Endplate volumetric bone mineral density measured by quantitative computed tomography as a novel predictive measure of severe cage subsidence after standalone lateral lumbar fusion

Comparison of predictive value for cage subsidence between MRI-based endplate bone quality and vertebral bone quality scores following transforaminal lumbar interbody fusion: a retrospective propensity-matched study

BACKGROUND CONTEXT

Cage subsidence after lumbar fusion can lead to many adverse outcomes. Low bone mineral density (BMD) is a widely recognized risk factor for cage subsidence. Conventional methods can predict and evaluate BMD, but there are many shortcomings. Recently, MRI-based assessment of bone quality in specific parts of the vertebral body has been proposed, including scores for vertebral bone quality (VBQ) and endplate bone quality (EBQ). However, the predictive accuracy of the two scoring systems for cage subsidence after transforaminal lumbar interbody fusion (TLIF) remains unknown. Therefore, we investigated MRI-based VBQ and EBQ scores for assessing bone quality and compared their predictive value for cage subsidence after TLIF.

PURPOSE

To compare the predictive value between MRI-based VBQ and EBQ scores for cage subsidence after TLIF.

STUDY DESIGN/SETTING

A retrospective case-control study.

PATIENTS SAMPLE

Patients with degenerative lumbar diseases underwent single-level TLIF at our medical center between 2014 and 2020, all of whom had preoperative MRIs available.

OUTCOMES MEASURES

Cage subsidence, disc height, VBQ score, EBQ score, upper and lower vertebral body bone quality (UL-VBQ) score.

METHODS

Data were retrospectively examined for a consecutive sample of 346 patients who underwent TLIF at our medical center between 2014 and 2020. Patients who subsequently experienced cage subsidence or not were matched to each other based on propensity scoring, and the two matched groups (52 patients each) were compared using conditional logistic regression to investigate the association between the potential radiographic factors and cage subsidence. Scores for VBQ and EBQ were assessed for their ability to predict cage subsidence in the matched patients based on the area under the receiver operative characteristic curve (AUC).

RESULTS

Among matched patients, those who suffered cage subsidence had significantly higher VBQ score (3.7 vs 3.1, p<.001) and EBQ score (5.0 vs 4.3, p<.001), and regression linked greater risk of subsidence to higher VBQ score (OR 4.557, 95% CI 1.076-19.291, p=.039) and higher EBQ score (OR 5.396, 95% CI 1.158-25.146, p=.032). A cut-off VBQ score of 3.4 predicted the cage subsidence among matched patients with an AUC of 0.799, sensitivity of 84.6%, and specificity of 69.2%. A cut-off EBQ score of 4.7 predicted subsidence with an AUC of 0.829, sensitivity of 76.9%, and specificity of 82.7%.

CONCLUSION

Higher VBQ and EBQ scores are associated with a greater risk of cage subsidence following TLIF, and EBQ may perform better because of greater specificity.

A novel MRI-based Cervical-Endplate Bone Quality score independently predicts cage subsidence after Anterior Cervical Discectomy and Fusion

INTRODUCTION

Postoperative cage subsidence after Anterior Cervical Discectomy and Fusion (ACDF) often has adverse clinical consequences and is closely related to Bone Mineral Density (BMD). Previous studies have shown that cage subsidence can be better predicted by measuring site-specific bone density. MRI-based Endplate Bone Quality (EBQ) scoring effectively predicts cage subsidence after lumbar interbody fusion. However, there is still a lack of studies on the practical application of EBQ scoring in the cervical spine.

PURPOSE

To create a similar MRI-based scoring system for Cervical-EBQ (C-EBQ) and to assess the correlation of the C-EBQ with endplate Computed Tomography (CT)-Hounsfield Units (HU) and the ability of this scoring system to independently predict cage subsidence after ACDF, comparing the predictive ability of the C-EBQ with the Cervical-Vertebral Bone Quality (C-VBQ) score.

METHODS

A total of 161 patients who underwent single-level ACDF for degenerative cervical spondylosis at our institution from 2012 to 2022 were included. Demographics, procedure-related data, and radiological data were collected, and Pearson correlation test was used to determine the correlation between C-EBQ and endplate HU values. Cage subsidence was defined as fusion segment height loss of ≥ 3 mm. Receiver operating characteristic analysis and area-under-the-curve values were used to assess the predictive ability of C-EBQ and C-VBQ. A multivariate logistic regression model was developed to identify potential risk factors associated with subsidence.

RESULTS

Cage subsidence was present in 65 (40.4%) of 161 patients. The mean C-EBQ score was 1.81 ± 0.35 in the group without subsidence and 2.59 ± 0.58 in the group with subsidence (P < 0.001). Multivariate analysis showed that a higher C-EBQ score was significantly associated with subsidence (OR = 5.700; 95%CI = 3.435-8.193; P < 0.001), was the only independent predictor of cage subsidence after ACDF, had a predictive accuracy of 93.7%, which was superior to the C-VBQ score (89.2%), and was significantly negatively correlated with the endplate HU value (r = -0.58, P < 0.001).

CONCLUSIONS

Higher C-EBQ scores were significantly associated with postoperative cage subsidence after ACDF. There was a significant negative correlation between C-EBQ and endplate HU values. The C-EBQ score may be a promising tool for assessing preoperative bone quality and postoperative cage subsidence and is superior to the C-VBQ.

MRI-based endplate bone quality score predicts cage subsidence following oblique lumbar interbody fusion

BACKGROUND CONTEXT

Cage subsidence is a common complication after lumbar interbody fusion surgery, with low bone mineral density (BMD) being a significant risk factor. ໿Endplate bone quality (EBQ) obtained from clinical MRI scans has been deemed reliable in determining regional BMD. However, the association between EBQ score and cage subsidence following oblique lumbar interbody fusion (OLIF) has not been clearly established.

PURPOSE

This study aims to assess the relationship between EBQ score and cage subsidence in patients who underwent single-level OLIF.

STUDY DESIGN/SETTING

A retrospective study.

PATIENT SAMPLE

The study included adults with degenerative spinal conditions who underwent single-level OLIF at our institution.

OUTCOME MEASURES

Cage subsidence, disc height, EBQ score, fusion rate.

METHODS

This retrospective study analyzed data from patients who underwent single-level OLIF surgery at our institution between October 2017 and August 2022. Postoperative CT scans were used to measure cage subsidence, while the EBQ score was calculated using preoperative non-contrast T1-weighted MRI. To determine the predictive ability of the EBQ score, receiver operating characteristic (ROC) curve analysis was conducted. Additionally, univariable and multivariable logistic regression analyses were performed.

RESULTS

In this study, a total of 88 patients were included and followed up for an average of 15.8 months. It was observed that 32.9% (n=29/88) of the patients experienced cage subsidence. The post-surgery disc height was significantly higher in patients who experienced subsidence compared to those who did not. The mean EBQ scores for patients with non-subsidence and subsidence were 2.31±0.6 and 3.48±1.2, respectively, and this difference was statistically significant. The ROC curve analysis showed that the AUC for the EBQ score was 0.811 (95% CI: 0.717-0.905). The most suitable threshold for the EBQ score was determined to be 2.318 (sensitivity: 93.1%, specificity: 55.9%). Additionally, the multivariate logistic regression analysis revealed a significant association between a higher EBQ score and an increased risk of subsidence (odds ratio [OR]=6.204, 95% CI=2.520-15.272, p<.001).

CONCLUSIONS

Our findings indicate that higher preoperative EBQ scores are significantly linked to cage subsidence following single-level OLIF. Preoperative measurement of MRI can serve as a valuable tool in predicting cage subsidence.

Systematic Review and Meta-Analysis of the Effect of Osteoporosis on Reoperation Rates and Complications after Surgical Management of Lumbar Degenerative Disease

BACKGROUND

There is considerable heterogeneity in findings and a lack of consensus regarding the interplay between osteoporosis and outcomes in patients with lumbar degenerative spine disease. Therefore, the purpose of this systematic review and meta-analysis was to gather and analyze existing data on the effect of osteoporosis on radiographic, surgical, and clinical outcomes following surgery for lumbar degenerative spinal disease.

