The past, present, and the future of disc nucleus replacement. A systematic review of a large diversity of ideas and experiences.

Disc nucleus replacement (NR) is a challenging surgical technique used as a medical treatment for early-stage disc herniation to restore disc height and the biomechanical function of a motion segment, which may reduce low back pain. The surgical procedure involves the removal and replacement of the degenerated nucleus pulposus with a substitute by accessing the annulus fibrosos via a created hole. Over the decades, nucleus replacement has been an important issue, leading to the development of different substitute alternatives. The first ideas are dated to the 1950s and since then, more than a hundred nucleus replacement concepts can be identified. There were numerous attempts and several clinical trials; however, after more than 70 years of research, no gold standard for nucleus pulposus replacement has been identified. This review aims to collect the different nucleus replacements reported in the literature, thus understanding what failed, what could be improved and what are the opportunities for the future. A systematic review of the literature was performed using a keyword-based search on PubMed, Web of Science, and Scopus databases to detect all nucleus replacements presented in the past by clinicians and engineers. Several studies were extracted from which the main nucleus replacements over the years were investigated, including the ones that received CE mark, FDA approval, or IDE approval and, also those involved in clinical trials. A total of 116 studies were included in this review. The extracted data concern the nucleus replacements proposed over the years to create a historical background as complete as possible, including their mechanical and biomechanical characterization and the clinical trials conducted over the years. Nucleus disc arthroplasty has been explored for many years. Unfortunately, even today there is still nothing safe and definitive in this surgical practice. This review provides an overview of the nucleus replacement history. A breakthrough could be the improvements in technologies for the annulus fibrous closing or sealing and the tissue engineering and medical regenerative techniques which could certainly ensure a higher NR implantation success rate in the future of this clinical treatment. It is not yet clear what is the future of this clinical practice. Only scientific research can answer the question: is the nucleus replacement still a possible clinical solution?

Combined effect of artificial cervical disc replacement and facet tropism on the index-level facet joints: a finite element study.

BACKGROUND: Artificial Cervical Disc Replacement (ACDR) is an effective treatment for cervical degenerative disc diseases. However, clinical information regarding the facet joint alterations after ACDR was limited. Facet tropism is common in the sub-axial cervical spine. Our previous research indicated that facet tropism could lead to increased pressure on the cervical facet joints. This study aimed to assess the impact of facet tropism on the facet contact force and facet capsule stress after ACDR. METHODS: A C2-T1 cervical finite element model was constructed from computed tomography (CT) scans of a 28-year-old male volunteer. Symmetrical, moderate asymmetrical (7 degrees tropism), and severe asymmetrical (14 degrees tropism) models were created at the C5/C6 level by altering the facet orientation at the C5-C6 level. The C5/C6 ACDR was simulated in the intact, moderate asymmetrical and severe asymmetrical models. A 75-N follower load with 1.0-Nm moments was applied to the top of C2 vertebra in the models to simulate flexion, extension, lateral bending, and axial rotation with the T1 vertebra fixed. The range of motions (ROMs) under all moments, facet contact forces (FCFs) and facet capsule strains were tested. RESULTS: In the asymmetrical model, the right FCFs considerably increased under flexion, extension, right bending, left rotation, especially under right bending the right sided FCF of the severe asymmetrical model was about 5.44 times of the neutral position, and 3.14 times of the symmetrical model. and concentrated on the cephalad part of the facets. The facet capsule stresses on both sides remarkably increased under extension, lateral bending and right rotation. In the moderate and severe asymmetrical models, the capsule strain was greater on both sides of each position than in the symmetric model. CONCLUSIONS: The face tropism increased facet contact force and facet capsule strain after ACDR, especially under extension, lateral bending, and rotation, and also could result in abnormal stress distribution on the facet joint surface and facet joint capsule. The results suggest that face tropism might be a risk factor for post-operative facet joint degeneration progression after ACDR. Facet tropism may be noteworthy when ACDR is considered as a surgical option.

