Orthopaedic Surgery - Osteogenesis Imperfecta

Basics

Osteogenesis imperfecta (OI) is a group of inherited connective-tissue disorders characterized primarily by abnormal collagen formation and increased bone fragility.

Although fractures and skeletal deformity are the most prominent manifestations, OI can also affect:

Teeth

Sclerae

Hearing

Ligaments and joints

Skin and other connective tissues

Cardiopulmonary function

The clinical severity ranges from very mild disease with occasional fractures to lethal perinatal forms.

Classification

The traditional Sillence classification remains widely used clinically, although many additional molecular subtypes have now been identified.

Type I

Type I is the:

Mildest and one of the most common forms.

Fractures generally begin during childhood and tend to become less frequent toward adolescence and adulthood.

Patients often have:

Blue sclerae

Relatively mild bone deformity

Normal or near-normal stature

The older classification subdivided Type I into:

Type IA – without dentinogenesis imperfecta

Type IB – with dentinogenesis imperfecta

Type II

Type II is the:

Most severe form and is usually lethal in the perinatal period.

Affected infants may have:

Multiple intrauterine fractures

Severe skeletal deformity

Markedly poor mineralization

Small thoracic cage

Death commonly results from profound respiratory insufficiency.

Type III

Type III is the:

Most severe form compatible with prolonged survival.

Typical findings include:

Numerous fractures beginning before or shortly after birth

Severe progressive bowing of long bones

Marked short stature

Progressive spinal deformity

Severe osteopenia

Patients frequently require repeated orthopaedic procedures.

Type IV

Type IV produces:

Moderate disease severity.

Patients generally have greater fracture and deformity burden than those with Type I but less severe disease than Type III.

Type V

Type V is a moderately severe form associated with characteristic findings such as:

Hyperplastic callus formation

Radial head dislocation

Interosseous membrane ossification in some patients

Unlike many classic OI types, Type V does not result from a primary Type I collagen structural mutation.

Additional Types

Many additional forms of OI have been identified through molecular testing.

Some result from abnormalities in:

Collagen synthesis

Collagen processing

Bone mineralization

Osteoblast function

The modern molecular classification is therefore considerably broader than the original Sillence system.

Pediatric Considerations

Severe forms may be diagnosed:

Prenatally or at birth.

Types II and severe Type III may present with:

Intrauterine fractures

Marked bowing

Multiple fractures at delivery

Milder Types I and IV may not become apparent until:

Infancy or early childhood, when fractures occur after relatively minor trauma.

In many forms, fracture frequency tends to decrease after puberty.

Epidemiology

OI affects approximately:

1 in 10,000–20,000 people, depending on the population and diagnostic definition.

Risk Factors

The major risk factor is:

Genetic inheritance or a de novo pathogenic variant.

There are no established environmental risk factors that independently cause OI.

Genetics

OI is genetically heterogeneous.

The majority of classic cases result from pathogenic variants involving:

COL1A1

or

COL1A2

which encode the chains of Type I collagen.

Many classic Type I–IV cases follow an:

Autosomal-dominant pattern, frequently from a new mutation.

Some rarer forms are:

Autosomal recessive

or follow other inheritance patterns.

Type I Collagen

Type I collagen is the principal collagen of:

Bone

Tendon

Skin

Sclera

and other connective tissues.

It forms a:

Triple-helical structure.

Glycine appears at every third position in the collagen chain.

Substitution of glycine with another amino acid may disrupt proper helix formation and produce an abnormal collagen molecule.

Dominant-Negative Effect

Certain structural collagen mutations produce abnormal collagen chains that interfere with normal chains.

This can exert a:

Dominant-negative effect, leading to more severe disease.

Other mutations primarily reduce the amount of otherwise normal collagen and often produce milder phenotypes.

Etiology

The fundamental abnormality is impaired production, structure, processing, or mineralization of bone matrix.

The result is bone that is:

Fragile

Osteopenic

and susceptible to:

Fracture and progressive deformity.

Associated Conditions

OI may be associated with:

Dentinogenesis imperfecta

Blue sclerae

Hearing loss

Ligamentous laxity

Joint dislocation

Scoliosis

Basilar impression or invagination

Hernias

Cardiopulmonary abnormalities

Dentinogenesis Imperfecta

Abnormal dentin formation may cause teeth that are:

Translucent

Brown, gray, or opalescent

Fragile

Both primary and permanent teeth may be affected.

