Subluxation of the Atlas Causing Spinal Cord Compression in a Case of Down's Syndrome with a “Manifestation of an Occipital Vertebra”

Spontaneous subluxation of the atlas is common in Down's syndrome (6) but is not usually accompanied by spinal cord compression. In 1966 Dzenitis (2) reported a case of Down's syndrome with atlanto-axial subluxation in which progressive quadriparesis and a neurogenic bladder developed following an ear infection. Two additional examples of symptomatic atlanto-axial subluxation requiring surgical correction have recently been documented (1). Torticollis developed in association with mumps and pharyngitis in one case, and in the other there was a history of upper respiratory tract infection. Inasmuch as atlas subluxation has been described as a nonspecific sequel to inflammation in the neck region in children (7), it is possible that in these instances a pre-existing atlanto-axial instability was somehow aggravated by the inflammation. This report concerns such a patient presenting with progressive neurologic deficits caused by atlanto-axial subluxation and having no prior cervical inflammation. Surgical treatment in this case was complicated by the presence of a “third condyle” which was not appreciated preoperatively. Case Report A 9 year-old Negro girl (E. W.) was admitted to the Wayne County General Hospital because of neck pain and progressive quadriparesis. She had been confined to the Plymouth State Home and Training School since the age of four years. The patient had the physical features of Down's syndrome, and her cells had 47 chromosomes with G-trisomy typical of this condition. She sat alone at six months of age, walked unassisted at age three, and at this age tendon reflexes were reportedly normal and Babinski signs were absent. At the age of seven years, however, her gait became abnormal, tendon reflexes were hyperactive, and Babinski signs were present. Progressive loss of the use of the lower extremities resulted, with the patient becoming nonambulatory. Roentgenograms of the cervical spine showed an anterior subluxation of the atlas; the atlanto-odontoid interval measured 12 mm (Fig. 1). The cerebrospinal fluid protein concentration was 59 mg/100 ml. Vincke tongs and traction were applied to the skull, but neither the cervical alignment nor the neurologic status improved. A posterior atlanto-axial wire-fixation and iliac bone graft-fusion were performed, but at operation the subluxation could not be completely reduced. Postoperative roentgenograms confirmed the per sistent subluxation, and laminagrams showed a bony projection arising from the basilar process and extending downward behind the anterior arch of the atlas (Fig. 2). This projection, thought to represent a so-called “third condyle,” one of the manifestations of an occipital vertebra, prevented reduction of the subluxation and, in retrospect, was evident in the preoperative films (Fig. 1). The atlanta-odontoid interval measured 10 mm postoperatively. Nevertheless, the patient regained motor ability and one year later was able to walk with support.