Achondroplasia 

Updated: May 11, 2020
Author: Shital Parikh, MD; Chief Editor: Jeffrey D Thomson, MD 

Overview

Practice Essentials

The skeletal dysplasias are a heterogeneous group of disorders characterized by intrinsic abnormalities in the growth or remodeling of cartilage and bone. They affect the skull, spine, and extremities in varying degrees.[1]  Skeletal dysplasias frequently cause a disproportionately short stature (dwarfism); the standing height falls below the third percentile for age. Achondroplasia is the most common type of short-limb disproportionate dwarfism.[2, 3]

The term achondroplasia, implying absent cartilage formation, was first used by Parrot in 1878.[4]  Although this term is inaccurate from a histopathologic perspective, its use is universal and has been accepted by the International Working Group on Constitutional Diseases of the Bone.[5, 6, 7]

Somatotropin (recombinant human growth hormone [GH]) has been used to augment the height of patients with achondroplasia. The greatest acceleration in growth velocity is seen during the first year of treatment and in those with the lowest growth velocities before treatment.

Most of the orthopedic problems encountered in patients with achondroplasia are related to the spine. Craniocervical stenosis, thoracolumbar kyphosis, spinal stenosis, angular deformities of the lower extremities, and lengthening of the short extremities are the orthopedic problems commonly addressed in these patients.

Anatomy

The bony skeleton is divided into two parts: the axial skeleton and the appendicular skeleton. The axial skeleton is the central core unit, consisting of the skull, vertebrae, ribs, and sternum. The appendicular skeleton comprises the bones of the extremities. For more information about the relevant anatomy, see Skeletal System Anatomy in Children and Toddlers, Skeletal System Anatomy in Adults, and Osteology (Bone Anatomy).

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 include the following:

  • Rhizomelic (proximal)
  • Mesomelic (middle)
  • Acromelic (distal)

In achondroplasia, the extremity involvement is rhizomelic, with the arms and thighs more severely involved than the forearms, legs, hands, and feet.[8]

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, the 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. The diagnosis is made on the basis of physical examination and radiographic findings.

Etiology

Genetic basis

A single gene mapped to the short arm of chromosome 4 (band 4p16.3) is responsible for achondroplasia and is transmitted as an autosomal dominant trait.[9]

At least 80% of cases result from a random new mutation. In sporadic cases, a paternal age older than 36 years is common. Most parents are of average size and have no family history of a dwarfing condition. The risk of the parents producing a second affected child is almost negligible. Reports have estimated that there is a 1 in 443 risk of recurrence of achondroplasia in the siblings of an affected child with unaffected parents. This is because of gonadal mosaicism in the parents. Average-sized siblings have no increased risk of producing a child with achondroplasia.

When both parents have achondroplasia, 50% of their offspring are heterozygous and affected, 25% are homozygous, which is ordinarily fatal in the first few months of life, and 25% are unaffected. When one parent has achondroplasia, the chance of transmitting this gene to each child is 50%.

Molecular basis

Fibroblast growth factors (FGFs) are structurally related proteins associated with cell growth, migration, wound healing, and angiogenesis. At the cellular level, their function is mediated by transmembrane tyrosine kinase receptors, known as FGF receptors (FGFRs).[10]

Mutation in FGFR3 is responsible for achondroplasia, hypochondroplasia, and thanatophoric dysplasia.[10] The primary function of FGFR3 is to limit osteogenesis. Mutation causes enhancement in its function of limiting endochondral ossification. Mutation in FGFR3 in achondroplasia is due to transition of guanine to adenine (G to A) at nucleotide 1138 of complimentary DNA.

Associated syndrome

Two reports exist of achondroplasia associated with Down syndrome.[11] On the basis of the current birth rate, the calculated risk of association is one case in every 8 years in the United States.

Epidemiology

Approximately 10,000 individuals are estimated to have achondroplasia in the United States. Worldwide, achondroplasia is the most common skeletal dysplasia, affecting about 1 in every 40,000 children. (This number varies, depending on the source.) A study using data provided by the European Surveillance of Congenital Anomalies (EUROCAT) network found achondroplasia to have a prevalence of 3.72 per 100,000 births.[12]

About 80% of all "little people" have achondroplasia. Approximately 150,000 persons have achondroplasia worldwide. The worldwide population of little people is approximately 190,000.