The effects of setup parameters on the measured kinetic output of cervical disc prostheses.

Mechanical testing machines are used to evaluate kinematics, kinetics, wear, and efficacy of spinal implants. The simulation of "physiological" spinal loading conditions necessitates the simultaneous use of multiple actuators. The challenge in achieving a desired loading profile lies in achieving close synchronization of these actuators. Errors in load application can be attributed to both the control system and the intrinsic sample response. Moreover, the presence of friction in the setup can have an impact on the measured outcome. The optimization of setup parameters can substantially improve the ability to simulate spinal loading conditions and obtain reliable data on implant performance. In this study, a reproducible kinematic test protocol was developed to evaluate the sensitivity of the kinetic response (i.e., measured loads, moments, and stiffnesses) of a cervical disc prosthesis to several testing parameters. In this context, five ceramic ball and socket sample implants were mounted in a 6 DOF material testing machine and tested with a constant axial compressive force of 100 N in two motion modes: 1) flexion-extension (±7.5°) and 2) lateral bending (±6°). Parameters including rotation rate, slider friction, friction between the samples' articulating surfaces, and moment arm were considered to determine their effects on measured kinetic parameters. The sensitivity analysis indicated that all setup parameters except friction between the samples' articulating surfaces had a substantial effect on the results. The findings were then compared to predictions from a free body diagram to determine the optimal setup parameters. Consequently, the setup with the lowest rotation rate and employing passive sliders yielded results that were consistent with the free body diagram. This study demonstrated the significance of a comprehensive setup evaluation for reliable and reproducible testing of spinal implants, also for comparison between labs.

The footprint mismatch of cervical disc arthroplasty comes from degenerative factor besides ethnic factor.

A mismatch in footprints of cervical total disc arthroplasty (CTDA) implants occasionally occurred in Asian population and it had been attributed solely to ethnic factor. Yet, cervical degeneration process may play a role. Our purpose was to compare the cervical vertebra morphometric data with and without degeneration. The study included patients with CT scans of cervical spine from our hospital between January, 2019, and September, 2021. The total cervical degenerative index (TCDI) of each patient were collected by adding CDI score for 5 disc-levels. Patients were categorized into normal (TCDI 0-5) and degeneration groups (TCDI 6-60). Various measurements of the C3-C7 vertebral body and endplate were taken. Forty-nine patients in the normal group and 55 in the degeneration group were included. No significant difference was noted in gender, BH, BW, or BMI except age and TCDI (p < .001). During degeneration, disproportional endplate size changes were observed, with an increment ratio of 12-20% in the anteroposterior and 5-17% in the mediolateral plane throughout C3-C7, while vertebral body height remained constant. In conclusion, degeneration process, besides ethnic factor, causes the endplate size and shape mismatch. This information can help spine surgeon choose appropriate implants in CTDA surgery.

Polyphenol-Mediated Adhesive and Anti-Inflammatory Double-Network Hydrogels for Repairing Postoperative Intervertebral Disc Defects.

Hydrogels have garnered tremendous attention for their applications in the repair of intervertebral disk (IVD) degeneration and postoperative IVD defects. However, it is still challenging to develop a hydrogel fulfilling the requirements for high mechanical properties, adhesive capability, biocompatibility, antibacterial properties, and anti-inflammatory performance. Herein, we report a multifunctional double-network (DN) hydrogel composed of physically cross-linked carboxymethyl chitosan (CMCS) and tannic acid (TA) networks as well as chemically cross-linked acrylamide (AM) networks, which integrates the properties of high strength, adhesion, biocompatibility, antimicrobial activity, and anti-inflammation for the repair of postoperative IVD defects. The treatment with CMCS/TA/PAM DN hydrogels can significantly decrease the levels of inflammatory cytokines and degeneration-related factors and upregulated collagen type II alpha 1. In addition, the hydrogels can effectively seal the annulus fibrosus defect, prevent nucleus pulposus degeneration, retain IVD height, and restore the biomechanical properties of the disc to some extent. This polyphenol-mediated DN hydrogel is promising for sealing IVD defects and preventing herniation after lumbar discectomy.