Joint Laxity

Abnormal connective tissue may produce:

Ligamentous laxity and hypermobile joints.

This can predispose to:

Joint instability

Dislocations

Ankle instability

Hernias

Connective-tissue weakness may contribute to:

Inguinal hernias

Umbilical hernias

Diaphragmatic hernias

Craniovertebral Abnormalities

Softening and deformation of the skull base may result in:

Platybasia

Basilar impression

or

Basilar invagination.

These conditions may compress the brainstem or upper cervical spinal cord.

Diagnosis

Diagnosis is based on:

Clinical findings

Fracture history

Family history

Radiographic features

and

Genetic testing.

Signs and Symptoms

Common manifestations include:

Recurrent fractures

Bone pain

Short stature

Bowing of long bones

Scoliosis

Back pain

Blue sclerae

Abnormal dentition

Hearing loss

Joint hypermobility

Fracture Pattern

A child with OI may sustain fractures after:

Minor trauma

or an injury mechanism that would not normally fracture healthy bone.

Fractures may occur repeatedly throughout childhood.

Blue Sclerae

The sclerae may appear blue because abnormal collagen makes them sufficiently thin for the underlying pigment to become visible.

This finding is particularly common in Type I OI.

Hearing Loss

Conductive or sensorineural hearing loss may develop, often later in life.

Conductive loss may result from abnormalities of the:

Middle-ear ossicles.

Craniofacial Features

Some patients have:

Relative macrocephaly

and

A triangular facial appearance.

Musculoskeletal Pain

Adults with OI have an increased prevalence of:

Chronic musculoskeletal pain

related to previous fractures, deformity, joint degeneration, and muscle fatigue.

Basilar Invagination Symptoms

Brainstem or upper cervical cord compression may produce:

Weakness

Spasticity

Poor coordination

Respiratory dysfunction

Swallowing difficulty

Voice change

Progressive contractures

These symptoms warrant urgent specialist evaluation.

Physical Examination

The diagnosis should be considered when there is:

An unusually high fracture frequency

or fractures occurring after:

Minimal trauma.

Helpful Clinical Findings

Findings supporting OI include:

Positive family history

Blue sclerae

Abnormal dentition

Ligamentous laxity

Short stature

Long-bone bowing

Scoliosis

Laboratory and Genetic Testing

Routine laboratory studies are generally not diagnostic.

Molecular Genetic Testing

Genetic analysis from blood is now a major diagnostic tool.

Testing may identify pathogenic variants involving:

COL1A1

COL1A2

or other genes associated with OI.

A negative result on a limited test does not completely exclude the diagnosis because of genetic heterogeneity.

Collagen Analysis

Historically, cultured dermal fibroblasts obtained from a skin biopsy were used to analyze:

Type I collagen synthesis and structure.

This is now required much less often because comprehensive genetic testing is widely available.

Imaging

Generalized Osteopenia

Radiographs frequently demonstrate:

Diffuse osteopenia.

Long Bones

Typical findings may include:

Thin cortices

Narrow gracile shafts

Long-bone bowing

Multiple old fractures

Recurrent acute fractures

Severe Deformity

Advanced disease may produce severely deformed long bones, including the classic:

“Crumpled” femur

appearance in severe cases.

Pelvis

Pelvic abnormalities may include:

Trefoil-shaped pelvis

and

Protrusio acetabuli.

Spine

Vertebral bodies may be:

Osteopenic

Compressed

Flattened

or

Biconcave.

Repeated compression fractures may contribute to:

Kyphosis

Scoliosis

Loss of trunk height

Skull

The skull may demonstrate multiple:

Wormian bones, which are accessory ossification centers within the cranial sutures.

These are characteristic but not specific for OI.

Metaphyseal Changes

In severe cases, metaphyses may show:

Cystic or irregular appearances.

Repeated bisphosphonate treatment may also produce transverse metaphyseal density lines.

Pathological Findings

Bone may demonstrate:

Thin cortices

Reduced trabecular volume

Disorganized woven bone

Abnormal or deficient lamellar bone

Soft-Tissue Collagen

Collagen within the:

Skin

and

Cornea

may have a looser or structurally abnormal arrangement.