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

Prognosis

The standardized mortality ratio is increased for all age groups by a factor of 2.27 over that of the general population.[13] In children younger than 4 years, death most commonly occurs as a consequence of brainstem compression, which causes sudden death. In individuals aged 5-24 years, central nervous system (CNS) 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)
  • Spinal deformities (eg, kyphosis, lordosis, scoliosis)
  • Obesity [14, 15]
  • Spinal canal stenosis
  • Cardiovascular complications

Patient Education

An important resource for individuals with short stature is the Little People of America. This is a national organization that addresses the social, physical, and medical needs of its constituency. It holds annual regional and national conventions. Philosophically, these organizations emphasize the positive aspects of their members' abilities and lives rather than viewing the issue of short stature as a disability.

The Dwarf Athletic Association of America is a member of the US Olympic Committee that promotes athletic participation for individuals with short stature.

When addressing height issues in patients with short stature, the term "less than average" should be used.

 

Presentation

History

Gross motor development frequently is delayed. Motor milestones (eg, head control and independent sitting, standing, and ambulation) may lag by 3-6 months. Speech and language problems may be caused by tongue thrust (due to an abnormal maxillomandibular relationship) but often resolve spontaneously. Some 20% of patients experience delayed speech acquisition. Cognitive skills are preserved, and the intelligence level is within normal limits. Cranial enlargement and poor head control place the infant at risk for extension injuries.

An Australian study assessed the functional milestones of achondroplasia children aged 3-7 years. The data showed that whereas milestones were delayed across all ages studied, functioning improved between the ages of 3 and 5 years, though not subsequently. Access to clinicians skilled in achondroplasia management may assist these children to become more independent.[16, 17]

Standing height is below the third percentile for both sexes. The mean adult standing height for men is 132 cm (52 in.), and that for women is 125 cm (49 in.). Sitting height, a reflection of trunk length, is within normal limits.

About 75% of patients have otitis media when younger than 5 years. Recurrent otitis media is common because of poor drainage of the eustachian tubes from underdevelopment of the midface, relative hypertrophy of tonsils and adenoids, and temporal bone abnormalities. Conductive hearing loss is present due to ossicular chain stiffness, and may be either congenital or acquired as a result of recurrent otitis media. Sensorineural hearing loss may be present in a few patients. Maxillary hypoplasia may lead to dental crowding and malocclusion.

Upper-airway obstruction, small chest wall, pectus excavatum, and neurogenic effects from brainstem compression reduce the vital capacity. The incidence of pneumonia, cyanotic spells, apnea, and other respiratory complications is increased. Symptoms of airway obstruction include snoring and sleeping with the neck in a hyperextended position.

Abnormal development of the base of the skull results in a foramen magnum that is smaller than in average individuals. Narrowing of the foramen magnum compresses the cervicomedullary region and can cause respiratory insufficiency, apnea, cyanotic episodes, feeding problems, quadriparesis, and sudden death. These symptoms are common in the first several years of life because of the failure of the anticipated enlargement of foramen magnum during infancy and childhood. Chronic brain-stem compression also may be a cause of hypotonia observed in the first 2 years of life.

Stenosis of the spinal canal and intervertebral foramen leads to symptoms such as low back pain, leg pain, dysesthesia, paresthesia, paraparesis, incontinence, and neurogenic claudication. Claudication may present as vague symptoms of aching or tiredness of the lower extremities induced by walking or standing. Symptoms may progress with a sensation of tingling and numbness and, eventually, weakness. Often, the pain is alleviated if the patient assumes a squatting position or bends forward.

More than 50% of patients experience symptoms of lower-extremity radiculopathy from nerve-root compression or cauda equina syndrome. The mean age of onset of back or lower-extremity symptoms is 26 years; one third of patients are younger than 15 years at onset.

Symptoms due to abnormal curvature of the spine (eg, kyphosis, lordosis, or scoliosis) may be present, such as deformity, back pain, respiratory dysfunction, neurologic involvement, or symptoms of spinal stenosis. The incidence of kyphoscoliosis may be as high as 33-50% in adults. However, the curve magnitude is generally less than 30° and generally does not necessitate treatment.

