Stand-alone Anterior Lumbar Interbody Fusion Research Articles

An economic analysis of bone morphogenic protein

Purpose of study: An economic model was developed to compare costs of bone morphogenic protein (BMP) versus autogenous iliac crest bone graft (AICBG) for spinal fusion. Fusion and complications rates were based on two multicenter, randomized, clinical trials comparing stand-alone anterior lumbar interbody fusion with BMP (recombinant human BMP-2 [rhBMP-2]) on an absorbable collagen sponge versus AICBG in either a tapered cylindrical cage (LT-CAGE clinical trial) or a threaded cortical bone dowel (Bone Dowel clinical trial). The objective of this study was to determine the effect of use of BMP on the process of care and costs of spinal fusion during the index hospitalization and in the subsequent 2 years. The economic model was developed based on data from clinical trials, peer-reviewed literature and expert opinion.Methods used: We identified and assigned costs to medical resources that would increase or decrease with the use of BMP. Direct medical costs in two distinct contexts were considered: those incurred by the hospital during the index hospitalization and those incurred during both the index hospitalization and 2 years afterwards. The price of BMP in the base case analyses was $3,380. The costs are reported in 2001 US dollars.of findings: In the base case analysis over a period of 2 years, total direct medical costs for spinal fusion were similar for BMP and AICBG ($9 difference favoring BMP) using clinical trial fusion rates of 94.5% and 88.7%, respectively (LT-CAGE clinical trial). In a sensitivity analysis over a period of 2 years using fusion rates of 100% for rhBMP-2 and 68.4% for AICBG, respectively (Bone Dowel clinical trial), BMP resulted in $4,564 in savings. In the base case analysis from a hospital perspective (index hospitalization only), nearly half of the $3,380 price of BMP was offset.Relationship between findings and existing knowledge: The upfront price of BMP is likely to be offset to a significant extent by reductions in the use of other medical resources, particularly if costs incurred during the 2-year period after the index hospitalization are taken into account.Overall significance of findings: Under the base case assumptions (fusion success rates of 94.5% for rhBMP-2 and 88.7% for AICBG; LT-CAGE clinical trial) over a 2-year period, cost-neutrality was achieved at a BMP price of $3,389. Sensitivity analyses indicate that under an alternative scenario about the fusion success rates (100.0% for rhBMP-2 and 68.4% for AICBG; Bone Dowel clinical trial), cost-neutrality would be achieved over a 2-year period at a BMP price of $7,944.Disclosures: Device or drug: rhBMP-2. Status: not approved.Conflict of interest: David Polly, Jr., grant research support: Medtronic Sofamor Danek and De Puy Acromed.

9:34 Comparison of impacted femoral ring allografts, threaded cortical bone dowels and titanium cages in lumbar fusion

