Abstract
-
Objective
Lumbar disc herniation is among the most common and disabling spinal disorders, driven by the interplay of mechanical overload, structural failure, and cellular dysfunction. Despite advances in surgical interventions, achieving true biological repair of herniated discs remains a major clinical challenge. This review aims to critically examine the biomechanical landscape of disc herniation, focusing on how altered load transmission, tissue stiffness, and structural disruption influence cellular behavior and tissue regeneration. It further explores mechanobiological mechanisms governing repair and highlights emerging biomimetic models and technologies that integrate mechanical and biological insights to promote functional disc restoration.
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Methods
A comprehensive literature review was conducted using the Web of Science Core Collection, PubMed (National Library of Medicine), and ScienceDirect databases. The search was limited to peer-reviewed journal articles published in English and focused on studies related to lumbar disc herniation.
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Results
While decades of research have elucidated the biomechanical factors contributing to disc herniation, recent advances in mechanobiology have uncovered how mechanical cues influence cellular behavior, tissue repair, and degeneration. Evidence suggests that true disc regeneration cannot be achieved through biological replacement or mechanical stabilization alone; rather, it requires restoring functional biomechanics, specifically, the disc’s ability to sense, adapt to, and sustain physiological loading.
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Conclusion
Viewing disc herniation through a mechanobiological lens offers new opportunities to develop targeted therapies aimed at restoring both tissue integrity and load-bearing functionality, paving the way for more effective regenerative interventions.
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Keywords: Lumbar spine, Intervertebral disc, Herniation, Mechanobiology, Biomechanics, Regeneration
INTRODUCTION
Lumbar disc herniation (LDH), a common and clinically important spinal pathology, is a multifactorial disorder that originates from a mechanical failure of the disc structure and progresses through complex biological responses. While estimates vary depending on the population studied and imaging modality used, the annual prevalence of symptomatic LDH, especially with radiculopathy, is often cited in the range of 1% to 3% in the adult population [
1]. A large-scale study reported the incidence of laminectomy for LDH in adults at 13 per 10,000 adults per year, depending on age, sex, and other risk factors [
2]. The point prevalence of symptomatic LDH with radiculopathy estimates ranging from 2.8 to 218 per 1,000 males depending on source population and case definition [
3]. Epidemiological studies show that LDH is more common in men than in women, with clinical cohorts reporting higher prevalence among males and earlier literature describing approximately a 2:1 male:female incidence ratio [
4,
5].
Treatment of LDH usually starts with conservative management, including activity modification, pain control, physical or chiropractic therapy, and epidural steroid injections. When these fail or in cases with severe or progressive neurological deficits, surgical options such as laminotomy with discectomy are considered [
6]. Recent randomized trials and meta-analyses show that surgical intervention generally provides more rapid relief of leg pain and improvement in disability compared to nonoperative care, though long-term outcomes may converge [
7,
8]. Minimally invasive and endoscopic techniques have been shown to have similar efficacy and complication rates to traditional open microdiscectomy, with potential advantages of shorter hospital stay, less intraoperative blood loss, and faster recovery [
9-
12]. Emerging therapies (e.g., biologics such as platelet-rich plasma, bone marrow aspirate concentrate, or low-intensity pulsed ultrasound) show promise in symptom relief and perhaps disc regeneration but currently lack sufficient long-term evidence and standardized protocols [
13,
14].
Biomechanically, LDH results from a complex interplay of axial compression, torsion, bending, and shear forces, often accumulated over years of repetitive loading [
15,
16]. These forces can cause localized annular delamination, radial fissures, and eventual extrusion or sequestration of nuclear material. Recent advances in imaging, computational modelling, and experimental biomechanics have provided valuable insights into the structure–function relationship of the disc and relevant regenerative strategies [
17-
20]. Finite element models incorporating detailed microstructural characteristics of the disc have enabled the prediction of stress concentrations, annular tears, and bulging behavior under different mechanical loading scenarios [
21,
22]. Although the mechanical causes of LDH (such as excessive compression, torsion, and flexion) are well documented, the underlying mechanobiological processes that determine whether a herniated disc degenerates or regenerates remain poorly defined. Traditionally, LDH has been conceptualized primarily as a structural disorder, managed through mechanical stabilization or tissue replacement. However, the disc is a dynamic, mechanosensitive tissue in which cell behavior, extracellular matrix (ECM) homeostasis, and fluid transport are tightly regulated by mechanical cues [
23]. The disruption of these cues after LDH alters the local stress environment, nutrient exchange, and cellular mechanotransduction, collectively navigating the tissue toward catabolism rather than repair [
24,
25].
Recent advances in biomechanics and tissue engineering have reshaped our understanding of disc biology, highlighting that effective regeneration depends on restoring disc homeostasis, including a favorable mechanical microenvironment [
26]. Mechanical loading not only drives degenerative cascades but also holds the potential to guide repair when appropriately modulated [
27]. In this context, the integration of biomechanical and mechanobiological knowledge is essential for improving diagnostic precision, preventive strategies, and the development of functional regenerative strategies.
