Osteogenesis imperfecta in details according Turek & newr classification
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Turek's orthopaedics osteogenesis imperfecta classification types
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Osteogenesis Imperfecta (OI) - Detailed Overview
Definition and Pathology
Osteogenesis imperfecta is a mesodermal connective tissue disorder characterized by abnormal or deficient type I collagen affecting bone, skin, sclerae, and dentin. The underlying defect lies in the COL1A1 gene (chromosome 17q) or COL1A2 gene (chromosome 7q), which encode the alpha-1 and alpha-2 chains of procollagen type I. 87% of cases arise from collagen type I defects.
The classic diagnostic triad is:
- Blue sclerae
- Dentinogenesis imperfecta
- Generalized osteoporosis with multiple fractures / bowing of long bones
The only two features present in all patients are fractures and generalized osteoporosis. There is no specific lab test; diagnosis relies on skin biopsy and DNA testing.
TUREK'S CLASSIFICATION (Historical / Traditional)
Turek's Orthopaedics uses the classical two-type clinical grouping based on time of onset:
Type I - Osteogenesis Imperfecta Congenita (Vrolik's Disease)
- Autosomal recessive inheritance
- Manifests at birth with multiple fractures, dwarfism, and deformities
- Short extremities, bowing of long bones, generalized osteoporosis
- Multiple wormian bones around the base of the skull (a major finding only in the congenital type)
- Blue sclerae present
- Generally more severe; high early mortality
- Associated with poor prognosis
Type II - Osteogenesis Imperfecta Tarda (Lobstein's Disease)
- Autosomal dominant inheritance
- Reveals itself later in life, near puberty (~10 years)
- Two subtypes:
- Tarda Gravis - more severe, presents in early childhood
- Tarda Levis - milder, presents later
- Blue sclerae often present
- Relatively better prognosis; patients survive to adulthood
This binary grouping (congenita vs. tarda) was the framework used in Turek's and earlier orthopedic texts before Sillence's molecular-based classification replaced it.
SILLENCE CLASSIFICATION (1979) - The Standard in Modern Orthopaedics
Sillence classified OI into four types based on clinical, genetic, and radiographic features. 90% of patients fall into Type I or Type IV.
| Type | Inheritance | Sclerae | Key Features |
|---|---|---|---|
| I | Autosomal dominant | Blue | Mildest form. Presents at preschool age (tarda). Hearing deficit in 50%. Divided into IA and IB based on tooth involvement |
| II | Autosomal recessive | Blue | Lethal in perinatal period. Most severe. Multiple rib/long bone fractures at birth |
| III | Autosomal recessive | Normal (may be faintly blue at birth) | Fractures at birth. Progressively short stature. Most severe survivable form |
| IV | Autosomal dominant | Normal or slightly blue | Moderate severity. Bowing of long bones and vertebral fractures common. Hearing normal. Divided into IVA and IVB based on tooth involvement |
Type I vs IB / IV vs IVB subtypes: The B subtype denotes dentinogenesis imperfecta (abnormal teeth with blue-gray or amber discoloration).
Collagen defect distinction:
- Type I: Quantitative disorder (reduced collagen production - null COL1A1 allele)
- Types II, III, IV: Qualitative disorder (structurally abnormal collagen - COL1A1 or COL1A2 mutations)
NEWER (EXTENDED) CLASSIFICATION - Types V to XVI+
Following Sillence, additional types have been added based on distinct histologic, genetic, or clinical features. As detailed in Campbell's Operative Orthopaedics (15th Ed, 2026) and the OI Foundation nosology chart:
Types V-VII (Glorieux/Clinical Extensions)
| Type | Key Features |
|---|---|
| V | Hypertrophic (hyperplastic) callus after fractures. Ossification of interosseous membrane (IOM) between radius-ulna and tibia-fibula. IFITM5 gene mutation. Autosomal recessive |
| VI | Moderate severity, similar to type IV but with distinctive "fish-scale" bone histology. SERPINF1 gene. Autosomal recessive |
| VII | Associated with rhizomelia and coxa vara. CRTAP gene mutation. Autosomal recessive |
Types VIII-XVI (Molecular/Genetic Extended Types)
These are all autosomal recessive. Grouped by mechanism of collagen defect:
Defects in Collagen Modification (Prolyl 3-Hydroxylation Complex):
| Type | Gene | Severity |
|---|---|---|
| VII | CRTAP | Severe (hypomorphic) to severe-lethal (null) |
| VIII | LEPRE1 (P3H1) | Severe to lethal |
| IX | PPIB (CyPB) | Moderate to lethal |
Defects in Collagen Folding and Cross-linking:
| Type | Gene | Severity |
|---|---|---|
| X | SERPINH1 | Severe to lethal |
| XI (Bruck syndrome 1) | FKBP10 | Mild to severe |
| BRKS2 | PLOD2 | Moderate to severe |
Defects in Osteoblast Development / Collagen Insufficiency:
| Type | Gene | Severity |
|---|---|---|
| XII | SP7 (Osterix) | Severe |
| XIII | BMP1 | Mild to severe |
| XIV | TMEM38B | Severe |
| XV | WNT1 | Severe |
| XVI | CREB3L1 | Severe |
HANSCOM CLASSIFICATION (for Spinal Deformity in OI)
Used specifically to grade the degree of bone involvement and predict scoliosis risk - Campbell's Operative Orthopaedics (Table 40.11):
| Type | Features |
|---|---|
| A | Mild bony abnormalities with normal vertebral contours |
| B | Bowed long bones and wide cortices with biconcave vertebral bodies and normal pelvic contour |
| C | Thin, bowed long bones with protrusio acetabuli developing around age 10 |
| D | Deformities similar to type C, plus cystic changes around the knee by age 5 |
| E | Total functional dependence |
Biconcave vertebrae are predictive of future scoliotic deformity (93% prevalence of severe scoliosis with 6 or more biconcave vertebrae).