Joint laxity may be present in children. Genu recurvatum is common. As the child grows, genu varum (tibial bowing) and lateral tibial torsion become apparent.

Macrocephaly represents ventriculomegaly or arrested hydrocephalus.

Mild but annoying neurologic disturbances can be attributed to local anatomic abnormalities and abnormal stretching of nerves. Examples include hip and knee pain from meralgia paresthetica, ankle pain from irritation of the peroneal nerve, or facial pain due to trigeminal neuralgia.

Fibromyalgia (trigger points located in the lower part of the back) and trochanteric bursitis can be seen in some patients.

Physical Examination

Achondroplasia is evident at birth as a disproportionate short-limb dwarfing condition (see the image below). Characteristics include an enlarged neurocranium, frontal bossing, flattening of the nasal bridge, midface hypoplasia, and a relatively prominent mandible. The anteroposterior diameter of the chest is flattened, the lower ribs are flared, and the abdomen protrudes.

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

Before walking, the child has a thoracolumbar kyphosis and lordosis in the interscapular thoracic region.[18] The kyphosis can be severe in the sitting position and may not reduce completely in the prone position. Once independent ambulation is established, an exaggerated lumbar lordosis with forward rotation of the pelvis develops, and the spinal deformity is associated with hip flexion contractures and a prominent abdomen and buttocks. However, some degree of kyphosis persists in 25% of adults.

Upper-extremity involvement is rhizomelic, with the proximal segments more severely affected than the distal segments. The shoulders appear broad because of the normal development of clavicle and well-developed musculature. The short arms may contribute to bulky muscle mass and apparent increased strength in such individuals. Loss of full extension of the elbow, in the range of 15-30°, is present. A trident hand is common and is characterized by a persistent space between the long and ring fingers when approximation of the fingers is attempted in full extension. The fingertips reach the level of the hips, which causes difficulty with hygiene and dressing.

Lower-extremity involvement is rhizomelic, with hip flexion contractures, ligamentous laxity and external rotation of the extremity, and genu recurvatum before walking age. The tibia is bowed, resulting in significant genu varum and some degree of ankle varus. Frequently, gaping of the lateral compartment or lateral translation of the tibia on the femur can be seen during the stance phase. Occasionally, a valgus deformity may develop. The gait is usually a waddling gait, and circumduction motion of the hips and lower extremities occurs when running is attempted.

Spinal deformities are the most common and potentially disabling problems.[19, 20, 21] Spinal canal stenosis and stenosis of the intervertebral foramen are secondary to short thickened pedicles, interpedicular narrowing, thickened laminae, intervertebral disc herniation, degenerative spondylolysis, excessive lumbar lordosis, or anterior wedging of the vertebral bodies from thoracolumbar kyphosis. Sensory deficits, posterior column dysfunction, lower and upper motor neuron signs, and signs of neurologic claudication may be present. Signs of lower-extremity radiculopathy from nerve-root compression or cauda equina syndrome are present in more than 50% of patients.

Macrocephaly is present as a consequence of triventricular enlargement and hydrocephalus.[22] However, intracranial pressure is not elevated significantly. In infants, a rough estimate of the pressure can be made by palpating the fontanelles.

 

DDx

Diagnostic Considerations

In addition to the conditions listed in the differential diagnosis, other problems to be considered include the following:

  • Achondrogenesis
  • Chondroectodermal dysplasia ( Ellis-van Creveld syndrome )
  • Metatrophic dwarfism
  • Asphyxiating thoracic dysplasia
  • Chondrodysplasia punctata (Conradi disease)
  • Pseudoachondroplastic dysplasia
  • Metaphyseal chondrodysplasia (Schmid type)

The diagnosis of achondroplasia in the fetus is made with certainty when one or both parents have this condition. In situations where the parents have normal stature, the diagnosis may only be suspected on the basis of the observation of disproportionately short limbs in the fetus upon ultrasonographic evaluation. In most cases, the specific diagnosis cannot be made with certainty until birth. Caution should be exercised in counseling the family.[20]

The diagnosis should be confirmed at birth by means of radiographic studies. The measurements, including arm span, occipital frontal circumference, body length, and ratio of upper body to lower body, should be documented.

