gms | German Medical Science

Objective: Anterior cervical discectomy and fusion (ACDF) followed by cage implantation represents the standard therapy for degenerative cervical disc disease and/or the treatment of cervical stenosis. However, primary anterior cage subsidence occurs frequently and may be responsible for recurrent radicular symptoms due to secondary foraminal stenosis. Factors such as low bone quality or cage design might be responsible for cage subsidence. Therefore, a prospective study has been conducted investigating the occurrence of subsidence using different cage designs in homogenous groups regarding age and cervical bone mineral density (cBMD).

Methods: 88 patients with mono- or bisegmental indications were prospectively enrolled in this study. Patients were assigned to the different study arms using the minimization method, controlling for age and cBMD using quantitative computed tomography (qCT). Group 1 received a symetrical fenestrated rectangular PEEK cage (Rabea, Fa. Signus, Alzenau, Germany). Group 2 received a newly designed round PMMA cage with identical contact surface compared to the PEEK cage but with an asymmetrical ventrally consolidated contact surface. Postsurgical follow-ups were performed at 3 and 12 months with assessment of segmental height using lateral radiographs and clinical outcome using the Neck Disability Index (NDI), the patient satisfaction index (PSI) and the Visual Analogue Scale (VAS) for neck pain.

Results: Within both treatment groups a significant rate of subsidence occurred (p < 0.01). Compared to the direct postoperative radiograph, in Group 1 the segmental height was 92.8% and 90.8% at 3 and 12 months and in Group 2 94.0% and 93.0%. cBMD decreased from C 3 (302 kg/m³) to C 7 (235 kg/m³). No correlation was found between age and bone mineral density (r = –1.86, p = 0.08). The degree of subsidence showed no correlation with cBMD at 3 months (r = –1.57, p = 0.3) and at 12 months (r = 0.03, p = 0.8). At 12 months postoperative, the observed cage subsidence showed no correlation to clinical scores (NDI, r = –0.06, p = 0.7; PSI, r = –0.16, p = 0.3; VAS neck r = –0.12, p = 0.4).

Conclusions: In two homogenous groups regarding age and cBMD cage subsidence occurred in an equal degree despite optimized cage contact surface. In order to prevent cage subsidence, the contact surface has to be enlarged. However, occurrence of cage subsidence should not be over interpreted, since it seems of minor clinical relevance.