Bibliometric and Visualization Analysis of Biomechanical Research on Lumbar Intervertebral Disc

Introduction

The lumbar intervertebral disc (IVD) is an essential component of the spinal system, playing a crucial role in maintaining the biomechanical balance of the spine.^1–3 With the advancements in modern medicine and the increasing aging population worldwide, diseases related to lumbar IVD degeneration have become a global health challenge, significantly impacting people’s quality of life and physical and mental health.^4–6 The biomechanical characteristics of the lumbar IVD are a crucial factor in its degeneration, and an in-depth understanding of these characteristics can provide more scientific theoretical basis for the prevention, treatment, and rehabilitation of relevant diseases caused by IVD degeneration.^7–9 In recent years, with the deepening of biomechanical research, people have gained a more profound understanding of the biomechanical characteristics of the lumbar IVD, and research on the biomechanics of the lumbar IVD has received increasing attention. Bibliometrics, as a research method that can conduct quantitative analysis and visualization of large-scale literature data, can reveal the development trends and evolution rules of specific research fields.^10–12 By adopting bibliometric visualization technology, a comprehensive and in-depth analysis of the literature related to lumbar IVD biomechanics can be conducted, which can not only contribute to a deeper understanding of the research history, current status, and future development trends in this field, but also reveal the weak areas and directions of research, providing new insights and guidance for further research. However, to the best of our knowledge, there is currently no bibliometric report on the study of lumbar IVD biomechanics.

The present study aims to utilize the data of relevant literature on biomechanical research of lumbar IVD, published in the Science Citation Index Expanded (SCI-Expanded) of Web of Science Core Collection (WoSCC) database over the past 2 decades, as the research object. Visual analysis software such as VOSviewer 1.6.19 and CiteSpace 6.2.R2, as well as the online analysis platform of literature metrology (https://bibliometric.com/) were used to generate scientific knowledge maps, displaying research hotspots and future development trends from multiple perspectives. Based on big data and visualization techniques, this study provides important guidance and insights for the research and academic development of the biomechanics of lumbar IVD, offering creative perspectives and ideas for the future development of relevant disciplines.

Materials and Methods

Data Source and Search Strategy

The SCI-Expanded dataset from the WoSCC database was selected as the data source for this study. To ensure accuracy and consistency of the data, both literature search and data extraction were conducted on the same day. To improve the accuracy of the search, we obtained the subject headings from MeSH and constructed the search strategy using a combination of subject headings and free words. The specific search formula was as follows: (((((TS = (lumbar)) AND TS = (intervertebral disc OR intervertebral disk)) AND TS = (biomechanical OR biomechanics OR biomechanic OR finite element)) AND DT = (Article OR Review)) AND LA = (English)) AND DOP = (2003-01-01/2022-12-31). Following screening, a total of 1,409 relevant publications that met the inclusion criteria were obtained.

Bibliometric Analysis

Export the publications that meet the inclusion criteria in a plain text format with “full record and cited references”, and name the file “download_xxx.txt.” Import this file to VOSviewer 1.6.19 and CiteSpace 6.2.R2 software for scientific knowledge map visualization. Simultaneously, export the publications in a tab delimited file and import it into the online analysis platform of document metrology for country/region collaboration analysis. In VOSviewer, set the normalization method to association strength and set the minimum thresholds for country, institution, and author publication to 15, 10, and 10, as well as for author, journal, and reference citation frequency to 100, 200, and 70, respectively. The minimum threshold for keyword frequency is set to 15. In CiteSpace, set the time span to January 2003 to December 2022, with a year per slice of 2. Select “keyword” and “reference” as node types and “top 50 each slice” as selection criteria. Use pathfinder, pruning sliced networks, and pruning the merged network in pruning, while keeping other settings as default.

Results

Analysis of Annual Publications and Citations

This study incorporates a total of 1,409 literature pieces related to biomechanical research on lumbar IVD, including 1,314 research papers (93.26% of the total) and 95 review papers (6.74% of the total). The total citations (TC) are 36,850, with an average of 26.15 citations per paper and an H-index of 86. As illustrated in Figure 1A, both the annual publications and citations have demonstrated a steady upward trend over the past two decades. Specifically, the number of publications increased nearly 3.5 times from 34 in 2003 to 118 in 2022, while the citations increased by over 300 times from 13 in 2003 to 4,335 in 2022. These findings indicate a growing research interest and recognition in this field, particularly in the last 3 years, when the citation frequency experienced a rapid rise. Figure 1B shows the changing trends in annual publications among the top 10 countries/regions in terms of publication, which have shown varying degrees of growth from 2003 to 2022. Notably, China has experienced the greatest increase in annual publications, with relatively low publication numbers in earlier years, but with rapid increases in later years, particularly in the past 5 years. In 2019, China surpassed the United States for the first time, ranking first in the annual publications.