METHODS

A systematic review was performed to determine the effect of osteoporosis on the incidence of adverse outcomes after surgical intervention for lumbar degenerative spinal diseases. The approach focused on the radiographic outcomes, reoperation rates, and other medical and surgical complications. Subsequently, a meta-analysis was performed on the eligible studies.

RESULTS

The results of the meta-analysis suggested that osteoporotic patients experienced increased rates of adjacent segment disease (ASD; p=0.015) and cage subsidence (p=0.001) while demonstrating lower reoperation rates than non-osteoporotic patients (7.4% vs. 13.1%; p=0.038). The systematic review also indicated that the length of stay, overall costs, rates of screw loosening, and rates of wound and other medical complications may increase in patients with a lower bone mineral density. Fusion rates, as well as patient-reported and clinical outcomes, did not differ significantly between osteoporotic and non-osteoporotic patients.

CONCLUSIONS

Osteoporosis was associated with an increased risk of ASD, cage migration, and possibly postoperative screw loosening, as well as longer hospital stays, incurring higher costs and an increased likelihood of postoperative complications. However, a link was not established between osteoporosis and poor clinical outcomes.

Preoperative MRI-based endplate quality: a novel tool for predicting cage subsidence after anterior cervical spine surgery

PURPOSE

The objective of this study was to examine the predictive value of a newly developed MRI-based Endplate Bone Quality (EBQ) in relation to the development of cage subsidence following anterior cervical discectomy and fusion (ACDF).

METHODS

Patients undergoing ACDF for degenerative cervical diseases between January 2017 and June 2022 were included. Correlation between EBQ scores and segmental height loss was analyzed using Pearson's correlation. ROC analyses were employed to ascertain the EBQ cut-off values that predict the occurrence of cage subsidence. Multivariate logistic regression analyses were conducted to identify the risk factors associated with postoperative cage subsidence.

RESULTS

23 individuals (14.56%) exhibited the cage subsidence after ACDF. In the nonsubsidence group, the average EBQ and lowest T-score were determined to be 4.13 ± 1.14 and - 0.84 ± 1.38 g/cm2 respectively. In contrast, the subsidence group exhibited a mean EBQ and lowest T-score of 5.38 ± 0.47 (p < 0.001) and - 1.62 ± 1.34 g/cm2 (p = 0.014), respectively. There was a significant positive correlation (r = 0.798**) between EBQ and the segmental height loss. The EBQ threshold of 4.70 yielded optimal sensitivity (73.9%) and specificity (93.3%) with AUC of 0.806. Furthermore, the lowest T-score (p = 0.045, OR 0.667) and an elevated cervical EBQ score (p < 0.001, OR 8.385) were identified as significant risk factors for cage subsidence after ACDF.

CONCLUSIONS

The EBQ method presents itself as a promising and efficient tool for surgeons to assess patients at risk of cage subsidence and osteoporosis prior to cervical spine surgery, utilizing readily accessible patient data.

Comparison of Lumbar Interbody Fusion with 3D-Printed Porous Titanium Cage Versus Polyetheretherketone Cage in Treating Lumbar Degenerative Disease: A Systematic Review and Meta-Analysis

OBJECTIVE

To compare the safety and radiological effectiveness of lumbar interbody fusion with a 3D-printed porous titanium (3D-PPT) cage versus a polyetheretherketone (PEEK) cage for the treatment of lumbar degenerative disease.

METHODS

This study was registered at PROSPERO (CRD42023461511). We systematically searched the PubMed, Embase, and Web of Science databases for related studies from inception to September 3, 2023. Review Manager 5.3 was used to conduct this meta-analysis. The reoperation rate, complication rate, fusion rate, and subsidence rate were assessed using relative risk and 95% confidence intervals.

RESULTS

Ten articles reporting 9 studies comparing lumbar interbody fusion with 3D-PPT cages versus PEEK cages for the treatment of lumbar degenerative disease were included. The subsidence rate at the 1-year follow-up in the 3D-PPT cage was significantly lower than that in the PEEK cage. The fusion rate in the 3D-PPT cage was significantly higher than that in the PEEK cage at the 6-month follow-up. No significant difference was identified between the 2 groups at the 12-month follow-up. No significant difference was identified between the 2 groups in terms of the complication rate and reoperation rate. There was a trend toward a lower complication rate and reoperation rate with the 3D-PPT cage.

CONCLUSIONS

Compared with the PEEK cage, the 3D-PPT cage may be a safer implant. The 3D-PPT cage was associated with a higher fusion rate and lower subsidence rate. The 3D-PPT cage may accelerate the intervertebral fusion process, improve the quality of fusion and prevent the occurrence of subsidence.

Comparison of Intraoperative Endplate Injury between Mini-Open Lateral Lumbar Interbody Fusion (LLIF) and Transforaminal Lumbar Interbody Fusion (TLIF) and Analysis of Risk Factors: A Retrospective Study

OBJECTIVE

The study aimed to compare the incidence of intraoperative endplate injury in patients who underwent Transforaminal interbody fusion (TLIF) and mini-open lumbar interbody fusion (LLIF) surgery. The independent risk factors related to endplate injury in LLIF procedure were analyzed.

METHODS

A total of 199 patients who underwent LLIF (n = 106) or TLIF (n = 93) surgery from June 2019 to September 2021 were reviewed. The endplate injury was assessed by postoperative sagittal CT scan. A binary logistic analysis model were used to identify independent risk factors related to LLIF endplate injury based on univariate analysis.

RESULTS

There was an obvious difference in the occurrence of intraoperative endplate injury between LLIF (42/106, 39.6%) and TLIF group (26/93, 28%), although it did not reach the significant level. L1 CT value (OR = 0.985, 95% CI = 0.972-0.998), cage position (OR = 3.881, 95% CI = 1.398-10.771) and height variance (OR = 1.263, 95% CI = 1.013-1.575) were independent risk factors for endplate injury in LLIF procedure. According to the cage settlement patterns, there 5 types of A to E. The severity of the facet joint degeneration was positively related to the occurrence of endplate injury.

CONCLUSIONS

The incidence of intraoperative endplate injury is higher in LLIF than in TLIF procedures. Low bone quantity, cage posterior position and larger height variance are risk factors to induce endplate injury in LLIF surgery. The facet joint degeneration may be related to severe endplate injuries and even fractures.

Cortical Endplate Bone Density Measured by Novel Phantomless Quantitative Computed Tomography May Predict Cage Subsidence more Conveniently and Accurately

OBJECTIVE

Previous studies have shown that bone mineral density (BMD) is a predictor of cage subsidence. Phantom-less quantitative computed tomography (PL-QCT) can measure volumetric bone mineral density (vBMD) of lumbar trabecular and cortical bone. The study of endplate vBMD (EP-vBMD) is important in predicting cage settlement after extreme lateral interbody fusion (XLIF). This study aimed to determine the risk factors for postoperative cage subsidence after XLIF, particularly focusing on the relationship between vBMD measured by automatic PL-QCT and cage subsidence.

METHODS

Patients who underwent XLIF surgery from January 2018 to October 2020 with a minimum of 6 months of follow-up were retrospectively included. Cage subsidence was defined as >2 mm cage sinking on the adjacent endplate in follow-up imaging evaluation. Outcome measures were localized vBMDs included EP-vBMDs with different region of interest (ROI) heights measured by PL-QCT based on a customized muscle-fat algorithm. Shapiro-Wilk test, one-way ANOVA, Mann-Whitney test, Fisher exact test, univariable and multivariable logistic regression and receiver operating characteristic (ROC) curve analysis were executed in this study.

RESULTS

One hundred and thirteen levels of 78 patients were included in the analysis. The mean age was 65 ± 7.9 years for 11 males and 67 females. Cage subsidence occurred on 45 (39.8%) surgical levels. There was no significant difference in demographics, fused levels, or preoperative radiographic parameters. 1.25-mm EP-vBMD (0.991 [0.985,0.997], p = 0.004) and P-TB-vBMD (cage-positioned trabecular volumetric bone mineral density) (0.988 [0.977-0.999], p = 0.026) were cage-subsidence relevant according to univariate analysis. Low 1.25-mm EP-vBMD (0.992 [0.985, 0.999], p = 0.029) was an independent risk factor according to multifactorial analysis.

