Influence of cervical bone mineral density on cage subsidence in patients following stand-alone anterior cervical discectomy and fusion

Anterior cervical discectomy and fusion (ACDF) is a common procedure for the treatment of cervical degenerative diseases. However, cage subsidence remains a frequent problem. We therefore investigated if cage design and site-specific bone mineral density (BMD) contribute to the rate and direction of subsidence following ACDF. Patients were prospectively included and received two different cages (groups 1 and 2) using minimization randomization. The degree and direction of cage subsidence were determined using plain radiographs. Neck pain intensity on the visual analogue scale (VAS), the neck disability index (NDI), and the patient satisfaction index were recorded up to 12 months after surgery. 88 patients were analysed with a mean age of 53.7 +/- A 11.8 years. BMD values decreased in craniocaudal direction from 302.0 +/- A 62.2 to 235.5 +/- A 38.9 mg/cm(3). Both groups showed significant height gain after the operation (both p < 0.001), followed by height loss at 3 months (both p < 0.05) and at 3-12 months after the operation (both p > 0.05). Both groups showed improvement of VAS neck pain intensity (both p < 0.05) and NDI (both p < 0.05). The direction of cage subsidence was similar, no correlations were found between cage subsidence and BMD or various clinical parameters. Implant geometry of both cages and variations of the operative procedure promoted a relatively high degree of cage subsidence. Further studies are necessary to identify a relation of BMD and subsidence using optimized implant geometry and by controlling additional intraoperative variables.