Figure 1 (A) Annual publications and citations trend chart of biomechanical research on lumbar IVD. (B) Stack bar plot of top 10 countries/regions by total papers from 2003 to 2022.

Analysis of Countries/Regions

Figure 2A illustrates a knowledge graph of national/regional cooperation network. where each colored block represents a country/region and its size is proportional to the number of publications. Lines indicate the cooperation relationships among countries/regions, with the thickness of the lines representing the frequency of cooperation.^13,14 As shown, the United States has published the most papers in this field and has close collaborations with China, Canada, Switzerland, Australia, and Germany. Figure 2B displays the cooperation relationships and the average publication time among countries/regions. Node size represents the number of publications, and the lines and thickness indicate the cooperation relationships and strength, respectively. The warmer colors of the nodes signify later average publication times.^15–18 It appears that the United States made outstanding contributions in the early research of this field with earlier average publication times, while China has recently published a large number of academic achievements. Additionally, Table 1 lists relevant information of the top 10 countries/regions in terms of publication volume, with the United States (484, 34.35%), China (272, 19.30%), and Germany (174, 12.35%) accounting for 66% of the total publications. The United States ranks first in TC (16,258), h-index (66), and total link strength (TLS) (154), while Switzerland, despite ranking seventh in publication output (61), exhibits the highest average citation per publication (ACPP) (38.26). The h-index is an indicator of academic influence, while TLS reflects the strength of relationships with other nodes.^19–22

Figure 2 (A) National/regional cooperative network knowledge graph. (B) Time superposition diagram of national/regional cooperation network.

Table 1 Top 10 Countries/Regions Ranked by Number of Publications

Analysis of Institutions

In Figure 3, the collaboration and average publishing time among institutions with a publication count of at least 10 are presented. It can be observed that Ulm University, University of Pennsylvania, and University of Bern have earlier average publishing times, while Icahn School of Medicine at Mount Sinai has shown increased activity in this field in recent years. Table 2 lists the top 10 institutions in terms of publication count, with Ulm University (53, 3.76%) being the most prolific institution, followed by University of Pennsylvania (41, 2.91%), University of California San Francisco (28, 1.99%), Northeastern University (28, 1.99%), and University of Bern (28, 1.99%). Ulm University also leads in TC (3,367) and h-index (32), while Rush University (23, 1.63%) and University of Vermont (23, 1.63%) have the highest TLS (29) and ACPP (66.43), respectively.

Figure 3 Time superposition diagram of institutional cooperation network.

Table 2 Top 10 Institutions Ranked by Number of Publications

Analysis of Authors

Figure 4A depicts the collaboration network and average publication time for authors who have published no fewer than 10 papers in this field. Notably, early research in this area featured contributions from distinguished authors such as Wilke HJ, Schmidt H, Elliott DM, and Heuer F, while research in recent years has seen prolific contributions from authors such as Iatridis JC, Shirazi-adl A, and Guo LX. Figure 4B presents a co-citation network of authors who have been cited no less than 100 times. Each node represents a cited author, with node size indicative of frequency of citation, and links between nodes indicating co-citation relationships. Different colors denote distinct clusters.^23,24 Table 3 reveals that Wilke HJ not only has the most publications (61, 4.33%), but also boasts the highest TC (3,613), h-index (33) and TLS (98), whereas Rohlmann A’s ACPP (88.80) ranks at the top. Additionally, Table 4 lists information about the top 10 authors with the highest citation frequency, including Adams MA (1065), Wilke HJ (919), and Panjabi MM (741), who are ranked in the top 3 for both citation frequency and TLS.

Figure 4 (A) Time superposition diagram of author’s cooperative network. (B) Author co-citation network knowledge graph.

