Radiographic and Clinical Outcomes Following Unilateral or Bilateral Posterior Fixation in Minimally Invasive Transforaminal Lumbar Interbody Fusions
Phase: NA
Conditions: Lumbar Disease
Sponsor: H Francis Farhadi, MD, PhD

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Radiographic and Clinical Outcomes Following Unilateral or 
Bilateral Posterior Fixation in Minimally Invasive 
Transforaminal Lumbar Interbody Fusions 
 
 
 
 
 
 
 
 
 
 
Principal Investigator: 
H. Francis Farhadi, M.D., Ph.D. 
E-Mail: Francis.Farhadi@osumc.edu 
Phone: 614-366-4691 

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TABLE OF CONTENTS 
 
1. Introduction ..............................................................................................2 
1.1 Background ......................................................................................2 
1.2 Rationale ..........................................................................................2 
2. Objectives ................................................................................................3 
3. Investigational Plan ..................................................................................3 
4. Subject Selection and Withdrawal Criteria ..............................................3 
4.1 Anticipated Number of Available Subjects .....................................3 
4.2 Inclusion Criteria .............................................................................4 
4.3 Exclusion Criteria ............................................................................4 
4.4 Subject Completion and Withdrawal ...............................................4 
5. Study Design ............................................................................................5 
6. Study Assessments and Procedures .........................................................5 
6.1 Demographic and Baseline Assessments .........................................6 
6.2 Intra/perioperative Assessments ......................................................6 
6.3 Assessments during Follow-Up .......................................................6 
6.4 Study Calendar .................................................................................7 
7. Data Management and Statistical Consideration .....................................7 
      7.1 Data Management ............................................................................7 
      7.2 Outcome Measurement ....................................................................7 
      7.3 Sample Sizes/ Power Calculations………………………………...8 
      7.4 Statistical Analysis…….…………………………………………..8 
      7.5 Quality Assurance…………………………………………………8 
8. Study Conduct Considerations .................................................................9 
8.1 Regulatory and Ethical Considerations ............................................9 
8.2 Publication Policy ............................................................................9 
9. Adverse Events………………………………………………………… 9 
10. Serious Adverse Events………………………………………………10 
11. References ............................................................................................11 
 
Appendix 1: BSF Scale………………………………………………12 
Appendix 2: X-Ray Based Classification Scale……………………...13 

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Abbreviations 
TLIF: Transforaminal Lumbar Interbody Fusion 
MI-TLIF: Minimally Invasive Transforaminal Lumbar Interbody Fusion 
PLIF: Posterolateral Lumbar Interbody Fusion 
ALIF: Anterior Lumbar Interbody Fusion 
X/DLIF: Lateral Lumbar Interbody Fusion 
ODI V2: Oswestry Disability Index 
VAS: Visual Analog Scale 
CT: Computed tomography 
  
1. INTRODUCTION 
 
1.1 Background 
 
Since its original description in 1982, transforaminal lumbar interbody fusion 
(TLIF) has grown in popularity as a means for achieving arthrodesis in the lumbar 
spine. As with PLIF, ALIF or X/DLIF procedures, TLIF surgery achieves high 
fusion rates with minimal complications. Minimally invasive TLIF (MI-TLIF) in 
particular has emerged as a valid alternative to standard or mini-open TLIF with 
equivalent clinical and radiographic outcomes (Foley et al., 2003; Karikari and 
Isaacs, 2010, Mummaneni and Rodts, 2005). Surgeons usually combine open or 
MI-TLIF with pedicle screw instrumentation in an attempt to achieve 
circumferential (i.e., anterior and posterior) fusion. Although bilateral pedicle 
screw placement is often performed in MI-TLIF procedures, only a single small 
study to date has been reported evaluating comparative radiologic and clinical 
outcomes with unilateral (ipsilateral) pedicle screws (Xue and Cai, 2012). 
 