Differential Diagnoses

 

Workup

Laboratory Studies

Plasma can be analyzed for the FGFR3 mutation in the mother when a short-limb skeletal dysplasia is diagnosed antenatally by means of ultrasonography (US).[20, 10] This can be confirmatory for achondroplasia and can help the family to make educated decisions.

DNA testing can be performed when both of the parents are affected. Infants with affected genes from both the parents (double homozygous) are either stillborn or die shortly after birth.

Imaging Studies

Radiography

Radiographs of the skull, spine, and extremities reveal the characteristic features. A lateral skull radiograph demonstrates midface hypoplasia, enlarged calvaria, frontal prominence, and shortening of the base of the skull. The size of the foramen magnum is diminished. (See the image below.)

Characteristic skull seen in patients with achondr Characteristic skull seen in patients with achondroplasia, with frontal bossing, small foramen magnum, midface hypoplasia, and relative enlargement of skull as compared with face.

A lumbar spine (anteroposterior [AP]) view reveals distinct narrowing on the interpedicular distances from proximal to distal in L1-5 (see the image below). Normally, the interpedicular distance from the cephalocaudad direction should increase. However, if this distance decreases or remains unchanged, it is abnormal. The changes should be observed in three consecutive vertebrae.

Progressive narrowing of coronal interpedicular di Progressive narrowing of coronal interpedicular distance in lumbar spine in patients with achondroplasia. Note characteristic shape of pelvis with horizontal sacral position.

The lateral view reveals shortening of the pedicles and vertebral bodies with significant posterior scalloping. Various degrees of thoracolumbar kyphosis may be present before walking age (see the image below). This may be associated with wedging of T12 or L1. Once ambulation is established, kyphosis generally improves, and lumbar lordosis develops. The inclination of the sacrum becomes increasingly horizontal.

Thoracolumbar kyphosis with narrow lumbar spinal c Thoracolumbar kyphosis with narrow lumbar spinal canal and concave posterior bodies in 13-month-old child with achondroplasia.

Scoliosis of more than 20° develops in some patients. The curves are relatively short and are located in the thoracolumbar or lumbar region. Rotation is not a prominent feature. Degenerative changes can be seen in the vertebral column, particularly at the anterior margins of the vertebral bodies located in the thoracolumbar area and in the cervical spine. However, such changes are compatible with the patient's age.

The pelvis is typically broad and short, and the ilium has a square appearance. The sacrosciatic notch is short, and the acetabular roof is horizontal (see the image below). The femoral neck is short with trochanteric overgrowth, giving an appearance of coxa vara. However, true coxa vara is not seen. Arthritic changes of the hip, even in older patients, usually are not observed. This can be attributed to the reduction of major joint lever arms and the comparative lightness (50 kg) of the patient.

Typical features of lower limbs in person with ach Typical features of lower limbs in 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.

The long bones have metaphyseal flaring and are short and thick. During the first year, the proximal metaphyses of the femur and the humerus have oval areas of radiolucency. Sites of major muscle attachments (eg, deltoid and patellar tendon tuberosity) are prominent.

The distal femoral physes are configured in the shape of an inverted V (chevron). Bowing usually affects the tibia more than the femur. The fibula is typically longer than the tibia.

The humerus is markedly shortened, and the radial head frequently is dislocated. The ulna is typically short with an elongated styloid process. The proximal and middle phalanges of the hand are broader, with greater shortening than the distal phalanges and metacarpals.

Primary radiographic criteria for diagnosis are as follows:

  • Decrease in interpedicular distance in the lumbar spine
  • Square short ilia
  • Short, broad neck of femur
  • Shortening of long tubular bones, with metaphyseal flaring
  • Brachydactyly

Secondary radiographic criteria for diagnosis are as follows:

  • AP shortening of lumbar pedicles
  • Dorsal concavity of lumbar vertebra
  • Long distal fibula
  • Short distal ulna
  • Long ulnar styloid

Computed tomography

The size of the foramen magnum can be measured most accurately by means of computed tomography (CT).[23, 24] The spinal canal is narrowed developmentally, particularly in the lower lumbar segments. The cross-sectional anatomy can be evaluated noninvasively with this modality. CT can be performed to develop a three-dimensional image of the rib cage, which can be used to calculate lung volumes and can substantiate a successful surgical chest expansion.