Table 3 Top 10 Authors Ranked by Number of Publications

Table 4 Top 10 Co-Cited Authors Ranked by Citation Frequency

Analysis of Journals

Table 5 illustrates the relevant information of the top 10 journals in the research field of biomechanics of lumbar IVD, ranked by publication count. Spine is the highest-ranked journal in terms of publications (163, 11.57%), TC (7,939), and h-index (228). Its impact factor (IF) and journal citation reports (JCR) quartile are 3.241 and Q2, respectively. J Biomech and Eur Spine J follow closely behind, with Eur Spine J having the highest ACPP (49.52). Notably, Spine J is the highest-ranked journal in terms of IF (4.297) and JCR quartile (Q1). Figure 5 displays the co-citation relationships among these journals, and Spine, J Biomech, and Eur Spine J are the top 3 journals in terms of citation frequency and TLS. J Bone Joint Surg Am has an IF of 6.558 and JCR quartile of Q1, making it a highly cited journal of high quality. Further information can be found in Table 6. The dual-map overlay analysis in Figure 6 visually displays the distribution of journals and their referencing relationships. The left side of the figure shows the citing journals, while the right side shows the cited journals, with colored paths representing citation relationships.^25–27 Five main citation paths are identified, indicating that papers published in journals related to molecular/biology/genetics, health/nursing/medicine, sports/rehabilitation/sport, and psychology/education/social are primarily cited by papers published in medicine/medical/clinical and neurology/sports/ophthalmology journals.

Figure 5 Journal co-citation network knowledge graph.

Figure 6 Double graph superposition of journals.

Table 5 Top 10 Journals Ranked by Number of Publications

Table 6 Top 10 Co-Cited Journals Ranked by Citation Frequency

Analysis of References

Figure 7 illustrates the co-citation relationships among 35 publications that have been cited no less than 70 times, whereas Table 7 presents relevant information on the top 10 most cited publications. The study conducted by Wilke et al published in Spine in 1999 stands out as the most cited document, with the highest TLS. By defining the minimum burst duration as 3 years, a total of 30 references with high burst strength were detected, of which 13 had a burst duration that ended in 2022 or later, as shown in Figure 8. The blue lines in the figure represent time intervals, the red lines indicate burstiness durations, while “Strength” denotes burst strength, and “Begin” and “End” respectively signify the start and end time of the burstiness.^28–31 Citation bursts refer to papers that are frequently cited within a period.^32–34 By analyzing these burst papers, researchers can gain insight into the research hotspots and future development trends in a particular field.

Figure 7 Literature co-citation network knowledge graph.

Figure 8 Top 30 references ranked by burst strength.

Table 7 Top 10 Co-Cited References Ranked by Citation Frequency

Analysis of Keywords

The succinct summary of research contents using keywords allows for an analysis of high-frequency keywords, providing insight into the main research content and hot topics within a particular field.^86–88 Figure 9 depicts the co-occurrence relationship and average appearance time of keywords appearing no less than 15 times. It can be observed that keywords such as biomechanics, lumbar spine, and IVD appear earlier due to the focus of the study, while keywords such as finite element analysis (FEA), low back pain, and IVD degeneration occur frequently in recent years. Additionally, Table 8 presents the top 20 high-frequency keywords and their TLS, which to some extent reflect the primary research content and hot topics within the field. Through keyword clustering, 12 clustering labels were obtained and presented in the form of a keyword timeline map (Figure 10) to facilitate the clear observation of the time evolution characteristics of each clustering field. Burst words are keywords that frequently appear in a certain period, and analyzing them can reveal the research hotspots and development trends of a field.^89–91 By setting the shortest burst duration to 3 years, 30 keywords with the highest burst strength were detected, of which 8 will continue to burst until 2022 or later (Figure 11), thereby reflecting recent hot research topics to some extent.

Figure 9 Keyword co-occurrence network knowledge graph.

Figure 10 Keyword timeline graph.

Figure 11 Top 30 keywords ranked by burst strength.

Table 8 Top 20 Keywords Ranked by Frequency of Occurrence

Discussion

This study employs bibliometric analysis and visualization techniques to comprehensively and systematically dissect the field of biomechanical research on lumbar IVD from multiple perspectives. By constructing scientific knowledge maps, the knowledge framework and development trajectory of this field were visually presented, and research hotspots and future trends were explored to some extent, offering valuable insights for further investigation.

