Radiographic Assessment of Effect of Congenital Monosegment Synostosis of Lower Cervical Spine between C2-C6 on Adjacent Mobile Segments

STUDY DESIGN: A prospective radiographic study of cervical spine with congenital monosegment fusion. PURPOSE: To evaluate the effect of cervical synostosis on adjacent segments and the vertebral morphology. OVERVIEW OF LITERATURE: There are numerous clinical studies of adjacent segment disease (ASD) after monosegment surgical fusion. However, there was no report on ASD in the cervical spine with congenital monosegment synostosis. METHODS: Radiograms of 52 patients, aged 5 to 90 years, with congenital monosegment synostosis (CMS) between C2 and C6, who complained of neck/shoulder discomfort or pain were studied. 51 were normally aligned and one was kyphotically aligned. RESULTS: Spondylosis was not found in the patients below 35 years of age. Only 12 out of 24 patients with normally aligned C2-3 synostosis had spondylosis in 19 more caudal segments, and only one at C3-4. A patient with kyphotic C2-3 had spondylolysis at C3-4. In 8 patients with C3-4 synostosis, spondylosis was found in only 9 caudal segments (4 at C4-5, 4 at C5-6, and 1 at C6-7). The caudate C4-5 disc was the most liable to degenerate in comparison with other caudate segments. Caudal corporal flaring and inwaisting of the synostotic vertebra were the features that were the most evident. In 2 of 9 C4-5 and 7 out of 10 C5-6 synostosis patients, spondylosis was found at the two adjacent cephalad and caudate segments, respectively. Only corporal inwaisting without flaring was found. In all cases, spondylosis was confined to the adjacent segments. More advanced spondylosis was found in the immediate caudal segment than the cephalad one. CONCLUSIONS: It is concluded that spondylosis at the mobile segments in a synostotic spine is thought to be a fusion-related pathology rather than solely age-related disc degeneration. Those data suggested that CMS definitely precipitated the disc degeneration in the adjacent segments.