Differential Diagnosis

Important differential diagnoses include:

Prematurity and very low birth weight

Primary hyperparathyroidism

Scurvy

Hypophosphatasia

Achondrogenesis

Chondroectodermal dysplasia

Juvenile osteoporosis

Rickets

Congenital infection

Leukemia or other malignancy

Nonaccidental injury

Nonaccidental Injury

Distinguishing OI from child abuse may occasionally be difficult.

Findings that raise concern for nonaccidental trauma include:

Multiple fractures of different ages

Posterior rib fractures

Classic metaphyseal lesions

Inconsistent history

These findings require careful multidisciplinary assessment and should not automatically be attributed to OI.

Features Supporting OI

Features favoring OI may include:

Positive family history

Generalized osteopenia

Blue sclerae

Dentinogenesis imperfecta

Characteristic long-bone deformity

A pathogenic genetic variant

However, neither OI nor abuse should be diagnosed or excluded based on a single feature.

Treatment

General Principles

Management depends heavily on:

OI subtype

Severity

Age

Fracture burden

Mobility

Degree of deformity

The objectives are to:

Reduce fractures

Preserve mobility

Correct significant deformity

Improve independence

Prevent secondary complications

Type I

Patients with Type I disease may have relatively little functional impairment and may require mainly:

Fracture care

Exercise

Bone-health management

Hearing and dental surveillance

Type II

Severe Type II disease is usually lethal around the perinatal period.

Management focuses on:

Supportive and family-centered care.

Types III and IV

Types III and IV frequently create the greatest long-term orthopaedic challenges because of:

Repeated fractures

Progressive bowing

Short stature

Scoliosis

Mobility limitations

Medical Treatments With Limited Benefit

Historical treatments such as:

Growth hormone

Calcium supplementation in patients without deficiency

and

Calcitonin

have not consistently corrected the underlying skeletal disorder.

Bisphosphonates

Bisphosphonates such as:

Pamidronate

and other agents may improve:

Bone mineral density

Vertebral morphology

Pain

and, in selected children,

Fracture burden and mobility.

They do not normalize the skeleton.

Benefits appear most established in children with moderate-to-severe OI.

Rehabilitation

Physical therapy should be involved early.

Goals include:

Muscle strengthening

Safe standing

Ambulation

Preservation of joint motion

Prevention of contractures

Promotion of independence

Mobility Planning

Rehabilitation should establish realistic goals.

Depending on disease severity, children may require:

Walking aids

Standing devices

Adaptive seating

Wheelchairs

The objective is maximal safe participation rather than avoidance of all physical activity.

Hydrotherapy

Aquatic therapy can allow:

Active movement with reduced fracture risk

and may improve:

Muscle strength and endurance.

Orthoses

Braces can be useful adjuncts.

They should generally be:

Lightweight

Well fitted

Total-contact when appropriate

and designed to avoid producing excessive focal stress.

Joint hinges may be incorporated when necessary.

Fracture Treatment

Most fractures can initially be managed nonoperatively.

OI fractures usually have:

Good intrinsic healing capacity, despite poor bone strength.

Immobilization

Prolonged heavy casting should be avoided whenever possible because it may worsen:

Osteopenia

Muscle weakness

Loss of mobility

Lightweight splints or casts are often preferred.

Alignment

Although fractures generally heal, substantial angular deformity may produce:

Progressive bowing

Mechanical dysfunction

Recurrent fracture

Therefore, alignment should be restored as well as reasonably possible.

Recurrent Fractures

Internal fixation may be indicated when there are:

Repeated fractures

Severe long-bone bowing

Difficulty maintaining alignment with casting

Loss of ambulatory potential

Fixation Principles

Intramedullary fixation is generally preferred to plates and screws because:

Screws have poor purchase in osteopenic bone

and

plates can create a stress riser at their ends.

A new fracture may occur adjacent to a rigid plate.

Olecranon Avulsion Fractures

Olecranon avulsion fractures are seen with increased frequency in children with OI compared with the general pediatric population.

Medication

Bisphosphonate therapy remains an important medical treatment for selected patients with moderate or severe OI.

More recent management may also include other bone-directed or molecular therapies in specialized centers, depending on age and disease type.

Surgery

Anaesthetic Considerations

Patients with OI require careful perioperative planning because of:

Fragile bones

Potential cervical spine abnormalities

Limited neck or jaw mobility

Dentinogenesis imperfecta

Chest-wall deformity and restrictive lung disease

Possible cardiac valvular disease

Gentle positioning and airway management are essential to avoid iatrogenic fracture.

