Achondroplasia

What is Achondroplasia?

Achondroplasia is a genetic disorder and the most common form of short-limb dwarfism. It occurs in approximately 1 in 26,000 to 1 in 40,000 births. Achondroplasia is an autosomal dominant condition. This means that a person with achondroplasia has a 1 in 2 or 50% chance of having children with achondroplasia.

Characteristics of Achondroplasia

Characteristic facial features, disproportionate short stature, andrhizomelic (the proximal ends of the limbs) shortening of the limbs.Diagnosis of achondroplasia is made by physical exam and skeletal x-rays.Most individuals have normal intelligence.

The facial features include a large head with a prominent forehead, a smallmidface with a flat nasal bridge and narrow nasal passages.Middle ear infections often occur in infants and children. Hearing loss may occur if left untreated.

Respiratory problems may occur in infants and children due to airway obstructions or the obstruction of the central nervous systemSymptoms of airway obstruction include snoring, or apnea.Treatment depends on the type of obstruction.

If obstruction of the central nervous system is present, a foramen magnum decompression is performed. If airway obstruction is present, therapy may include tonsillectomy, adenoidectomy, ortracheostomy placement.

The limbs present with rhizomelicshortening. In infancy the legs are straight but when a child starts walking, they can develop a knock-knee position.As the child continues to walk, the legs assume a bow-leg appearance. Occasionally, children have these leg curvatures corrected together with limb lengthening. The fingers and toes are short.

Dwarfism Correction By Extensive Limb

Lengthening

Treatment was begun at the age of 6 years for this girl as early treatment has several benefits and allows better integration of the child with its peers at school and play.In this child, most of the strategies of treatment were used to give her the maximum benefit.

Dwarfism Correction By Extensive Limb

Lengthening

Bilateral double level tibiallengthening was done in the tibia. 11 cm of length was achieved in both the legs without any deformities. This is about 110% lengthening as compared to the original length of the fragment.

Dwarfism Correction By Extensive Limb

Lengthening

At the end of thetibial lengthening, movement in all joints was normal as was the LateralPopliteal Nerve function.

Dwarfism Correction By Extensive Limb

Lengthening

3 years after the initial tibiallengthening, these were her body proportions: notice that the arms are reaching only to the level of the top of the thigh, unlike other normals in whom the hands should reach the middle of the thigh.

Dwarfism Correction By Extensive Limb

Lengthening

This photograph shows Bilateral single level humeral lengthening in progress, showing excellent function in both the shoulder and elbow during treatment as well as good bone formation.

Dwarfism Correction By Extensive Limb

Lengthening

After lengthening of the arms, this picture shows the restoration of normal body proportions with the hands reaching upto the mid-thigh.

Dwarfism Correction By Extensive Limb

Lengthening

This is the final strategy used in which Cross lengthening was performed with one thigh and the other leg in the first stage and in the second stage this sequence was reversed. This permitted maximum length to be achieved with minimum wastage of time.

Dwarfism Correction By Extensive Limb

Lengthening

The other thigh and leg are being lengthened after a gap of about 6-8 months after the completion of the first stage of treatment. Total lengthening achieved in this way: 33 cm.

Infants have athoracolumbar kyphosis in the sitting position,but as the child begins to walk, thekyphosis disappears and the back assumes a lordoticposture.

Since infants with chondroplasia often have reduced tone, it is recommended that they not be placed in umbrella-type strollers, jumpers, or swings that do not provide good back support since these devices may lead to the development of a gibbus or hump in the back.If a child is delayed in walking, the spine should be monitored closely for signs ofgibbus formation.

Neurologiccomplications:

in infancy, hydrocephalus can develop. Infants should be monitored monthly with measurements of their head circumference to detest a rapidly enlarging head size that can indicate hydrocephalus.

What is hydrocephalus?

The term hydrocephalus indicates excess fluid within the cranium. This is a pathological condition which occurs as a result of imbalance between the production and absorption of cerebro-spinal fluid (CSF). Hydrocephalus only forms if the CSF is unable to leave the ventricular cavities or if its absorption is disturbed.

Common radiologic procedures that are used to identify hydrocephalus:

head ultrasound,CT-scan or MRI of the head.

If intervention is necessary, aventriculoperitoneal (VP)-shunt is placed to relieve the excess pressure.

Normal infant ultrasound of the head. Courtesy J Bender, MD

Ultrasound showing hydrocephalus in an infant. Note the large ventricles compared to the normal

CT scan of an adult with Normal Pressure Hydrocephalus

Normal CT scan of the head in an adult

If intervention is necessary, aventriculoperitoneal (VP)-shunt is placed to relieve the excess pressure.

Treatment of hydrocephalus

A VP-shunt is a soft but durable structure which remove excess CSF pressure from the brain, draining to either the abdomen or the heat.

Foramen magnum compression:

The foramen magnum is the opening at the base of the skull through which the brainstem and cervical spinal cord exit.Individuals withachondroplasia have narrowed foramen magnums which can then compress the brain stem and spinal cord.

Symptoms of narrowing include apnea(cessation of breathing) and cervicalmyelopathy. CT-scans and MRI scans are done to examine the size of the foramen magnum.

If a child is having symptoms, a neurosurgicalprocedure called a foramen magnum decompression is done to enlarge the foramen magnum and alleviate further symptoms. Adolescents and adults are at risk of developing lumbosacral spinal stenosis. The lumbar spinal cord or nerve roots become compressed producing neurologicsymptoms. Initial symptoms include weakness, tingling, and pain of the legs. Often the pain is alleviated by assuming a squatting position.

As the condition worsens, pain in the low back or buttocks occurs. Diagnosis is made by a neurologicexam, SERs (somatic evoked responses), and CT or MRI scans.Treatment is a neurosurgical procedure called a lumbar laminectomy.

Referenceshttp://www.med.jhu.edu/Greenberg.Center/achon.htmhttp://www.ilizarov.ru/Ahondr_e.htmhttp://www.ilizarov.org/amle1.htmhttp://www.yoursurgery.com/ProcedureDetails.cfm?BR=4&Proc=44http://www.sophysa.com/patient/hydrocephalus/hydrocephalus3.htmhttp://www.asbah.org/whatishyd.html