Clinical Features Summary
| Feature | Detail |
|---|---|
| Fractures | Present in all types; often from minimal trauma; healing usually satisfactory but healed bone no stronger than original |
| Bone deformity | Long bone bowing (femur, tibia), vertebral compression fractures |
| Blue sclerae | Thin sclerae allow choroidal vessel pigment to show through; present in Types I, II; absent in III, IV |
| Dentinogenesis imperfecta | Opalescent, discolored teeth; distinguishes A vs B subtypes |
| Hearing loss | In ~50% of Type I; otosclerosis-like mechanism |
| Short stature | Especially prominent in Type III |
| Wormian bones | Multiple sutural (wormian) bones around skull base - major finding in congenital type |
| Hyperplastic callus | Especially in Type V; can mimic osteosarcoma |
| Ligamentous laxity | Joint hypermobility common |
| Basilar invagination | Can occur; risk with anesthesia |
Treatment (Orthopedic Focus)
Medical
- Bisphosphonates (pamidronate IV, zoledronate, risedronate): reduce osteoclast-mediated resorption, increase bone density, decrease pain, improve ambulation. Cochrane review confirms increased BMD but optimal dose/duration/fracture prevention not fully established. Must stop 6 months before and resume 6 months after spinal fusion.
- No cure; treatment is supportive and aimed at maximizing function.
Surgical
- Intramedullary (IM) rodding of long bones (femur, tibia, humerus): preferred for correcting progressive bowing deformities. Fassier-Duval telescoping nails allow longitudinal growth.
- Goals: correct deformity, prevent further fractures, allow ambulation.
- Results inconsistent; healed bone may be no stronger than before.
- Transfusion rate ~14% with IM rods, but blood loss is generally manageable.
Rehabilitation
- Long-leg bracing with comprehensive rehabilitation can maintain ambulation with acceptable fracture risk.
- Physical therapy to maintain muscle strength and prevent disuse atrophy.
Anesthetic Risks
- Malignant hyperthermia susceptibility
- Basilar invagination limiting neck extension
- Cardiac abnormalities and platelet dysfunction (bleeding risk)
- Elevated thyroid levels (~50%) + anesthetic agents can cause hyperthermia
- Fragile bones fracture with positioning
Genetics Summary
| OI Type | Inheritance | Gene(s) |
|---|---|---|
| I, IV | Autosomal dominant | COL1A1, COL1A2 |
| II, III | Autosomal dominant (new mutations) or recessive | COL1A1, COL1A2 |
| V | Autosomal recessive | IFITM5 |
| VI | Autosomal recessive | SERPINF1 |
| VII-XVI | Autosomal recessive | CRTAP, LEPRE1, PPIB, SERPINH1, FKBP10, PLOD2, SP7, BMP1, TMEM38B, WNT1, CREB3L1 |
Sources:
- Campbell's Operative Orthopaedics, 15th Ed (2026), Table 34.6 and Chapter 34/40
- Miller's Review of Orthopaedics, 9th Ed, Chapter 3
- Turek's Orthopaedics: Principles and Their Application - traditional congenita/tarda classification
- OI Foundation Nosology Chart - types I-XVI with gene defects
- Recent review: Hasegawa K, Clin Pediatr Endocrinol 2025 [PMID: 40636817]
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