CONCLUSION

Preoperative low EP-vBMD was an independent risk factor for postoperative cage subsidence after XLIF. EP-vBMD measured by most cortex-occupied ROI may be the optimal vBMD parameter for cage subsidence prediction.

MRI-based Endplate Bone Quality score independently predicts cage subsidence following transforaminal lumbar interbody fusion

BACKGROUND CONTEXT

Cage subsidence following transforaminal lumbar interbody fusion (TLIF) has closely correlated with poor vertebral bone quality. Studies have shown better predictive value for cage subsidence by measuring bone density at specific site. However, few studies have been performed to examine the relationship between site-specific MRI bone assessment and cage subsidence in patients who have undergone lumbar interbody fusion. The association between MRI-based assessment of endplate bone quality and cage subsidence after TLIF remains unclear.

PURPOSE

To study the predictive value of MRI-based endplate bone quality (EBQ) score for cage subsidence following TLIF, using QCT bone densitometry as a reference standard.

STUDY DESIGN/SETTING

A retrospective study.

PATIENT SAMPLE

A total of 280 adult patients undergoing single-segment TLIF for degenerative lumbar spine disease from 2010 to 2020 at our institution who had preoperative T1-weighted MRIs.

OUTCOME MEASURES

Cage subsidence, disc height, endplate bone quality (EBQ) score, bone mineral density, fusion rate.

METHODS

The retrospective study reviewed patients who underwent TLIF at one institution between March 2010 and October 2020. Cage subsidence was measured with postoperative lumbar X-rays based on the cage protrusion through into the superior or inferior end plate or both by more than 2 mm. The EBQ score was measured from preoperative T1-weighted MRI in accordance with the previously reported method.

RESULTS

Cage subsidence was observed in 42 of the 280 patients. Bone densitometry with quantitative computed tomography was visibly reduced in the subsidence group. The mean EBQ scores of the lumbar endplate bone was 4.3±0.9 in nonsubsidence and 5.0±0.6 in subsidence. On multivariate logistic regression, the difference between the two groups was remarkable. Risk of cage subsidence increases significantly with higher EBQ scores (odds ratio [OR]=2.063, 95% confidence interval [CI] 1.365-3.120, p=.001) and was an independent factor in predicting subsidence after TLIF. On receiver operating characteristic curve, the AUC for the EBQ score was 0.820 (95% confidence interval [CI]: 0.755-0.844) and the most suitable threshold for the EBQ score was 4.730 (sensitivity: 76.2%, specificity: 83.2%).

CONCLUSIONS

Higher EBQ scores measured on preoperative MRI correlated significantly with cage subsidence following TLIF. Performing EBQ assessment prior to TLIF may be a valid method of predicting the risk of postoperative subsidence.

Advances in Hounsfield units value for predicting cage subsidence on spinal interbody fusion surgery

PURPOSE

A growing number of studies have demonstrated that Hounsfield units (HU) value can effectively assess bone quality and predict cage subsidence (CS) after spinal surgery. The purpose of this review is to provide an overview of the utility of the HU value for predicting CS after spinal surgery and to raise some of the unresolved questions in this field.

METHODS

We searched on PubMed, EMBASE, MEDLINE, and Cochrane Library for studies correlating HU value to CS.

RESULTS

Thirty-seven studies were included in this review. We found that HU value can predicted the risk of CS effectively after spinal surgery. Moreover, the HU value of the cancellous vertebral body and the cortical endplate were used for predicting CS, in comparison, the measurement method of HU value in the cancellous vertebral body was more standardized, but which region is more important to CS remains unknown. Different cutoff thresholds of HU value have been established in different surgical procedures for predicting CS. The HU value may be superior to dual-energy X-ray absorptiometry (DEXA) for CS prediction; however, the usage standard of HU value has not been well established.

CONCLUSIONS

The HU value shows great potential for predicting CS and constitutes an advantage over DEXA. However, general consensuses about how CS is defined and HU is measured, which part of HU value is more important, and the appropriate cutoff threshold of the HU value for osteoporosis and CS still require exploration.

Biomechanical effect of endplate defects on the intermediate vertebral bone in consecutive two-level anterior cervical discectomy and fusion: a finite element analysis

BACKGROUND

Intermediate vertebral collapse is a newly discovered complication of consecutive two-level anterior cervical discectomy and fusion (ACDF). There have been no analytical studies related to the effects of endplate defects on the biomechanics of the intermediate vertebral bone after ACDF. This study aimed to compare the effects of endplate defects on the intermediate vertebral bone biomechanics in the zero-profile (ZP) and cage-and-plate (CP) methods of consecutive 2-level ACDF and to determine whether collapse of the intermediate vertebra is more likely to occur using ZP.

METHODS

A three-dimensional finite element (FE) model of the intact cervical spine (C2-T1) was constructed and validated. The intact FE model was then modified to build ACDF models and imitate the situation of endplate injury, establishing two groups of models (ZP, IM-ZP and CP, IM-ZP). We simulated cervical motion, such as flexion, extension, lateral bending and axial rotation, and compared the range of motion (ROM), upper and lower endplate stress, fusion fixation device stress, C5 vertebral body stress, intervertebral disc internal pressure (intradiscal pressure, or IDP) and the ROM of adjacent segments in the models.

RESULTS

There was no significant difference between the IM-CP model and the CP model in the ROM of the surgical segment, upper and lower endplate stress, fusion fixation device stress, C5 vertebral body stress, IDP, or ROM of the adjacent segments. Compared with the CP model, the endplate stress of the ZP model is significantly higher in the flexion, extension, lateral bending and axial rotation conditions. Compared with the ZP model, endplate stress, screw stress, C5 vertebral stress and IDP in IM-ZP were significantly increased under flexion, extension, lateral bending and axial rotation conditions.

CONCLUSIONS

Compared to consecutive 2-level ACDF using CP, collapse of the intermediate vertebra is more likely to occur using ZP due to its mechanical characteristics. Intraoperative endplate defects of the anterior lower margin of the middle vertebra are a risk factor leading to collapse of the middle vertebra after consecutive 2-level ACDF using ZP.

Resisting subsidence with a truss Implant: Application of the "Snowshoe" principle for interbody fusion devices

The primary objective was to compare the subsidence resistance properties of a novel 3D-printed spinal interbody titanium implant versus a predicate polymeric annular cage. We evaluated a 3D-printed spinal interbody fusion device that employs truss-based bio-architectural features to apply the snowshoe principle of line length contact to provide efficient load distribution across the implant/endplate interface as means of resisting implant subsidence. Devices were tested mechanically using synthetic bone blocks of differing densities (osteoporotic to normal) to determine the corresponding resistance to subsidence under compressive load. Statistical analyses were performed to compare the subsidence loads and evaluate the effect of cage length on subsidence resistance. The truss implant demonstrated a marked rectilinear increase in resistance to subsidence associated with increase in the line length contact interface that corresponds with implant length irrespective of subsidence rate or bone density. In blocks simulating osteoporotic bone, comparing the shortest with the longest length truss cage (40 vs. 60 mm), the average compressive load necessary to induce subsidence of the implant increased by 46.4% (383.2 to 561.0 N) and 49.3% (567.4 to 847.2 N) for 1 and 2 mm of subsidence, respectively. In contrast, for annular cages, there was only a modest increase in compressive load when comparing the shortest with the longest length cage at a 1 mm subsidence rate. The Snowshoe truss cages demonstrated substantially more resistance to subsidence than corresponding annular cages. Clinical studies are required to support the biomechanical findings in this work.

Increased risks of vertebral fracture and reoperation in primary spinal fusion patients who test positive for osteoporosis by Biomechanical Computed Tomography analysis

BACKGROUND CONTEXT

While osteoporosis is a risk factor for adverse outcomes in spinal fusion patients, diagnosing osteoporosis reliably in this population has been challenging due to degenerative changes and spinal deformities. Addressing that challenge, biomechanical computed tomography analysis (BCT) is a CT-based diagnostic test for osteoporosis that measures both bone mineral density and bone strength (using finite element analysis) at the spine; CT scans taken for spinal evaluation or previous care can be repurposed for the analysis.

PURPOSE

Assess the effectiveness of BCT for preoperatively identifying spinal fusion patients with osteoporosis who are at high risk of reoperation or vertebral fracture.

