Interbody Fusion Cages Research Articles

Patient-Specific Variations in Local Strain Patterns on the Surface of a Trussed Titanium Interbody Cage.

Introduction: 3D printed trussed titanium interbody cages may deliver bone stimulating mechanobiological strains to cells attached at their surface. The exact size and distribution of these strains may depend on patient-specific factors, but the influence of these factors remains unknown. Therefore, this study aimed to determine patient-specific variations in local strain patterns on the surface of a trussed titanium interbody fusion cage. Materials and Methods: Four patients eligible for spinal fusion surgery with the same cage size were selected from a larger database. For these cases, patient-specific finite element models of the lumbar spine including the same trussed titanium cage were made. Functional dynamics of the non-operated lumbar spinal segments, as well as local cage strains and caudal endplate stresses at the operated segment, were evaluated under physiological extension/flexion movement of the lumbar spine. Results: All patient-specific models revealed physiologically realistic functional dynamics of the operated spine. In all patients, approximately 30% of the total cage surface experienced strain values relevant for preserving bone homeostasis and stimulating bone formation. Mean caudal endplate contact pressures varied up to 10 MPa. Both surface strains and endplate contact pressures varied more between loading conditions than between patients. Conclusions: This study demonstrates the applicability of patient-specific finite element models to quantify the impact of patient-specific factors such as bone density, degenerative state of the spine, and spinal curvature on interbody cage loading. In the future, the same framework might be further developed in order to establish a pipeline for interbody cage design optimizations.

Comparison of corrective and clinical effects between SRS-Schwab grade IV osteotomy combined with the interbody fusion cage and pure grade IV osteotomy in the treatment of old thoracolumbar vertebral osteoporotic fractures with kyphosis.

To compare the corrective and clinical effects between Scoliosis Research Society (SRS)-Schwab grade IV osteotomy combined with the interbody fusion cage and pure grade IV osteotomy in the treatment of old thoracolumbar vertebral osteoporotic fractures with kyphosis. Twenty-four cases of old thoracolumbar osteoporotic fractures with kyphosis treated by grade IV osteotomy in Sichuan Provincial Orthopedic Hospital from January 2018 to December 2019 were reviewed. Eleven cases were treated with grade IV osteotomy combined with the interbody fusion cage (group A), and 13 cases were treated with grade IV osteotomy alone (group B). Operation time, blood loss, and perioperative conditions of the 2 groups were recorded. After operation and the last follow up, the kyphosis angle (Cobb angle) and sagittal vertical axis (SVA) were measured by whole-spine splicing X-ray; clinical effect was analyzed by visual analog score (VAS) and Oswestry disability index (ODI). All operations were successful. Operation time was 239.5±29.0 min in group A and 179.2±22.7 min in group B (P<0.05). Intraoperative blood loss in group A was 1,560.9±378.6 mL and 1,242.3±339.0 mL in group B (P<0.05). Cerebrospinal fluid leakage occurred in 3 cases in group A and 1 case in group B (P<0.05). There were 3 cases of transient neurological symptoms in group A and 1 case in group B (P<0.05). There was no significant difference in Cobb angle and SVA between the 2 groups (P>0.05). There was no significant difference in ODI and VAS between the 2 groups (P>0.05). There were no complications, such as spinal cord injury, internal fixation loosening and fracture, or orthopedic loss. SRS-Schwab grade IV osteotomy combined with the interbody fusion cage and pure grade IV osteotomy can achieve good short-term orthopedic and clinical effects in the treatment of old thoracolumbar osteoporotic fractures with kyphosis. Corrective and clinical effects of the two groups are equivalent, but the operation time of grade IV osteotomy combined with the interbody fusion cage is longer, the amount of intraoperative blood is greater, and the incidence of complications is higher.

Experimental analysis on the resistance of fixing nails for spine cages

Arthrodesis is one of the most common surgical treatment for the management of pathologies concerning the intervertebral discs. Special cages replace the intervertebral disc and realize the fusion between the vertebral body, often together with a fixing plate, screws, and rods. An alternative method is a cage that contains integrated screws, designed with suitable holes, it allows an easier insertion of fixing system during surgery. Mt Ortho company offers a cage equipped with two diverging locking nails in Ti6Al4V-ELI titanium alloy. These nails are placed directly inside the cage inclined by 30° with respect to the horizontal. This paper, performed in collaboration with Mt Ortho, reports the experimental tests aimed at evaluating the performance of locking nails under pull-out stresses. To evaluate the nails pull-out in a more physiological way, together to the standard condition, tests were performed on a composite layer made of wood and foam. Furthermore, the notch effects generated by the locking nails are qualitatively evaluated by photoelastic analysis, in view of a geometry able to reduce the stress concentration factor on the bone tissue, without reducing the pull-out resistance.