The Impact of Endplate Coverage on Heterotopic Ossification Following Cervical Disc Replacement: A Systematic Review and Meta Analysis.

STUDY DESIGN: Systematic review and meta-analysis. OBJECTIVE: Describe the impact of endplate coverage on HO in cervical disc replacement (CDR). SUMMARY OF BACKGROUND DATA: CDR is a motion-sparing alternative to anterior cervical discectomy and fusion. However, the high prevalence of heterotopic ossification threatens to diminish range of motion and limit this benefit associated with CDR. MATERIALS AND METHODS: A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. EMBASE and PubMed databases were queried. Results were deduplicated and screened. Relevant studies were included. All metrics that were reported in ≥3 studies were aggregated for analysis. SPSS was used to perform the meta-analysis. RESULTS: A total of 10 studies were included in the systematic review. Endplate coverage was assessed using a wide variety of measurements, including anteroposterior implant depth (ID), endplate depth (ED), exposed endplate depth (EED), implant depth to endplate depth ratio (ID:ED), EED to ED ratio (EED:ED), implant width (IW) to endplate width (EW) ratio (IW:EW), and the implant area (IA) to endplate area (EA) ratio (IA:EA). No evidence has linked ID (three studies) to HO. Mixed evidence has linked ID:ED (3/5) and IW:ED (1/2) to HO. All available evidence has linked ED (2), EED (4), EED:ED (2), and IA:EA (1) to HO. In our meta-analysis, ID was not found to be a significant risk factor for HO. However, EED and ID:ED were found to be significant risk factors for HO formation. CONCLUSIONS: Exposed endplate, especially as assessed by EED and ID:ED, is a significant risk factor for HO. Surgeons should focus on preoperative planning and intraoperative implant selection to maximize endplate coverage. While optimizing technique and implant selection is crucial, improved implant design may also be necessary to ensure that appropriate implant-endplate footprint matching is possible across the anatomic spectrum.

Sagittal morphometry of intervertebral spaces in subaxial cervical region of asymptomatic Chinese.

PURPOSE: This study aimed to quantify and evaluate morphology of intervertebral space between neighboring cervical units using radiographic imaging indices, to help spine surgeons when performing anterior cervical discectomy and fusion (ACDF) surgery on the Chinese population. METHODS: The background and imaging parameters of the subjects were assessed. Cervical lateral radiographs were employed to measure the intervertebral height (IH), intervertebral height index (IHI), and segmental lordosis (SL). Endplate parameters measurements were conducted on sagittal T2-weighted magnetic resonance imaging (MRI), including endplate sagittal diameter (ESD), and endplate concavity depth (ECD). All individuals were divided into three age groups: individuals aged 20-35 were in group A, individuals aged 36-50 were in group B, and individuals aged over 50 were in group C. A comparison of the variables was conducted among the three groups. Additionally, these radiographic parameters were also compared between males and females. RESULTS: A total of 102 individuals were included in this study. IH was greater at C6/7 than those at other segmental levels (p < 0.001). The largest SL values were found at C6/7, while the least were found at C3/4. The superior ESD (ESDs) and ECD (ECDs) of the intervertebral space were significantly greater than those of the inferior endplates (p < 0.05). The ESD and ECD values were the largest at C6/7, while the least at C3/4. Additionally, age and gender had an influence on several parameters. IH was significantly lower in group A compared to group B (p < 0.05) and group C (p < 0.05) from C3/4 level to C6/7 level. ECDs were lower in group A compared to group B (p < 0.05) and group C (p < 0.05) at each level. IH and ESD in males were generally significantly greater than those in females at all levels (p < 0.05). CONCLUSION: The current study found that C6/7 had the greatest IH, SL, ESD, and ECD values in asymptomatic Chinese. SL gradually increased from C3/4 to C6/7 levels. IH and ECD were significantly associated with age. Males had greater IH and ESD values than females. These findings provide baseline information for planning for selection of anterior screws and intervertebral implants.