1.2 Rationale 
 
Several retrospective reports have confirmed that unilateral pedicle screw 
instrumentation is equally as effective as bilateral pedicle screw instrumentation 
when used solely without any other devices (Fernandez-Fairen et al., 2007; 
Kabins et al., 1992; Suk et al., 2000). Based on these results, a number of 
subsequent reports have evaluated unilateral pedicle screw instrumentation 
following MI-TLIF surgery and also reported good outcomes with no significant 
untoward effects (Beringer and Mobasser, 2006; Deutsch and Musacchio, 2006; 
Tuttle et al, 2006). 
 
Despite these reassuring findings, biomechanical studies using cadaveric 
specimens have shown that placing unilateral posterior instrumentation allows for 
significantly increased segmental range of motion, less stiffness, and produces 
off-axis movement (Harris et al., 2204; Schleicher et al., 2008; Slucky et al., 
2006). It remains unknown at this time whether this observed increased flexibility 
in cadaveric specimens has any clinical correlations in terms of either radiologic 
fusion rates or pain/functional outcome measures. A unilateral construct has the 
benefit of avoiding soft-tissue disruption on the contralateral side, decreasing 

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operative time, and is associated with lower implant costs.  This study will assess 
radiologic interbody fusion rates and clinical outcomes between the following 
arms following MI-TLIF surgery: stand-alone unilateral pedicle screw 
instrumentation, unilateral pedicle screw instrumentation with contralateral facet 
screw fixation, bilateral pedicle screw instrumentation.   
 
2. OBJECTIVES 
 
Primary Outcome: To compare bony fusion rates at one year between the three study 
arms, using the Brantigan, Steffee and Fraser scale.  Post-operative CT scans will be 
evaluated at 12 months for evidence of new solid osseous trabeculations bridging 
across the interspaces. 
 
Secondary Outcomes: To compare clinical outcomes between the three study arms 
utilizing the VAS, ODI V2, and SF-36V2TM serially. Additionally, immediate and 
delayed medical and surgical (including neurological) complications between the 
three study arms will be compared.  
 
Exploratory outcomes: Bony fusion rates at 12 and 24 months between the three 
study arms, using an X-ray based classification scale (see appendix 2).   
 
3. INVESTIGATIONAL PLAN 
 
Study Design 
 
All patients will undergo the following preoperative procedures: lumbar CT, lumbar 
MRI, lumbar x-rays, and medical evaluation including clinical history and physical 
examination. Patients will be randomized to MI-TLIF followed by either stand-alone 
unilateral pedicle screw instrumentation, unilateral pedicle screw instrumentation 
with contralateral facet screw fixation, or bilateral pedicle screw instrumentation 
using Redcap (Research Electronic Data Capture), a web-based randomization 
process. Post-operative follow-up will occur at 6 weeks and 3, 6, 12, and 24 months. 
CT scans will occur at the 12 month visit. 
 
4. SUBJECT SELECTION AND WITHDRAWAL CRITERIA 
 
4.1 Anticipated number of available subjects 
 
Based on our current case numbers, we estimate approximately 100-120 MI-TLIF 
surgeries over approximately 24 months, corresponding to approximately 35-40 
cases for each arm of the study. 
 
The target population includes patients with degenerative lumbar spine disease 
(e.g. spondylolisthesis, facet arthropathy with foraminal stenosis, recurrent disc 
herniation, far lateral disc herniation) who have failed non-operative management 
and require lumbar fusion surgery. 

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4.2 Inclusion criteria 
 
1. Age 18-80 years. 
2. Symptomatic single-level lumbar disease including lumbosacral junction. 
3.   Unilateral leg-dominant pain non-responsive to conservative management 
with concordant imaging findings. These include degenerative 
spondylolisthesis (grade 1 or 2), facet arthropathy +/- lateral disc herniation, 
recurrent disc herniation, or large central disc herniation OR back pain of 
confirmed discogenic origin (single level disease only). 
5.   Failed conservative management for a minimum of 3 months. 
6. Negative serum pregnancy test for women of childbearing potential.  
 