The United States, as the most prolific country, has made significant contributions in this field, constituting 34.35% of the total publications. Furthermore, it ranks first in TC, h-index, and TLS, signifying its notable academic influence and standing in this research sphere, as well as its close collaborations with other countries/regions. Conversely, China, while being the second-highest producer of publications, and surpassing the US in annual paper output since 2019, ranks last in terms of ACPP, and only seventh in terms of h-index. This indicates that China, while having a significant edge in publication quantity, has not achieved extensive recognition and citation by researchers in the same field due to its research quality. Therefore, while pursuing publication volume, China needs to focus on improving research quality and strengthening international exchange and cooperation in order to produce high-quality research results and enhance its academic influence in this field. Meanwhile, Switzerland, despite having relatively fewer publications, has the highest ACPP, indicating that its research results have gained widespread recognition and citations from scholars in the same field, reflecting its high-quality research level and academic prestige. Moreover, it is noteworthy that 70% of the top 10 high-productivity countries/regions come from North America and Europe, indicating that they are the main research hubs in this field.

Ulm University, located in Germany, is the institution with the most publications, highest TC, and highest h-index, indicating its exceptional academic research caliber and the attention its research achievements receive. Among these, a highly cited study published by the institution investigated the impact of IVD degeneration on the mechanics of the motion segment by constructing a three-dimensional (3D) nonlinear finite element model (FEM) of L3/L4 functional units. The results showed that the predicted trends of intersegmental rotation and intradiscal pressure were consistent with the results of in vitro studies. Mildly degenerated IVD increased intersegmental rotation under all loading conditions, while with further degeneration, intersegmental rotation decreased. Regarding axial rotation, the decrease occurred in the final stages. In comparison with healthy discs, degenerated discs showed lower intradiscal pressure but higher facet joint forces and maximum von Mises stresses in the annulus fibrosus (AF).⁴² The Ulm University has close collaborations with institutions such as the University of Bern, Charite, Ecole Polytechnique, the University of British Columbia, and the Eindhoven University of Technology. The University of Vermont, located in the United States, ranks 10th in terms of publications, but has the highest ACPP, reflecting its outstanding research level and high academic influence. One of the most highly cited publications from this institution reviewed literature evidence in the fields of biomechanics, epidemiology, animal models, and IVD physiology to explore the mechanical conditions that accelerate IVD degeneration. The conclusion was that any abnormal loading conditions, including overload and immobilization, could cause tissue trauma and/or adaptive changes, leading to IVD degeneration.⁹² Although Northeastern University in China ranks high in terms of publications, it has the lowest citation frequency and h-index and lacks international communication and cooperation. Therefore, its ability to conduct high-level research should be improved and international communication should be strengthened. Furthermore, it is evident that the majority of highly productive and influential institutions are situated in Europe and the United States, with the United States alone accounting for 50% of these institutions. This indicates that the primary research forces in this field are distributed in Western countries, which is consistent with the analysis of countries/regions.

Wilke HJ from Ulm University in Germany is the most prolific author with the highest TC, h-index and TLS, which attests to his exceptional academic accomplishments and influence in the field, and has established extensive collaborations with Schmidt H, Galbusera F, Heuer F, Shirazi-adl A, Rohlmann A, Clses L, and Iatridis JC. One of his highly cited papers used a 3D nonlinear FEM of the lumbar L4-L5 segment to investigate intradiscal pressure, shear strains between the AF and adjacent endplate, and fiber strains of the AF under pure and combined moments. The results showed that combined moments may lead to higher stresses in the disc, especially in the posterior-lateral region, which may be more susceptible to disc injury and herniation.⁹³ Rohlmann A from Charite Universitatsmedizin Berlin in Germany is the author with the highest ACPP, indicating that his research findings are frequently cited by scholars in the same field and he has a high academic reputation. One of his highly cited papers used 3D FEMs of the lumbar L4-L5 segment with different IVD degeneration grades (healthy, mild, moderate, and severe) to investigate the loading conditions resulting in the highest internal stresses in healthy and degenerated discs. The results showed that intradiscal pressure is highest during flexion in all degeneration grades, and shear and fiber strains increased significantly in healthy discs during lateral bending + flexion and in all degenerated discs during axial rotation and lateral bending + axial rotation, mainly in the posterior-lateral AF, with mild degeneration exhibiting increased intradiscal pressure and fiber strains when compared to healthy discs.⁷⁷ Guo LX from Northeastern University in China has relatively lower citation frequency and h-index, indicating the need to continuously improve research capability, strengthen international cooperation and communication, and publish high-quality academic research. Adams MA from the University of Bristol in the UK has the highest citation frequency and TLS among cited authors, indicating his high academic influence and the broad referencing of his research results, as well as active co-citation relationships with researchers such as Wilke HJ, Panjabi MM, Schmidt H, Iatridis JC, Rohlmann A, Goel VK, Shirazi-adl A, Urban JPG, and Nachemson A.