This review aims to critically synthesize current understanding of the biomechanical landscape of disc herniation and the mechanobiological principles governing post-injury regeneration. We highlight how alterations in tissue mechanics influence cellular and molecular responses, discuss recent progress in experimental and computational modelling, and outline emerging strategies that couple biological repair with mechanical functionality. By reframing LDH as both a mechanical and biological disorder, we aim to provide new insights into the development of next-generation regenerative therapies.
REVIEW METHODOLOGY
This critical narrative review employed a structured literature search of the Web of Science Core Collection, PubMed (National Library of Medicine), and ScienceDirect to identify peer-reviewed, English-language articles relevant to LDH. These databases were selected to provide complementary coverage of biomedical, biomechanical, and engineering literature central to the topic. Databases with substantial content overlap or a primary focus on pharmacological studies (e.g., Embase) were not included, consistent with the narrative scope of the review. Search terms included combinations of “lumbar disc herniation,” “biomechanics,” “mechanobiology,” and “regeneration.”
The search timeframe was limited to publications from 2015 to 2025 to emphasize recent methodological and conceptual advances in the field. Seminal earlier studies were incorporated selectively where necessary to provide historical context and conceptual grounding. Article selection was guided by relevance to biomechanical and biological mechanisms of disc pathology and repair, rather than by formal systematic review criteria. Reference lists of selected articles were manually screened to identify additional relevant studies. This approach was designed to support a thematic and interpretive synthesis rather than a fully reproducible systematic review.
THE BIOMECHANICAL LANDSCAPE OF LDH
Disc functions as a complex load-bearing structure that dissipates forces through a finely tuned interaction between the nucleus pulposus (NP), annulus fibrosus (AF), and cartilage endplates (EP). Under physiological loading, the NP maintains hydrostatic pressure, allowing uniform transmission of stress to the AF lamellae. LDH occurs when this mechanical equilibrium is disrupted, most often by repetitive or excessive mechanical loading that exceeds the tissue’s adaptive capacity. Compressive overload and asymmetric loading are key mechanical drivers of AF rupture and NP extrusion; as such, LDH is fundamentally a mechanically driven process arising from the interaction of complex loading scenarios acting on a structurally vulnerable disc [
28]. Studies have shown that excessive or repetitive mechanical loading—particularly combined axial compression, flexion, and shear—can disrupt this load-sharing balance, generating localized stresses that exceed the mechanical strength of the AF [
29]. The posterolateral regions of the disc, where lamellae are thinner, collagen and elastic architecture are weaker, and the posterior longitudinal ligament provides less reinforcement, are particularly susceptible to microstructural damage [
30,
31]. Microdamage accumulation within the lamellae, followed by delamination and radial fissuring, represents the mechanical precursor to LDH (
Fig. 1) [
15,
30-
41]. These biomechanical principles explain why herniations predominantly occur at L4–5 and L5–S1, the segments experiencing the highest mechanical demand in the lumbar spine [
32]. These regions are also subjected to the highest flexion and compressive forces during daily activities such as lifting or bending.
From the macrostructural point of view, once herniation occurs, the mechanical environment of the disc undergoes profound reorganization. The loss of NP material compromises internal pressurization, resulting in altered load distribution across the motion segment and contributing to disc height reduction [
42]. This shift increases compressive stress on the posterior AF and endplates, while adjacent vertebrae experience higher facet joint loads and instability. Herniated disc material can exacerbate local mechanical strain within the disc, while associated EP deformation and impaired diffusion pathways further compromise disc nutrition [
43]. Furthermore, herniation compromises the disc’s viscoelastic damping behaviors, thereby reducing its ability to recover shape after deformation. Studies have demonstrated that even small annular defects can significantly reduce disc stiffness, promoting micromotion at the injured site [
44]. Importantly, the mechanical threshold for LDH and AF failure is not fixed and is influenced by hydration state, aging-related tissue degradation, and local anisotropy in disc microstructure (i.e., fiber orientation) [
45,
46]. Over time, these biomechanical alterations accelerate degenerative processes and may contribute to recurrent herniation or chronic low back pain. Degenerative changes, such as reduced NP hydration, loss of proteoglycans, or annular stiffening, exacerbate stress concentrations, lowering the threshold for disc failure even under physiological loads [
47]. Although the natural history of LDH is often favorable, clinical outcomes vary considerably among individuals [
48]. Spontaneous symptom resolution is frequently associated with biological resorption of herniated disc material, particularly in extruded or sequestrated herniations, through macrophage-mediated phagocytosis, neovascularization, and matrix remodeling [
49,
50]. Concurrent reductions in inflammatory signaling and mechanical nerve root compression further contribute to recovery [
51]. In contrast, persistent symptoms may reflect ongoing mechanical compression, sustained inflammatory activity, impaired disc resorption, failure to restore physiological load transfer, altered mechanobiological responses to loading, or neural sensitization [
49]. These observations highlight that LDH outcomes are regulated by dynamic interactions between biological, mechanical, and neural factors rather than disc morphology alone.