4.3 Exclusion criteria 
 
1. Severe bilateral leg symptoms. 
2. Prior instrumented arthrodesis at any lumbar level. 
3. History of osteoporosis. 
4.   Co-morbidity requiring medication that may interfere with bone or soft tissue 
healing (i.e., oral or parenteral glucocorticoids, immunosuppressive agents, 
methotrexate). 
5. Severe co-morbidities (e.g., heart, respiratory, or renal disease). 
6. Recent (<3 yrs) or co-incident spinal tumor or infection. 
7. Greater than single level symptomatic involvement. 
8. Associated thoracolumbar kyphotic or scoliotic deformity (> 10°). 
9. Morbid obesity (BMI > 40). 
10. History of metal sensitivity/foreign body sensitivity. 
11. Concurrent involvement in another investigational drug or device study that 
could confound study data. 
12. History of substance abuse (recreational drugs, prescription drugs or alcohol) 
that could interfere with protocol assessments and/or with the subject’s ability to 
complete the protocol required follow-up.  
13. Subjects who are pregnant or plan to become pregnant in the next 24 months. 
14. Prisoner. 
 
4.4 Subject completion and Withdrawal 
 
Every attempt will be made to maintain patient participation in the study.  
However, patients have the option of withdrawing consent at any time.  Patients 
who do not receive assigned treatment (those who refuse treatment after 
randomization or who decide to have other treatment after randomization) or 
those who have subsequent treatment, will still be followed and analyzed as 
randomized for the primary analysis.   Should a patient be lost to follow-up (after 
3 attempts), all data will be included during the period of participation. 
 
 
 

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5. STUDY DESIGN 
 
All patients will undergo unilateral approach MI-TLIF. All patients will be 
randomized 
into 
one 
of 
the 
following 
treatment 
groups 
using  
Redcap, a web-based randomization process: Group 1 will also have unilateral 
percutaneous pedicle screws placed. Group 2 will have unilateral (ipsilateral) 
percutaneous pedicle screws placed along with a contralateral facet screw through a 
minimally-invasive approach. Finally, Group 3 will have bilateral percutaneous 
pedicle screws placed.  This web-based randomization process will be managed by 
the study statisticians within the OSU Center for Biostatistics.  Randomization will be 
stratified by patient age (<60 vs. 60+) and will be generated with varying block sizes.     
 
Patients will be randomized to one of the following three groups and will be followed 
and asked to return at 6 weeks, 3 months, 6 months, 12 months and 24 months for 
assessment (See study calendar in 6.4).   
 
Group 
Interbody 
fusion 
Posterolateral fusion 
1 
MI-TLIF 
Unilateral pedicle screws 
2 
MI-TLIF 
Ipsilateral pedicle screws, contralateral 
facet screw 
3 
MI-TLIF 
Bilateral pedicle screws 
 
 
6. STUDY ASSESSMENTS AND PROCEDURES 
 
All patients randomized in the trial will be followed according to the schedule. Surgical 
outcome will be evaluated by pre-operative and post-operative VAS back and leg scales 
(Attachment 1), ODI V2 (Attachment 2) and SF-36V2TM (Attachment 3). If a patient is 
unable to follow-up in person at 6 months, he/she will be asked to fill out the forms via 
mail or over the telephone. Fusion rates will be evaluated based on CT scans at 12 
months follow-up after surgery using a CT interbody fusion rating scale. Each CT scan 
will be interpreted by the same independent radiologist. Interbody fusion rates will be 
graded by the method of Brantigan, Steffee and Fraser (BSF scale) (Santos et al., 2003; 
Appendix 1). Solid osseous trabeculations bridging across the interspaces will be 
considered as a fusion. All pseudoarthroses, heterotopic ossifications or 
migration/malposition of implants will also be evaluated separately.  Pre-operative and 
post-operative clinical outcomes will be evaluated at 3 months, 6 months, 12 months and 
24 months using VAS (back and leg), ODI V2 and SF-36V2TM index measures. 
 