Spine, J Biomech, Eur Spine J, Spine J, and Clin Biomech are renowned high productivity and highly cited journals that hold significant academic influence and exhibit strong co-citation relationships in the field. Thus, when publishing research findings or searching for relevant literature, these five journals should be considered as a priority. Notably, 80% of the top 10 high productivity journals are from the United States and the United Kingdom, while all of the top 10 highly cited journals are from these two countries as well. This indicates that journals from these countries make significant contributions to research in this field, attracting broad attention and recognition from global researchers. Therefore, it is crucial to recognize the importance of these journals and regard them as valuable channels for publishing and retrieving high-level research achievements.

To a significant extent, highly cited publications can reflect the main research themes and knowledge structure of a given field, and are considered to be high-quality research with significant academic influence.^94–96 Among them, the most cited publication is a study by Wilke et al published in Spine in 1999, which measured intradiscal pressure in a volunteer and found that sitting may actually result in lower intradiscal pressure than standing, and that muscle activity increases pressure. The study also emphasized the importance of continuously changing positions to promote fluid (nutrient) flow to the disc, and suggested that some of the physical therapy methods studied may need to be re-evaluated.⁶⁰ Secondly, Pfirrmann et al⁵⁴ developed and optimized an algorithm for assessing and grading lumbar disc degeneration based on conventional magnetic resonance imaging (MRI), and tested the reliability of the grading system. The results showed that the grading system and algorithm can reliably grade disc degeneration on MRI. Additionally, Adams et al⁵⁷ researched the distribution of compression stress in cadaveric IVD and found that age and degeneration have a greater effect on the L4/L5 segment than on the L2/L3 segment, with the posterior AF being more affected than the anterior AF. Adams et al⁵² also discovered through literature review that structural defects, such as endplate fractures, radial fissures, and herniation, are clear indicators of IVD dysfunction. The reason for biological progress is that structural failure decouples the local mechanical environment of the IVD cells from the overall load on the IVD, resulting in potentially inappropriate or abnormal responses by the IVD cells. Excessive mechanical load damages the structure of the IVD, triggering a series of cell-mediated reactions that lead to further damage. Schmidt et al⁴⁴ developed a method for calibrating the double composite structure of the AF, the ground substance, and collagen fibers by constructing a 3D nonlinear FEM of the L4-L5 segment. They found that the combinations of infinite material parameters for collagen fibers and ground substance resulted in the same range of motion (ROM), but different ROM for each bending moment. However, there was only one combination that was applicable to all bending moments and in all loading directions. Goel et al³⁸ found through FEA that the interlaminar shear stress was higher in the posterolateral regions of the intact IVD, further demonstrating that tears originate from the posterior-lateral part of the IVD. The significant inter-laminar shear stress caused by the asymmetry of the IVD structure due to damage and the chemical and structural changes of the IVD with age may be important reasons for the further degeneration via laminae separation. Holzapfel et al³⁹ conducted an in vitro study of single lamellar anulus lamellae, showing that the single layer of AF lamellae could be regarded as the basic structural unit of the AF, displaying significant anisotropy and clear regional variation of tensile properties and fiber angles. Shirazi-Adl et al⁴⁰ analyzed the response of the L2-3 lumbar motion segment to pure axial torque and combined compression using a nonlinear 3D finite element program, finding that with increasing torque, the axis of rotation moved backward in the IVD of the intact segment, such that at the maximum torque, the axis of rotation was behind the IVD itself. The loss of IVD pressure increased this backward movement, while resection of the facets reduced it. Torque itself did not cause fiber damage in the IVD, but when combined with other types of loads (such as flexion), it increased the vulnerability of fibers located in the posterior-lateral and posterior regions. The posterior bony structure was the most fragile part of this segment in torque. The aforementioned highly cited literature serves as the primary research foundation in the field, carrying considerable academic influence and reference significance. These works represent significant objects of focus for gaining a comprehensive understanding of the field.