The Impact of Demographic Characteristics, Obesity, Surgical Level, and Intervertebral Disc Properties on Recurrence of Lumbar Disc Herniation.

BACKGROUND: This study focused on identifying factors influencing recurrent lumbar disc herniation (RLDH) by analyzing demographic data, body mass index (BMI), and radiologic disc properties in patients undergoing single-level unilateral lumbar disc herniation surgery. METHODS: Our retrospective analysis included 2 groups from our clinic: Group 1 (n = 41) with patients experiencing RLDH requiring a second surgery, and Group 2 (n = 73) with patients having a single surgery and no recurrence over at least a 5-year follow-up. We assessed age, sex, diabetes mellitus (DM), hypertension (HT), BMI, Pfirrmann disc degeneration type, herniation types (protrusion, extrusion, and sequestration), and surgical level. RESULTS: The mean ages of Groups 1 and 2 were 48.93 ± 13.47 and 44.4 ± 11.79 years, respectively, with no significant age difference (P = 0.064). Gender distribution was also not significantly different, with 63.41% males in Group 1 and 56.16% in Group 2 (P = 0.450). DM prevalence was similar in both groups (P = 0.727). Notably, HT was significantly lower in Group 2 (P = 0.018). The average BMI was comparable between groups (P = 0.607), and no significant difference in Pfirrmann disc degeneration scores was observed (P = 0.547). Radiologic disc type distributions did not significantly differ (P = 0.448). Most surgeries in both groups were at the L4-5 level, with no significant differences in surgical levels (P = 0.456). CONCLUSIONS: We found that factors like gender, age, DM, obesity, surgical level, disc degeneration, and disc types do not significantly impact RLDH. However, the higher occurrence of HT in recurrent cases indicates a potential area for further research.

Domain adaptation using AdaBN and AdaIN for high-resolution IVD mesh reconstruction from clinical MRI.

PURPOSE: Deep learning has firmly established its dominance in medical imaging applications. However, careful consideration must be exercised when transitioning a trained source model to adapt to an entirely distinct environment that deviates significantly from the training set. The majority of the efforts to mitigate this issue have predominantly focused on classification and segmentation tasks. In this work, we perform a domain adaptation of a trained source model to reconstruct high-resolution intervertebral disc meshes from low-resolution MRI. METHODS: To address the outlined challenges, we use MRI2Mesh as the shape reconstruction network. It incorporates three major modules: image encoder, mesh deformation, and cross-level feature fusion. This feature fusion module is used to encapsulate local and global disc features. We evaluate two major domain adaptation techniques: adaptive batch normalization (AdaBN) and adaptive instance normalization (AdaIN) for the task of shape reconstruction. RESULTS: Experiments conducted on distinct datasets, including data from different populations, machines, and test sites demonstrate the effectiveness of MRI2Mesh for domain adaptation. MRI2Mesh achieved up to a 14% decrease in Hausdorff distance (HD) and a 19% decrease in the point-to-surface (P2S) metric for both AdaBN and AdaIN experiments, indicating improved performance. CONCLUSION: MRI2Mesh has demonstrated consistent superiority to the state-of-the-art Voxel2Mesh network across a diverse range of datasets, populations, and scanning protocols, highlighting its versatility. Additionally, AdaBN has emerged as a robust method compared to the AdaIN technique. Further experiments show that MRI2Mesh, when combined with AdaBN, holds immense promise for enhancing the precision of anatomical shape reconstruction in domain adaptation.

[Expert consensus on clinical application of cervical artificial disc replacement].

Cervical artificial disc replacement preserves the range of motion after the decompression, and this technology has achieved good clinical results. The indications, surgical procedures, and perioperative management of cervical disc arthroplasty are different from traditional anterior cervical decompression and fusion. The Health Management and Enhanced Recovery of Cervical Spine Disorders Committee, Chinese Research Hospital Association has established an expert group to draw up this expert consensus through literature analysis and professional discussions. The purpose of this consensus is to standardize the surgical indications and patient selection of cervical artificial disc replacement, to guide surgical procedures and perioperative management, and to improve the clinical outcomes of cervical artificial disc replacement.

