- Spondyloepithelial Displasias (SED)
- Collagen Defects
- Multiple Epiphyseal Dysplasia (MED)
- Metaphyseal Chondrodysplasia (MChD)
- Mucopolysaccharidoses (MPS)
- Sclerosing Bone Dysplasias
- Multiple Hereditary Exostoses (MHE)
- Trevor Disease
Dysostoses are developmental anomalies from abnormal migration, usually limited to defined embryological structures. Dysplasias are from mutations in regulators of skeletal organogeneses (eg signaling molecules), or matrix components.
Uncommon congenital malformations, usually failure of a bone to develop (eg phalanx, rib, clavicle), formation of extra bones (eg supernumery ribs or digits), fusion of digits (syndactyly), or long spider digits. Usually from alterations in transcription factors esp homeobox genes.
Most from defects in hormones and signal transduction mechanisms. Source of defects include cartilage (chondro-), bone (osteo-), vertebrae (spondylo-), formation (-plasia) and growth (-trophy). Skeletal dysplasia with disproportionate limb or spinal shortening. Limb shortening classified as '''rhizomelic''' (root/proximal ie humerus and femur), '''mesomelic''' (middle ie radius-ulna and tibia-fibula; rare), '''acromelic''' (end/distal), or '''micromelic''' (entire limbs). Need to know other bone involvement (skull, spine, thorax, pelvis), epiphyseal/metaphyseal/diaphyseal, narrow/wide bones. Other features to note include epiphyseal fragmentation (small punctate or irregular ossicles), abnormal acetabulum (horizontal or near horizontal roof, trident acetabulum), skull enlargement, short ribs, short spine, abnormal vertebral bodies, abnormal iliac wings (short, tall or squared). Trident acetabulum – 3 inferior-pointing spikes (upside-down trident), seen in Jeune syndrome, Ellis-van Creveld syndrome, thanatrophoric dysplasia. Screening radiographs should include lateral skull, AP and lateral T/L spine, chest including shoulders, AP pelvis/hips, AP single upper and lower extermity, PA hand.
Achondroplasia and mimics:
Very short ribs:
Spondyloepithelial Displasias (SED)
Includes OI, achondrogenesis, hypochondrogenesis, Sticlker syndrome, MED, MChD.
Osteogenesis Imperfecta (OI)
(Type 1 collagen disease, brittle bone disease). Abnormal type 1 collagen with osteopenia and propensity for fracture (DDx child abuse, Caffey's disaese, Menkes syndrome). Most autosomal dominant. Multiple fractures of various ages. Multiple wormian bones (>12 ossicles along cranial sutures), '''blue sclera''' (in 90%), thin skin, '''hearing loss''' (otic bone fractures), grey teeth ('''dentinogenesis imperfecta'''). May cause '''platybasia''' with basilar invagination.
Multiple Epiphyseal Dysplasia (MED)
(Fairbank disease). AD, defect in type 9 collagen. Presenting late childhood/adolescence with joint pain/limb, mildly short limbs. Defective secondary growth centres esp tubular bones, wrists and ankles with delayed ossification, small and fragmented epiphyses. Schmorls nodes and mild vertebral flattening. Coxa vara. Early OA.
Metaphyseal Chondrodysplasia (MChD)
Group of dysplasias with metaphyseal deformity, short stature. Defect in type 10 collagen.
AD defect in collagen type II or XI. Underdeveloped midface with flattening, U/V-shaped cleft palate, Pierre Robin sequence (micrognathia, glossoptosis, upper airway obstruction), hearing loss, joint hypermobility, precocious OA, early cataract, myopia.
Inborn errors of mucopolysaccharide metabolism causing accumulation in bone marrow, brain, liver, other organs and excretion in urine. Cartilage formation is severely affected. Skeletal findings are similar, being dysostosis multiplex. Short stature from platyspondyly or oval vertebral bodies, anterior beak (mid vetebral body in Morquio, inferior in Hunter/Hurler) most prominent in lumbar spine, focal thoracolumbar kyphosis (gibbus deformity from small or retrolisthesed ~L1). Thickened clavicles and ribs with narrowing posteromedially ('''canoe paddle/oar-shaped'''). Flared iliac wings (similar to achondroplasia) with shallow acetabuli. Dysplastic femoral heads, femoral necks gracile/broad and coxa valga. Short long bones with wide metaphyses and diaphyses. '''Squared metacarpals with tapered/pointed proximal ends''' (fan-like appearance) and notched ulnar aspect (esp 5th metacarpal base). Flattening of nasal bones. Osteopenia with coarse trabuculae. '''J-shaped sella turcica'''.