Magnetic resonance imaging

Given the incidence and potential severity of neurologic symptoms associated with foramen magnum stenosis, baseline magnetic resonance imaging (MRI) is strongly recommended in infancy.[25] Cervicomedullary compression at the foramen magnum, fusion of C1, or isolated subaxial cervical stenosis can be demonstrated (see the image below). In addition, MRI can show myelomalacia, intramedullary cyst, or angulation at the craniocervical junction.

MRI showing cervicomedullary compression at forame MRI showing cervicomedullary compression at foramen magnum in patient with achondroplasia.

MRI may be used to establish the cause of neurocranial enlargement. Dilated ventricles without hydrocephalus, and communicating and noncommunicating forms of hydrocephalus may be observed.

MRI is also recommended for preoperative evaluation of lumbar spinal stenosis, especially to determine whether associated disc herniations exist and the proximal level of compression. The average area of L1 is decreased by 39%, and that of L5 is decreased by 27%. Kyphosis correlates strongly with neurologic symptoms, and MRI can demonstrate apical wedging and neurologic involvement.

Ultrasonography

In the fetus, heterozygous achondroplasia is associated with normal or near-normal femur lengths until 20-24 weeks of pregnancy. Thereafter, the growth rate of the femur decreases. Hence, US may not be useful for diagnosing achondroplasia in the first half of the pregnancy. Later in the pregnancy, US can detect short-limb dysplasia. However, differentiation among various skeletal dysplasias is difficult.

In the neonate, US can be used to detect ventricle size and other abnormalities. It cannot be used once the sutures and fontanelles close. MRI is the imaging modality of choice at that time.

Cine-phase contrast and magnetic resonance angiography

Cine-phase contrast and magnetic resonance angiography (MRA)[26]  are useful for studying the pathophysiology of brainstem compression and hydrocephalus. Gated cine-phase contrast cerebrospinal fluid (CSF) flow studies can be used to evaluate CSF dynamics across the foramen magnum. MRA (venography) can be used to depict obstructed venous drainage due to jugular foramen stenosis.[27]  Steno-occlusive disease of the internal jugular vein, reduced blood flow in the superior sagittal sinus, and compensatory enlargement in the emissary veins can be depicted.

Other Tests

Somatosensory evoked potential (SSEP) abnormalities have been reported for 44% of neurologically intact persons with achondroplasia and are probably related to brainstem compression at the level of the foramen magnum.

Pulmonary function tests are useful for preoperative evaluation when respiratory symptoms are present. Typically, the vital capacity is decreased, averaging 68% for affected males and 72% for affected females.

A sleep study may be performed if symptoms suggest airway obstruction.[28] The cause of airway obstruction can be established to guide the treatment. Differentiating between central sleep apnea (due to brain stem or upper cervical cord compression) and obstructive sleep apnea (due to midface hypoplasia) is helpful.

Procedures

Reports exist of sudden blindness associated with an increase in the intracranial pressure (ICP). Hence, ICP monitoring is recommended in persons with achondroplasia with moderate ventriculomegaly, as demonstrated by MRI. This is performed with a percutaneous spinal catheter. Treatment is recommended when the ICP is higher than 15 mm Hg.

Histologic Findings

Biopsy from the growth plates of the ilium and proximal fibula reveal an essentially normal structure. Glycosaminoglycan determination is normal. The proportion of proteoglycan aggregates increases in the fibular head. The defect is mainly quantitative and lies in the proliferative zone of the growth plate.

 

Treatment

Medical Care

The availability of somatotropin (recombinant human growth hormone [GH]) has revolutionized the treatment of short stature.[29] GH is used to augment the height of patients with achondroplasia. The greatest acceleration in growth velocity is seen during the first year of treatment and in those with the lowest growth velocities before treatment.

