Achondroplasia

Micromelia, Chondrodystrophic fetalis

Achondroplasia is a congenital/ developmental disorder characterized by defective endochondral ossification affecting long bones clinically present with disproportionate dwarfism

Etiology

The most common form of short limb dwarfism in human beings is Achondroplasia

Autosomal dominant

Chromosome: 4p16.3

Affects fibroblast growth factor receptor gene (FGFR-3)

Pathology

Enchondral ossification: Epiphyseal growth plate disturbed

Instead of orderly proliferation, palisading, and forming of the scaffolding of calcified cartilages, the cartilages are degenerative and vascular

Perinatal ossification(maximum in metaphysics) proceeds normally/ bone diameter is ensured but longitudinal growth is retarded

Cortex flare outward appears to embrace epiphysis

Growth is retarded with the base remaining short while the rest of the skull grows normally

Clinical features

Dwarfism: often apparent at or seen after birth

The limb appears short in comparison to the trunk

Hyperextension of joints (especially at the knee and hands)

Movement of the elbow is restricted

Hand:

• Short
• fingers short and thick
• Diversant

Trident appearance of hand

The fibula is relatively unaffected in comparison to the tibia

The Head of the fibula lies at the higher level on the lateral aspect of the knee joint

The hip joint lies posterior to the central axis of the pelvis

Peculiar rolling of gait in Achondroplasia

• Pelvis tilted forward
• Buttocks are prominent
• Sacrum lies in the horizontal plane
• Increase in lumbar lordosis
• Compensatory increase in thoracic kyphosis

Head:

• Brachycephalic
• Forehead: Prominent
• Midface: Hypoplastic, bridge of the nose is depressed

The chest is small, and flat, ribs are abnormally short

Radiological Investigation

Long bones are short

Due to a reduction in length, rather than an increase in diameter end of the shaft is splayed

Epiphysis border of metaphysics: Often indented at its center

The epiphyseal ossification center which forms by endochondral ossification is well-developed and well-circumscribed

V-Shaped Indentation: Illusion of making widening of joint space

Clavicles and fibula are less affected

Ribs are short; sternum broad and thick

Scapulae: Rectangular and small

Vertebrae: endochondral ossification seems to be relatively unaffected

The total length of the spine is less decreases as compared to limbs

Pelvis: reduced in all direction

Illum: Rectangular in shape

Acetabular roof: Flat and horizontal

Sacrum: Narrow and horizontally disposed

Skull:- Large, premature fusion of the basal centers considerably shortened the base of the skull with the foramen magnum remaining small and funnel-shaped

Treatment

Prenatal ultrasound screening: many affected fetuses are recognized early

DNA testing can confirm a suspected prenatal diagnosis

Monitor growth curves ( Height, Weight, Head circumference, chest circumference)

Obesity is common: dietary management

The disproportionate increase in head size: Increase in ICP (shunting)

Cervical cord compression and spinal stenosis

Surgery:

• Recurrent otitis media
• Dental misalignment

Osteotomies:

• To correct bowing of the legs should be done
• Realign the knee

See also: Osteogenesis Imperfecta

See also: Osteopetrosis

See also: Skeletal Dysplasia ( Classifications)