Neck
Individuals with SED have odontoid hypoplasia. If the odontoid is unstable or forms abnormally, it presses on the spinal cord to cause atlantoaxial instability, which is common to many skeletal dysplasias. It is diagnosed on the basis of neck X-rays and MRI scans. The instability causes cervical myelopathy; it manifests even earlier than in patients with Morquio Syndrome. Symptoms, usually of the respiratory type, can be noted in newborns or young infants. Patients will begin to have great difficulty standing independently. Chronic motor weakness will begin to occur in the upper and lower limbs especially, followed by episodes of quadriplegia. Any inability to independently stand and remained balance does suggest myelopathy. Typically, cord compression is treated by surgical fusion of the vertebrae in the upper part of the neck.
Spine
Kyphoscoliosis in the thoracolumbar spine is a common feature in SED. It is present is over 50% of patients. Early diagnosis is by means of regular scheduled physical examinations and x-rays. For small curvatures bracing may be attempted, but this is not always successful. If serial x-rays demonstrate a progressive curve, surgical fusion of the spine may be necessary. In one study, the use of a brace was found to be effective for kyphosis when the brace was worn until maturity. Exaggerated lumbosacral lordosis affects nearly every SED-congenita patient. It causes imbalance of the spine in the sagittal plane. The lordosis is most likely caused by a changes in the structure of the vertebral bodies: the pedicles appear abnormally long and the vertical height of the posterior arches appears considerably low. Bracing, around the age of 4 or 5, is a successful attempt to correct the lordosis. However, small children typically do not tolerate the cumbersome brace very well, thereby its practicality is somewhat questionable.
Lower Limbs
Coxa vara is characteristic. The hip is a ball-and-socket joint formed between the pelvis (acetabulum) and the upper part of the femur (head). The head of the femur is connected to the shaft by the neck. Normally the neck makes an angle of 130° with the shaft. In SED, due to abnormal cartilage formation, the neck is unable to withstand the mechanical forces applied to it and the ball gradually bends downwards. Any change in the alignment of the femoral neck weakens the muscles around the hip joint (principally the abductors that stabilize the pelvis during walking) and causes hip joint contractures. Surgery to realign the femoral neck is recommended if symptomatic or if the neck-shaft angle is less than 100°. Genu valgus is more common than genu varus.
Feet
Though the medical literature indicates an association between SED and clubfeet, this is not our experience. We find flatfeet (planovalgus) to be much more common in children with SED.
Osteoarthritis
In SED, the part of the bone adjacent to joints is affected. Joint cartilage is also predominantly composed of Type II collagen. Premature osteoarthritis is typical. Joint replacement surgery (hips and knees) may be necessary in early adulthood, but this is variable. The presence of associated joint contractures and bony deformities in SED makes such surgery a technically challenging exercise.