STUDY DESIGN

Observational cohort study in a multi-center integrated managed care system using existing data from patient medical records and imaging archives.

PATIENT SAMPLE

We studied a randomly sampled subset of all adult patients who had any type of primary thoracic (T4 or below) or lumbar fusion between 2005 and 2018. For inclusion, patients with accessible study data needed a preop CT scan without intravenous contrast that contained images (before any instrumentation) of the upper instrumented vertebral level.

OUTCOME MEASURES

Reoperation for any reason (primary outcome) or a newly documented vertebral fracture (secondary outcome) occurring up to 5 years after the primary surgery.

METHODS

All study data were extracted using available coded information and CT scans from the medical records. BCT was performed at a centralized lab blinded to the clinical outcomes; patients could test positive for osteoporosis based on either low values of bone strength (vertebral strength ≤ 4,500 N women or 6,500 N men) and/or bone mineral density (vertebral trabecular bone mineral density ≤ 80 mg/cm³ both sexes). Cox proportional hazard ratios were adjusted by age, presence of obesity, and whether the fusion was long (four or more levels fused) or short (3 or fewer levels fused); Kaplan-Meier survival was compared by the log rank test. This project was funded by NIH (R44AR064613) and all physician co-authors and author 1 received salary support from their respective departments. Author 6 is employed by, and author 1 has equity in and consults for, the company that provides the BCT test; the other authors declare no conflicts of interest.

RESULTS

For the 469 patients analyzed (298 women, 171 men), median follow-up time was 44.4 months, 11.1% had a reoperation (median time 14.5 months), and 7.7% had a vertebral fracture (median time 2.0 months). Overall, 25.8% of patients tested positive for osteoporosis and no patients under age 50 tested positive. Compared to patients without osteoporosis, those testing positive were at almost five-fold higher risk for vertebral fracture (adjusted hazard ratio 4.7, 95% confidence interval = 2.2-9.7; p<.0001 Kaplan-Meier survival). Of those positive-testing patients, those who tested positive concurrently for low values of both bone strength and bone mineral density (12.6% of patients overall) were at almost four-fold higher risk for reoperation (3.7, 1.9-7.2; Kaplan-Meier survival p<.0001); the remaining positive-testing patients (those who tested positive for low values of either bone strength or bone mineral density but not both) were not at significantly higher risk for reoperation (1.6, 0.7-3.7) but were for vertebral fracture (4.3, 1.9-10.2). For both clinical outcomes, risk remained high for patients who underwent short or long fusion.

CONCLUSION

In a real-world clinical setting, BCT was effective in identifying primary spinal fusion patients aged 50 or older with osteoporosis who were at elevated risks of reoperation and vertebral fracture.

The predictive value of Hounsfield units for titanium mesh cage subsidence after anterior cervical corpectomy and fusion

Objective

To investigate whether bone mineral density (BMD) measured in Hounsfield units (HUs) correlates with titanium mesh cage (TMC) subsidence after anterior cervical corpectomy and fusion (ACCF).

Methods

A total of 64 patients who underwent one or two levels of ACCF with TMC with a mean follow-up of 19.34 ± 7.86 months were analysed. HU values were measured three times in 3 different planes in the upper and lower vertebrae according to published methods. Subsidence was defined as segmental height loss of more than 3 mm. Pearson correlation analysis was performed. Receiver operating characteristic (ROC) curve analysis was used to obtain optimal thresholds. A multivariate logistic regression analysis was also conducted.

Results

Twenty-two patients (34.38%) had evidence of TMC subsidence on follow-up x-ray. The mean HU values in the subsidence group (317.34 ± 32.32, n = 22) were significantly lower than those in the nonsubsidence group (363.07 ± 25.23 n = 42, p < 0.001, t test). At last follow-up, mean disc height loss was 4.80 ± 1.16 mm in the subsidence group and 1.85 ± 1.14 mm in the nonsubsidence group (p < 0.001). There was a negative correlation between HU values and disc height loss (Pearson's coefficient -0.494, p < 0.001). HU values decreased gradually from the C3 vertebra to the C7 vertebra, and the HU values of the C5, C6, and C7 vertebrae in the nonsubsidence group were significantly higher than those in the subsidence group (p < 0.05). Furthermore, there were significant differences between the groups in the segmental angle at the last follow-up and the mean changes in segmental angle (p < 0.05). The area under the ROC curve was 0.859, and the most appropriate threshold of the HU value was 330.5 (sensitivity 100%, specificity 72.7%). The multivariate logistic regression analysis showed that older age (p = 0.033, OR = 0.879), lower LIV HU value (p < 0.001, OR = 1.053) and a greater segmental angle change (p = 0.002, OR 6.442) were significantly associated with a higher incidence of TMC subsidence after ACCF.

Conclusion

There are strong correlations between a lower HU value and TMC subsidence after ACCF. More accurate assessment of bone quality may be obtained if HU measurement can be used as a routine preoperative screening method together with DXA. For patients with HU values <330.5, a more comprehensive and cautious preoperative plan should be implemented to reduce TMC subsidence.

The predictive value of psoas and paraspinal muscle parameters measured on MRI for severe cage subsidence after standalone lateral lumbar interbody fusion

BACKGROUND CONTEXT

The effect of psoas and paraspinal muscle parameters on cage subsidence after minimally invasive techniques, such as standalone lateral lumbar interbody fusion (SA-LLIF), is unknown.

PURPOSE

This study aimed to determine whether the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae), and psoas FCSA normalized to the vertebral body area (FCSA/VBA) differ among levels with severe cage subsidence after SA-LLIF when compared to levels without severe cage subsidence.

STUDY DESIGN

Retrospective single center cohort study.

PATIENT SAMPLE

Patients who underwent SA-LLIF between 2008 and 2020 for degenerative conditions using exclusively polyetheretherketone (PEEK) cages, had a lumbar magnetic resonance imaging (MRI) scan within 12 months, a lumbar computed tomography (CT) scan within 6 months prior to surgery, and a postoperative clinical and radiographic follow-up at a minimum of 6 months were included.

OUTCOME MEASURES

Severe cage subsidence.

METHODS

MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA and FCSA/VBA at the L3-L5 pedicles. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8.0), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat and muscle. Mean volumetric bone mineral density (vBMD) at L1/2 was measured by quantitative CT. The primary endpoint was severe cage subsidence per level according to the classification by Marchi et al. Multivariable logistic regression analysis was performed using generalized linear mixed models. All analyses were stratified by biological sex.

RESULTS

95 patients (45.3% female) with a total of 188 operated levels were included in the analysis. The patient population was 92.6% Caucasian with a median age at surgery of 65 years. Overall subsidence (Grades 0-III) was 49.5% (53/107 levels) in men versus 58.0% (47/81 levels) in women (p=.302), and severe subsidence (Grades II-III) was 22.4% (24/107 levels) in men versus 25.9% (21/81 levels) in women (p=.608). In men, median psoas FCSA and psoas FCSA/VBA at L3 and L4 were significantly greater in the severe subsidence group when compared to the non-severe subsidence group. No such difference was observed in women. Paraspinal muscle parameters did not differ significantly between non-severe and severe subsidence groups for both sexes. In the multivariable logistic regression analysis with adjustments for vBMD and cage length, psoas FCSA at L3 (OR 1.002; p=.020) and psoas FCSA/VBA at L3 (OR 8.655; p=.029) and L4 (OR 4.273; p=.043) were found to be independent risk factors for severe cage subsidence in men.

CONCLUSIONS

Our study demonstrated that greater psoas FCSA at L3 and psoas FCSA/VBA at L3 and L4 were independent risk factors for severe cage subsidence in men after SA-LLIF with PEEK cages. The higher compressive forces the psoas exerts on lumbar segments as a potential stabilizer might explain these findings. Additional pedicle screw fixation might be warranted in these patients to avoid severe cage subsidence.