Effects of Ozone Disc Nucleolysis in Management of Herniated Lumbar Intervertebral Disc: A Retrospective Single-Center Study of 149 Patients.

BACKGROUND Lower back pain is a common problem in the general population. Medical treatment is the first choice for patients without severe pain and major motor weakness. If patients do not benefit from conservative treatment, minimally invasive treatment is recommended. Ozone nucleolysis has recently been used to reduce pain and inflammation in herniated discs and other spinal conditions. This retrospective study from a single center aimed to evaluate the effects of ozone disc nucleolysis in the management of 149 patients with herniated lumbar intervertebral discs from 2022 to 2024. MATERIAL AND METHODS Between 2022 and 2024, intradiscal ozone nucleolysis was performed under operating room C-arm scopy in 149 patients who received medical treatment and physical therapy without surgical indication but did not benefit, and the results were evaluated retrospectively. Visual Analog Scale (VAS) scores and Oswestry Disability Index (ODI) scores were recorded before the procedure, and at 1 month, 3 months, 6 months, and 1 year. RESULTS The study enrolled 149 patients, comprising 61 males and 88 females, with an overall mean age of 43.9±4.7 years. The procedure was performed as 1 level in 138 patients and 2 levels in 11 patients. Among patients who underwent procedures based on lumbar MRI findings, 15 involved the L3-L4 intervertebral disc, 3 involved both the L3-L4 and L4-L5 discs, 90 involved the L4-L5 disc, and 31 involved the L5-S1 disc. Post-procedure VAS scores were significantly different at 1 month and 6 months (P<0.05). Post-procedure ODI scores were also significantly different at 1 month and 6 months. CONCLUSIONS Due to its low complication rate and effectiveness in treating lumbar disc herniation, ozone chemonucleolysis should be considered for use in patients who do not have a surgical indication or do not accept surgical intervention and did not benefit from medical treatment and physical therapy.

Prosthesis optimization and mechanical analysis of artificial lumbar disc replacement.

BACKGROUND: Artificial lumbar disc replacement is an effective method for the treatment of lumbosacral degenerative diseases. An appropriate artificial intervertebral disc device is of great significance for the maintenance of spinal stability and activity. METHODS: Two finite element models of ProDisc-L prosthesis replacement and improved prosthesis replacement were constructed by using the finite element model of complete lumbar L1-L5 segment established by CT image data. The mechanical properties of the surgical models before and after improvement were analyzed and evaluated. RESULTS: The ProDisc-L group and the improved group showed similar lumbar's ROM and maintained a similar ROM with the normal lumbar spine. There was no significant change in the intervertebral disc's pressure between the adjacent segments of the two prosthesis groups compared with the normal group, but the stress value of the improved prosthesis group was slightly lower than that of the ProDisc-L group. In addition, the improved prosthesis replacement has more reasonable stress distribution. CONCLUSIONS: Compared with the ProDisc-L prosthesis, the improved prosthesis can reduce the pressure in the intervertebral disc of the adjacent segment, the contact stress of the facet joint and the artificial prosthesis, which provides reference for the subsequent design of the prosthesis structure.

Effect of device constraint: a comparative network meta-analysis of ACDF and cervical disc arthroplasty.