Early revision events among patients with a three dimensional (3D) printed cellular titanium or PEEK (polyetheretherketone) spinal cage for single-level lumbar spinal fusion

ABSTRACT Introduction Three-dimensional (3D) printed spinal cages are a new design of intervertebral body fusion devices. Clinical data on these devices are limited. The objective of this study was to describe six-month events for a new and older cage design. Methods A retrospective, descriptive cohort study of patients that received a 3D-printed-titanium or PEEK (polyetheretherketone) cage with single-level lumbar fusion was performed using a United States hospital-based database. Outcomes evaluated were device-related revision and non-device related reoperation events 6 months after lumbar fusion. The 3D-printed-titanium and PEEK groups were propensity-score matched. Both unmatched and matched groups were descriptively analyzed. There were 93 and 2,082 patients with a 3D-printed-titanium and PEEK cage that met study criteria. The sample size was 93 patients per group after matching. Results There were no occurrences of revisions in the 3D-printed-titanium and eleven occurrences in the PEEK group before matching; PEEK had no occurrences of revision after matching. Ten total reoperation events were identified. Discussion Our findings suggest occurrence of 6-month revision or reoperation is similar or lower for both cages than reported in published literature. The low occurrence of early events for 3D-printed-titianium cages is promising. Further, real-world studies on 3D-printed cages are warranted.

Do Obliquity and Position of the Oblique Lumbar Interbody Fusion Cage Influence the Degree of Indirect Decompression of Foraminal Stenosis?

ObjectiveOblique lumbar interbody fusion (OLIF) is a surgical technique that utilizes a large interbody cage to indirectly decompress neural elements. The position of the cage relative to the vertebral body could affect the degree of foraminal decompression. Previous studies determined the position of the cage using plain radiographs, with conflicting results regarding the influence of the position of the cage to the degree of neural foramen decompression. Because of the cage obliquity, computed tomography (CT) has better accuracy than plain radiograph for the measurement of the obliquely inserted cage. The objective of this study is to find the correlation between the position of the OLIF cage with the degree of indirect decompression of foraminal stenosis using CT and magnetic resonance imaging (MRI). MethodsWe review imaging of 46 patients who underwent OLIF from L2-L5 for 68 levels. Segmental lordosis (SL) was measured in a plain radiograph. The positions of the cage were measured in CT. Spinal canal cross-sectional area (SCSA), and foraminal crosssectional area (FSCA) measurements using MRI were taken into consideration. ResultsPatients’ mean age was 69.7 years. SL increases 3.0±5.1 degrees. Significant increases in SCSA (33.3%), FCSA (43.7% on the left and 45.0% on the right foramen) were found (p<0.001). Multiple linear regression analysis shows putting the cage in the more posterior position correlated with more increase of FSCA and decreases SL correction. The position of the cage does not affect the degree of the central spinal canal decompression. Obliquity of the cage does not result in different degrees of foraminal decompression between right and left side neural foramen. ConclusionCage position near the posterior part of the vertebral body increases the decompression effect of the neural foramen while putting the cage in the more anterior position correlated with increases SL.

Design and 3D Printing of Interbody Fusion Cage Based on TPMS Porous Structure

To solve the mismatch between the comprehensive mechanical properties of the spinal fusion cage and body, a fusion cage inner hole design method based on controllable TPMS-P to characterize the inner hole structure is proposed to solve the related problems. Firstly, the method of TPMS-P parameterization was used to construct the bionic porous structure model, which was designed as the linear gradual internal porous structure model. Then, we optimized the topology of the obtained porous structure implants to achieve precise control of the overall comprehensive mechanical properties of the fusion cage structure and obtain an optimized model that matched the mechanical properties of the fusion cage. To verify whether the method met the requirements, its simulation model was established. The porous structure was fabricated by selective laser processing, and its properties were tested and analyzed. The results show that its yield strength is 79.83 MPa, which match well with spinal bone tissue.

