Contemporary Management of Osteogenesis Imperfecta

Courtesy: Michael Uglow, FRCS Orth, UK

OVERVIEW

Osteogenesis imperfecta is a genetic disorder of connective tissue.
It is commonly known as brittle bone disease.
The disorder is characterized by bone fragility and recurrent fractures.
The underlying defect involves type I collagen, which constitutes approximately 90 percent of total body collagen.

CLINICAL FEATURES

Bone fragility with recurrent long bone fractures
Skeletal deformities
Blue sclerae
Hearing loss
Fragile, opalescent teeth (dentinogenesis imperfecta)
Short stature in moderate to severe forms

TYPE I COLLAGEN AND PATHOGENESIS

Type I collagen is composed of a triple helix structure:
- Two procollagen alpha-1 chains
- One procollagen alpha-2 chain
Procollagen alpha-1 is encoded by the COL1A1 gene.
Procollagen alpha-2 is encoded by the COL1A2 gene.

Collagen Defects in Osteogenesis Imperfecta

Type I Osteogenesis Imperfecta

Caused by a stop codon mutation on the long arm of chromosome 17.
Results in reduced production of the alpha-1 chain.
Leads to a quantitative reduction of normal type I collagen.
Approximately 50 percent reduction in collagen production.

Types II, III, and IV Osteogenesis Imperfecta

Caused by abnormal production of alpha-1 or alpha-2 chains.
Results in defective cross-linking.
Leads to qualitative abnormalities in collagen structure.

SILLENCE CLASSIFICATION (SIMPLIFIED)

Type I

Autosomal dominant inheritance
Blue sclerae
Mildest form
Presents in early childhood
Hearing loss in approximately 50 percent
Subtypes A and B based on dentinogenesis imperfecta

Type II

Autosomal recessive inheritance
Blue sclerae
Perinatal lethal form

Type III

Autosomal recessive inheritance
Normal sclerae
Fractures present at birth
Progressive deformity and short stature
Most severe survivable form

Type IV

Autosomal dominant inheritance
Normal sclerae
Moderate severity
Bowing of long bones and vertebral fractures common
Hearing usually normal
Subtypes A and B based on dentinogenesis imperfecta

Type V

Autosomal recessive inheritance
Hypertrophic callus formation after fractures
Ossification of interosseous membranes between:
- Radius and ulna
- Tibia and fibula

Type VI

Autosomal recessive inheritance
Moderate severity
Clinically similar to type IV

Type VII

Autosomal recessive inheritance
Associated with rhizomelia
Coxa vara commonly present

OTHER CLASSIFICATIONS

Sillence classification (1979)
Shapiro classification (1985)
Congenita type A and B (based on bone morphology)
Tarda type A and B:
- Type A: fractures before walking age
- Type B: fractures after walking age

MANAGEMENT PRINCIPLES

Reduce fracture incidence
Correct deformities
Maintain mobility and function
Promote safe weight bearing
Improve bone strength

BISPHOSPHONATE THERAPY

Commonly Used Agent

Zoledronic acid

Dosage

0.025 to 0.05 milligrams per kilogram
Intravenous administration
Every 6 months
Dose adjusted based on age

Timing Relative to Surgery

First dose administered approximately 2 weeks before surgery
Second dose administered 12 weeks after surgery

Pre-Treatment Evaluation

Complete metabolic panel including:
- Calcium
- Phosphate
- Magnesium
Serum 25-hydroxy vitamin D
Target vitamin D level greater than 50 nanograms per milliliter

Vitamin D Supplementation

Infants: 1,000 to 1,500 international units per day
Children 1 to 8 years: 2,500 to 3,000 international units per day
Children older than 9 years: 4,000 international units per day
Ergocalciferol may be used as high-dose replacement when indicated

Calcium Supplementation

Begin 2 weeks prior to infusion
Calcium 1,200 milligrams daily
Vitamin D 1,000 international units daily if not on high-dose therapy

Infusion Protocol

Pre-hydration required
Intravenous fluids at 10 milliliters per kilogram over 1 hour
Zoledronic acid diluted in 50 to 100 milliliters of normal saline
Infusion over approximately 30 minutes
Acetaminophen may be administered to reduce infusion-related symptoms

WOLFF LAW AND FROST UTAH PARADIGM

Disuse

Reduced bone loading
Decreased bone mass and strength

Adapted State

Balanced bone resorption and formation
Bone mass remains stable

Overload

Increased bone modeling
Increased bone mass and strength

Fracture

Occurs when elastic deformation limits are exceeded

SURGICAL MANAGEMENT

Aims of Surgical Correction

Correct deformity
Provide internal stabilization
Allow growth and remodeling
Maintain alignment and rotation

Preferred Implant

Intramedullary telescopic nails
Tethering to epiphysis when required
Additional rotational control if needed

FASSIER–DUVAL ROD COMPLICATIONS

Loss of proximal or distal fixation
Implant migration
Implant breakage
Limited telescoping
Intra-articular or cortical protrusion
Fracture
Rod bending

BENT ROD OUTCOMES IN OSTEOGENESIS IMPERFECTA

Approximately 27.4 percent of telescopic rods bend during follow-up
Average angulation approximately 7.3 degrees
Higher bending rates in non-severe osteogenesis imperfecta
Over half of bent rods require revision
Some bent rods continue telescoping but may increase angulation
Refracture risk remains significant

“STAND” PRINCIPLE

Straight bones
Therapy
Adjunctive medicines
Nails and plates
Vitamin supplementation

KEY RECOMMENDATIONS

Use the largest feasible intramedullary nail
Maintain optimal bone health
Ensure secure proximal and distal fixation
Maintain adequate vitamin D levels
Provide additional rotational stability when needed
Use plates when appropriate, or casting if plating is not possible
Monitor with serial radiographs
Recognize ongoing risks of rod bending and fracture
Continue bisphosphonate therapy every 6 months
Encourage safe ambulation and walking

CONCLUSION

Osteogenesis imperfecta requires multidisciplinary, lifelong management.
Medical therapy, surgery, and rehabilitation must be coordinated.
Functional independence and fracture prevention are the primary goals.
Early intervention and vigilant follow-up improve long-term outcomes.

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