The relationship between spinal flexion, compression rate, and traumatic disc failure has been extensively investigated [
32,
52,
53]. Studies have shown that high physiological flexion combined with rapid compressive loading significantly increases the risk of herniation [
29]. Under these conditions, failure typically originates from subtle tears in the mid-to-outer annular region, where collagen fiber strains are highest due to the curvature of the EP and the anisotropic structure of the AF [
31]. These microstructural tears can propagate under continued mechanical stress, eventually allowing nuclear material to extrude and form a herniation. This mechanistic understanding aligns with clinical observations of LDH failure anatomy, in which herniation frequently originates at the EP–AF junction rather than from AF rupture [
54]. Moreover, the findings underscore the importance of considering both the magnitude and rate of loading in injury prevention and rehabilitation strategies and they provide a rationale for developing biomechanically informed therapies, such as motion-preserving interventions and targeted regenerative treatments for AF repair.
At the microstructural level, AF tears and structural abnormalities disrupt the collagen–elastin network, impairing fiber recruitment and load sharing between adjacent lamellae [
55]. The EP, which normally distributes compressive forces and facilitates nutrient transport, may also exhibit microfractures, further compromising mechanical and metabolic integrity [
54]. Collectively, these structural changes transform the disc from a pressurized, load-bearing structure into a mechanically unstable system prone to progressive degeneration. The AF itself exhibits multiple modes of structural disruption that precede and contribute to LDH, including circumferential tears, delamination, radial fissures, and rim lesions [
30,
31,
56]. Circumferential tears are commonly observed in cadaveric discs from as early as adolescence, suggesting that lamellar delamination may be one of the earliest events in the cascade leading to disc degeneration and eventual LDH. Mechanistically, these tears are thought to result from high interlamellar shear stresses, which propagate along the boundaries of adjacent lamellae [
57]. The interlamellar matrix, the connective interface between lamellae, is therefore a critical structural element, serving as the primary site of failure initiation [
58,
59]. Circumferential disruption of the interlamellar matrix not only facilitates lamellar delamination but also provides a low-resistance pathway for NP material during herniation. Recent microstructural imaging has provided quantitative insights into these processes [
60] (
Fig. 2).
The regional mechanical properties of the interlamellar matrix are substantially lower than those of the surrounding lamellae, with this disparity becoming more pronounced as the disc progresses toward LDH [
39]. Experiments on isolated AF samples show that the failure stress of the interlamellar matrix decreases significantly during the transition from preherniated to herniated states, identifying it as the weakest structural component of the AF [
39]. Other studies have demonstrated that discs with preexisting AF defects exhibit significantly greater susceptibility to LDH than discs with an intact AF [
55]. Such defects compromise the structural integrity of the inner and middle annular layers, reducing their ability to distribute load effectively. As a result, once the mid-to-outer AF is subjected to elevated stress or repetitive loading, the weakened regions facilitate the propagation of tears and subsequent nuclear material extrusion [
56]. These findings underscore the critical role of micromechanical heterogeneity within the AF in dictating both the initiation and progression of disc herniation and they provide a mechanistic basis for targeted studies on prevention, early diagnosis, and repair strategies.
BIOMECHANICAL FEEDBACK AND DEGENERATIVE PROGRESSION POST-LDH
LDH initiates a vicious biomechanical-biological feedback loop in which altered disc structure and load distribution increase abnormal stress and strain on residual disc tissue and surrounding structures, including the facet joints and ligaments. These mechanical changes promote inflammation, cellular stress, and matrix degradation, driving an imbalance between anabolic and catabolic signaling. Elevated shear and tensile strains upregulate proinflammatory cytokines (e.g., interleukin [IL]-1β, tumor necrosis factor-α) and matrix-degrading enzymes (MMPs), further weakening the ECM and reducing its load-bearing capacity [
61] (
Fig. 3). The resulting stress redistribution amplifies local damage, perpetuating degeneration. The reduction in disc height also alters spinal kinematics, increasing segmental mobility and facet joint stress, which can accelerate adjacent-level degeneration [
62]. Importantly, these biomechanical consequences are not confined to the injured disc, regional mechanical imbalance across the lumbar spine contributes to global postural and loading changes that impede healing.
From a regenerative standpoint, the postherniation disc microenvironment represents a hostile niche for both endogenous and implanted cells, where excessive strain, hypoxia, and acidic pH impair matrix synthesis and cell survival [
63]. Understanding disc degeneration following LDH requires an integrated perspective that considers the biomechanical environment in conjunction with biological responses. Mechanical loading is not only a physical stressor but also a potent regulator of cellular and ECM behaviors within the AF [
64,
65]. However, the impact of mechanical stimuli must be interpreted in the context of inflammatory activity, as inflammatory mediators can alter cellular mechanosensitivity and impair the tissue’s ability to maintain homeostasis. Few studies have examined the combined effects of mechanical loading and proinflammatory conditions on AF structural and functional integrity. One such study used a bovine AF organ culture model to apply cyclic tensile strain under defined proinflammatory conditions [
61]. The findings of this study demonstrated that the combination of mechanical overload and inflammatory stimulation significantly alters the AF homeostasis, as evidenced by disrupted matrix organization, reduced cell viability, and region-specific changes in the synthesis and spatial distribution of key ECM components. These results indicate a synergistic detrimental effect of mechanical and inflammatory stress, suggesting that the AF is vulnerable to mechano-inflammatory environments. Collectively, these findings provide new evidence that mechanical overload in the presence of inflammation compromises AF integrity, thereby contributing to microstructural weakening and the early pathogenesis of LDH [
61]. Beyond elucidating the pathomechanisms underlying LDH, mechanobiology plays a central role in guiding the development of regenerative and tissue engineering strategies aimed at restoring AF integrity after injury. Mechanical loading is a key determinant of cellular behavior, influencing mesenchymal stem cell differentiation, ECM synthesis, and the organization of collagen lamellae, all of which are essential for functional AF repair [
64]. Incorporating physiologically relevant mechanical stimuli, such as cyclic tensile strain, hydrostatic pressure, and compressive loading, into tissue-engineered constructs has been shown to enhance matrix deposition and promote the alignment of collagen fibers that mimic native AF architecture [
66]. Conversely, inappropriate or excessive loading can impair matrix organization and cell viability, emphasizing the need for precisely controlled biomechanical conditioning during the development of AF repair models [
67]. Consequently, understanding the mechanical microenvironment is essential not only for preventing LDH but also for designing effective mechanobiologically informed therapies capable of achieving durable AF regeneration and restoring disc function [
66].