Expandable versus Static Transforaminal Lumbar Interbody Fusion Cages: 1-year Radiographic Parameters and Patient-Reported Outcomes

Expandable transforaminal lumbar interbody fusion (TLIF) cages capable of multidirectional in situ expansion have gained popularity as they increase axial surface area for fusion and may enhance lordotic correction through a traditional minimally invasive surgery (MIS) surgical corridor. We evaluated and compared the radiographic and clinical outcomes between a novel expandable versus static minimally invasive surgery TLIF cage for the treatment of degenerative disk disease. A single-center retrospective review of 120 consecutive adult patients undergoing 1- or 2-level MIS TLIF with an expandable (n= 60) or static cage was performed between 2015 and 2019. Preoperative and 1-year postoperative radiographic and clinical outcomes were assessed by upright flexion/extension radiographs and serial confidential surveys. One-hundred twenty patients (mean age 63.5 years, 60.0% female) undergoing 1- and 2-level MIS TLIF met inclusion criteria. A statistically significant reduction of spondylolisthesis, restoration of foraminal height as well as anterior and posterior disk height was achieved in both cohorts, however was greater in the expandable cage cohort (ECC) (all P < 0.05). Comparable rates of fusion, 93% and 91%, were observed in the ECC and static cage cohort. A significant reduction in Numeric Pain Rating Scale back and Oswestry Disability Index scores were observed in both cohorts but were more pronounced in the ECC (5.9 ± 2.4 to 2.2 ± 1.9 and 37.3 ± 16.2 to 17.1 ± 15.2) versus static cage cohort (6.2 ± 2.8 to 3.2 ± 2.5 and 41.8 ± 16.1 to 24.3 ± 17.5) (P < 0.05). One instance of cage migration requiring reoperation occurred in the ECC. Taken together, these radiographic and clinical findings suggest an expandable cage placed through an MIS corridor represents a safe, equitable, and efficacious alternative to a static TLIF in adults with degenerative lumbar pathology.

Anterior Cervical Discectomy and Fusion Combined with Foraminotomy Assisted by High-Definition 3-Dimensional Exoscope in the Treatment of Cervical Spondylotic Radiculopathy Secondary to Bony Foraminal Stenosis.

ObjectiveTo evaluate the outcomes of cervical spondylotic radiculopathy secondary to bony foraminal stenosis treated with anterior cervical discectomy and fusion (ACDF) combined with anterior cervical foraminotomy (ACF) assisted by High‐Definition 3‐Dimensional Exoscope.MethodsIn this retrospective study, a total of 19 consecutive patients (12 males and seven females, with an average of 49.2 years, range from 40 to 59 years) with spondylotic radiculopathy caused by bony foraminal stenosis underwent ACDF combined with ACF assisted by High‐Definition 3‐Dimensional Exoscope in our hospital between January 2019 and December 2019 were included in this study. All patients signed the consent form before the surgery. The patient baseline information such as gender, age, body mass index (BMI), surgery time, blood loss, hospital stay, lesion segment, side, follow‐up time and postoperative complications were recorded. The Japanese Orthopedic Association (JOA), Neck Disability Index (NDI), and Visual Analogue Scale (VAS) were measured and compared before surgery, 1 months and final follow‐up after surgery. The radiographic outcomes were evaluated using the C2‐C7 angel, disc height, foraminal height, superior diagonal distance, inferior diagonal distance, and foraminal area.ResultsThe involved levels included C4‐C5 (six cases), C5‐C6 (10 cases), C6‐C7 (three cases). The mean duration of the surgery, mean blood loss, mean hospital stay, and mean follow‐up were 100 ± 11.10 min, 19.4 ± 7.05 mL, 7.1 ± 0.99 days, and 12.1 ± 2.25 months, respectively. The average preoperative JOA score was 11.9 ± 1.31, then improved to 15.7 ± 0.73 (t = −13.45, P < 0.001) and 16.2 ± 0.74 (t = −14.39, P < 0.001) at 1 month after operation and at last follow‐up, respectively. The average preoperative NDI score was 27.3 ± 3.36, then decreased to 5.1 ± 1.79 (t = 20.63, P < 0.001) and 4.5 ± 1.21 (t = 25.53, P < 0.001) 1 month after operation and at last follow‐up, respectively. The average preoperative VAS score was 6.7 ± 0.93, then decreased to 2.4 ± 0.69 (t = 15.05, P < 0.001) and 1.9 ± 0.78 (t = 16.40, P < 0.001) 1 month after operation and at last follow‐up, respectively. As compared with the condition before surgery, there was a significant improvement in the C2‐C7 angel, disc height, foraminal height, and foraminal area (P < 0.05). None of the patients developed postoperative vascular injury, nerve injury, loosening and rupture of the internal fixation, displacement of interbody fusion cage, and pseudarthrosis.ConclusionACDF combined with ACF assisted by High‐Definition 3‐Dimensional Exoscope is effective and safe for the treatment of CSR caused by secondary to bony foraminal stenosis.

