Anterior cervical interbody fusion with a titanium box cage: early radiological assessment of fusion and subsidence

The use of stand-alone cervical interbody cages in anterior cervical discectomy with fusion (ACDF) has become popular, but high subsidence rates have been reported in the literature. The authors present short-term radiological results of a titanium box cage with regard to fusion and subsidence. Reliable fusion and lack of subsidence may influence long-term clinical results. Early radiological data are necessary before implementation of this device on a larger scale can be accepted. Retrospective radiological quality assessment study. ACDF using the titanium cage was performed in 71 consecutive patients at 106 levels. Diagnoses included cervical disc disease (57) and cervical spinal stenosis (14) after failed conservative treatment. Subsidence and kyphosis were assessed on lateral cervical radiographs made directly postoperative and at 3- and 6-month follow-up. At 6-month follow-up, lateral flexion-extension radiographs were made to assess fusion. Subsidence of the cage was defined as a decrease in total vertical height of the two fused vertebral bodies as measured on the lateral cervical radiographs made 3 and 6 months postoperatively compared with the directly postoperative radiographs. Segmental kyphosis was measured as the angle between the posterior borders of the two vertebral bodies on the lateral radiograph. No patients were lost to follow-up. Fusion was achieved after 6 months in all patients. At 3 and 6 months postoperative the same 10 cages (each in a different patient) had subsided. The C6-C7 level was significantly more frequently involved compared with all other levels. A segmental kyphotic alignment was observed in five patients at the C6-C7 level and in one patient at the C4-C5 level. For patients with cervical disc disease, the high subsidence tendency of the cage into the end plate of predominantly C7 is a disturbing phenomenon found in this study. A modified cage design that improves and extends contact with the inferior surface could be expected to reduce subsidence into C7.