Threaded titanium cages for lumbar interbody fusions.

STUDY DESIGN

This study evaluated safety, fusion success rate, and clinical outcome of a new lumbar interbody hollow, threaded titanium fusion cage in a multicenter, prospective 236-case program adhering to a United States Food and Drug Administration Investigational Device Exemption controlled protocol.

OBJECTIVES

The results were evaluated to demonstrate the safety and effectiveness of this new method to achieve solid lumbar interbody fusions.

SUMMARY OF BACKGROUND DATA

Interbody fusions have certain distinct mechanical advantages over lateral or posterolateral ones. Autologous, cancellous bone is the preferred graft material, but is too soft to maintain the space during fusion without mechanical support. Various methods have been used in the past to maintain the graft integrity during fusion development.

METHODS

An initial pilot study began on 10 patients (followed for 84 months, average 80 months). Two years after that investigation started, the multicenter United States Food and Drug Administration Investigational Device Exemption study began, with cases followed for 28-46 months (average, 32). Ninety-six percent of the investigational Device Exemption study cases had severe, disabling back pain; in addition, 74% had major annular degeneration; 57% had herniations; 21% had osteophytes; and 43% had disc height reduced by greater than 10%. Forty-five percent of cases had previous spinal surgeries, and none were posterior lumbar interbody fusions. Titanium fusion cage pairs were screwed into bored and threaded, parallel intradiscal holes, and 3-8 ml autologous cancellous bone was packed inside each. Fusion success was judged by absence of motion on flexion-extension radiographs, absence of bone halo around the implants, and maintenance of visible bone inside the cages on Ferguson view radiographs.

RESULTS

Segments fused rapidly; the pilot study cases fused at 10 (91%) of 11 levels, with a reported 80% average clinical improvement. Ninety-six percent of the 208 2-year follow-up Investigational Device Exemption cases had fusion, and the Prolo socioeconomic/ functional improvement scale showed: 40% excellent, 25% good, 21% fair, and 14% poor results. Less than 1% of Investigational Device Exemption cases had complications that persisted beyond the average 5 days of hospitalization, and none were serious.

CONCLUSIONS

The Ray titanium fusion cage (Surgical Dynamics, Norwalk, CT) implant method has been found to be an effective, rapid, safe procedure for lumbar spine fusions, demonstrating a high fusion rate and clinical success with rare, serious, or permanent complications.