Defects of Tubular Bone or Spinal Growth Present at Birth

Achondroplasia

More than 350 conditions (319) may be defined in these mostly inheritable groups of skeletal dysplasias of which achondroplasia is the most common. Achondroplasia is an autosomal-dominant disorder; with approximately 85 % new mutations, it is the most common of the skeletal dysplasias (320).

Clinical Features. The diagnosis of achondroplasia is made clinically with characteristic features on radio­graph. These conditions are often associated with shortened trunk, narrow thorax, and variant body proportions, including enlarged head size with fron­tal bossing, hypoplasia of the midface, short limbs and fingers, lordotic lumbar spine, and bowed legs. Although typically normal in intelligence, second­ary to their size, these individuals are often looked upon and treated as younger than their stated age. Secondary to transitory muscular hypotonia, early motor milestones are frequently delayed in infancy. Visual spatial learning issues or deficits similar to other children with compensated hydrocephalus may be observed. Physical therapy that includes exercises with these babies prone are also important in order to minimize thoracolumbar gibbus (320).

Prevention: Obesity. There are specific weight charts for those with achondroplasia (321). Obesity is also correlated with the increase in cardiovascular-related deaths (322). Lumbar-region symptomatic spinal steno­sis may be seen in achondroplasia; it is aggravated by obesity. Signs of this include lower back and leg pain, and may be observed in 50% of those with this con­dition. There may be weakness, altered deep tendon reflexes, paresthesia, and later, claudications. Early treatment includes anti-inflammatory medication and corticosteroid injections to treat lumbar radiculopathy, with one-third eventually needing lumbar laminec­tomy (323). Kyphoscoliosis is common.

Prevention: Ear, Nose and Throat.

Precautions, Monitoring, and Surgical Intervention. This group requires precautions with regard to atlantoaxial instability. The instability may be from maldevelop- ment of the odontoid, transverse ligament laxity, or longitudinal ligament abnormalities. MRI of the brain, including the cervical junction and the spinal cord, is recommended between the ages of 6-12 months. Signs of cervical cord compression (myelopathy) are increased reflexes of the lower extremities, clonus, severe hypotonia, central sleep apnea, and sudden death. Polysomnography is used to demonstrate the central sleep apnea (323). Referral to the appropriate specialist is necessary for evaluation and treatment.

Hydrocephalus, if present in achondroplasia, must be carefully evaluated and may need surgical inter­vention (324). Head circumference must be monitored every six months while growing (especially in the first two years of life), and symptoms of increased cranial pressure must be evaluated (320,323). MRI of the cervi- comedullary junction, as well as CSF flow studies, may be normal with a neutral neck position. With flexion and extension of the cervical spine, complete blockage of CSF flow in the former and posterior cervicomedullary compression in the latter may be demonstrated (324). Flexion and extension imaging is warranted if there are mild to severe symptoms and signs present, as surgi­cal options such as ventriculoperitoneal (VP) shunt or decompressive surgery can be corrective (324).

Treatment. This may include human growth hormone therapy. The long-term sequelae of this are unknown. Parathyroid hormone has been shown to improve bone growth and mitigate the effects of FGFR3 mutations found in achondroplasia (325). Limb lengthening is a possibility, but has many risks involved, includ­ing infections as well as soft tissue, nerve, and joint damage. This remains controversial (323). There is an increased number, compared to the general pop­ulation, of sudden deaths thought to be caused by foramen magnum stenosis in children under 5 years of age, and an increase from cardiac disease and neu­rological diseases, including drug overdose and sui­cide in older patients (322). Reports of depression, low self-esteem, poor body image, and chronic pain need to be addressed. The key to successfully treating this condition is a multidisciplinary team that includes the rehab specialist, occupation and physical therapists, social worker and/or psychologist, neurosurgeon, car­diologist, and orthopedist.