Research progress on three-dimensional printed interbody fusion cage

Spinal fusion is a standard operation for treating moderate and severe intervertebral disc diseases. In recent years, the proportion of three-dimensional printing interbody fusion cage in spinal fusion surgery has gradually increased. In this paper, the research progress of molding technology and materials used in three-dimensional printing interbody fusion cage at present is summarized. Then, according to structure layout, three-dimensional printing interbody fusion cages are classified into five types: solid-porous-solid (SPS) type, solid-porous-frame (SPF) type, frame-porous-frame (FPF) type, whole porous cage (WPC) type and others. The optimization process of three-dimensional printing interbody fusion cage and the advantages and disadvantages of each type are analyzed and summarized in depth. The clinical application of various types of 3D printed interbody fusion cage was introduced and summarized later. Lastly, combined with the latest research progress and achievements, the future research direction of three-dimensional printing interbody fusion cage in molding technology, application materials and coating materials is prospected in order to provide some reference for scholars engaged in interbody fusion cage research and application.

Comparative analysis of the results using direct lateral interbody spondilodesis and transforaminal lumbar interbody spondilodesis in patients with degenerative diseases of the lumbar spine

Introduction Various spondylodesis techniques are used in patients with degenerative diseases of the lumbar spine, but the benefits of these techniques have not been proven.Objective of the study was to assess the effect of the type of fusion on the incidence of implant instability and related revision surgeries.Material and Methods This monocentric prospective study included 133 patients with degenerative stenosis of the lumbar spine and confirmed instability of spinal motion segments. Patients underwent transforaminal lumbar interbody fusion (TLIF) with a single cage or direct lateral interbody fusion (DLIF) using standard-sized cages. The conventional open technique was used to supplement TLIF with pedicle screws while percutaneous screw placement was applied in patients treated with DLIF. The duration of follow-up was 18 months. Fisher's exact test was used to assess differences in the incidence of fixator instability based on MSCT and revision interventions. Logistic regression was used to assess the association between potential risk factors and complication rates.Results The use of DLIF detected by MSCT (32.9 vs 3.6%, p &lt; 0.0001) resulted in a significant reduction in the incidence of screw instability and associated revision interventions (11.8 vs 0%, p = 0.0122). The results of logistic regression, taking into account factors such as bone density and the number of levels at which spondylodesis was performed, confirm the relationship between the reduced incidence of complications and the use of DLIF technology. Conclusion Using DLIF instead of TLIF in patients with degenerative stenosis at the lumbar spine level can lead to a significant reduction in the frequency of screw instability and associated revision surgeries.

Effectiveness of three-dimensional printing artificial vertebral body and interbody fusion Cage in anterior cervical surgery