OI itself is not considered a proven direct cause of malignant hyperthermia; anaesthetic planning should instead focus on the patient’s specific airway, cardiopulmonary, and skeletal risks.

Corrective Osteotomy

Corrective osteotomy may be performed for:

Severe long-bone bowing

Repeated fractures

Loss of mechanical alignment

In appropriate children, these procedures may begin during early childhood when deformity interferes substantially with function.

Intramedullary Rodding

Intramedullary rods are particularly useful in children who:

Have recurrent fractures

Have severe bowing

Have realistic standing or ambulatory potential

Telescoping Rods

Telescoping devices such as the:

Fassier–Duval rod

can lengthen as the child grows.

This decreases the need for repeated revision compared with fixed-length rods.

Timing of Rodding

There is no single universal age or fracture number that mandates intramedullary fixation.

The decision should balance:

Fracture frequency

Severity of deformity

Functional potential

against risks such as:

Infection

Implant migration

Pain

Need for revision

Scoliosis

Scoliosis in OI may be:

Progressive and difficult to control.

Bracing often has limited ability to stop progression because the ribs and vertebrae are osteopenic.

Spinal Surgery

Surgical fusion may be considered for:

Progressive significant curves

especially when deformity threatens:

Sitting balance

Pulmonary function

Mobility

Older recommendations sometimes used approximately 40° as a threshold for considering fusion, although modern decisions are individualized according to progression, age, bone quality, pulmonary function, and overall condition.

Spinal Instrumentation

Modern segmental instrumentation has improved options for correction, but surgery remains technically difficult because of:

Poor bone quality

Thin pedicles

Fragile vertebrae

Risk of fixation failure

Craniocervical Junction

The craniovertebral junction must also be monitored.

Progressive basilar invagination can compress:

The brainstem

or

Upper cervical spinal cord.

Basilar Invagination Surgery

Symptomatic or progressive neural compression may require:

Decompression

and

Craniovertebral stabilization.

Follow-Up

Because OI can affect multiple systems, patients are best managed through:

A multidisciplinary or specialized OI clinic.

Care may involve:

Orthopaedics

Genetics

Endocrinology or metabolic bone specialists

Physical therapy

Dentistry

Audiology

Pulmonology

Cardiology

Neurosurgery

Prognosis

Prognosis varies dramatically according to OI type.

Type II

Type II is generally:

Lethal in the perinatal period.

Type III

Type III is severe and often requires:

Multiple orthopaedic procedures

Mobility aids

Long-term management of spinal and limb deformity

Type IV

Type IV generally has:

Intermediate severity.

Type I

Type I is typically the mildest classic form.

Many patients remain independently ambulatory.

Fracture Frequency

Across many OI types, fracture frequency tends to decline:

Around or after puberty.

However, fractures may recur later in adulthood as bone density decreases.

Hearing Loss

In Type I disease, progressive hearing loss can become one of the most important long-term functional complications.

Complications

Potential complications include:

Recurrent fracture

Progressive long-bone deformity

Scoliosis and kyphosis

Protrusio acetabuli

Joint instability

Hearing loss

Dental abnormalities

Chronic pain

Pulmonary restriction

Basilar invagination

Platybasia and Basilar Invagination

Softening of the skull base may produce progressive cranial deformation.

Neurologic consequences can include:

Weakness

Spasticity

Coordination difficulty

Swallowing or respiratory dysfunction

Patient Monitoring

Scoliosis

Children should be examined regularly from an early age for:

Development and progression of scoliosis.

Monitoring should continue into adulthood when clinically indicated.

Long-Bone Deformity

Follow-up should assess:

Fracture frequency

Bowing

Alignment

Mobility

Implant position in patients with rods

Neurologic Monitoring

Patients should be monitored for signs of:

Brainstem or upper cervical cord compression, particularly when cranial base abnormalities are known.

Hearing and Dental Monitoring

Periodic:

Audiologic

and

Dental evaluation

is important because these complications may progress independently of skeletal symptoms.

Key Principle

Osteogenesis imperfecta is a heritable disorder of collagen and bone formation characterized by skeletal fragility and multisystem connective-tissue abnormalities.

Orthopaedic management focuses on:

Preventing and treating fractures, minimizing deformity, preserving mobility, using intramedullary fixation when necessary, monitoring scoliosis and the craniocervical junction, and coordinating lifelong multidisciplinary care.