 
 

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6.1. Demographic and baseline assessments 
 
A signed, written, informed consent form will be obtained before surgery. The 
following will be obtained at the first visit. 
• Demographic data: date of birth, race, gender, height, body weight 
• Medical and surgical history 
• Physical exam, vital signs, VAS back and leg, ODI V2, SF-36V2TM 
• Serum pregnancy test (only required for Women of childbearing potential) 
• Lumbar CT 
• Lumbar MRI 
• Lumbar x-rays 
 
6.2. Intra/perioperative Assessments 
 
The following assessments will be performed during the patient’s 
hospitalization: 
• Demographic data: height, body weight, Index Level(s) 
• Operative Time 
• Blood Loss 
• Length of stay 
• Infection rate 
• Use of opiates 
 
6.3. Assessments during follow-up 
 
The following assessments are to be performed as close as possible to the 
schedule: 
• Follow-up visits at 6 weeks (+/- 7 days), 3 months (+/- 30 days), 6 months(+/- 
30 days) , 12 months (+/- 30 days) and 24 months(+/- 60 days)  following 
surgery 
• Note: if 6 month follow-up visit is not completed in person, study teams will 
follow up via phone and mail 
• History and physical exam, including vital signs 
• VAS back and leg, ODI V 2, and SF-36V2TM (these questionnaires will be 
collected by mail or completed over the phone should patients not return to 
clinic at the designated follow-up time points) 
• X-rays of lumbar spine at 6weeks, 3months, 12 months, and 24 months 
• Lumbar CT scan at 12  months 
• Infection rate 
• Return to work 
 
 
 
 

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6.4 Study Calendar 
 
Pre-Study 
6 wk. F/U 
3 mo. F/U 
6 mo. F/U 
12 mo F/U 
24 mo F/U 
Test and Observations 
H&P 
Height 
Weight 
Vital Signs 
Serum Pregnancy Test 
Consent 
 
X 
X 
X 
X 
Xb 
X 
 
X 
X 
X 
X 
 
 
X 
X 
X 
X 
 
 
Xa 
Xa 
Xa 
Xa 
 
 
Xa 
Xa 
Xa 
Xa 
 
 
X 
X 
X 
X 
 
Procedures 
Lumbar MRI 
Lumbar CT 
Lumbar X-Rays 
 
X 
X 
X 
 
 
 
X 
 
 
 
X 
 
 
 
       
 
 
X 
X 
 
 
 
X 
Surgical Outcome 
Measures 
VAS back and leg 
ODI V 2 
SF-36V2TM 
 
 
X 
X 
X 
 
 
 
 
 
 
 
X 
X 
X 
 
 
X 
X 
X 
 
 
X 
X 
X 
 
 
X 
X 
X 
a. Optional 
b. Only Women of childbearing potential will undergo a serum pregnancy test 
prior to enrollment in the study to confirm that they are not pregnant. 
 
Findings from any additional imaging studies deemed necessary (as per standard of 
care) by the principal investigator will be recorded and reported with study results. 
 
 
7.  DATA MANAGEMENT AND STATISTICAL CONSIDERATIONS 
 
7.1 Data Management Clinical data management will be performed by the Integrated 
Healthcare Information System (IHIS) program. In all cases, subject names will not be 
collected or transmitted to the instrumentation company. Subject data necessary for 
analysis and reporting will be entered and transmitted into Redcap. 
 
7.2 Outcome Measures 
 
Primary Outcome: 
• Bony fusion at 12 months is being measured using the Brantigan, Steffee and 
Fraser scale which is a three-point scale, used to measure interbody fusion 
success.  Possible values range from 1-3 with higher scores indicating more 
fusion (a better outcome).  The scores will be dichotomized in the following 
categories: BFS-1 or 2 and BFS-3 where fusion is defined as BFS-3.   
 
