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Dysplasia Overview

Definition: dysplasia means abnormal development.

Shortening of the involved bones affects specific portions of the growing bone (Fig. 3.38), hence the term dwarfism. Most forms of dwarfism are related to genetic defects (single or multiple genes [Table 3.16]).

 

Proportionate dwarfism: symmetric decreases in both trunk and limb length (e.g., as occurs with mucopolysaccharidoses)

Disproportionate dwarfism

Short-trunk variety (e.g., Kniest syndrome–spondyloepiphyseal)

Short-limb variety (e.g., achondroplasia, diastrophic dysplasia)

Short-limb dwarfism can be subclassified by the region of the limb that is short (e.g., rhizomelic—proximal, mesomelic—middle, acromelic—distal)

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Summary of mary types of Dwarfism

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AChondroplasia

Introduction and etiology

Achondroplasia is the most common form of disproportionate short-limbed dwarfism.

Autosomal dominant condition; 80% of cases caused by a spontaneous mutation in the fibroblast growth factor receptor 3 (FGFR3)

Leads to a gain-of-function mutation or uncontrolled activation

Abnormal endochondral bone formation that is more affected than appositional growth

Achondroplasia is categorized as a physeal dysplasia (cartilaginous proliferative zone)

Quantitative, not qualitative, cartilage defect

May be associated with advanced paternal age

Signs and symptoms

Normal trunk and short limbs (rhizomelic) with hypotonia

Frontal bossing, button nose, small nasal bridge, trident hands (inability to approximate extended middle and ring fingers) (Fig. 3.39)

Thoracolumbar kyphosis (which usually resolves around the age at ambulation)

Lumbar stenosis (most likely to cause disability) and excessive lordosis (short pedicles with decreased interpedicular distances)

Compression at foramen magnum may cause periods of sleep apnea

Radial head subluxation

Normal intelligence but delayed motor milestones

Although sitting height may be normal, standing height is below the third percentile.

Radiographic findings

Spine: narrowed interpedicular distance in the distal spine (L1–S1), T12–L1 wedging, generalized posterior vertebral scalloping

Pelvis: champagne glass pelvic outlet (wider than deep), tombstone pelvis (squaring of iliac wings)

Treatment

Lumbar stenosis: decompression and fusion of the spine for a developing neurologic deficit (usually in children >10 years)

Decompression for foramen magnum stenosis

Progressive kyphosis: if fail bracing fails, anterior and posterior fusion is indicated for residual kyphosis greater than 60 degrees by age 5 years

Genu varum: tibial osteotomies or hemiepiphysiodesis

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Summary of dysplasias on the bone

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Pseudoachondroplasia

Clinically similar to achondroplasia

Autosomal dominant

Defect of cartilage oligometric matrix protein (COMP) on chromosome 19

Signs and symptoms

Normal facies

Cervical instability and scoliosis with increased lumbar lordosis

Significant lower extremity bowing

Hip, knee, and elbow flexion contractures with precocious osteoarthritis

Radiographic findings: metaphyseal flaring and delayed epiphyseal ossification

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MED

COMP gene

Type 9 Collagen

Multiple epiphyseal dysplasia in two sisters and their 40-year-old father. Anteroposterior (AP) (A) and frog-leg lateral (B) radiographs of both hips of a 12-year-old girl. Note the irregularity and flattening of the capital femoral epiphyses. Involvement is bilateral. AP (C) and lateral (D) views of both hips of the 14-year-old sister showing similar changes. AP (E) and lateral (F) radiographs of the father’s hips. Note the irregularity of the femoral heads and marked degenerative arthritis in both hips.

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SED

Defect in type II collagen

must be differentiated from MED

The distinguishing factor is SED has spine involvement

Retinal detachment and respiratory disorders are common

 

Spine component is axial instability with myelopathy and sharp curve scoliosis