Achondroplasia 

  • Author: Shital Parikh, MD; Chief Editor: Dennis P Grogan, MD   more...
 
Updated: Feb 7, 2012
 

Background

The skeletal dysplasias are a heterogeneous group of disorders characterized by intrinsic abnormalities in the growth and/or remodeling of cartilage and bone. These dysplasias affect the skull, spine, and extremities in varying degrees.[1] They frequently cause a disproportionately short stature (dwarfism; see image below); the standing height falls below the third percentile for age. Achondroplasia is the most common type of short-limb disproportionate dwarfism. The term achondroplasia, implying absent cartilage formation, was first used by Parrot in 1878.[2] Although the word achondroplasia is inaccurate from a histopathologic perspective, its use is universal and accepted by the International Working Group on Constitutional Diseases of the Bone.[3, 4, 5]

Typical features of a person with achondroplastic Typical features of a person with achondroplastic dwarfism, including normal trunk with rhizomelic shortening and genu varum.
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Pathophysiology

Dwarfing conditions are frequently referred to as short-limb or short-trunk types, according to whether the trunk or limbs are more extensively involved. Achondroplasia, hypochondroplasia, and metaphyseal chondrodysplasias are considered short-limb dwarfing conditions. These patients' sitting height is within normal range. Additional terms used to describe the segment of the limb with the greatest involvement are rhizomelic (proximal), mesomelic (middle), and acromelic (distal). In achondroplasia, the extremity involvement is rhizomelic, with the arms and thighs more severely involved than the forearms, legs, hands, and feet.[6]

The primary defect found in patients with achondroplasia is abnormal endochondral ossification. Periosteal and intramembranous ossification is normal. Tubular bones are short and broad, reflecting normal periosteal growth. The iliac crest apophyses (appositional growth) are normal, giving rise to large, square iliac wings. The growth of the triradiate cartilage (endochondral growth) is abnormal, giving rise to horizontal acetabular roofs. Thus, these patterns of defect help to explain many of the observed clinical and radiographic characteristics of achondroplasia.

The characteristic features of achondroplasia are apparent at birth. Diagnosis is made based on physical examination and skeletal radiographic findings.

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Epidemiology

Frequency

United States

Approximately 10,000 individuals are estimated to have achondroplasia in the United States.

International

Achondroplasia affects about 1 in every 40,000 children. (This number varies, depending on the source.) Eighty percent of all "little people" have achondroplasia. Approximately 150,000 persons have achondroplasia worldwide. The worldwide population of little people is approximately 190,000.

Mortality/Morbidity

  • The standardized mortality ratio is increased for all age groups by a factor of 2.27 over that of the general population.[7]
    • In children younger than 4 years, death most commonly occurs due to brain stem compression, which causes sudden death.
    • In individuals aged 5-24 years, central nervous system and respiratory abnormalities are the common causes of death.
    • In persons aged 25-54 years, cardiovascular problems are the most frequent causes of death.
  • Morbidity associated with achondroplasia may include the following:
    • Recurrent otitis media (hearing loss)
    • Neurologic complications due to cervicomedullary compression (eg, hypotonia, respiratory insufficiency, apnea, cyanotic episodes, feeding problems, quadriparesis, sudden death)[1]
    • Obstructive and restrictive respiratory complications (eg, upper airway obstruction, pneumonia, apnea)
    • Hydrocephalus
    • Spinal deformities (eg, kyphosis, lordosis, scoliosis)
    • Obesity[8, 9]
    • Spinal canal stenosis
    • Genu varum
    • Cardiovascular complications

Race

Achondroplasia occurs in all the races with equal frequency.

Sex

Achondroplasia occurs with equal frequency in males and females. (It is inherited in an autosomal dominant manner.)

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Contributor Information and Disclosures
Author

Shital Parikh, MD  Assistant Professor, Department of Pediatric Orthopaedic Surgery, Cincinnati Children's Hospital Medical Center

Shital Parikh, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Medical Association, and Orthopaedic Research Society

Disclosure: Nothing to disclose.

Coauthor(s)

Preeti Batra, MBBS, MD  Staff Physician, Department of Radiology, VS Hospital, India

Disclosure: Nothing to disclose.

Specialty Editor Board

Mininder S Kocher, MD, MPH  Associate Professor of Orthopedic Surgery, Harvard Medical School/Harvard School of Public Health; Associate Director, Division of Sports Medicine, Department of Orthopedic Surgery, Children's Hospital Boston

Mininder S Kocher, MD, MPH is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Association for the History of Medicine, American College of Sports Medicine, American Orthopaedic Society for Sports Medicine, Massachusetts Medical Society, and Pediatric Orthopaedic Society of North America

Disclosure: Smith & Nephew Endoscopy Consulting fee Consulting; EBI Biomet Consulting fee Consulting; OrthoPediatrics Consulting fee Consulting; Pivot Medical Stock Consulting; pediped Consulting fee Consulting; WB Saunders Royalty None; Fixes-4-Kids Consulting

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

George H Thompson, MD  Director of Pediatric Orthopedic Surgery, Rainbow Babies and Children's Hospital, University Hospitals Case Medical Center, and MetroHealth Medical Center; Professor of Orthopedic Surgery and Pediatrics, Case Western Reserve University School of Medicine

George H Thompson, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Association, Pediatric Orthopaedic Society of North America, and Scoliosis Research Society

Disclosure: OrthoPediatrics None Consulting; Journal of Pediatric Orthopaedics Salary Management position; SpineForm None Consulting; SICOT None Board membership

Dinesh Patel, MD, FACS  Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital

Dinesh Patel, MD, FACS is a member of the following medical societies: American Academy of Orthopaedic Surgeons

Disclosure: Nothing to disclose.

Chief Editor

Dennis P Grogan, MD  Clinical Professor, Department of Orthopedic Surgery, University of South Florida College of Medicine; Chief of Staff, Department of Orthopedic Surgery, Shriners Hospital for Children of Tampa

Dennis P Grogan, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Medical Association, American Orthopaedic Association, American Orthopaedic Foot and Ankle Society, Eastern Orthopaedic Association, Irish American Orthopaedic Society, Pediatric Orthopaedic Society of North America, and Scoliosis Research Society

Disclosure: Nothing to disclose.

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Typical features of a person with achondroplastic dwarfism, including normal trunk with rhizomelic shortening and genu varum.
The characteristic skull seen in patients with achondroplasia, with frontal bossing, small foramen magnum, midface hypoplasia, and relative enlargement of the skull compared to the face.
The progressive narrowing of the coronal interpedicular distance in the lumbar spine in patients with achondroplasia. Note the characteristic shape of the pelvis with horizontal sacral position.
Thoracolumbar kyphosis with narrow lumbar spinal canal and concave posterior bodies in a 13-month-old child with achondroplasia.
Typical features of the lower limbs in a person with achondroplasia, including horizontal acetabular roofs, small sacrosciatic notches, genu varum and ankle varum with relative overgrowth of fibula, and inverted "V" shaped distal femoral physis.
MRI showing cervicomedullary compression at foramen magnum in a patient with achondroplasia.
 
 
 
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