Endplate volumetric bone mineral density biomechanically matched interbody cage

Disc degenerative problems affect the aging population, globally, and interbody fusion is a crucial surgical treatment. The interbody cage is the critical implant in interbody fusion surgery; however, its subsidence risk becomes a remarkable clinical complication. Cage subsidence is caused due to a mismatch of material properties between the bone and implant, specifically, the higher elastic modulus of the cage relative to that of the spinal segments, inducing subsidence. Our recent observation has demonstrated that endplate volumetric bone mineral density (EP-vBMD) measured through the greatest cortex-occupied 1.25-mm height region of interest, using automatic phantomless quantitative computed tomography scanning, could be an independent cage subsidence predictor and a tool for cage selection instruction. Porous design on the metallic cage is a trend in interbody fusion devices as it provides a solution to the subsidence problem. Moreover, the superior osseointegration effect of the metallic cage, like the titanium alloy cage, is retained. Patient-specific customization of porous metallic cages based on the greatest subsidence-related EP-vBMD may be a good modification for the cage design as it can achieve biomechanical matching with the contacting bone tissue. We proposed a novel perspective on porous metallic cages by customizing the elastic modulus of porous metallic cages by modifying its porosity according to endplate elastic modulus calculated from EP-vBMD. A three-grade porosity customization strategy was introduced, and direct porosity-modulus customization was also available depending on the patient's or doctor's discretion.

The predictive value of a novel site-specific MRI-based bone quality assessment, endplate bone quality (EBQ), for severe cage subsidence among patients undergoing standalone lateral lumbar interbody fusion

BACKGROUND CONTEXT

Studies have shown that site-specific bone density measurements had more predictive value for complications than standard whole-region measurements. Recently, MRI-based assessments of vertebral bone quality (VBQ) were introduced. However, there have been few studies that investigate the association between site-specific MRI bone assessment and osteoporosis-related complications in patients undergoing lumbar interbody fusion. In this work, we created a novel site-specific MRI-based assessment of the endplate bone quality (EBQ) and assessed its predictive value for severe cage subsidence following standalone lateral lumbar interbody fusion (SA-LLIF).

PURPOSE

To investigate the predictive value of a novel MRI-based bone assessment for severe cage subsidence after SA-LLIF.

STUDY DESIGN/SETTING

Retrospective cohort study.

PATIENT SAMPLE

Patients who underwent SA-LLIF from 2008 to 2019 at a single, academic institution with available preoperative lumbar CT and T1-weighted MRIs.

OUTCOME MEASURES

Association between EBQ and severe subsidence after SA-LLIF.

METHODS

We retrospectively reviewed the records of SA-LLIF patients treated between 2008 and 2019. EBQ was measured using preoperative non-contrast T1-weighted MRIs of the lumbar spine. EBQ was defined as the average value of signal intensity of both endplates divided by that of the cerebrospinal fluid space at the level of L3. Bivariate and multivariable analyses with generalized linear mixed models were performed and set binary severe subsidence as the outcome.

RESULTS

Two hundred five levels in 89 patients were included. Fifty levels (24.4%) demonstrated severe subsidence. Bone mineral density measured by quantitative computed tomography was significantly lower in the subsidence group. Both VBQ and EBQ were significantly higher in the subsidence group. The EBQ plus Modic change (MC) model demonstrated that the effect of EBQ was independent of MC. In multivariate analyses adjusted with QCT-vBMD, EBQ showed a significant association with cage subsidence whereas VBQ only showed a marginal trend. The EBQ-based prediction model for severe subsidence showed better goodness of fit compared to the VBQ-based model.

CONCLUSIONS

High EBQ was an independent factor for severe cage subsidence after SA-LLIF and the EBQ-based model showed better goodness of fit compared to VBQ- or MC-based models. EBQ assessment before SA-LLIF may provide insight into a patient's risk for severe subsidence.

Low Hounsfield units on computed tomography are associated with cage subsidence following oblique lumbar interbody fusion (OLIF)

BACKGROUND CONTEXT

Cage subsidence is one of the most common complications following lumbar interbody fusion surgery. Low bone mineral density (BMD) is an important risk factor that contributes to cage subsidence. Hounsfield units (HU) obtained from clinical computed tomography (CT) scans provided a reliable method for determining regional BMD. The association between HU and cage subsidence following oblique lumbar interbody fusion (OLIF) remains unclear.

PURPOSE

The objective of this study is to evaluate the association between vertebral HU value and cage subsidence following OLIF.

STUDY DESIGN/SETTING

A retrospective study.

PATIENT SAMPLE

Adults with degenerative spinal conditions underwent single-level OLIF at our institution from October 2017 and August 2020 OUTCOME MEASURES: Cage subsidence, disc height, vertebral body global HU value, upper and lower instrumented vertebrae HU value, endplate HU value, fusion rate.

METHODS

This retrospective study was conducted on patients who underwent single-level OLIF at one institution between October 2017 and August 2020. Cage subsidence was measured using the CT scan postoperatively based on the cage protrusion through the vertebral endplates. The HU values were measured from preoperative CT according to previously reported methods.

RESULTS

A total of 70 patients with a mean follow-up of 15.4 months were included in the analysis. The subsidence rate was 25.7% (n=18/70). The average cage subsidence was 2.2 mm, with a range of 0-7.7 mm. No significant difference was found in age, sex, or body mass index (BMI) between the two groups. The mean global HU value of the lumbar vertebral body (L1-5) was 142.7±30.1 in nonsubsidence and 103.7±11.5 in subsidence (p=.004). The upper instrumented vertebrae (UIV) HU value was 141.4±29.7 in the nonsubsidence and 101.1±10.2 in subsidence, (p=.005). The lower instrumented vertebrae (LIV) HU value was 147.4±34.9 in nonsubsidence and 108.1±13.7 in subsidence, (p<.001). The AUC of the UIV HU value was 0.917 (95% CI: 0.853-0.981), and the most appropriate threshold of the HU value was 115 (sensitivity: 84.6%, specificity: 100%). The AUC of the LIV HU value was 0.893 (95%CI: 0.819-0.966), and the most appropriate threshold of the HU value was 125 (sensitivity: 76.9%, specificity: 100%). The mean upper endplate HU value was 235.4±50.9, and the mean lower endplate HU value was 193.4±40.3. No significant difference (upper endplate p=.314, lower endplate p=.189) was observed between the two groups.

CONSLUSIONS

Lower preoperative vertebral body HU values were associated with cage subsidence after single-level OLIF. However, the endplate HU values were not associated with cage subsidence. Preoperative HU measurement is useful in the prediction of the cage subsidence.

Biomechanical Study of Cervical Endplate Removal on Subsidence and Migration in Multilevel Anterior Cervical Discectomy and Fusion

Study Design

This study compares four cervical endplate removal procedures, validated by finite element models.

Purpose

To characterize the effect of biomechanical strength and increased contact area on the maximum von Mises stress, migration, and subsidence between the cancellous bone, endplate, and implanted cage.

Overview of Literature

Anterior cervical discectomy and fusion (ACDF) has been widely used for treating patients with degenerative spondylosis. However, no direct correlations have been drawn that incorporate the impact of the contact area between the cage and the vertebra/endplate.

Methods

Model 1 (M1) was an intact C2C6 model with a 0.5 mm endplate. In model 2 (M2), a cage was implanted after removal of the C4-C5 and C5-C6 discs with preservation of the osseous endplate. In model 3 (M3), 1 mm of the osseous endplate was removed at the upper endplate. Model 4 (M4) resembles M3, except that 3 mm of the osseous endplate was removed.

Results

The range of motion (ROM) at C2C6 in the M2-M4 models was reduced by at least 9º compared to the M1 model. The von Mises stress results in the C2C3 and C3C4 interbody discs were significantly smaller in the M1 model and slightly increased in the M2-M3 and M3-M4 models. Migration and subsidence decreased from the M2-M3 model, whereas further endplate removal increased the migration and subsidence as shown in the transition from M3 to M4.

Conclusions

The M3 model had the least subsidence and migration. The ROM was higher in the M3 model than the M2 and M4 models. Endplate preparation created small stress differences in the healthy intervertebral discs above the ACDF site. A 1 mm embedding depth created the best balance of mechanical strength and contact area, resulting in the most favorable stability of the construct.

Biomechanical Effects of Pedicle Screw Positioning on the Surgical Segment in Models After Oblique Lumbar Interbody Fusion: An in-silico Study

Background

Bilateral pedicle screw (BPS) is the “gold standard” of fixation methods for patients with lumbar interbody fusion. Biomechanical deterioration initially triggers complications in the surgical segment. Studies proved that BPS positions and trajectory changes affect the local biomechanical environment. However, no study illustrates the biomechanical effect of insertional screw positions’ change on the surgical segment.