The phenomenon of literature burst refers to specific publications that have garnered substantial attention within a given time frame. By analyzing burst literature during this period, one can gain insight into the current hot topics and trends within a research field.^97–99 Accordingly, this study will focus on the analysis of literature that has remained in the spotlight until 2022 or later, in order to better reflect recent research hotspots and future development trends within this field. Wilke et al⁷³ implanted pressure sensors into the nucleus pulposus (NP) of a non-degenerative L4-5 IVD in a volunteer to measure intra-disc pressure data as a basis for validating predicted spinal load models. Results showed that intra-disc pressure is dependent on the type of prior activity, posture, external load, and muscle activity. Dreischarf et al⁵³ conducted a study on eight established lumbar (L1-5) FEMs from various research centers globally, using pure and combined loading modes, and compared in vivo and in vitro measurement results of intervertebral rotations, intra-disc pressures, and facet joint forces. Results indicated that in pure moment loading, almost all models predicted L1-5 rotation angles within the reported range of in vitro measurements, with median values differing by only 2° for flexion/extension, 1° for lateral bending, and 5° for axial rotation, and predicted facet joint forces and disc pressures median values also corresponded well with published in vitro medians. Schmidt et al⁷⁶ performed FEA on multi-level total disc arthroplasty (TDA) by establishing a complete human lumbar spine 3D FEM and implanting multiple Charité IVDs in the L1-L5 region from level two to four. The results indicated that the more artificial IVD are implanted, the stronger the predicted flexion and extension motion increased compared to the intact state. Deviation from the optimal implantation location could lead to adverse kinematics, high facet joint forces, and even delamination. Therefore, multi-level TDA should only be performed in suitable patients with good muscle condition and surgical doctors who can ensure optimal implantation positions. Park et al⁷⁸ conducted an analysis of how degeneration of IVD affects the biomechanics of the lumbar spine and established and verified lumbar spine FEM with different grades of degeneration in L4-L5 functional spinal unit (FSU). Results found that as degeneration progressed, intersegmental rotation in the degenerated FSU decreased during flexion/extension and lateral bending, while adjacent FSU’s intra-disc pressure increased during flexion and lateral bending. Additionally, facet joint forces in the degenerated FSU increased during lateral bending and axial rotation. Newell et al⁷⁹ conducted a comprehensive review of testing techniques and outcomes related to human IVD biomechanics. They found that the mechanical properties of the entire IVD can be conveniently assessed by testing “motion segment”, consisting of two vertebrae and the intervening IVD and ligaments. However, the accuracy of these evaluations may be influenced by various factors, including the testing environment, preprocessing methodology, loading rate, sample age and degeneration, and the spinal level being tested. Schmidt et al⁸⁰ conducted a study to examine the accuracy disparities of calibrated and uncalibrated FEM of lumbar segments with various clinical defects. The results found that both FEM performed well in simulating the intact state. However, in cases of defects, the calibrated model demonstrated exceptional consistency in predicting movement behavior, while the uncalibrated model exhibited significant deviation. A comprehensive review conducted by Iatridis et al explored the role of biomechanics in IVD degeneration and regeneration therapy, including the specific mechanical characteristics that need to be repaired and how to evaluate and achieve such reparative processes using biomaterials. The study concluded that IVD height, neutral zone features, and torsional biomechanics are sensitive to specific changes in the compression of the NP and the integrity of the AF, which require effective functional repair. Synthetic and natural biomaterials hold promise for NP replacement, AF repair, AF sealant, or total IVD replacement. To attain optimal efficacy and durability of the repair, it is critical that the biomaterials meet both mechanical and biocompatibility criteria.⁸¹ Ayturk et al⁸² employed a FEM based on the human lumbar L1-L5 to verify the mesh convergence for every component of the tissue, and extensively validated their model using kinematic/kinetic and stress/strain data. Meanwhile, Renner et al⁸³ utilized a 3D FEM of the lumbar L1-S1 to analyze the effects of a significant compressive follower preload on the ROM in all three planes. The results indicated that the compressive follower preload led to a reduction in both the total and segmental ROM during flexion-extension by 18%, lateral bending by 42%, and torsion by 26%. Xu et al⁸⁴ employed the same modeling approach to develop five FEMs of human lumbar (L1-L5) based on five healthy live subjects, and conducted extensive validation using literature data as well as mesh convergence and material sensitivity analysis. The results demonstrated that the results generated by the five FEMs developed by the authors were in alignment with both experimental data and simulation outcomes reported within the current literature. Adams et al⁸⁵ reviewed evidence for two types of IVD degeneration. The “endplate-driven” type involves endplate defects and inward buckling of the AF, has a higher genetic predisposition, and primarily affects IVDs of the upper lumbar and thoracic regions, whereas the “annulus-driven” type involves radial fissures and/or disc herniation, has a lower heritability, and mainly affects IVDs of the lower lumbar region. Structural defects triggering both processes play a role in decompressing the IVD nucleus, reducing the likelihood of subsequent defect occurrence, hence, these two phenotypes of IVD degeneration can be considered distinct. Based on the analysis of highly cited and burst literature, it can be inferred that the main research topics in this field include the construction and validation of 3D FEM of the lumbar spine, measurement of intradiscal pressure, biomechanical effects of lumbar IVD degeneration, biomechanical risk factors of lumbar IVD degeneration, mechanical response to different torque load combinations, and MRI classification of lumbar IVD degeneration.