Secondary Outcomes: 
• Visual analog scales will be used to assess neck, back, arm and leg pain.  Scores 
can range from 0 to 10 with higher scores indicating higher levels of pain.   
• The Oswestry Disability Index (version 2) will be used to assess how back pain 
affects patients’ ability to function in everyday life.  Scores can range from 0% to 
100% with higher scores indicating higher levels of disturbance in everyday life.   
• The Short Form (36) Health Survey (version 2) will be used to assess patients’ 
physical and mental health.  Scores range from 0 to 100 with higher scores 
indicating better physical and mental health.   
 

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Safety Outcomes: Comparison of immediate and delayed medical and surgical (including 
neurological) complications between the three study arms will be compared. 
Exploratory Outcomes:   Comparison of bony fusion rates at 12 and 24 months between 
the three study arms, using an X-ray based classification scale (see appendix).   
 
 
7.3 Sample size/Power Calculation 
 
Assuming an average proportion of 0.7 and estimated variance of proportions of 0.027, a  
sample size of 90 patients (30/group) gives the study over 80% power to detect 
significant differences for the overall test comparing proportions across groups (α=0.05).   
It is anticipated that the attrition rate will be approximately 10% therefore 102 patients 
will be accrued to the study (34/group). Every effort will be made to reduce attrition; 
consent documents will emphasize the importance of complete data and encourage 
patients to return for follow-up visits.  
 
 
7.4 Statistical Analyses 
 
Primary Analysis:  
To compare the overall effect of treatment, the proportion of patients with BFS-3 will be 
compared across groups using Cochran-Mantel-Haenszel statistic.  Given a statistically 
significant result for this overall test, all possible pair-wise comparisons between the 
study arms will be evaluated.  Details of multiple comparisons adjustments and modeling 
details will be provided in the Statistical Analysis Plan (SAP).   
We will employ generalized linear models (specifically Poisson regression) to estimate the 
relative risk of bony fusion between each study arm.  We prefer to estimate adjusted risks, rather 
than adjusted odds ratios and will employ a ‘Poisson working model’ within the survey 
framework.   
 
Primary Analysis will be performed according to the intention-to-treat principle. Using 
this approach, patients will be included in the analysis as they were randomly assigned to 
treatment, regardless of the procedure actually performed.  Methods to address missing 
data will be considered and detailed in the SAP. 
 
Secondary and Exploratory Analyses:   
Descriptive statistics, overall and by study arm for each secondary outcome.  Generalized 
linear models will be used to compare secondary outcomes between study arms.  Details 
will be provided in the SAP.      
 
 
7.5 Quality Assurance 
 
Our team has substantial experience in all elements necessary to successfully conduct 
high-quality RCTs: representative samples, adequate random assignment, outcome 
assessment blinding, high follow-up rate, and attention to preventing potential errors. 
 

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8. STUDY CONDUCT CONSIDERATIONS 
 
8.1. Regulatory and ethical considerations, including the informed consent 
process 
 
This study will be conducted in accordance with all applicable regulatory 
requirements. The study will also be conducted in accordance with “good clinical 
practice (GCP), all applicable subject privacy requirements, and the guiding 
principles of the Declaration of Helsinki. This process includes, but is not limited 
to, the following: 
• IRB review and favorable opinion/approval to conduct the study and of any 
subsequent relevant amended documents 
• Subject informed consent 
• Investigator reporting requirements 
 
Written informed consent will be obtained for each subject before he or she can 
participate in the study. 
 
 
       8.2.   Publication policy 
 
Publications and oral presentations of any results from the study shall be in 
accordance with accepted scientific practice, academic standards and customs 
and in accordance with the specific policy developed for the study. 
 