Methods

Oblique lumbar interbody fusion (OLIF) with different BPS insertional positions has been simulated in a well-validated lumbo-sacral model. Fixation stability and stress responses on the surgical segment were evaluated under identical loading conditions.

Results

There is no clear variation tendency for the risk of BPS failure and the change of strain energy density of the grafted bone. However, shifting the insertional screw position close to the surgical segment will increase the range of motions (ROM) in the surgical segment and lead to stress concentration of bony structures, especially in the caudal side of the surgical segment.

Conclusion

Adjusting the insertional position of BPS close to the surgical segment in OLIF models will lead to stress concentration of bony structures and surgical segmental instability. Therefore, reducing BPS’s fixation length was not recommended, which may increase the risk of segmental instability, non-union, and cage subsidence.

Poor Bone Quality, Multilevel Surgery, and Narrow and Tall Cages Are Associated with Intraoperative Endplate Injuries and Late-onset Cage Subsidence in Lateral Lumbar Interbody Fusion: A Systematic Review

BACKGROUND

A major complication of lateral lumbar interbody fusion (LLIF) is cage subsidence, which may lead to clinical problems, including loss of disc height correction, altered spinal alignment, recurrent pain, and vertebral body fracture. A thorough review of the current knowledge about the risk factors for the two types of cage subsidence after LLIF-intraoperative endplate injury and late-onset cage subsidence-could bring attention to well-established risk factors for clinical consideration while identifying any incompletely characterized factors that require further research to clarify.

QUESTIONS/PURPOSES

We performed a systematic review to answer the following questions: (1) Are bone quality and surrogates for bone quality, such as patient age and sex, associated with an increased likelihood of cage subsidence? (2) Are implant-related factors associated with an increased likelihood of cage subsidence?

METHODS

Two independent reviewers comprehensively searched Medline, Embase, Cochrane Library, PubMed, and Web of Science from 1997 to 2020 to identify all potential risk factors for cage subsidence after LLIF. Discrepancies were settled through discussion during full-text screening. Search terms included "lateral" AND "interbody fusion" AND "subsidence" OR "settling" OR "endplate injury" OR "endplate violation" WITHOUT "cervical" OR "transforaminal" OR "biomechanical." Eligible studies were retrospective or prospective comparative studies, randomized controlled trials, and case series with sample sizes of 10 patients or more reporting risk factors for cage subsidence or endplate injury after LLIF. Studies that involved cervical interbody fusions and biomechanical and cadaveric experiments were excluded. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was used to assess the studies' quality of evidence. The initial database review found 400 articles. Thirty-four articles with moderate- to very-low-quality evidence met the inclusion criteria for analysis. A total of 3233 patients (58% [1860] of whom were female) were included in this review. Two types of cage subsidence were reviewed: late-onset cage subsidence, which occurs gradually postoperatively, and intraoperative endplate injury, which is derived from iatrogenic endplate violation during endplate preparation or cage insertion. Among 20 studies with moderate quality of evidence according to the GRADE criteria, eight studies reported risk factors for cage subsidence related to bone mineral density and its surrogates and 12 studies focused on risk factors regarding implant factors, including cage dimension, cage material, construct length, and supplementary instrumentation.

RESULTS

Patients with a dual x-ray absorptiometry T-score of -1.0 or less, age older than 65 years, and female sex were considered to have a high risk of both types of cage subsidence. Regarding cage size, cage width ≥ 22 mm helped to avoid late-onset cage subsidence, and cage height ≤ 11 mm was recommended by some studies to avoid intraoperative endplate injuries. Studies recommended that multilevel LLIF should be conducted with extra caution because of a high risk of losing the effect of indirect decompression. Studies found that standalone LLIF might be sufficient for patients without osteoporosis or obesity, and supplementary instrumentation should be considered to maintain the postoperative disc height and prevent subsidence progression in patients with multiple risk factors. The effect of the bone graft, cage material, endplate condition, and supplementary instrumentation on cage subsidence remained vague or controversial.

CONCLUSION

Patients with poor bone density, patients who are older than 65 years, and female patients should be counseled about their high risk of developing cage subsidence. Surgeons should avoid narrow cages when performing LLIF to minimize the risk of late-onset cage subsidence, while being cautious of an aggressive attempt to restore disc height with a tall cage as it may lead to intraoperative endplate injury. For multilevel constructs, direct decompression approaches, such as posterior and transforaminal LIF, should be considered before LLIF, since the effect of indirect decompression may be difficult to maintain in multilevel LLIF because of high risks of cage subsidence. The effect of the cage material and supplementary instrumentation require stronger evidence from prospectively designed studies with larger sample size that randomly assign patients to polyetheretherketone (PEEK) or titanium cages and different fixation types. Future research on intraoperative endplate injuries should focus on the specific timing of when endplate violation occurs with the help of intraoperative imaging so that attempts can be made to minimize its occurrence.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Improving the Management of Patients with Osteoporosis Undergoing Spinal Fusion: The Need for a Bone Mineral Density-Matched Interbody Cage

With an increasingly aging population globally, a confluence has emerged between the rising prevalence of degenerative spinal disease and osteoporosis. Fusion of the anterior spinal column remains the mainstay surgical intervention for many spinal degenerative disorders. However, decreased vertebral bone mineral density (BMD), quantitatively measured by dual x-ray absorptiometry (DXA), complicates treatment with surgical interbody fusion as weak underlying bone stock increases the risk of post-operative implant-related adverse events, including cage subsidence. There is a necessity for developing cages with advanced structural designs that incorporate bioengineering and architectural principles to tailor the interbody fusion device directly to the patient’s BMD status. Specifically, lattice-designed cages that mimic the web-like structure of native cancellous bone have demonstrated excellent resistance to post-operative subsidence. This article provides an introductory profile of a spinal interbody implant designed intentionally to simulate the lattice structure of human cancellous bone, with a similar modulus of elasticity, and specialized to match a patient’s bone status across the BMD continuum. The implant incorporates an open pore design where the degree of pore compactness directly corresponds to the patient’s DXA-defined BMD status, including patients with osteoporosis.

Hounsfield unit value on CT as a predictor of cage subsidence following stand-alone oblique lumbar interbody fusion for the treatment of degenerative lumbar diseases

BACKGROUND

To investigate the correlation between vertebral Hounsfield unit (HU) values and cage subsidence in patients treated with stand-alone (SA) OLIF.

METHODS

A retrospective review of collected data was performed on 76 patients who underwent SA OLIF. We utilized the HU value for lumbar bone mineral density (BMD) obtained on preoperative CT. The vertebral HU values of patients with subsidence were compared to those without subsidence. The correlation between cage subsidence and clinical score was investigated.

RESULTS

Sixteen patients (21.1%) had at least radiographic evidence of interbody cage subsidence. The average cage subsidence was 2.5 ± 1.3 mm (range 0.9-4.8 mm). There were no significant differences in sex, BMI, preoperative diagnoses, or fused level (p > 0.05); however, there were significant differences between the cage subsidence group and the nonsubsidence group in age, average of the lowest T-score, and average HU value, including for the L1 vertebrae, L1-L4 horizontal plane, and L1-L4 sagittal plane (p < 0.05). The average HU value of the L1-L4 horizontal plane showed a more predictable AUC of 0.909 (95% CI, 0.834-0.984; P < 0.001) compared with the average of the lowest T-score following an AUC of 0.791 (95% CI, 0.674-0.909; P < 0.001). Based on logistic regression analysis, the average HU value of the L1-L4 horizontal plane (OR, 0.912; 95% CI, 0.861-0.966; P = 0.002) was an independent factor influencing cage subsidence.

CONCLUSIONS

Patients with lower average HU values of the lumbar vertebrae are at a much higher risk of developing cage subsidence after SA OLIF. Measurement of preoperative HU values on preexisting CT scans could be rapid, simple and feasible.

[CT value of vertebral body predicting Cage subsidence after stand-alone oblique lumbar interbody fusion]

Objective

To investigate the correlation between CT value and Cage subsidence in patients with lumbar degenerative disease treated with stand-alone oblique lumbar interbody fusion (OLIF).