Analysis of keyword co-occurrence, clustering, and burst reveals that the primary research topics in this field includes biomechanics, IVD, lumbar spine, and FEA, which have high frequency of occurrence and strong TLS. The FEA, low back pain, IVD degeneration, AF, MRI, tissue engineering, and endplate are relatively new research subjects that have gained attention in recent years. The 12 clustering labels, including #0 finite element, #1 hydraulic permeability, #2 follow up, #3 finite element method, #4 FEA, #5 disc degeneration, #6 IVD degeneration, #7 intradiscal pressure, #8 FEM, #9 lumbar spine, #10 strength, and #11 NP, to some extent reflect the main research themes in this field. Meanwhile, the burst keywords, such as classification, risk factors, herniation, validation, stepwise reduction, disc, and loads, have duration that ends in 2022 or later, indicating the research hotspots and future development trends in this field.

Strengths and Limitations

This study conducted a comprehensive and systematic analysis of the literature pertaining to the biomechanics of lumbar IVD using bibliometrics and visualization techniques. Unlike traditional reviews that rely on subjective screening and incorporate a limited sample size of research objects, bibliometrics, as a big data analysis methodology, can thoroughly evaluate research objects from multiple perspectives while presenting the results in a more comprehensive and intuitive manner through visualization.^100,101 Nevertheless, this study also has some limitations. Firstly, our study focused solely on the SCI-Expanded in WoSCC database, which may have potentially excluded relevant studies, although WoSCC database is the most commonly used database in bibliometrics.^102–105 Secondly, some high-quality studies published recently may have been underestimated in our analysis due to their limited citation frequency. Finally, due to the constantly updating nature of databases, the dataset for this year is still incomplete and therefore not included in this study. Despite these limitations, our study results still hold significant reference value, particularly in facilitating the development of research areas and guiding future research directions.

Conclusion

The field of biomechanics of lumbar IVD has seen steady growth in the number of publications and citations over the past 20 years, attracting increasing attention from researchers. The United States has emerged as the most productive country, with Ulm University making the largest contribution. Wilke HJ is both the most prolific author and one of the highly cited authors, with extremely high academic impact and prestige, while Adams MA has the highest citation frequency. Spine, J Biomech, Eur Spine J, Spine J, and Clin Biomech are not only the journals with the most publications, but also highly cited journals, making outstanding contributions to this field and having high academic influence. The main research topics in this field include the construction and validation of 3D FEM of the lumbar spine, measurement of intradiscal pressure, exploration of the biomechanical effects and related risk factors of lumbar IVD degeneration, study of the mechanical response to different moment load combinations, and MRI classification of lumbar IVD degeneration, which are also the hot research topics in recent years. Future research trends are expected to focus on the establishment of more sophisticated FEM of the lumbar spine for multidimensional biomechanical analysis of IVD. Additionally, based on the biomechanical characteristics of IVD, research will explore the effective repair and regenerative treatment of disc degeneration and injuries using biomaterials. These trends will bring new concepts and methods to the research and clinical treatment of lumbar IVD, promoting faster development in this field.