Purpose of study: To test the efficacy of recombinant human bone morphogenic protein (rhBMP-2), we compared clinical and radiographic outcomes in patients who underwent a single-level anterior lumbar interbody fusion (ALIF) and were treated with impacted femoral rings and autogenous bone graft, threaded cortical allograft dowels or titanium cages. Patients who received dowels or titanium cages were randomized to receive either BMP-soaked collagen sponges or autogenous iliac crest bone graft.Methods used: At 22 investigational sites, 387 patients with symptomatic, single-level degenerative lumbar spondylosis that was unresponsive to nonoperative treatment were enrolled in this prospective, randomized, nonblinded study. All patients had a single-level stand-alone ALIF through an open approach. Patients who received dowels or cages were randomized into two groups to receive autogenous iliac crest bone graft or rhBMP-2 on a collagen sponge carrier (InFUSE). All 62 patients who received impacted femoral rings were treated with autogenous bone graft, 46 patients received bone dowels (24 with BMP and 22 with autograft) and 279 patients received the LT-CAGE interbody fusion device (143 with BMP and 136 with autograft). Patients' average age at surgery was 42 years, average weight was 173 pounds and 34% used tobacco products. Clinical outcomes were assessed using the Oswestry Low Back Pain Disability Questionnaire. Anteroposterior, lateral, flexion-extension lateral radiographic views and computed tomography scans, used to evaluate the progression of fusion at 6, 12 and 24 months, were interpreted by two independent, blinded radiologists.of findings: at 24 months, there were no adverse events related to the use of rhBMP-2. At all follow-up visits, all groups showed statistically significant improvements in their Oswestry scores compared with their preoperative scores. Patients in the bone dowel/BMP and LT-CAGE fusion device groups showed greater improvement than the bone dowel/autograft and femoral ring groups. Of patients in the bone dowel/BMP group, 71% showed an improvement of at least 15 points in their Oswestry scores at 3 months after surgery. At all follow-up intervals, the bone dowel/BMP group and both LT-CAGE groups had greater improvements in Oswestry scores than the bone dowel/autograft and femoral ring groups. At 3, 6, 12 and 24 months, the differences in improvement were statistically significant (p=.032, p=.0389, p=.039 and p=.039, respectively). At 24 months, the mean improvement in Oswestry scores was 33.5 points in the bone dowel/BMP group and 29.3 points in the LT-CAGE groups. At 24 months, 84% of the bone dowel/BMP and LT-CAGE patients improved more than 15 points compared with 58% of the bone dowel/autograft and femoral ring groups. At 6 months after surgery, more than 90% of patients in both LT-CAGE groups and the bone dowel/BMP group had evidence of fusion compared with 65% of patients in the bone dowel/autograft group (p=.067) and 10% in the femoral ring group. At 24 months, more than 94% of patients in the two BMP groups had evidence of fusion. The LT-CAGE/autograft fusion rate decreased to 90%, the bone dowel/autograft fusion rate was 68% and the femoral ring fusion rate was 50%.Relationship between findings and existing knowledge: The use of BMP improves clinical outcomes and fusion rates of ALIF over previous standard of care spinal implants.Overall significance of findings: Overall, the groups in which BMP was used showed faster clinical improvement and higher rates of success than the autograft and impacted femoral ring allograft groups. No adverse events related to the use of BMP and the collagen sponge carrier occurred.Disclosures: Devise or Drug: LT-CAGE. Status' approved. Device or Drug: bone dowel. Status: approved. Device or Drug: rhBMP2. Status: approved.Conflict of interest: Kenneth Burkus, consultant for Medtronic Sofamor Danek.

Biomechanical stability of five stand-alone anterior lumbar interbody fusion constructs

Anterior lumbar interbody fusion (ALIF) cages are expected to reduce segmental mobility. Current ALIF cages have different designs, suggesting differences in initial stability. The objective of this study was to compare the effect of different stand-alone ALIF cage constructs and cage-related features on initial segmental stability. Human multisegmental specimens were tested intact and with an instrumented L3/4 disc level. Five different ALIF cages (I/F, BAK, TIS, SynCage, and ScrewCage) were tested non-destructively in axial rotation, flexion/extension and lateral bending. A cage 'pull-out' concluded testing. Changes in neutral zone (NZ) and range of motion (ROM) were analyzed. Cage-related measurements normalized to vertebral dimensions were used to predict NZ and ROM. No cage construct managed to reduce NZ. The BAK and TIS cages had the largest NZ increase in flexion/extension and lateral bending, respectively. Cages did reduce ROM in all loading directions. The TIS cage was the least effective in reducing the ROM in lateral bending. Cages with sharp teeth had higher 'pull-out' forces. Antero-posterior and mediolateral cage dimensions, cage height and wedge angle were found to influence initial stability. The performance of stand-alone ALIF cage constructs generally increased the NZ in any loading direction, suggesting potential directions of initial segmental instability that may lead to permanent deformity. Differences between cages in flexion/extension and lateral bending NZ are attributed to the severity of geometrical cage-endplate surface mismatch. Stand-alone cage constructs reduced ROM effectively, but the residual ROM present indicates the presence of micromotion at the cage-endplate interface.