Methods

The clinical data of 35 patients with lumbar degenerative diseases treated with stand-alone OLIF between February 2016 and October 2018 were retrospectively analyzed. There were 15 males and 20 females; the age ranged from 29 to 81 years, with an average of 58.4 years. There were 39 operative segments, including 32 cases of single-segment, 2 cases of double-segment, and 1 case of three-segment. Preoperative lumbar CT was used to measure the CT values of the axial position of L ₁ vertebral body, the axial and sagittal positions of L _1-4 vertebral body, surgical segment, and the axial position of upper and lower vertebral bodies as the bone mineral density index, and the lowest T value was recorded by dual-energy X-ray absorptiometry. The visual analogue scale (VAS) and Oswestry disability index (ODI) scores were recorded before operation and at last follow-up. At last follow-up, the lumbar interbody fusion was evaluated by X-ray films of the lumbar spine and dynamic position; the lumbar lateral X-ray film was used to measure the subsidence of the Cage, and the patients were divided into subsidence group and nonsubsidence group. The univariate analysis on age, gender, body mass index, lowest T value, CT value of vertebral body, disease type, and surgical segment was performed to initially screen the influencing factors of Cage subsidence; further the logistic regression for multi-factor analysis was used to screen fusion independent risk factors for Cage subsidence. The receiver operating characteristic (ROC) curve and area under curve (AUC) were used to analyze the CT value and the lowest T value to predict the Cage subsidence. Spearman correlation analysis was used to determine the correlation between Cage subsidence and clinical results.

Results

All the 35 patients were followed up 27-58 months, with an average of 38.7 months. At last follow-up, the VAS and ODI scores were significantly decreased when compared with preoperative scores ( t=32.850, P=0.000; t=31.731, P=0.000). No recurrent lower extremity radiculopathy occurred and no patient required revision surgery. Twenty-seven cases (77.1%) had no Cage subsidence (nonsubsidence group); 8 cases (22.9%) had at least radiographic evidence of Cage subsidence, the average distance of Cage subsidence was 2.2 mm (range, 1.1-4.2 mm) (subsidence group). At last follow-up, there was 1 case of fusion failure both in the subsidence group and the nonsubsidence group, there was no significant difference in the interbody fusion rate (96.3% vs. 87.5%) between two groups ( P=0.410). Univariate analysis showed that the CT value of vertebral body (L ₁ axial position, L _1-4 axial and sagittal positions, surgical segment, and upper and lower vertebral bodies axial positions) and the lowest T value were the influencing factors of Cage subsidence ( P<0.05). According to ROC curve analysis, compared with AUC of the lowest T value [0.738, 95% CI (0.540, 0.936)], the AUC of the L _1-4 axis CT value was 0.850 [95% CI (0.715, 0.984)], which could more effectively predict Cage subsidence. Multivariate analysis showed that the CT value of L _1-4 axis was an independent risk factor for Cage subsidence ( P<0.05).

Conclusion

The CT value measurement of the vertebral body based on lumbar spine CT before stand-alone OLIF can predict the Cage subsidence. Patients with low CT values of the lumbar spine have a higher risk of Cage subsidence. However, the Cage subsidence do not lead to adverse clinical results.

Incidence and risk factors of lateral cage migration occurred after the first-stage lateral lumbar interbody fusion surgery

BACKGROUND

Lateral lumbar interbody fusion (LLIF) is a novel, minimally invasive technique for the surgical treatment of lumbar diseases. The aim of this study was to identify the incidence and risk factors of lateral cage migration (LCM) occurred after the first-stage LLIF.

HYPOTHESIS

The hypothesis was that LCM occurred after the first-stage LLIF was associated with some demographic characteristics, surgical variables and radiographic parameters.

PATIENTS AND METHODS

Between June 2016 and August 2020, 335 patients (901 levels) underwent staged LLIF were retrospectively reviewed. Patients were classified into LCM and non-LCM group based on the experience of LCM before the second-stage posterior instrumentation. 100 patients in non-LCM were randomly sampled as a control group. Incidence of LCM was determined; demographic characteristics, surgical variables and radiographic parameters associated with LCM were compared between the LCM and control group. Univariate analyses and multivariable logistic regression analysis were used to identify the risk factors.

RESULTS

LCM occurred after the first-stage LLIF was found in 19 (5.7%) patients. Bony endplate injury (OR, 106.255; 95% CI, 1.265-8924.765; p=0.039) and greater preoperative range of motion (ROM) (OR, 2.083, 95% CI, 1.068-4.066, p=0.031) were high risk factors for LCM. LCM occurred mainly 3 days later after the first-stage LLIF, while 4 cases experienced severe neural symptoms, intolerable low back pain and finally underwent reoperation.

DISCUSSION

LCM occurred after the first-stage LLIF was significantly associated with bony endplate injury and greater preoperative ROM. Second-stage posterior fixation should be performed as soon as possible or a supplement lateral fixation/self-locking cage should be used in high-risk patients.

LEVEL OF EVIDENCE

IV.

The Role of Vertebral Porosity and Implant Loading Mode on Bone-Tissue Stress in the Human Vertebral Body Following Lumbar Total Disc Arthroplasty

STUDY DESIGN

Micro-computed tomography- (micro-CT-) based finite element analysis of cadaveric human lumbar vertebrae virtually implanted with total disc arthroplasty (TDA) implants.

OBJECTIVE

(1) Assess the relationship between vertebral porosity and maximum levels of bone-tissue stress following TDA; (2) determine whether the implant's loading mode (axial compression vs. sagittal bending) alters the relationship between vertebral porosity and bone-tissue stress.

SUMMARY OF BACKGROUND DATA

Implant subsidence may be related to the bone biomechanics in the underlying vertebral body, which are poorly understood. For example, it remains unclear how the stresses that develop in the supporting bone tissue depend on the implant's loading mode or on typical inter-individual variations in vertebral morphology.

METHODS

Data from micro-CT scans from 12 human lumbar vertebrae (8 males, 4 females; 51-89 years of age; bone volume fraction [BV/TV] = 0.060-0.145) were used to construct high-resolution finite element models (37 μm element edge length) comprising disc-vertebra-implant motion segments. Implants were loaded to 800 N of force in axial compression, flexion-, and extension-induced impingement. For comparison, the same net loads were applied via an intact disc without an implant. Linear regression was used to assess the relationship between BV/TV, loading mode, and the specimen-specific change in stress caused by implantation.

RESULTS

The increase in maximum bone-tissue stress caused by implantation depended on loading mode (P < 0.001), increasing more in bending-induced impingement than axial compression (for the same applied force). The change in maximum stress was significantly associated with BV/TV (P = 0.002): higher porosity vertebrae experienced a disproportionate increase in stress compared with lower porosity vertebrae. There was a significant interaction between loading mode and BV/TV (P = 0.002), indicating that loading mode altered the relationship between BV/TV and the change in maximum bone-tissue stress.

CONCLUSION

Typically-sized TDA implants disproportionately increase the bone-tissue stress in more porous vertebrae; this affect is accentuated when the implant impinges in sagittal bending.Level of Evidence: N/A.

Endplate volumetric bone mineral density is a predictor for cage subsidence following lateral lumbar interbody fusion: a risk factor analysis

BACKGROUND CONTEXT

It has been reported in previous studies that a decreased bone mineral density (BMD) as measured by dual X-ray absorptiometry (DXA) is associated with subsidence. However, there is limited research on the role of volumetric BMD (vBMD) as measured by quantitative computed tomography (QCT). Further, metabolic conditions such as obesity and type 2 diabetes have been associated with poor bone quality, but the impact of these metabolic conditions on on subsidence rates following lateral lumbar interbody fusion (LLIF) remains unclear. As such, risk factors for subsidence following LLIF is an area of ongoing research.

PURPOSE

The purpose of this study is to identify risk factors for subsidence following LLIF with a focus on metabolic conditions and vBMD as measured by QCT.

STUDY DESIGN/SETTING

Retrospective cohort study at a single academic institution.

PATIENT SAMPLE

Consecutive patients undergoing LLIF with or without posterior screws from 2014 to 2019 at a single academic institution who had a pre-operative CT and radiological imaging including radiographs or CT scans between 5 and 14 months post-operatively to assess for cage subsidence.

