9:40 Comparative study of titanium interbody spacer and BAK fusion devices: a prospective randomized clinical study with minimum 2-year follow-up

Abstract

Purpose of study: Lumbar interbody fusion devices have been developed. These devices are packed with the patient's own cancellous bone and provide immediate segmental fixation. The purpose of the TIS Equivalence Study was to evaluate the safety and effectiveness of the titanium interbody spacer (TIS) compared to the commercially available BAK.Methods used: This was a randomized, multicenter, prospective study approved by the Food and Drug Administration with a minimum follow-up of 2 years. Patients were randomized in a 1:1 ratio. Both the TIS and the BAK were filled with autogenous bone and implanted using an open, anterior approach to the lumbar spine. The protocol did not allow for additional anterior or posterior instrumentation to be used during the initial surgery. Subjects up to 70 years of age with degenerative disc disease at one to two consecutive levels between L2 and S1, and with at least 6 months of nonoperative treatment, were enrolled in the study. Patients were evaluated preoperatively and at 6, 12, 18 and 24 months by means of Short Form (SF)-36 McGill Pain Questionnaire, Oswestry Questionnaire and independent clinical examination. All radiographs were sent out for digitization and blinded evaluation by board-certified radiologists. Study success was based on deomonstrating that the proportion of subjects in the TIS group achieving success at 24 months was equivalent to or better than that for subjects in the BAK group. Patient success was defined as the occurrence of fusion, improvement in pain, maintenance or improvement of functional ability, maintenance or improvement of neuromuscular status, maintenance of device integrity and placement and absence of a device-related surgical intervention. Patient success requires success for each of the six criteria. Failure in any criteria equaled overall failure.of findings: Eighty-seven percent of patients were available for 24-month evaluation. A total of 116 were treated with the TIS cage and 111 were treated with the BAK fusion cages. Minimum follow-up was 2 years. There was no significant difference in demographic data between the two groups. Average age was 42 years; 39% were receiving workers compensation benefits. Sixty-one percent of the TIS group and 63% of the BAK group had no prior back surgery. Forty percent of the TIS group and 37% of the BAK group were smokers. Ninety-five percent of patients had surgery performed at L4–L5 or L5–S1. The average operative time was 171 minutes for the 73% TIS and 70% of the BAK patients had a single-level fusion. At 2-year follow-up, overall fusion rate was 77% TIS and 71% BAK; pain improvement 64% both TIS and BAK groups; functional improvement 87% TIS and BAK; neurologic improvement 94% TIS and 78% BAK patients. There were no reports of device breakage for either the TIS or the BAK device. Twenty-two patients (12 TIS, 10 BAK) required additional surgery for pseudarthrosis or continued pain. There were no infections or catastrophic vascular injuries. At 24 months, the patient success rate was 42% for TIS patients and 25% for BAK patients.Relationship between findings and existing knowledge: This is the first study evaluating the Synthes TIS device.Overall significance of findings: The TIS cage is as effective and safe as the BAK fusion cage. The low success rates for both treatment groups in this study suggests that requiring a subject to succeed on six individual criteria may be too rigorous an analysis. The success rates for the six criteria are all substantially higher than the overall success rate. Unless there is a strong relationship between the six outcomes, the success rates for each outcome must be high if the overall success rate is to be even moderate.Disclosures: Device or drug: TIS interbody fusion cage. Status: investigational.Conflict of interest: Patrick Connolly, Institutional research support from Synthes USA.