9. Adverse Events 
An adverse event (AE) is any symptom, sign, illness or experience that develops 
or worsens in severity during the course of the study. Intercurrent illnesses or 
injuries should be regarded as adverse events. Abnormal results of diagnostic 
procedures are considered to be adverse events if the abnormality:  
• Results in study withdrawal, or 
• Is associated with a serious adverse event, or 
• Leads to additional treatment or to further diagnostic tests, or 
• Is considered by the investigator to be of clinical significance.  
 
For this study, all AE’s rather reported, observed, or elicited by direct or indirect 
questioning will be recorded from the time of study enrollment through study 
completion. Minimum information required for each AE includes type of event, 
duration (start and end dates), severity, seriousness, causality to study 
intervention, action taken, and outcome.  
 
All unresolved AE’s will be followed, whenever possible, until the events are 
resolved or stabilized, the subject is lost to follow up, and/or it has been 
determined that the study treatment or participation in the study is not the cause. 
At the last scheduled assessment, the investigator should instruct each subject to 

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report any subsequent event(s) that the subject or the subject’s personal physician 
believes might reasonably be related to participation in this study.  
 
Information on AE’s should be recorded in the patient research record, and also in 
the appropriate AE page on the REDCap database.  
 
10. Serious Adverse Event Reporting 
A serious adverse event is an AE that is:  
• Fatal, or 
• Life-threatening, or 
• Requires or prolongs hospital stay, or  
• Results in persistent or significant disability or incapacity, or a congenital 
anomaly or birth defect, or  
• An important medical event. Important medical events are those that may 
not be immediately life threatening, but are clearly of major clinical 
significance. They may jeopardize the subject, and may require 
intervention to prevent one of the other serious outcomes noted above. For 
example, drug overdose or abuse, a seizure that did not result in inpatient 
hospitalization, or intensive treatment of bronchospasm in an emergency 
department would typically be considered serious.  
 
Information on SAE;s should be recorded in the patients research record, and also 
in the appropriate SAE page on the REDCap database.  
 

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11. REFERENCES 
 
Beringer WF, Mobasser JP: Unilateral pedicle screw instrumentation for minimally 
invasive transforaminal lumbar interbody fusion. Neurosurg Focus 20:E4, 2006 
 
Carter RE, Lipsitz SR, Tilley BC.  Quasi-likelihood estimation for relative risk regression 
models.  Biostatistics. 2005; 6: 39-44. Carter RE, Lipsitz SR, Tilley BC.  Quasi-
likelihood estimation for relative risk regression models.  Biostatistics. 2005; 6: 39-44. 
 
Deutsch H, Musacchio MJ, Jr.: Minimally invasive transforaminal lumbar interbody 
fusion with unilateral pedicle screw fixation. Neurosurg Focus 20:E10, 2006 
 
Fernandez-Fairen M, Sala P, Ramirez H, Gil J: A prospective randomized study of 
unilateral versus bilateral instrumented posterolateral lumbar fusion in degenerative 
spondylolisthesis. Spine (Phila Pa 1976) 32:395-401, 2007 
 
Foley KT, Holly LT, Schwender JD: Minimally invasive lumbar fusion. Spine (Phila Pa 
1976) 28:S26-35, 2003 
 
Greenland, S.  Model based estimation of relative risks and other epidemiologic measures 
in studies of common outcomes and in case control studies.  American Journal of 
Epidemiology.  2004; 160: 301-305. 
 
Harris BM, Hilibrand AS, Savas PE, Pellegrino A, Vaccaro AR, Siegler S, et al: 
Transforaminal lumbar interbody fusion: the effect of various instrumentation techniques 
on the flexibility of the lumbar spine. Spine (Phila Pa 1976) 29:E65-70, 2004 
 
Harris, Paul; Taylor, Robert; Thielke, Robert; Payne, Jonathan; Gonzalez,  Nathaniel; 
Conde, Jose;  Research electronic data capture (Redcap) - A metadata-driven 
methodology and workflow process for providing translational research informatics 
support, J Biomed Inform. 2009 Apr; 42(2):377-81 
 