OUTCOME MEASURE

Subsidence prevalence following LLIF.

METHODS

We reviewed patients undergoing LLIF with or without posterior screws from 2014 to 2019 with a follow-up ≥5 months. Cage subsidence was assessed using the grading system by Marchi et al. Endplate volumetric BMD (EP-vBMD), vertebral bone volumetric BMD (VB-vBMD), BMI, and diabetes status were measured. Univariable analysis and multivariable logistic regression analyses with a generalized mixed model were conducted. Ad hoc analysis, including receiver operative characteristic curve analysis, was used for identifying the cut-off values in significant continuous variables for subsidence. Chi-Squared and ANOVA tests were used for categorical comparisons.

RESULTS

Five hundred sixty-seven levels in 347 patients were included in the final analysis. Mean age (± SD) was 61.7 ± 11.1yrs, 50.3% were male, and 89.6% were Caucasian. Subsidence was observed in 160 levels (28.2%). Multivariable analysis demonstrated an absence of posterior screws [OR = 2.854 (1.483 - 5.215), p=.001] and decreased EP-vBMD [0.996 (0.991 - 1.000), p=.032] were associated with an increased risk of subsidence. Increased BMI and diabetes status were not associated with increased rates of subsidence. Patients without posterior screws and low EP-vBMD experienced subsidence at 44.9% of levels.

CONCLUSIONS

Our results demonstrated that decreased EP-vBMD and standalone status were significantly associated with increased rates of subsidence following LLIF independent of BMI or diabetes status. Further analysis demonstrated that patients with a decreased EP-vBMD and without posterior screws experienced subsidence nearly 2.5 times higher than patients with no risk factors. In patients with a low EP-vBMD undergoing LLIF, posterior screws should be considered.

Truss implant technology™ for interbody fusion in spinal degenerative disorders: profile of advanced structural design, mechanobiologic and performance characteristics

Introduction: Interbody fusion devices are customarily used in fusion of the anterior spinal column for treatment of degenerative disc disease. Their traditional role is to reestablish and maintain intervertebral disc height, contain bone graft and provide mechanical support for the spine while osseointegration takes place. Utilizing the principles of mechanobiology, a unique biokinetic interbody fusion device has been developed that employs an advanced structural design to facilitate and actively participate in the fusion consolidation process.Areas covered: This article profiles and characterizes 4WEB Medical's Truss Implant Technology™ which includes a range of 3D-printed titanium spinal interbody implants and non-spinal implants whose design is based on truss structures enabled by advances in additive manufacturing. Four main areas of the implant design and functionality are detailed: bio-architecture, mechanobiologic underpinnings, bioactive surface features, and subsidence resistance. Pre-clinical and clinical examples are provided to describe and specify the bioactive roles and contributions of each design feature.Expert opinion: The distinct and unique combination of features incorporated within the truss cage design results in a biokinetic implant that actively participates in the bone healing cascade and fusion process.

Is stand-alone lateral lumbar interbody fusion superior to instrumented lateral lumbar interbody fusion for the treatment of single-level, low-grade, lumbar spondylolisthesis?

BACKGROUND

The aim of this study was to compare surgical trauma and radiographic and clinical outcomes of stand-alone and instrumented lateral lumbar interbody fusion (LLIF) in the treatment of single-level low-grade lumbar spondylolisthesis.

METHODS

Ninety-five patients with single-level low-grade lumbar spondylolisthesis, who underwent stand-alone LLIF (stand-alone group, [n = 54]) or LLIF plus percutaneous posterior fixation (instrumented group, [n = 41]) were enrolled in this study. Operative time, intraoperative blood loss, serum C-reactive protein (CRP) and creatine kinase (CK) levels, the length of postoperative bed rest time, and hospital stay were compared between the 2 groups. Disc height, the percent of slip, segment lordosis, lumbar lordosis, the visual analog scale score, the Oswestry Disability Index and complications were also compared.

RESULTS

Operative and bed rest time were shorter, intraoperative blood loss was less, and postoperative CRP and CK levels were lower in the stand-alone group. During follow-up, 6 patients in stand-alone group underwent posterior fixation due to cage subsidence. Although satisfactory radiographic results were achieved in both groups, the maintenance of increased disc heights and segment lordosis was inferior in the stand-alone group at the final follow-up. Greater improvement in postoperative VAS scores and ODI were observed in the stand-alone group, although the rates of cage subsidence and revision were higher.

CONCLUSION

Stand-alone LLIF was superior to instrumented LLIF in terms of tissue trauma for the treatment of single-level low-grade lumbar spondylolisthesis. However, stand-alone LLIF was inferior in the maintenance of disc height and segment lordosis, and the occurrence of cage subsidence and revision.

Application of Titanium Alloy 3D-Printed Artificial Vertebral Body for Stage III Kümmell's Disease Complicated by Neurological Deficits

Purpose

The current study aimed to compare the clinical and radiographic results of the 3D-printed artificial vertebral body (3DP-AVB) and titanium mesh cage (TMC) for the treatment of Kümmell’s disease (KD) complicated by neurological deficits.

Patients and Methods

From January 2014 to July 2018, 28 consecutive patients diagnosed with KD and nerve injuries in our department were treated by posterior vertebral column resection and internal fixation. The patients were divided into two groups (3DP-AVB group and TMC group) based on the different anterior column reconstruction implants. Clinical and radiographic parameters were used to evaluate the outcomes.

Results

The two groups achieved excellent clinical and radiographic results 1 month after surgery with no significant difference (P>0.05), while 3DP-AVB group showed better outcomes compared with TMC group during the follow-up after 6 months (P<0.05). The risk of subsidence in 3DP-AVB group was lower than that in TMC group (41.6% vs 87.5%, P<0.05), and severe subsidence (≥5 mm) was correlated with the recurrence of back pain and bad daily life function. No significant difference was found in the improvement of neurological function between the two groups (P>0.05). The blood loss and operation time in 3DP-AVB group were significantly less than both in TMC group (P<0.05).

Conclusion

The lower incidence of cage subsidence, with a better long-term efficacy in maintaining the height of the fused segment, relieving back pain, and improving daily life function indicates that the 3DP-AVB may be a superior alternative for KD with neurological deficits.

The Association Between Endplate Changes and Risk for Early Severe Cage Subsidence Among Standalone Lateral Lumbar Interbody Fusion Patients

STUDY DESIGN

Retrospective case series.

OBJECTIVE

The aim of this study was to investigate the association of Modic type endplate changes with the risk of severe subsidence after standalone lateral lumbar interbody fusion (SA-LLIF).

SUMMARY OF BACKGROUND DATA

It has been reported that certain endplate radiolographic features are associated with higher regional bone mineral density (BMD) in the adjacent vertebrae in the lumbar spine. It remains unclear whether these changes have protective effects against osteoporotic complications such as cage subsidence after lumbar surgery.

METHODS

We reviewed patients undergoing SA-LLIF from 2007 to 2016 with a follow-up >6 months. Cage subsidence was assessed utilizing the grading system by Marchi et al. As potential contributing factors for cage subsidence, we measured the endplate volumetric BMD (EP-vBMD) and the standard trabecular volumetric BMD measurement in the vertebral body. Modic changes (MC) on magnetic resonance imaging were measured as a qualitative factor for endplate condition. Univariate analysis and multivariate logistic regression analyses with a generalized mixed model were conducted.

RESULTS

Two hundred six levels in 97 patients were included in the final analysis. Mean age (± SD) was 66.7 ± 10.7. Sisty-sdpercent of the patients were female. Severe subsidence was observed in 66 levels (32.0%). After adjusting for age, bone morphogenetic protein (BMP) use, and number of levels fused, the presence of MC type 2 was significantly associated with lower risk of severe subsidence (OR = 0.28 [0.09-0.88], P = 0.029). Whereas, EP-vBMD did not demonstrate a statistical significance (p = 0.600).

CONCLUSION

The presence of a Modic type 2 change was significantly associated with lower odds of severe subsidence after SA-LLIF. Nonetheless, this significant association was independent from regional EP-vBMD values. This finding suggests that microstructural and/or material property changes associated with Modic type 2 changes might have a protective effect in this patient population.

LEVEL OF EVIDENCE

4.