BACKGROUND CONTEXT: Clinical trials have demonstrated that cervical disc arthroplasty (CDA) is an effective and safe alternative treatment to anterior cervical discectomy and fusion (ACDF) for cervical degenerative disc disease in the appropriately indicated patient population. Various devices for CDA exist, differing in the level of device constraint. PURPOSE: To investigate outcomes following Anterior Cervical Discectomy and Fusion (ACDF) versus CDA stratified based on the level of device constraint: Constrained, Semiconstrained, and Unconstrained. STUDY DESIGN: Systematic review and network meta-analysis. PATIENT SAMPLE: A total of 2,932 CDA patients (979 Constrained, 1,214 Semiconstrained, 739 Unconstrained) and 2,601 ACDF patients from 41 studies that compared outcomes of patients undergoing CDA or ACDF at a single level at a minimum of 2 years follow-up. OUTCOME MEASURES: Outcomes of interest included the development of adjacent segment degeneration (ASD), index and adjacent segment reoperation rates, range of motion (ROM), high-grade heterotopic ossification (HO, McAfee Grades 3/4), and patient-reported outcomes (NDI/VAS). METHODS: CDA devices were grouped based on the degrees of freedom (DoF) allowed by the device, as either Constrained (3 DoF), Semiconstrained (4 or 5 DoF), or Unconstrained (6 DoF). A random effects network meta-analysis was conducted using standardized mean differences (SMD) and log relative risk (RR) were used to analyze continuous and categorical data, respectively. RESULTS: Semiconstrained (p=.03) and Unconstrained CDA (p=.01) demonstrated a significantly lower risk for ASD than ACDF. All levels of CDA constraint demonstrated a significantly lower risk for subsequent adjacent segment surgery than ACDF (p<.001). Semiconstrained CDA also demonstrated a significantly lower risk for index level reoperation than both ACDF and Constrained CDA (p<.001). Unconstrained devices retained significantly greater ROM than both Constrained and Semiconstrained CDA (p<.001). As expected, all levels of device constraint retained significantly greater ROM than ACDF (p<.001). Constrained and Unconstrained devices both demonstrated significantly lower levels of disability on NDI than ACDF (p=.02). All levels of device constraint demonstrated significantly less neck pain than ACDF (p<.05), while Unconstrained CDA had significantly less arm pain than ACDF (p=.02) at final follow-up greater than 2 years. CONCLUSION: CDA, particularly the unconstrained and semiconstrained designs, appears to be more effective than ACDF in reducing the risk of adjacent segment degeneration and the need for further surgeries, while also allowing for greater range of motion and better patient-reported outcomes. Less constrained CDA conferred a lower risk for index level reoperation, while also retaining more range of motion than more constrained devices.

Bone Marrow Aspirate Concentrate Combined with Ultra-Purified Alginate Bioresorbable Gel Enhances Intervertebral Disc Repair in a Canine Model: A Preclinical Proof-of-Concept Study.

Although discectomy is commonly performed for lumbar intervertebral disc (IVD) herniation, the capacity for tissue repair after surgery is limited, resulting in residual lower back pain, recurrence of IVD herniation, and progression of IVD degeneration. Cell-based therapies, as one-step procedures, are desirable for enhancing IVD repair. This study aimed to investigate the therapeutic efficacy of a combination of newly developed ultra-purified alginate (UPAL) gel and bone marrow aspirate concentrate (BMAC) implantation for IVD repair after discectomy. Prior to an in vivo study, the cell concentration abilities of three commercially available preparation kits for creating the BMAC were compared by measuring the number of bone marrow mesenchymal stem cells harvested from the bone marrow of rabbits. Subsequently, canine-derived BMAC was tested in a canine model using a kit which had the highest concentration rate. At 24 weeks after implantation, we evaluated the changes in the magnetic resonance imaging (MRI) signals as well as histological degeneration grade and immunohistochemical analysis results for type II and type I collagen-positive cells in the treated IVDs. In all quantitative evaluations, such as MRI and histological and immunohistochemical analyses of IVD degeneration, BMAC-UPAL implantation significantly suppressed the progression of IVD degeneration compared to discectomy and UPAL alone. This preclinical proof-of-concept study demonstrated the potential efficacy of BMAC-UPAL gel as a therapeutic strategy for implementation after discectomy, which was superior to UPAL and discectomy alone in terms of tissue repair and regenerative potential.

A Morphometric Study of Cadavers for the Anterior Approach to the Lower Lumbar Spine.