To evaluate the effectiveness of three-dimensional (3D) printing artificial vertebral body and interbody fusion Cage in anterior cervical disectomy and fusion (ACCF) combined with anterior cervical corpectomy and fusion (ACDF). The clinical data of 29 patients with multilevel cervical spondylotic myelopathy who underwent ACCF combined with ACDF between May 2018 and December 2019 were retrospectively analyzed. Among them, 13 patients were treated with 3D printing artificial vertebral body and 3D printing Cage as 3D printing group and 16 patients with ordinary titanium mesh Cage (TMC) and Cage as TMC group. There was no significant difference in gender, age, surgical segment, Nurick grade, disease duration, and preoperative Japanese Orthopaedic Association (JOA) score, visual analogue scale (VAS) score, and Cobb angle of fusion segment between the two groups ( P>0.05). The operation time, intraoperative blood loss, hospitalization stay, complications, and implant fusion at last follow-up were recorded and compared between the two groups; JOA score was used to evaluate neurological function before operation, immediately after operation, at 6 months after operation, and at last follow-up; VAS score was used to evaluate upper limb and neck pain. Cobb angle of fusion segment was measured and the difference between the last follow-up and the immediate after operation was calculated. The height of the anterior border (HAB) and the height of the posterior border (HPB) were measured immediately after operation, at 6 months after operation, and at last follow-up, and the subsidence of implant was calculated. The operation time of 3D printing group was significantly less than that of TMC group ( t=3.336, P=0.002); there was no significant difference in hospitalization stay and intraoperative blood loss between the two groups ( P>0.05). All patients were followed up 12-19 months (mean, 16 months). There was no obvious complication in both groups. There were significant differences in JOA score, VAS score, and Cobb angle at each time point between the two groups ( P<0.05). There was an interaction between time and group in the JOA score ( F=3.705, P=0.025). With time, the increase in JOA score was different between the 3D printing group and the TMC group, and the increase in the 3D printing group was greater. There was no interaction between time and group in the VAS score ( F=3.038, P=0.065), and there was no significant difference in the score at each time point between the two groups ( F=0.173, P=0.681). The time of the Cobb angle interacted with the group ( F=15.581, P=0.000). With time, the Cobb angle of the 3D printing group and the TMC group changed differently. Among them, the 3D printing group increased more and the TMC group decreased more. At last follow-up, there was no significant difference in the improvement rate of JOA score between the two groups ( t=0.681, P=0.502), but the Cobb angle difference of the 3D printing group was significantly smaller than that of the TMC group ( t=5.754, P=0.000). At last follow-up, the implant fusion rate of the 3D printing group and TMC group were 92.3% (12/13) and 87.5% (14/16), respectively, and the difference was not significant ( P=1.000). The incidence of implant settlement in the 3D printing group and TMC group at 6 months after operation was 15.4% (2/13) and 18.8% (3/16), respectively, and at last follow-up were 30.8% (4/13) and 56.3% (9/16), respectively, the differences were not significant ( P=1.000; P=0.264). The difference of HAB and the difference of HPB in the 3D printing group at 6 months after operation and last follow-up were significantly lower than those in the TMC group ( P<0.05). For patients with multilevel cervical spondylotic myelopathy undergoing ACCF combined with ACDF, compared with TMC and Cage, 3D printing artificial vertebrae body and 3D printing Cage have the advantages of shorter operation time, better reduction of height loss of fusion vertebral body, and maintenance of cervical physiological curvature, the early effectiveness is better.

Mid- and Long-Term Follow-Up Efficacy Analysis of 3D-Printed Interbody Fusion Cages for Anterior Cervical Discectomy and Fusion.

ObjectiveTo evaluate the safety and stability of 3D‐printed interbody fusion cages (3D‐printed cages) in anterior cervical discectomy and fusion (ACDF) by investigating the mid‐ and long‐term follow‐up outcomes.MethodsIn this prospective study, the clinical data of 30 patients with CSM admitted to the Second Hospital of Shanxi Medical University from May 2012 to May 2014 were analyzed. The cohort comprised 18 males and 12 females with an average age of 60.22 ± 3.2 years. All patients were examined by X‐ray, CT and MRI before the operation. A total of 30 cases of CSM were treated by ACDF with 3D printed cage implantation. Mid‐ and long‐term follow‐ups were performed after the surgery. Clinical efficacy was evaluated by comparing the JOA score, SF‐36 score, change in neurological function, cervical curvature index (CCI), vertebral intervertebral height (VIH) and fusion rate before the operation, 6 months after the operation, and at the last follow‐up.ResultsTwo of the 30 patients were lost to follow‐up. The remaining patients were followed up for 48–76 (65.23 ± 3.54) months. The patients recovered satisfactorily with a significant clinical effect. The JOA score increased meanfully and the improvement rate was 89.4% at the final follow‐up. The SF‐36 score increased significantly from pre‐ to postoperatively. The height of the intervertebral space at the last follow‐up was not statistically significantly different from that at 6 months after surgery (P > 0.05), showing that the height of the intervertebral space did not change much and the severity of cage subsidence (CS) decreased. The CCI improved from pre‐ to postoperatively. The CCI did not change much from the 6‐month follow‐up to the last follow‐up. and the cage rate (CR) was 100% at the 6‐month and last follow‐ups. No severe complications, such as spinal cord injury, esophageal fistula, cerebrospinal fluid leakage, cervical hematoma or wound infection, occurred in any of the patients.ConclusionThe clinical and radiological results show that the application of 3D‐printed cages in ACDF can significantly relieve symptoms. Moreover, 3D‐printed cages can restore the curvature of the cervical spine, effectively maintain the intervertebral height for a long time, and prevent complications related to postoperative subsidence.