Thus, successful regeneration requires not only biological repair but also the restoration of mechanical stability and physiological load sharing. Recent studies underscore that the capacity for disc healing depends on re-establishing mechanical homeostasis [
26]. Restorative biomechanics, achieved through surgical stabilization, biomaterial implantation, or physiologically guided loading, may modulate cell mechanosensing pathways, thereby promoting anabolic remodeling. Conversely, mechanical environments that are too rigid or too compliant can induce stress shielding or overstrain, both detrimental to tissue integration [
24]. Mechanical parameters such as intradiscal pressure, AF tensile strain, and endplate permeability emerge as critical determinants of regenerative success. Optimal load conditions appear to fall within a narrow window: sufficient to stimulate mechanotransducive signaling but below the threshold of damage. Identifying and replicating these “proregenerative” mechanical cues remains an unmet challenge that mechanobiology seeks to address. From a mechanobiological perspective, it is believed that optimal disc recovery depends on appropriately dosed mechanical loading [
68,
69]. Low-magnitude cyclic loading generally represents a physiological stimulus if activity remains within a pain-tolerable range [
69]. Physiological stimuli support disc nutrition, fluid transport, and matrix homeostasis [
70]. In contrast, sustained mechanical unloading or physical inactivity lacks mechanobiological justification, as sustained unloading may impair nutrient diffusion, promote matrix degradation, and exacerbate deconditioning [
71-
73]. Following partial discectomy, a short period of protective loading may be warranted to allow early tissue healing; however, progressive reintroduction of controlled mechanical loading is essential to support mechano-adaptation and functional recovery [
74].
MECHANOBIOLOGY OF DISC REGENERATION
The disc is a mechanically sensitive organ in which resident cells continuously perceive and respond to physical stimuli. Disc cells (NP and AF cells, and EP chondrocytes) translate mechanical forces into biochemical signals through a process known as mechanotransduction [
24]. This occurs via cell surface receptors (e.g., integrins, stretch-activated ion channels, primary cilia), the cytoskeleton, and downstream signaling pathways such as mitogen-activated protein kinase (MAPK), nuclear factor-kappa B (NF-κB), and YAP/TAZ (yes-associated protein/transcriptional coactivator with PDZ-binding motif) [
75,
76]. In addition to mechanical disruption, biochemical signaling pathways contribute to the disc microenvironment following LDH, with muscle-derived factors such as irisin influencing NP cell metabolism and matrix turnover [
77]. However, abnormal or excessive mechanical stress activates catabolic pathways, suppresses matrix production, and promotes apoptosis. Studies have shown that hyper-physiological loading elevates MMP expression while downregulating aggrecan and collagen II, leading to progressive matrix breakdown [
78]. Mechanotransduction also governs inflammatory responses within the disc, as mechanical overload induces nuclear translocation of NF-κB and upregulation of proinflammatory cytokines, further disrupting ECM organization [
79]. Mechanical dysregulation contributes to cytoskeletal disruption of NP cells highlighting the importance of tightly controlled mechanical cues in maintaining a healthy cellular phenotype [
80]. These findings underscore the dual role of mechanical stimuli as regulators of homeostasis and as drivers of degeneration.
Following LDH, the local mechanobiological environment becomes profoundly disrupted. The mechanical integrity of the AF is compromised, NP pressure decreases, and the surrounding tissues experience abnormal strain distributions. These changes directly affect cell viability and function, as cells at the LDH site are exposed to elevated tensile strains and shear stresses beyond their physiological tolerance, leading to necrosis, apoptosis, and senescence. Concurrently, LDH alters the tissue’s biochemical microenvironment. Reduced diffusion through the damaged AF and EP results in hypoxia, glucose deprivation, and accumulation of acidic metabolites [
81]. These factors synergise with mechanical stress to impair cellular metabolism and suppress the synthesis of ECM. Mechanically stressed NP cells under acidic, low-nutrient conditions exhibit a shift toward a proinflammatory, catabolic phenotype, marked by increased IL-6, cyclooxygenase-2, and nitric oxide release [
82].
