Achondroplasia—Clinical Manifestations of Spine

Midfacial hypoplasia of variable degree is manifested by a flat or depressed nasal bridge, narrow nasal passages, and malar hypoplasia (see Plate 4-2). The nose has a fleshy tip and upturned nostrils. These features result from restricted development of the chondrocranium and the middle third of the face.

Recurrent and chronic middle ear infections (otitis media) are common in infancy and early childhood and, if untreated, may lead to significant hearing loss. Generally, these infections become less frequent by the time the patient is 8 to 10 years of age.

A relative protrusion of the jaw is often mislabeled as prognathism. Dental development is normal, but underdevelopment of the maxilla may cause dental crowding and malocclusion. About 70% of patients have tongue thrust or other speech defects that seem to be related to the dysplastic bone structure. These problems usually subside spontaneously by school age.

The root portions of the limbs are shorter than the middle or distal segments. Soft tissues may appear excessive with redundant, partially encircling folds and grooves on the limbs. Because the long bones are shortened, the muscle mass looks bunched up, creating the appearance of great strength.

Initially, the legs appear straight but with ambulation may develop a varus position, resulting in bowleg (genu varum) with or without back knee (genu recurvatum).

The hands and feet may appear large in relation to the limbs, but the digits are short, broad, and stubby (brachydactyly). The so-called trident hand (see Plate 4-2) is common but becomes less apparent in late childhood and adulthood. The fingertips may reach only to the level of the trochanters or even the iliac crests. Elbow extension is restricted (30 to 45 degrees), but this has little functional significance. In some instances, this may be due to radial head subluxation.

Although the trunk is relatively long, deformities contribute to the overall height reduction. The chest tends to be flat and broad and the abdomen and buttocks protuberant. Excessive lumbar lordosis and a tilted pelvis cause a waddling gait, and fixed flexion contractures of the hip appear early.

In a sitting position, infants commonly exhibit thoracolumbar kyphosis (see Plate 4-1). A hump, or gibbus, seen in some infants, may be associated with anterior wedging of the first or second lumbar vertebra. The kyphosis is related to a variety of factors, including ligamentous laxity, hypotonia, and immature strength and motor skills. Although it requires monitoring, the kyphosis usually disappears when the child begins to walk.

Neurologic complications are common. Respiratory abnormalities suggest stenosis of the foramen magnum and compression of the normal-sized medulla oblongata and/or cervical spinal cord. This quite frequent complication results in hypoventilation or apnea, paralysis of voluntary respiration, and compressive myelopathy at the level of the foramen magnum (see Plate 4-4). (Therefore, hyperextension of the neck and sudden, whiplash-like movement should be avoided.) Sudden infant death syndrome has also been reported. Somatosensory evoked potential (SSEP) and polysomnography coupled with CT and MRI can provide valuable information to help avert both short-term and long-term complications.

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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Achondroplasia—Clinical Manifestations of Spine

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