AIM: To explore the relationship between the retroperitoneal vasculature and anterior surface of the lower spine, and to establish values for aiding in prediction of the pertinence of anterior approach at the L4-L5 and L5-S1 intervertebral discs. MATERIAL AND METHODS: The study included 13 fresh human cadavers. After exploration of the abdominal cavity and removal of the visceral organs, the vasculature, and anterior spinal surface were revealed beneath the lower extension of the perirenal fascia. Morphometric measurements of the great vessels and the intervertebral discs were obtained. All measurements were analyzed and presented as mean and standard deviation. Differences in the values between sexes were assessed. RESULTS: The anterior height of the L4-L5 and L5-S1 intervertebral disc was 6.8 ± 0.81 mm and 6.7 ± 0.99 mm, respectively. The widths of the aorta, inferior vena cava, right and left common iliac arteries, and right, and left common iliac veins were 16.4 ± 3.58, 20.6 ± 3.36, 11.5 ± 2.32, 11.5 ± 2.43, 14.7 ± 3.13, and 15.5 ± 3.27 mm, respectively. The mean aortic bifurcation angle was 45.5°. The aortic bifurcation was located above the lower endplate of the L4 vertebrae in 53.8% of the cadavers. The area of the interarterial and interiliac trigones was 14.6 ± 5.33 cm < sup > 2 < /sup > and 7.1 ± 4.35 cm2, respectively. No statistically significant differences were noted between the sexes. CONCLUSION: An elaborate radiological examination of the vasculature should be performed prior to surgery to avoid unwanted vascular complications during the anterior approach. Knowing the area of the interarterial and interiliac triangles and the aortic bifurcation location could be aid in assessing the safe working zone.

Biomechanical analysis of adjacent segments after correction surgery for adult idiopathic scoliosis: a finite element analysis.

The biomechanical aspects of adjacent segment degeneration after Adult Idiopathic Scoliosis (AdIS) corrective surgery involving postoperative changes in motion and stress of adjacent segments have yet to be investigated. The objective of this study was to evaluate the biomechanical effects of corrective surgery on adjacent segments in adult idiopathic scoliosis by finite element analysis. Based on computed tomography data of the consecutive spine from T1-S1 of a 28-year-old male patient with adult idiopathic scoliosis, a three-dimensional finite element model was established to simulate the biomechanics. Two posterior long-segment fixation and fusion operations were designed: Strategy A, pedicle screws implanted in all segments of both sides, and Strategy B, alternate screws instrumentation on both sides. The range of motion (ROM), Maximum von Mises stress value of intervertebral disc (IVD), and Maximum von Mises stress of the facet joint (FJ) at the fixation adjacent segment were calculated and compared with data of the preoperative AdIS model. Corrective surgery decreased the IVD on the adjacent segments, increased the FJ on the adjacent segments, and decreased the ROM of the adjacent segments. A greater decrease of Maximum von Mises stress was observed on the distal adjacent segment compared with the proximal adjacent segment. The decrease of Maximum von Mises stress and increment of Maximum von Mises stress on adjacent FJ in strategy B was greater than that in strategy A. Under the six operation modes, the change of the Maximum von Mises stress on the adjacent IVD and FJ was significant. The decrease in ROM in the proximal adjacent segment was greater than that of the distal adjacent segment, and the decrease of ROM in strategy A was greater than that in strategy B. This study clarified the biomechanical characteristics of adjacent segments after AdIS corrective surgery, and further biomechanical analysis of two different posterior pedicle screw placement schemes by finite element method. Our study provides a theoretical basis for the pathogenesis, prevention, and treatment of adjacent segment degeneration after corrective surgery for AdIS.

Optimizing Disc and Cartilage Endplate Preparation in Full-Endoscopic Lumbar Interbody Fusion: An In-Depth Exploration of Surgical Instruments with a Technique Note and Narrative Review.