The inflammatory response following AF rupture adds another layer of complexity, as infiltrating immune cells release cytokines and degradative enzymes that further weaken the ECM, altering local mechanical stiffness and thereby perpetuating abnormal cell mechanosensing. The resulting loss of appropriate mechanical cues prevents adoption of a regenerative phenotype, reinforcing a cycle of mechanical instability and biological degradation [
24,
76,
80]. Another major challenge is the loss of the disc’s intrinsic mechanical and material gradient. In healthy discs, stiffness transitions smoothly from the compliant NP to the stiffer AF, allowing uniform stress transfer. LDH disrupts this gradient, creating stress concentration that hinder tissue integration and ECM remodeling. Without restoration of these mechanical boundaries, even biologically promising regenerative approaches may fail to restore function.
INTEGRATING MECHANOBIOLOGY INTO CLINICAL TRANSLATION
Recognizing the central role of mechanobiology in disc repair following LDH has prompted the development of therapies that harness mechanical cues to guide regeneration. Three major directions have emerged: mechanically tuned biomaterials, dynamic loading paradigms, and mechanosensitive cellular therapies.
Mechanically tuned biomaterials: hydrogels, scaffolds, and injectable biomaterials have been designed to replicate the native stiffness and anisotropy of the disc. Gradient hydrogels, for example, mimic the NP–AF transition, enabling spatially controlled stress distribution [
83]. Materials that degrade or stiffen in response to mechanical loading offer the potential for adaptive regeneration, in which material properties evolve with tissue healing [
84]. Importantly, overly rigid implants can induce stress shielding, while overly compliant materials fail to support load transfer, underscoring the need for precise mechanical matching.
Dynamic loading and rehabilitation:
In vitro and
ex vivo studies have demonstrated that cyclic compressive loading within physiological magnitudes promotes proteoglycan synthesis and ECM deposition, whereas static or excessive loading is deleterious [
85,
86]. Mechanically active bioreactors and organon-chip systems are increasingly used to apply controlled mechanical regimes to disc cells or tissue explants, enabling systematic study of proregenerative load profiles [
17,
87-
89]. Translationally, this concept supports the idea that postsurgical or post-implantation rehabilitation should aim not merely to limit load but to restore physiological loading to re-establish mechanobiological equilibrium.
Mechanosensitive cellular therapies: stem cells and progenitor cells derived from bone marrow, adipose tissue, or the disc itself exhibit mechanoresponsive behavior. Substrate stiffness, strain magnitude, and fluid shear can direct their differentiation toward NP-like or AF-like phenotypes. Combining these cells with mechanically optimized matrices or dynamic culture conditions enhances their anabolic activity and integration potential [
90-
92]. However, a persistent challenge lies in maintaining cell functionality under the harsh mechanical and biochemical conditions of the post-LDH niche.
Despite growing mechanobiological insight, clinical translation remains limited. Most regenerative interventions, such as annular closure devices, hydrogel replacements, or biologic injections, fail to account for the evolving mechanical environment of the herniated disc. The absence of standardized mechanical evaluation in preclinical testing contributes to inconsistent outcomes and poor reproducibility. Integrating biomechanical restoration with biological repair represents a promising strategy. For example, combining annular closure systems that restore tensile integrity with biomaterials engineered to provide appropriate compressive resistance may help re-establish functional load distribution within the disc [
93]. Computational models and finite element simulations can further predict how such interventions alter local strain fields, guiding the optimization of material design and implantation strategies [
94]. Ultimately, integrating mechanobiology into regenerative disc therapy requires a paradigm shift from the replacement of lost tissue toward re-establishing a mechanically competent organ. Success will depend on defining mechanical thresholds for cellular activation, developing materials that dynamically respond to loading, and implementing patient-specific mechanical assessments in both research and clinical practice.
Table 1 summarizes representative loading modes (compression, shear, torsion; static vs. cyclic), associated biological pathways, and reported outcomes, including anabolic matrix synthesis (e.g., proteoglycans and aggrecan), catabolic remodeling (MMP/ADAMTS), inflammation, and apoptosis/senescence. Reported loading windows frequently cluster around moderate cyclic compression or hydrostatic pressure, whereas sustained static loading or high-magnitude multiaxial regimes preferentially induce NF-κB/MAPK-linked catabolic programmers and cell death [
95-
101].
Table 2 further summarizes NP, AF, and EP phenotypes, representative ECM markers, and key post-LDH microenvironmental constraints that bias cells toward catabolic/inflammatory or anabolic phenotypes [
24,
68,
102-
108].