Long-term studies to determine final height have been lacking, as have randomized controlled studies to justify prolonged treatment with GH in patients with short stature. A 2017 study by Harada et al evaluated the gain in final height in 22 (eight male, 14 female) adult patients with achondroplasia who received long-term GH therapy (10.7 ± 4.0 years for males, 9.3 ± 2.5 years for females) at a dosage of 0.05 mg/kg/day.[30] ​ They found that long-term GH treatment contributed to 2.6% of final adult height in males and 2.1% in females.

For maximum benefit, it is recommended that therapy be intiated at a young age (1-6 years).

Surgical Care

Most of the orthopedic problems encountered in patients with achondroplasia are related to the spine. Craniocervical stenosis, thoracolumbar kyphosis, spinal stenosis, angular deformities of the lower extremities, and lengthening of the short extremities are the orthopedic problems commonly addressed in achondroplasia.[1, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]

Treatment of spinal canal stenosis

Wide multilevel laminectomies extending to the pedicles and lateral recesses with foraminotomies may be necessary. Extradural removal of herniated disk material is performed as necessary.[38]  To prevent recurrence, decompression usually extends from the lower thoracic spine to the sacrum. Maintaining the integrity of facet joints is necessary to prevent postlaminectomy instability. If instability does occur, anterior fusion may be necessary.

To obtain successful results, it is important to ensure that laminectomies are carried out to the appropriate extent, which should be three levels cephalad to the proximal extent of compression, distal to the second sacral level, and lateral to the facet joints. The results of this more extensive approach are encouraging.

Treatment of thoracolumbar kyphosis

For the child who has not begun to walk, treatment of thoracolumbar kyphosis consists of mere observation because spontaneous resolution frequently occurs. Reports exist that demonstrate the efficacy of early prohibition of unsupported sitting.[18]  If wedging of the apical vertebra persists after independent ambulation (typically, wedging of T12 or L1), an extension-type thoracolumbosacral orthosis should be used.

Xu et al evaluated the outcome of brace treatment for correction of thoracolumbar kyphosis in 33 patients with achondroplasia (mean age, 27.5 ± 13.4 months; mean treatment period, 32.2 ± 15.7 months; mean follow-up, 25.7 ± 11.3 months).[41]  By the final visit, the mean value for thoracolumbar kyphosis had been reduced from 41.7  ±  15.4º to 29.5  ±  20.8º, and the percentage of apical vertebral wedging had been reduced from 61.4  ±  16.2% to 52.1  ±  18.7%. Initial thoracolumbar kyphosis, apical vertebral translation, percentage of apical vertebral wedging, and pelvic tilt were independent factors associated with correction of thoracolumbar kyphosis.

If the thoracolumbar kyphosis persists and measures greater than 30° at age 5 years, then surgery should be performed. Surgery is usually in the form of combined anterior and posterior fusion. Posterior instrumentation generally is not recommended, because of the narrow canal size. Placement of any instrumentation (eg, hooks or sublaminar wires) in the canal is contraindicated because of the marked stenosis and decreased subarachnoid fluid space.

If kyphosis is associated with a neurologic deficit such as paraplegia, laminectomy alone is not indicated, because it can destabilize the spine further. Treatment should consist of anterior cord decompression with strut grafting and posterior fusion.

Correction of genu varum

Surgical correction of genu varum may be required.[42]  This may be in the form of proximal tibiofibular osteotomy or of proximal and distal fibular epiphysiodesis. Osteotomy is performed when rapid correction of symptomatic deformity is required. It can be performed through small incisions without internal fixation, with long-leg cast immobilization for 6 weeks.

Lengthening of limbs

Limb lengthening of the upper and lower extremities is promoted in Europe.[34, 35, 36, 37, 43, 44] However, the Little People of America (LPA) and the Dwarf Athletic Association of America (DAAA) are generally opposed to these procedures (see Patient Education).

If lengthening is to be performed, any existing angular deformities should be corrected simultaneously. With the current techniques of distraction osteogenesis, 30 cm of length can be gained. Gradual lengthening of the osteotomy callus (callostasis) or through the epiphyseal plates (chondrodiastasis) can be obtained using monolateral frames or Ilizarov ring fixators.[31, 45] The six-segment lengthening (femur, tibia, humerus) can be performed as staged procedures in various sequences.

