A fusion classification system for the advent of bioactive interbody implants
Background: Historically, intervertebral fusion required bone bridging for stability. Bioactive interbody devices enable bone integration at the endplate–implant interface, prompting an updated radiographic assessment and classification system that recognizes implant adhesion as contributing to fusion. Aim: This study aims to develop and evaluate a reliable computed tomography (CT)-based grading system for assessing spinal fusion and stability associated with interbody devices, including factors such as osseointegration, implant type, and bone connectivity. Methods: A novel fusion grading system was developed, incorporating both bone and fusion consolidation through and around the device and the apposition of bone to the implants. A total of 10 cases with one-year postoperative CT scans were provided for the survey. Surveys were administered twice, more than two weeks apart and in a different order. Inter- and intra-rater reliability were assessed using the intraclass correlation coefficient (ICC). Results: A total of 51 spine surgeons participated, of whom 37 completed both survey rounds. For all 51 participants, the ICC was 0.618 (95% confidence interval = 0.435–0.834; p < 0.001), and the mean intra-rater reliability was 0.778 (standard deviation = 0.211). Four raters had outlier intra-rater scores, with an average of 0.259. After removing these four raters (10.8% of the cohort) and analyzing the remaining 89.2% of raters, the ICC was 0.628 (95% confidence interval = 0.445–0.841; p < 0.001), and the mean intra-rater reliability was 0.831 (standard deviation = 0.125; p ≤ 0.015). Conclusions: The novel CT-based classification system showed moderate-to-good inter-rater and good-to-excellent intra-rater reliability in clinical cases. Future work should use it to assess the relative contributions of on-growth, in-growth, and bone healing around bioactive interbody devices. Relevance for patients: This new classification system may be utilized to account for the stabilizing effects of bone in-growth at the implant interface when studying fusion with bioactive implants.
- Christensen FB, Karlsmose B, Hansen ES, et al. Radiological and functional outcome after anterior lumbar interbody spinal fusion. Eur Spine J. 1996;5(5):293-298. doi: 10.1007/bf00304343
- Kakadiya DG, Gohil DK, Soni DY, et al. Clinical, radiological and functional results of transforaminal lumbar interbody fusion in degenerative spondylolisthesis. N Am Spine Soc J. 2020;2:100011. doi: 10.1016/j.xnsj.2020.100011
- Pearcy M, Burrough S. Assessment of bony union after interbody fusion of the lumbar spine using a biplanar radiographic technique. J Bone Joint Surg Br. 1982;64-B(2):228-232. doi: 10.1302/0301-620x.64b2.7040410
- Lenke LG, Bridwell KH, Bullis D, et al. Results of in situ fusion for isthmic spondylolisthesis. J Spinal Disord. 1992;5(4):433-442. doi: 10.1097/00002517-199212000-00008
- Brantigan JW, Steffee AD. A carbon fiber implant to aid interbody lumbar fusion. Two-year clinical results in the first 26 patients. Spine. 1993;18(Supplement):2106-2107. doi: 10.1097/00007632-199310001-00030
- Tan GH, Goss BG, Thorpe PJ, et al. CT-based classification of long spinal allograft fusion. Eur Spine J. 2007;16(11):1875-1881. doi: 10.1007/s00586-007-0376-0
- Seo DK, Kim MJ, Roh SW, et al. Morphological analysis of interbody fusion following posterior lumbar interbody fusion with cages using computed tomography. Medicine. 2017;96(34):e7816. doi: 10.1097/md.0000000000007816
- Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. J Chiropr Med. 2016;15(2):155-163. doi: 10.1016/j.jcm.2016.02.012
- Moore MS, McAuley JP, Young AM, et al. Radiographic signs of osseointegration in porous-coated acetabular components. Clin Orthop Relat Res. 2006;444:176-183. doi: 10.1097/01.blo.0000201149.14078.50
- Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958;40(3):607-624. doi: 10.2106/00004623-195840030-00009
