Failure of porous tantalum cervical interbody fusion devices: two-year results from a prospective, randomized, multicenter clinical study.

OBJECTIVE

The objective of this study was to assess the safety and efficacy of 2 novel cervical interbody fusion devices in the treatment of single-level degenerative cervical disk disease. Both devices were fabricated from a porous tantalum material. The high overall porosity of the devices was intended to facilitate anterior cervical interbody fusion.

METHODS

A prospective, randomized, 3-armed, clinical study was initiated with the following treatment groups: porous tantalum ring device packed with autograft, porous tantalum block device, and iliac crest autograft control. All the patients had single-level symptomatic cervical disk disease that had failed to respond to nonoperative therapy. Clinical and radiographic data were collected preoperatively, during surgery, before hospital discharge, and at 6 weeks, 3 months, 6 months, 12 months, and 24 months postoperatively.

RESULTS

Six investigators participated in the clinical study at 6 investigational centers in the United States. Enrollment into the study was terminated after 39 patients had been accrued because of concerns over delayed fusion in the porous tantalum treatment groups. Of the 39 patients enrolled into the clinical study, 11 patients received the control treatment of iliac autograft fusion, 13 patients received the porous tantalum ring device with the center cavity packed with cancellous iliac crest autograft, and 15 patients received the porous tantalum block device. These patients were evaluated for 24 months as per the study protocol. There were no significant differences in any of the patient demographic variables collected. The mean operative times for both the ring and block device groups were slightly lower than the control treatment. Two patients in the block treatment group were determined to be nonunion between the 6- and 12-month time points and underwent additional surgery. Five patients with porous tantalum devices showed radiographic evidence of device fragmentation, and one patient in addition had radiographic evidence of erosion of the involved vertebral bodies by the device. One patient in the ring treatment group died from a myocardial infarction and kidney failure subsequent to the 12-month follow-up visit, which was unrelated to the device or the spinal fusion procedure. Fusion rate at 2 years for the tantalum device was very low as compared with the control arm (44% vs. 100%). Patient Neck Disability Index scores, Short Form-36 scores, and neurological status scores were similar between the 3 treatment groups.

CONCLUSIONS

This study demonstrates that stand-alone porous tantalum material is not ideal for a cervical spine interbody fusion because of the low rate of arthrodesis and the risk of device fragmentation in patients who fail to fuse.