Other storage diseases may also cause dysostosis multiplex (eg mucolipidoses, Gaucher disease) but take years to develop as metabolites accumulate.
Sclerosing Bone Dysplasias
Dense bones, most from failed osteoclasts. Mixing sclerosing bone dysplasia – simultaneous melorheostosis, osteopathia striata and/or osteopoikilosis.
Acquired diseases include:
(Infantile cortical hyperostosis). Self-limiting disease of infants with exuberant periosteal new bone. Esp mandible, ulna, clavicle. Usually presents <6/12.
(Marble bone disease, Albers-SchÃ¶nberg disease). Rare, osteoclasts defective in resorbing and remodeling bone -> very dense brittle bones (like chalk). Osteoclasts may have periods of more normal function causing dense metaphyseal bands, '''bone-within-bone''' appearance (DDx normal periods of rapid growth). Undertubulation with wide metaphyses ('''Erlenmeyer flask''' deformity). '''Sandwich vertebra''' – dense endplates with prominent posterior vascular notches. Thickened skull base encroaching on cranial nerves -> blindness, hearing loss. Dental dysplasia and infections. Serum calcium paradoxically low, may have superimposed rickets. Lack of marrow space -> '''pancytopaenia''', often -> complications and death.
Rare, AR. ?Type of osteopetrosis. Dwarfism, diffuse osteosclerosis, transvere fractures, wormian bones, preservation of anterior fontanelle as adult, progressive resorption and fragmentation of distal phalanges +/- distal clavicles.
Progressive Diaphyseal Dysplasia
(Diaphyseal dysplasia Englemann type, Camurati-Englemann disease). AD. Symetric endosteal and periosteal thickening, expansion of diaphyses (esp legs). Epiphyses spared.
Ribbing Disease II
(Hereditary multiple diaphyseal sclerosis). ?Variant of progressive diaphyseal dysplasia, similar findings except asymmetric and less widely distributed, later presentation.
Benign, familial. Multiple enostoses clustered around joints including epiphyses (cf blastic metastases tend to spare epiphyses). Occasional subcutaneous fibrous nodules/plaques. Rarely reduced joint ROM, contractures.
(Voorhoeve's disease). Benign. Uniform dense metaphyseal longitudinal bands. In ilium radiate from acetabulum in sunburst pattern.
Dense bone along cortex (usually periosteal, may be endosteal) of otherwise normal bone in irregular wavy pattern ('''dripping candle wax'''). Usually single extremity in portion of skeleton innervated by a spinal nerve (sclerotome). Pain, contractures, overlying erythema/shiny skin, reduced ROM, premature physeal closure. Normal life expectancy.
Multiple Hereditary Exostoses (MHE)
(Osteochondromatosis, diaphyseal aclasis). Multiple bilateral osteochondromas, bony growths from metaphysis continuous with bony cortex, tend to point away from joints, esp knee. May -> limb shortening, leg length discrepancy, bowing, deformity, compression of nerves/vessels, malignant degeneration -> chondrosarcoma (5%, esp proximal lesions).
(Ollier disease). Multiple enchondromas, commonly bilateral, esp hands and feet. Metaphyses of long bones, oblong/flame-shaped/linear perpendicular to physis. Malignant degeneration in 30%.
Maffucci syndrome – Enchondromatosis in association with soft tissue venous malformations. Phleboliths. Higher risk of malignant degeneration as well as malignancy in abdomen, CNS.
Metachondromatosis – Rare combination of Ollier disease and diaphyseal aclasis.
(Fairbank's disease). Rare, asymmetrical limb deformity due to localised overgrowth of cartilage resembling osteochondroma in an epiphysis. ?Defect in limb bud in early foetal life. Mostly ankle or knee, always confined to a single limb.