A potential exists for major complications during six-segment lengthening. Neurologic injury has been reported in 35% of procedures. Foot drop, vascular compromise, soft-tissue contractures, loss of motion, knee subluxation, infection, psychological changes, and death have been reported with extensive lengthening procedures.

Foramen magnum decompression (neurosurgery)

Narrowing of the foramen magnum may result in a variety of neurologic problems in the first several years of life. Significant improvement of severe neurologic symptoms has been reported with foramen magnum decompression and C1 laminectomy; however, prophylactic surgery is not recommended.

Ventriculoperitoneal shunts are indicated for patients with rapidly progressive head enlargement, increased intracranial pressure (ICP), or neurologic signs and symptoms. Neurosurgery is also indicated for other neurologic abnormalities, such as Chiari malformation.

Diet

Nutritional counseling is helpful. Obesity is a lifelong issue, and dietary therapy should be initiated early in life.

Consultations

The following consultations may be considered:

  • Orthodontist - Maxillary hypoplasia leads to dental crowding and malocclusion, often necessitating orthodontic treatment.
  • Speech therapist - Although most of the speech problems resolve by the time patients are of school age, children with persistent problems should be referred to a speech therapist
  • Otolaryngologist - Early recognition and treatment of chronic otitis media is required to prevent hearing loss; relative hypertrophy of tonsils and adenoids due to midface hypoplasia may require treatment; an otolaryngologist may be involved in the treatment of sleep apnea syndrome, for which tonsillectomy, adenoidectomy, and, rarely, tracheostomy are the procedures performed
  • Geneticist - A clinical geneticist may be of help by providing counseling to the family and may also may be a valuable resource for the pediatrician seeking additional information or consultation; the proper establishment of the mode of inheritance not only aids in genetic counseling but also enables the orthopedist to distinguish achondroplastic dwarfism from other forms of dwarfism, many of which have an autosomal recessive inheritance
  • Pulmonologist - Pulmonary function should be evaluated, and respiratory complications such as apnea, pneumonia, and cyanosis should be avoided
  • Pediatrician - The American Academy of Pediatrics Committee on Genetics has issued guidelines to assist the pediatrician in caring for children with achondroplasia and their families [46] ; occasionally, the pediatrician is called on to advise pregnant women who have been informed of an antenatal diagnosis of achondroplasia
 

Guidelines

JSPE Guidelines for Achondroplasia

In January 2020, the Japanese Society for Pediatric Endocrinology (JSPE) published the following clinical practice guidelines regarding achondroplasia[47] :

  • Cranial magnetic resonance imaging (MRI) is recommended to identify spinal cord compression due to foramen magnum stenosis.
  • Foramen magnum decompression is recommended for managing spinal cord compression due to foramen magnum stenosis associated with neurologic symptoms, abnormal neurologic findings, and central respiratory disorders.
  • An MRI cranial examination is recommended to identify ventricular enlargement with neurologic symptoms (hydrocephalus).
  • Shunt surgery is recommended for managing ventricular enlargement associated with neurologic symptoms (hydrocephalus).
  • Simple sleep studies and polysomnography (PSG) are selected for diagnosis of sleep apnea on the basis of circumstances. 
  • Noninvasive positive-pressure ventilation (PPV) is suggested for managing obstructive sleep apnea (OSA). 
  • Surgical treatment (tonsillectomy or adenoidectomy) is suggested when OSA is present with tonsillar or adenoid hypertrophy.
  • Spinal decompression is recommended for managing spinal canal stenosis associated with neurologic symptoms.
  • Delayed speech is observed in 25% of cases of achondroplasia.
  • Leg lengthening should be possible after the age of 12 years, under informed consent.
 

Medication

Medication Summary

Growth hormone is used to increase the height of patients with achondroplasia (see Medical Care). However, no long-term studies exist to justify prolonged treatment for short stature.

Growth hormone

Class Summary

The anabolic and growth-promoting effects of growth hormone are indirect effects mediated by IGF-I. Growth hormone also increases transport of amino acids and protein synthesis.

Growth hormone, human (Humatrope, Genotropin, Nutropin)

Stimulates growth of linear bone, skeletal muscle, and organs. Stimulates erythropoietin, which increases red blood cell mass.