Karikari IO, Isaacs RE. Minimally invasive transforaminal lumbar interbody fusion. A 
review of techniques and outcomes. Spine 35:S294-S301, 2010 
 
Kabins MB, Weinstein JN, Spratt KF, Found EM, Goel VK, Woody J, et al: Isolated L4-
L5 fusions using the variable screw placement system: unilateral versus bilateral. J 
Spinal Disord 5:39-49, 1992 
 
Lenke LG, Bridwell KH, Bullis D, Betz RR, Baldus C, Schoenecker PL: Results of in 
situ fusion for isthmic spondylolisthesis. J Spinal Disord 5:433-442, 1992 
 
Lumley T, Kronmal R, Ma S.  Relative Risk Regression in Medical Research:  Models, 
contrasts, estimators and algorithms.  UW Biostatistics working paper series.  2006, 
paper 293 
 

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Mummaneni PV, Rodts GE, Jr.: The mini-open transforaminal lumbar interbody fusion. 
Neurosurgery 57:256-261, 2005 
 
Santos ER, Goss DG, Morcom RK, Fraser RD: Radiologic assessment of interbody 
fusion using carbon fiber cages. Spine (Phila Pa 1976) 28:997-1001, 2003 
 
Schleicher P, Beth P, Ottenbacher A, Pflugmacher R, Scholz M, Schnake KJ, Haas NP, 
Kandziora F: Biomechanical evaluation of different asymmetrical posterior stabilization 
methods for minimally invasive transforaminal lumbar interbody fusion. J Neurosurg 
Spine 9:363-371, 2008 
 
Slucky AV, Brodke DS, Bachus KN, Droge JA, Braun JT: Less invasive posterior 
fixation method following transforaminal lumbar interbody fusion: a biomechanical 
analysis. Spine J 6:78-85, 2006 
 
Suk KS, Lee HM, Kim NH, Ha JW: Unilateral versus bilateral pedicle screw fixation in 
lumbar spinal fusion. Spine (Phila Pa 1976) 25:1843-1847, 2000 
 
Tuttle J, Shakir A, Choudhri HF. Paramedian approach for transforaminal lumbar 
interbody fusion with unilateral pedicle screw fixation. Neurosurg Focus 20:E5, 2006 
 
Xue H, Tu Y, Cai M: Comparison of unilateral versus bilateral instrumented 
transforaminal lumbar interbody fusion in degenerative lumbar diseases. Spine J, 2012 
 
 

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APPENDIX 1 
 
 
 
BSF scale  
 
Classification of interbody fusion success: Brantigan, Steffee, Fraser (BSF) 
 
BSF-1 
Radiographical pseudoarthrosis is indicated by collapse of the construct, loss 
of disc height, vertebral slip, broken screws, displacement of the carbon 
cage, or significant resorption of the bone graft, or lucency visible around the 
periphery of the cage or graft. 
BSF-2 
Radiographical locked pseudoarthrosis is indicated by lucency visible in the 
middle of the cages with solid bone growing into the cage from each 
vertebral endplate. 
BSF-3 
Radiographical fusion: bone bridges at least half of the fusion area with at 
least density the originally achieved at surgery. Radiographical fusion 
through one cage (half of the fusion area) is considered to be mechanically 
solid fusion even if there is lucency on the opposite side. 
 
 
1 Zou, G.  A modified Poisson regression approach to prospective studies with binary data.  
Am J Epidemiol  2004;159:702-706. 
 
 

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APPENDIX  2:  
 
X-Ray Based Classification Scale  
 
• Grade 1 - No graft incorporation 
• Grade 2 - Incomplete graft incorporation 
• Grade 3 - Graft Incorporation 
• Grade 4 - Solid fusion with graft incorporation 
 
Radiographic Success: Radiographic success (Grades 3 or 4) is defined by graft incorporation 
or solid fusion with graft incorporation