- Peters MJM, Bastiaenen CHG, Brans BT, et al. The diagnostic accuracy of imaging modalities to detect pseudarthrosis after spinal fusion-a systematic review and meta-analysis of the literature. Skeletal Radiol. 2019;48(10):1499-1510. doi: 10.1007/s00256-019-03181-5
- Kitchen D, Rao PJ, Zotti M, et al. Fusion Assessment by MRI in Comparison With CT in Anterior Lumbar Interbody Fusion: A Prospective Study. Global Spine J. 2018;8(6):586-592. doi: 10.1177/2192568218757483
- Cizek GR, Boyd LM. Imaging pitfalls of interbody spinal implants. Spine. 2000;25(20):2633-2636. doi: 10.1097/00007632-200010150-00015
- Kant AP, Daum WJ, Dean SM, et al. Evaluation of lumbar spine fusion. Spine. 1995;20(21):2313-2317. doi: 10.1097/00007632-199511000-00009
- Lang P, Genant HK, Chafetz N, et al. Three-dimensional computed tomography and multiplanar reformations in the assessment of pseudarthrosis in posterior lumbar fusion patients. Spine. 1988;13(1):69-75. doi: 10.1097/00007632-198801000-00017
- Cunningham BW, Kanayama M, Parker LM, et al. Osteogenic protein versus autologous interbody arthrodesis in the sheep thoracic spine: A comparative endoscopic study using the Bagby and Kuslich interbody fusion device. Spine. 1999;24(6):509-518. doi: 10.1097/00007632-199903150-00002
- Engelke K, Graeff W, Meiss L, et al. High spatial resolution imaging of bone mineral using computed microtomography: Comparison with microradiography and undecalcified histologic sections. Invest Radiol. 1993;28(4):341-349. doi: 10.1097/00004424-199304000-00016
- Cook SD, Patron LP, Christakis PM, et al. Comparison of methods for determining the presence and extent of anterior lumbar interbody fusion. Spine. 2004;29(10):1118-1123. doi: 10.1097/00007632-200405150-00013
- Christensen FB, Laursen M, Gelineck J, et al. Interobserver and intraobserver agreement of radiograph interpretation with and without pedicle screw implants: the need for a detailed classification system in posterolateral spinal fusion. Spine. 2001;26(5):538-543. doi: 10.1097/00007632-200103010-00018
- Kanemura T, Ishikawa Y, Matsumoto A, et al. The maturation of grafted bone after posterior lumbar interbody fusion with an interbody carbon cage: a prospective five-year study. J Bone Joint Surg Br. 2011;93(12):1638-1645. doi: 10.1302/0301-620X.93B12.26063
- Mokawem M, Katzouraki G, Harman CL, et al. Lumbar interbody fusion rates with 3D-printed lamellar titanium cages using a silicate-substituted calcium phosphate bone graft. J Clin Neurosci. 2019;68:134-139. doi: 10.1016/j.jocn.2019.07.011
- Gruskay JA, Webb ML, Grauer JN. Methods of evaluating lumbar and cervical fusion. Spine J. 2014;14(3):531-539. doi: 10.1016/j.spinee.2013.07.459
- Rodgers WB, Gerber EJ, Patterson JR. Fusion after minimally disruptive anterior lumbar interbody fusion: Analysis of extreme lateral interbody fusion by computed tomography. SAS J. 2010;4(2):63-66. doi: 10.1016/j.esas.2010.03.001
- Ortega B, Gardner C, Roberts S, et al. Ceramic Biologics for Bony Fusion-a Journey from First to Third Generations. Curr Rev Musculoskelet Med. 2020;13(4):530-536. doi: 10.1007/s12178-020-09651-x
- McAfee PC, Boden SD, Brantigan JW, et al. Symposium: a critical discrepancy-a criteria of successful arthrodesis following interbody spinal fusions. Spine. 2001;26(3):320-334. doi: 10.1097/00007632-200102010-00020
- Malham GM, Parker RM, Blecher CM, et al. Assessment and classification of subsidence after lateral interbody fusion using serial computed tomography. J Neurosurg Spine. 2015;23(5):589-597. doi: 10.3171/2015.1.Spine14566
- Malone H, Mundis GM, Collier M, et al. Can a bioactive interbody device reduce the cost burden of achieving lateral lumbar fusion? J Neurosurg Spine. 2022;37(5):646-653. doi: 10.3171/2022.4.SPINE211070
- Shirazi C, Ochoa MA, Malone H, et al. Can titanium surface technology reduce cost for biologics in anterior lumbar interbody fusion? J Neurosurg Spine. 2024;41(5):589-595. doi: 10.3171/2024.5.SPINE231323