Posterior Thoracic Cage Interbody Fusion Offers Solid Bone Fusion with Sagittal Alignment Preservation for Decompression and Fusion Surgery in Lower Thoracic and Thoracolumbar Spine.

ObjectiveIt is challenging to make solid fusion by posterior screw fixation and laminectomy with posterolateral fusion (PLF) in thoracic and thoracolumbar (TL) diseases. In this study, we report our experience and follow-up results with a new surgical technique entitled posterior thoracic cage interbody fusion (PTCIF) for thoracic and TL spine in comparison with conventional PLF. MethodsAfter institutional review board approval, a total of 57 patients who underwent PTCIF (n=30) and conventional PLF (n=27) for decompression and fusion in thoracic and TL spine between 2004 and 2019 were analyzed. Clinical outcomes and radiological parameters, including bone fusion, regional Cobb angle, and proximal junctional Cobb angle, were evaluated. ResultsIn PTCIF and conventional PLF, the mean age was 61.2 and 58.2 years (p=0.46), and the numbers of levels fused were 2.8 and 3.1 (p=0.46), respectively. Every patient showed functional improvement except one case of PTCIF. Postoperative hematoma as a perioperative complication occurred in one and three cases, respectively. The mean difference in the regional Cobb angle immediately after surgery compared with that of the last follow-up was 1.4° in PTCIF and 7.6° in conventional PLF (p=0.003), respectively. The mean durations of postoperative follow-up were 35.6 months in PTCIF and 37.3 months in conventional PLF (p=0.86). ConclusionPTCIF is an effective fusion method in decompression and fixation surgery with good clinical outcomes for various spinal diseases in the thoracic and TL spine. It provides more stable bone fusion than conventional PLF by anterior column support.

Minimally Invasive Transforaminal Lumbar Interbody Fusion Using Expandable Cages: Increased Risk of Late Postoperative Subsidence Without a Real Improvement of Perioperative Outcomes: A Clinical Monocentric Study

Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is one of several approaches to lumbar interbody fusion that has proven to be a safe and effective treatment for symptomatic lumbar degenerative disease The clinical outcomes of MIS-TLIF are generally favorable, but there is still controversy regarding its ability to restore sagittal alignment. For this reason, expandable transforaminal lumbar interbody fusion cages have been developed and designed to improve ability to restore disc height and segmental lordosis. The use of expandable cages in transforaminal lumbar interbody fusion has increased drastically; however, it is not clear how effective cage expansion is in regard to disc space lordosis, distraction, and long-term outcome. We reviewed a cohort of patients with symptomatic lumbar degenerative disc pathology who underwent MIS-TLIF at our institution. We compared clinical and radiographic outcomes of expandable versus nonexpandable cage use in MIS-TLIF focusing on mean changes in segmental lordosis, disc height, and postoperative complications. The results were compared with other studies reported in the international literature. Mean change in segmental lordosis was not significantly different between the 2 groups. A significantly higher rate of postoperative subsidence was demonstrated in the expandable cage group. This study established that expandable cage use in single-level transforaminal lumbar interbody fusion did not reduce the rate of postoperative complications, but rather significantly increased a patient's risk of postoperative subsidence. Expandable cages do not presently demonstrate improved clinical outcomes or improved sagittal alignment compared with static cages.

Computational Investigation for Biomechanical Characteristics of Lumbar Spine with Various Porous Ti–6Al–4V Implant Systems

(1) Background: Metallic materials are predominantly used for spinal implants, and they can damage adjacent bones and intervertebral discs (IVDs) owing to their high elastic moduli. Consequently, there is a possibility that serious complications, such as kyphosis, may occur as the sequelae progresses. In this study, the behavior of the lumbar spine and implant system was evaluated using the finite element (FE) method, by applying the porous structure to the spinal implants to resolve the problem of metal spinal implants. (2) Methods: An FE model was developed for lumbar 3–5, and it was assumed that, owing to disease occurrence, spinal implants were placed in lumbar 3–4. Currently, Ti–6Al–4V is the most commonly used material for spinal implants. The shape of the porous structure was set in the form of a diamond, and porosity was varied over nine values ranging from 0 to 81%. Finally, equivalent material properties of the porous structure were derived using the Ramberg–Osgood formula, with reference to experimental study. (3) Results: The range of motion was increased, and the equivalent stress of adjacent IVD, and adjacent bone stress of the pedicle screw and spinal cage, decreased with increasing porosity of the spinal implants. As the porosity decreased, the safety factor exhibited a tendency to decrease rapidly. (4) Conclusion: Motor capacity of the spine was improved, and the equivalent stress of the spinal tissues decreased with the increasing porosity of the spinal implants. Therefore, in the future, porous structures can significantly contribute to the improvement of implants through continuous complementary research.

