much the same way as they are treated in the general population—oi bone heals at the same rate as non-oi bone.: 431 a greater emphasis is placed on using lightweight materials to immobilize the fracture, as in moderate or severe types of oi, using heavy casts, such as hip spica casts, can cause fractures at the bones at the boundaries of the cast, as well as generalized osteopenia.: 431 the lightweight cast or splint is then replaced with a removable orthosis after a few weeks and once evidence of union is seen on x-ray.: 431 in order to prevent a nonunion or malunion, all fractures should be immobilized, even if the fracture seems trivial (microfracture),: 439 as people with oi are at greater risk of nonunion.: 438 bone infections secondary to fractures are treated as and when they occur with the appropriate antibiotics and antiseptics, as in the general population.: 424 bisphosphonates pamidronate in 1998, an initial observational trial demonstrated the effectiveness of intravenous pamidronate, a bisphosphonate which had previously been used in adults to treat osteoporosis. in severe oi, this trial showed that pamidronate reduced bone pain, prevented new vertebral fractures, reshaped previously fractured vertebral bodies, and reduced the number of long-bone fractures. although oral bisphosphonates are more convenient and cheaper, they are not absorbed as well, and intravenous bisphosphonates are generally more effective, although this is under study. some studies have found oral and intravenous bisphosphonates, such as oral alendronate and intravenous pamidronate, equivalent. in a 2013 double-blind trial of children with mild oi, oral risedronate increased bone mineral densities, and reduced nonvertebral fractures. however, it did not decrease new vertebral fractures. a cochrane review in 2016 concluded that though bisphosphonates seem to improve bone mineral density, it is uncertain whether this leads either to a reduction in bone fractures or improvement in the quality of life of individuals with osteogenesis imperfecta. even in trials with as many as 125 children, no causal link has been found between bisphosphonates and decreased fracture rates; placebo controlled trials were also unable to prove that they brought about increased strength, motor control or lower pain levels. bisphosphonates are not as effective at increasing the bone mineral density of adults. nutritional supplements oi is a genetic disorder and is not caused by insufficient intake of any vitamin or mineral; supplementation cannot cure oi. with that said, people with oi tend to be severely deficient in vitamin d at much higher rates than the general population, and the cause of this is not well understood. the severity of the deficiency and the likelihood of its occurrence is thought to be related to severity of oi. vitamin d supplementation may be recommended, at least until levels of 25(oh)d3 in blood return to normal. below normal levels of vitamin d are also concerning as they may decrease the benefit of bisphosphanates. surgery a surgery of any type inherently carries more risks when done on a patient who has (especially moderate to severe) oi. skeletal deformities and dentinogenesis imperfecta may hinder access to the airway.: 333 use of, and weaning off of, mechanical ventilation is also more challenging to carry out on patients with oi.: 333 during the procedure itself or the healing process, defective oi collagen may lead to bleeding diatheses.: 333 the safety of anesthesia is also of more concern among patients with oi,: 333 with anesthetic complications 5.6x more likely to occur when the patient has oi type iii. a unique concern of anesthesia in oi is perioperative fracture—fractures sustained due to patient transfer and airway access techniques that, while routine when a patient's bones are strong, may cause injury with brittle oi bones. as an example, due to a 1972 report of a humerus fracture from a sphygmomanometer cuff sustained in an oi patient during surgery, blood pressure monitoring protocols are often modified for patients with oi, with neonatal size cuffs and machine settings being used even in adults;: ¶11.72 further, the least deformed of the patient's limbs is preferred to receive the cuff.: ¶14.23 rodding the tip of a modern fassier–duval telescoping intramedullary rod, manufactured by pega medical for use in osteogenesis imperfecta.the right femur (2a) and tibia (2b) of a 10-year-old girl immediately after her rodding surgery, which involved implantation of the same type of telescoping intramedullary rod photograhed at left. note the bone fragmentation, an important step in the procedure, clearly visible on the x-ray of the femur. metal rods can be surgically inserted in the long bones to improve strength, a procedure developed by harold a. sofield when he was chief of staff at chicago's shriners hospitals for children, a hospital that offers orthopedic care and surgery to children regardless of their family's ability to pay. large numbers of children with oi came to shriners, and sofield experimented with various methods to strengthen their bones. in 1959, with edward a. millar , sofield wrote a seminal article describing a three-part surgery that seemed radical at the time: precisely breaking the bones ("fragmentation"), putting the resulting bone fragments in a straight line ("realignment"), then placing metal rods into the intramedullary canals of the long bones to stabilize and strengthen them ("rod fixation"). his treatment proved useful for increasing the mobility of people with oi, and it has been adopted throughout the world—it became standard surgical treatment for severe oi by 1979, in which year david sillence found that ≈2⁄3 of the patients he surveyed with oi type iii had undergone at least one rodding surgery.: 108 rodding surgery is often done with the hope that it will offer a path to ambulation, walking, to patients with moderate or severe oi. a 2020 review in the journal of bone and joint surgery (jb&js) found it remains broadly popular: ≈2⁄3 of people with oi types iii and iv (severe oi) have undergone some form of rodding surgery in their lives, at a mean age of 4+1⁄10 and 7+1⁄2 years respectively;: table i one possible explanation for a tendency towards earlier intervention in type iii is that one half of affected children could not walk at all without the surgery, as their limbs were more bowed, so surgery was sought sooner. in those with type iii oi who had undergone rodding surgery, 79.5% had the femurs and tibias of both legs rodded.: table i the most common form of rods used are intramedullary (im) rods, some of which, such as the fassier–duval im rod, are telescoping, meaning that they are designed to grow as the child grows, in an attempt to avoid the necessity of revision surgeries. telescoping im rods are widely used, and the common fassier–duval im rod is designed to be used to rod the femur, tibia, and humerus.: 1 the surgery involves breaking the long bones in between one and three (or more): figure 4 places, then fixing the rod alongside the bone to keep it straight.: 11 while telescoping im rods are intended to grow along with both the femur and tibia in developing children; surgeons have a preference to use non-telescoping im rods, such as rush rods, in the tibia, which grows less comparatively—the jb&js review found that while 69.7% of femurs were treated with telescoping im rods, only 36.9% of tibiae were.: table iv while the review in the jb&js was able to correlate receiving rodding surgery with greater mobility across all types of oi, in patients with type iv, the surgery did not decrease the incidence of broken bones as