The translation of mechanobiological insights into clinical practice demands models that capture the complexity of the human disc while remaining experimentally tractable. Although animal and cadaveric studies provide useful boundary conditions, they often fail to replicate the chronic loading environment and biological nuances of the human spine. Accordingly, advanced
ex vivo and micro-engineered systems should be viewed as essential complementary translational tools rather than laboratory curiosities [
41]. Conventional
in vivo models have provided valuable insights into LDH and degeneration; however, they are limited by anatomical variability, ethical constraints, and difficulties in controlling mechanical and biochemical parameters. As a result,
ex vivo and in vitro systems have emerged as indispensable tools for dissecting the mechanobiological processes underlying disc injury and regeneration [
87]. Whole-disc organ culture systems preserve native architecture, enabling controlled mechanical loading and nutrient supply while maintaining cellular viability [
109]. These systems allow the application of static or injurious compressive loading to model degenerative disc conditions [
110]. Using such models, studies have shown that moderate cyclic loading preserves disc hydration and ECM synthesis, whereas excessive or static compression accelerates catabolism. Importantly, organ cultures can be coupled with real-time imaging and biochemical analyses, providing a valuable bridge between cellular studies and whole-tissue biomechanics [
111-
113]. At the cellular level, 3-dimensional hydrogels, scaffolds, and engineered microtissues offer controlled environments for studying mechanotransduction in disc cells. These constructs permit systematic variation of substrate stiffness, strain, and shear to define mechanical thresholds for anabolic versus catabolic responses. Coculture systems incorporating multiple disc cell populations within mechanically heterogeneous environments enable exploration of cross-tissue mechanobiological communication, a critical yet understudied factor in disc repair [
114,
115]. More recently, microfluidic platforms have been developed to recapitulate the intervertebral disc’s physiological complexity at the microscale. These devices integrate channels, stiffness gradients, and dynamic loading mechanisms, allowing simultaneous control of oxygen, glucose, pH, and mechanical stress [
87,
116,
117]. Such systems are ideally suited to investigate the interplay between mechanical forces and the harsh biochemical microenvironment following LDH. They also offer opportunities for high throughput testing of regenerative materials and drugs under defined mechanobiological conditions. The integration of real-time sensors for strain, pressure, and pH further enhances their utility for continuous monitoring of cellular responses.
Clinically, these models can inform the design of implants, annular closure systems, and injectable biomaterials by providing a mechanobiologically relevant testing platform. For example, disc-on-a-chip systems can be used to prescreen biomaterials under physiologically relevant mechanical and biochemical conditions before progressing to animal trials [
87,
118]. Similarly, computational models can assist surgeons in evaluating how specific repair techniques alter segmental mechanics, potentially reducing the risk of recurrent LDH [
94]. Modern finite element models incorporate anisotropic material properties, nonlinear viscoelastic behavior, and realistic geometries derived from patient imaging. Parametric studies using these models have identified critical regions of high shear and tensile stress within the posterolateral AF, supporting experimental observations of typical herniation sites. Moreover, coupling computational models with biological data enables the simulation of mechanobiological processes, such as ECM turnover, inflammation, and nutrient transport, across a range of loading conditions [
119]. This multiphysics framework offers a powerful means of predicting how mechanical interventions, such as implants and injections, influence both mechanical stability and biological outcomes.
The integration of experimental and computational technologies is moving the field toward precision mechanobiology, where patient-specific anatomy, load profiles, and cellular responses are considered simultaneously. Ultimately, this convergence may enable the development of personalized regenerative therapies capable of restoring both biological integrity and mechanical competence of the spinal motion segment. The emerging use of machine learning and artificial intelligence (AI)-driven modelling further extends these capabilities [
120,
121]. By integrating patient-specific imaging, motion data, and tissue properties, AI models can predict LDH risk, progression, and response to therapeutic interventions. Such computational tools hold promises for personalized load management and the design of individualized regenerative strategies.
CRITICAL PERSPECTIVES AND FUTURE DIRECTIONS
Despite significant advances in understanding the biomechanics and mechanobiology of LDH, meaningful translation of regenerative strategies into completed clinical trials remains limited [
122]. Much of the current research continues to address either the mechanical or biological dimensions in isolation, overlooking the interdependence that governs tissue behavior. The next phase of innovation in disc repair requires bridging these domains through integrated, multiscale approaches that combine structural, cellular, and molecular perspectives.
A major limitation in the field lies in the lack of standardization across regenerative studies, with many interventions focusing on biological outcomes while providing limited assessment of the associated mechanical environment [
123]. Without this mechanical context, it is difficult to assess whether apparent biological “repair” restores functional competence. Defining mechanobiological benchmarks, such as optimal intradiscal pressure or annular tensile strain, would improve cross-study comparability and clinical translation [
92]. Another critical challenge is the temporal evolution of the mechanical environment following LDH. Most models assess static endpoints, whereas the disc’s loading environment evolves continuously during healing and degeneration [
24,
75]. Time-resolved measurements of mechanical and biological parameters, supported by computational simulations, could help elucidate the dynamic feedback loops that determine whether repair stabilizes or fails [
94]. In parallel, longitudinal mechanobiological monitoring using imaging or biosensors may provide early indicators of regenerative success. From a regenerative design perspective, there is a pressing need for mechanically intelligent biomaterials that not only withstand loading but dynamically adapt to it. Next-generation biological modalities may integrate mechanoresponsive elements capable of stiffening, softening, or releasing bioactive molecules in response to physiologically relevant cues [
124]. When combined with mechanosensitive cells, these systems may recapitulate the disc’s inherent capacity to remodel in response to mechanical cues. Likewise, integrating biophysical stimulation, including dynamic compression or ultrasound, with biological therapies may help restore physiological mechanotransduction and enhance matrix synthesis [
124]. In addition, emerging cell-free therapeutic strategies show remarkable promise and warrant further investigation as potential treatments for disc degeneration [
125]. To accelerate translation, interdisciplinary collaboration is essential. Biomechanists, biologists, material scientists, and clinicians must work within a unified mechanobiological framework. Incorporating quantitative biomechanics into clinical decision-making—through patient-specific modelling, motion analysis, and imaging—can transform how we define “successful” regeneration, shifting the focus from structural repair alone to restoration of mechanical and biological harmony.
