THREADED TITANIUM CAGES FOR LUMBAR INTERBODY FUSIONS

Study Design. This study evaluated safety, fusion success rate, and cl inical outcome of a new lumbar interbody hollow, threaded titanium fus ion cage in a multicenter, prospective 236-case program adhering to a United States Food and Drug Administration Investigational Device Exem ption-controlled protocol. Objectives. The results were evaluated to d emonstrate 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 po sterolateral 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 main tain the graft integrity during fusion development. Methods. An initia l 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 Exem ption study began, with cases followed for 28-46 months (average, 32). Ninety-six percent of the Investigational Device Exemption study case s had severe, disabling back pain; in addition, 74% had major anular d egeneration; 57% had herniations; 21% had osteophytes; and 43% had dis c height reduced by greater than 10%. Forty-five percent of cases had previous spinal surgeries, and none were posterior lumbar interbody fu sions. Titanium fusion cage pairs were screwed into bored and threaded , parallel intradiscal holes, and 3-8 ml autologous cancellous bone wa s packed inside each. Fusion success was judged by absence of motion o n flexion-extension radiographs, absence of bone halo around the impla nts, and maintenance of visible bone inside the cages on Ferguson view radiographs. Results. Segments fused rapidly; the pilot study cases f used at 10 (91%) of 11 levels, with a reported 80% average clinical im provement. Ninety-six percent of the 208 2 year follow-up Investigatio nal Device Exemption cases had fusion, and the Prolo socioeconomic/fun ctional improvement scale showed: 40% excellent, 25% good, 21% fair, a nd 14% poor results. Less than 1% of Investigational Device Exemption cases had complications that persisted beyond the average 5 days of ho spitalization, and none were serious. Conclusions. The Ray titanium fu sion cage (Surgical Dynamics, Norwalk, CT) implant method has been fou nd to be an effective, rapid, safe procedure for lumbar spine fusions, demonstrating a high fusion rate and clinical success with rare, seri ous, or permanent complications.