Full-endoscopic lumbar interbody fusion (FELIF) is a critical yet challenging procedure. However, extensive analyses of discectomy and cartilage endplate preparation techniques are limited. This can be attributed to the lack of universal protocols owing to diverse surgical practices and equipment preferences. Therefore, this narrative review presents a comprehensive overview of discectomy and cartilage endplate preparation techniques in FELIF. A literature search of the PubMed, Embase, and Google Scholar databases in December 2023 retrieved 490 studies, of which 53 met the predefined inclusion criteria, and 1373 patients were included in the analyses. Spinal endoscopic disc and cartilage endplate removal can be categorized into 2 main types: removal under direct endoscopic visualization and removal under radiographic guidance with the protection of a working sheath following the endoscope's removal. Removal under direct visualization ensures the safety and precision of the procedure. Radiographic guidance can enhance the efficiency of the removal process. Specially designed instruments can be utilized through the narrow working channels of spinal endoscopes for the scraping surgery. Moreover, many traditional spinal endoscopic instruments, through specific techniques and manipulations, can also aid in cartilage removal. The approaches and techniques vary significantly among physicians, but overall, these instruments and techniques aim to achieve a safe and efficient disc-scraping outcome. Thus, this review may offer a comprehensive guidance to surgeons in selecting the most efficient practices for FELIF. Uniform procedural protocols are needed to ensure broader adoption and standardized practice.

Biomechanical analysis of single and multi-level artificial disc replacement (ADR) in cervical spine using multi-scale loadings: A finite element study.

Artificial disc replacement (ADR) is a clinical procedure used to diagnose cervical degenerative disc disease, preserving range of motion (ROM) at the fixation level and preventing adjacent segment degeneration (ASD). This study analyzed the biomechanics of ADR by examining range of motion (ROM), stress levels in bone and implants, and strain in the bone-implant interface using multi-scale loadings. The study focused on single- and double-level patients across various loading scales during physiological motions within the cervical spine. Results showed increased ROM in single-level and double-level fixations during physiological loadings, while ROM decreased at the adjacent level of fixation with the intact cervical spine model. The Prodisc-Implant metal endplate experienced a maximum von Mises stress of 432 MPa during axial rotation, confirming the long durability and biomechanical performance of the bone-implant interface.

Disc-coloration of an ochronotic cervical intervertebral disc in a patient with alkaptonuria: Case report and review of the literature.

OBJECTIVES: Alkaptonuria is a rare inborn disorder of phenylalanine and tyrosine metabolism. It is characterized by an accumulation of homogentisic acid and its oxidation products, possibly resulting into connective tissue damaging. "Ochronosis" is a main feature, which is characterized by tissue discoloration and even alkaptonuric arthropathy. Cervical spine involvement is exceptional and there is a paucity of reports on surgical interventions in these patients. We explored the literature concerning cervical spine involvement in patients with alkaptonuria. PATIENTS AND METHODS: We performed a review of the literature, in which patients with alkaptonuric degenerative changes of the cervical spine were examined. Articles were obtained from MEDLINE. Search terms included: "cervical", "alkaptonuria", "alkaptonuric changes" and "black disc". Additional studies were identified by checking reference lists. Furthermore, we present the case of a 46 year old patient with critical cervical spinal canal stenosis who underwent C6-C7 anterior cervical microdiscectomy and interbody fusion, in order to prevent myelopathic changes. CARE statement guidelines were followed. RESULTS: Peroperatively, we did not encounter any macroscopic abnormalities of the skin, muscles or ligaments. A black discoloration of the nucleus pulposus was observed. Peroperative and postoperative course was uneventful. CONCLUSION: Alkaptonuric degenerative abnormalities most commonly involve the lumbar spine, although the cervical spine can be affected in rare cases. Most frequently, the diagnosis of alkaptonuria can be made based on the clinical phenotype many years before symptoms secondary to ochronotic arthropathy develop. A retrospective diagnosis based on peroperative black discoloration of spinal structures has been described. A black discoloration of the intervertebral disc should encourage the neurosurgeon to further explore the possibility of alkaptonuria, even in the absence of a clear phenotype. Surgical results are mostly satisfactory. Further studies are required in order to better understand this pathology and its postoperative course.