CONCLUSION
LDH is a mechanical failure of a biological system. Its progression and regenerative potential are governed by the delicate interplay between load distribution, ECM integrity, and cellular mechanotransduction. Decades of research have established the biomechanical causes of LDH, yet only recently has mechanobiology revealed how mechanical cues dictate cellular fate and tissue repair. The disc regeneration will not be achieved through biological replacement or mechanical stabilization alone. Instead, it demands strategies that re-establish functional biomechanics, the capacity of the disc to sense, adapt to, and sustain physiological loading. Emerging tools such as organ-on-a-chip systems, mechanosensitive biomaterials, cell-free strategies, and integrative computational models are beginning to provide the experimental and translational foundation for this paradigm shift. By viewing LDH through the lens of mechanobiology, researchers and clinicians can move beyond symptomatic management toward therapies that restore both structural and functional integrity.
NOTES
-
Conflict of Interest
The authors have nothing to disclose.
-
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
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Author Contribution
Conceptualization: GV, FR, IHH, AJ, JT; Formal analysis: GV, FR, IHH, AJ, JT; Funding acquisition: AO Spine Knowledge Forum Degenerative; Methodology: GV, FR, IHH, AJ, JT; Visualization: GV, FR, IHH, AJ, JT; Writing – original draft: JT; Writing – review & editing: GV, FR, IHH, AJ.
Fig. 1.Schematic drawings (top and side views) of structural damages and abnormalities during mechanically induced LDH, including NP tracking into the AF (NP migration)[
15,
33]; AF-NP interface disintegration[
30,
34]; AF radial fissures,[
35-
37] interlamellar delamination, [
37,
38] localized deformation[
39,
40]; and full thickness rupture.[
31,
32,
40,
41] LHD, lumbar disc herniation; NP, nucleus pulposus; AF, annulus fibrosus.
Fig. 2.Lumbar disc herniation (LDH) pathway in ovine discs under realistic loading scenarios, including the initiation at the lateral region, propagation pathway via the interlamellar matrix of the AF layers and LDH site at the posterolateral region of the disc. LHD, lumbar disc herniation; NP, nucleus pulposus; AF, annulus fibrosus. Reproduced from Tavakoli J, et al. Ann Biomed Eng 2018;46:1280-91, with permission of Springer Nature.[
39]
Fig. 3.The biomechanical-biological feedback loop post-LDH accelerates disc degeneration. Structural disruption of the annulus fibrosus and nucleus pulposus alters load distribution and generates abnormal stress and strain within the disc (1). These biomechanical changes are sensed by disc cells through integrin–cytoskeletal coupling and mechanosensitive ion channels (e.g., Piezo/TRPV), activating inflammatory and catabolic signaling pathways. Biological responses include upregulation of proinflammatory cytokines (e.g., IL-1β, TNF-α), induction of matrix-degrading enzymes (e.g., MMP-3, ADAMTS-5), and cellular stress (2). Progressive loss of key ECM components, including aggrecan depletion and collagen II fragmentation, weakens disc microstructure (3), further exacerbating mechanical instability and perpetuating a self-reinforcing degenerative cycle. LHD, lumbar disc herniation; TRPV, transient receptor potential vanilloid; IL, interleukin; TNF, tumor necrosis factor; MMP-3, matrix metalloproteinase-3; ADAMTS-5, a disintegrin and metalloproteinase with thrombospondin motifs-5.
Table 1.Representative mechanical loading modes associated with mechanosensors, signaling pathways, and downstream disc cell outcomes
Table 1.