3D printed personalized lumbar spinal fusion device design and biomechanical performance analysis

The finite element analysis method was used to compare the biomechanical performance of the individualized interbody fusion cage, the clinically common double bullet type fusion cage and the healthy lumbar spine model under different working conditions. According to the CT scan data of the lumbar spine of a real healthy human body, a finite element model of the lumbar spine of a healthy human body was designed using finite element software as a normal control group. On this basis, the individualized lumbar fusion cage model and the clinical standard bullet type fusion cage lumbar spine model were further established. These three finite element models were applied with different loads such as vertical compression, forward flexion, extension, and lateral bending to observethe changes in the stress distribution and stress magnitude of each component of the lumbar spine. The maximum stress values of the vertebral body and the fusion cage under the extension condition in the clinical standard bullet type fusion cage lumbar spine model were 45.81 MPa and 97.07 MPa, respectively. The stress of the vertebral body and the fusion cage in the individualized lumbar fusion cage model was closer to the stress of the vertebral body and the intervertebral disc in the healthy lumbar spine model. From the perspective of displacement, the displacement of each component of the lumbar spine models of the two fusion cages was smaller than that of the healthy lumbar spine model, indicated that the internal fixation of the fusion cage limited the range of motion of the vertebral body. On the other hand, it also confirmed the validity of the finite element model established in the study. The displacement of the fusion cage and the vertebral body in the individualized model under different working conditions was generally smaller thanthat of the standard model fusion cage and the vertebral body. The fusion cage can replace the diseased intervertebral disc to a certain extent, so as to reduce the patient's pain and restore the lumbar function. The personalized design of the fusion cage can better meet the needs of individual patients, which has the great significance to the recovery of the patient's lumbar spine function, the service life of the fusion cage and the protection of the contact vertebral body, and provides certain guidance for actual clinical treatment.

Adult spinal deformity surgery: posterior three-column osteotomies vs anterior lordotic cages with posterior fusion. Complications, clinical and radiological results. A systematic review of the literature.

The aim of our study is to analyse mid- to long-term severe adult spinal deformity (ASD) surgery outcomes by comparing three-column osteotomies (3CO) and multiple anterior interbody fusion cages (AC). The PRISMA flowchart was used to systematically review the literature. Only articles with a minimum 24-month follow-up were examined, and 11 articles were included. The following radiological parameters were observed: pelvic incidence (PI), pelvic tilt(PT), lumbar lordosis (LL), sagittal vertical axis(SVA), Cobb angle and T1-sacrum plumbline. Clinical outcome was assessed using the visual analogue scale(VAS) and Oswestry disability index (ODI)scores. The main complications were analysed, and the two groups were compared. Except for age, the two populations were homogeneous. Both techniques had the same number of posterior instrumented levels (7.4 ± 1.7). The AC group had a mean 3 ± 1.4 interbody fusions per patient. In the PSO group, all patients had 1 3CO and 89.8% of the osteotomies were performed at L2 or L3 vertebrae. No difference was observed between the two groups in terms of clinical outcomes. Both techniques were effective in sagittal parameters restoration with a final PI-LL mismatch = 4.4°. The PSO group had a statistically higher rate of intraoperative blood loss (p = 0.036), major complications, pseudoarthrosis and dural tears (p < 0.001). Both PSO and multiple AC are effective in treating ASD. Multiple AC seems more suitable when treating older patients because of a lower intraoperative blood loss, lower rate of major complications and fewer number of revision surgeries.

Finite element study on the influence of pore size and structure on stress shielding effect of additive manufactured spinal cage

The stress shielding effect occurs when the orthopedic implant reduces the load delivered to the bone, causing inefficient stress transfer to the host bone. The usage of porous additive manufactured (AM) cages reduces the stress shielding effect and promotes bone ingrowth also. The purpose of this work is to study the stress and deformation on porous hybrid spinal cages under different loading conditions using Finite Element Analysis (FEA). The spinal cages consisting of three porous structures with pore sizes ranging from 0.4 to 0.6 mm were investigated for stress shielding and fatigue strength. The results showed a significant reduction in stress shielding for the studied designs and conclude that the pore size has a greater significant effect on stress shielding than the porous structure in spinal cages.

Biomechanical Properties of 3D-Printed Cervical Interbody Fusion Cage With Novel SF/nHAp Composites

Anterior cervical discectomy and fusion (ACDF) is a commonly used surgical method for the treatment of cervical spondylosis. As ACDF surgery is widely used in clinics, identifying suitable materials to design and prepare cervical interbody fusion cages is a hot research topic. Here, we describe a new three-dimensional (3D) printing approach to create stretchable and tough silk fibroin/nano-hydroxyapatite (SF/nHAp) composites with tunable mechanical properties. The compressive strength of the novel composites with biomimetic structure could reach more than 128 MPa. More importantly, the composites were prepared using 30% silk fibroin and 70% hydroxyapatite, a composition similar to the human bone tissue. Finite element analysis results indicate that the stress distribution of SF/nHAp composite cervical interbody fusion cages in vivo is more uniform than that of commercial Ti alloy cages. This study evaluates the effectiveness of SF/nHAp composites for application in cervical interbody fusion cages and in the field of bone tissue engineering.

37. The minimally invasive ante-psoas (MIS-ATP) fusion is safe in octogenarians with spinal deformity

<h3>BACKGROUND CONTEXT</h3> The elderly population, greater than 70 years old, is the fastest growing demographic in the U.S. Nearly 50% of individuals over 60 will experience lumbar spinal stenosis and 68% will develop scoliosis and adult spinal deformity (ASD). The octogenarian group, in particular, is considered at increased risk of complications following complex spine surgery. <h3>PURPOSE</h3> To assess the postoperative complications in order to determine the safety of MIS-ATP fusion in octogenarians. <h3>STUDY DESIGN/SETTING</h3> Retrospective case series. <h3>PATIENT SAMPLE</h3> A total of 43 patients with ASD who underwent MIS-ATP fusion surgery between January 2010 and December 2020. <h3>OUTCOME MEASURES</h3> The Charlson comorbidity index (CCI), American Society of Anesthesiologists (ASA), 30 days, one-year postoperative mortality. Demographic data included age, sex, BMI, number of fused segments, operation time, estimated blood loss, length of hospital stay, peri- and postoperative complications. <h3>METHODS</h3> A total of 43 patients with ASD who underwent surgery between January 2010 and December 2020 were retrospectively reviewed. Inclusion criteria were octogenarian adults (80-89 years old) with lumbar spinal deformity (scoliosis and/or kyphosis) treated with combined anterior (MIS-ATP) posterior (percutaneous fixation) fusion. The CCI was calculated, and outcomes measured were 30 days and one-year post-operative mortality. Demographic data included age, sex, BMI, number of fused segments, operation time, estimated blood loss, length of hospital stay, perioperative and postoperative complications. <h3>RESULTS</h3> A total of 43 patients were included for analysis in this study with an average age of 82.3 years old (range: 80-88 years). Of these, 24 patients were female (55.8%) and the average BMI was 28.0. Three patients (7.0%) were active smokers, 13 (30.2%) former smokers, 27 (62.8%) never smoked, and 7 patients (16%) reported alcohol consumption. The studied operative parameters (in averages) were: levels fused (3.9), operative time (3.1 hours), operative blood loss (412 cc) and length of hospital stay (7.5 days). Overall, the average CCI and ASA score were 5 and 3 respectively. Thirteen patients (30.2%) experienced complications (hardware-related, neurological, infectious and cardiovascular) of whom 6 (14.0%) required a revision surgery. No mortalities were noted at 30 days and at 1-year after surgery. Two patients died 2-3 years after surgery, from medical reasons unrelated to the spinal surgery. <h3>CONCLUSIONS</h3> This study highlights the relative safety of MIS-ATP surgery in the octogenarian population, despite the underlying medical vulnerability. Satisfactory recovery can still be achieved without major increase in operative morbidity and mortality. <h3>FDA DEVICE/DRUG STATUS</h3> Posterior longitudinal rod implants (Approved for this indication), Iliac screws (Approved for this indication), pedicle screws (Approved for this indication), interbody cage fusion (Approved for this indication).