|
Model/cell type |
Representative loading range |
Key mechanosensors |
Dominant signaling pathways |
|
Loading mode: Compression/hydrostatic pressure (cyclic, physiological) [68,75,76,95] |
|
NP cells (3D hydrogel); whole-disc organ culture |
0.1–1.0 MPa; 0.1–1 Hz; intermittent (2–4 hr/day) |
Integrins (β1), cytoskeleton/FAK, mechanosensitive ion channels, primary cilia |
MAPK (ERK), Ca2+ signaling, balanced YAP/TAZ activity |
|
Typical downstream outcomes: |
|
Anabolic homeostasis: proteoglycan (ACAN)↑, COL2A1↑, maintained hydration and cell viability |
|
Loading mode: Compression (static or high-magnitude cyclic; overload) [68,78,96] |
|
Whole-disc organ culture; NP and AF cells |
Sustained static compression or high-magnitude cyclic loading beyond the physiological window |
Integrins, stretch-activated ion channels (e.g., Piezo/TRP), and cytoskeletal stress fibers |
NF-κB, p38/JNK MAPK, oxidative stress pathways |
|
Typical downstream outcomes: |
|
Catabolic shift: MMP1/MMP3↑, TIMP imbalance, ECM breakdown, apoptosis/senescence |
|
Loading mode: Shear stress (cyclic or sustained) [80,97] |
|
AF cells in vitro; disc-on-chip systems |
Device-dependent shear stress; higher shear associated with degeneration models |
Integrins, cytoskeleton, mechanosensitive ion channels, primary cilia |
Ca2+-dependent signaling, MAPK, NF-κB |
|
Typical downstream outcomes: |
|
Dose-dependent response: moderate shear supports matrix organization; excessive shear promotes inflammation and collagen remodeling |
|
Loading mode: Torsion (cyclic, low vs. high amplitude) [80,98] |
|
Whole-disc organ culture (NP vs. AF regions) |
Low torsion (2°) vs. high torsion (5°); 0.1 Hz; 1 hr/day (reported ranges) |
Integrins, cytoskeleton, AF lamellar architecture (structural mechanosensing) |
MAPK, NF-κB; region-specific YAP/TAZ modulation |
|
Typical downstream outcomes: |
|
Regional sensitivity: AF remodeling under moderate torsion; NP apoptosis and catabolism under high torsion |
|
Loading mode: Tensile strain (cyclic; AF-focused) [99,100] |
|
AF cells in vitro; AF tissue injury models |
Wide protocol range: high strain linked to damage accumulation |
Integrins (β1), caveolae, cytoskeleton |
MAPK, NF-κB; YAP-mediated regulation of inflammatory signaling |
|
Typical downstream outcomes: |
|
Strain-dependent effects: moderate strain supports alignment and survival; high strain induces apoptosis and inflammatory mediators |
|
Loading mode: Multiaxial complex loading (compression, shear, and torsion) [101] |
|
Whole-disc organ culture; computational–experimental models |
Combined loading mimicking physiological motion or injury scenarios |
Integrins, mechanosensitive ion channels, cytoskeleton |
NF-κB, MAPK, mechano-metabolic coupling pathways |
|
Typical downstream outcomes: |
|
Degenerative cascade: stress concentration, matrix damage, inflammation, impaired regeneration |
|
Loading mode: Mechanical stress combined with microenvironment (acidic pH, low nutrients) [81] |
|
NP cells; degeneration and herniation models |
Mechanical overload under hypoxia, low glucose, acidic pH |
Ion channels (Piezo/TRP), integrins, mitochondrial stress sensors |
NF-κB, inflammasome-related signaling, metabolic stress pathways |
|
Typical downstream outcomes: |
|
amplified catabolism: IL-6, COX-2, NO↑; suppressed ECM synthesis |
|
Loading mode: Physiological loading with biochemical crosstalk (muscle–disc signaling) [77] |
|
Human NP cells |
Physiological mechanical context with myokine exposure |
Integrins, mechanosensitive signaling interfaces |
MAPK, metabolic-mechanical crosstalk |
|
Typical downstream outcomes: |
|
Enhanced anabolic responsiveness: PG synthesis↑, improved NP cell metabolism |
Table 2.Disc cell biology primer: NP, AF, and EP phenotypes and the post-LDH niche
Table 2.
|
Tissue compartments and dominant cell phenotypes |
|
NP: Gel-like, highly hydrated region optimized for compressive load distribution. NP cells are chondrocyte-like with an ECM program enriched for aggrecan/proteoglycans (ACAN) and type II collagen (COL2A1) (often with SOX9-associated chondrogenic regulation in many models). [102,103] |
|
AF: Fibrocartilaginous lamellae with aligned collagen bundles supporting tensile and shear loads. AF cells (particularly outer AF) are associated with a more fibrous matrix profile enriched in type I collagen (COL1A1) and related fibrillar collagens, consistent with their tensile role. [102,104] |
|
EP: Thin hyaline-cartilage-like interface controlling transport between vertebral body and disc; EP chondrocytes maintain a cartilage-like ECM (often described with COL2/ACAN features) and are central to nutrient diffusion constraints. [102,103] |
|
Representative ECM components and markers (high-level) |
|
NP: ACAN (proteoglycans) controls hydration and osmotic swelling; COL2A1; matrix homeostasis genes in pro-anabolic states. [24] |
|
AF: COL1A1-dominant fibrillar collagen network (especially outer AF), with remodeling enzymes upregulated during degeneration or injury. [102,105] |
|
EP: cartilage-like ECM and transport regulation; degeneration or calcification impairs diffusion and shifts disc cell biology toward stress phenotypes. [102,106] |
|
Key microenvironmental constraints relevant to herniation or annular defects |
|
Hypoxia/limited vascularity: The disc is largely avascular; oxygen gradients shape basal metabolism and stress susceptibility. [102,103] |
|
Nutrient limitation (low glucose) and transport dependence on EP/AF integrity: Transport constraints worsen with EP changes and annular disruption, compounding metabolic stress. [102,106] |
|
Acidic pH/metabolite accumulation: Reduced diffusion and altered loading can promote accumulation of acidic metabolites; acidic and low-nutrient conditions potentiate inflammatory-catabolic shifts under mechanical stress. [102] |
|
Mechanobiology and microenvironment coupling |
|
Toward anabolic/homeostatic: Moderate cyclic compression or hydrostatic pressure supports ECM synthesis and hydration maintenance, partly by sustaining balanced mechanotransduction rather than sustained NF-κB stress signaling. [68] |
|
Toward catabolic/inflammatory: Static overload, high-magnitude complex loading, and/or mechanically disrupted matrices promote NF-κB/MAPK-linked inflammation, matrix-degrading enzyme induction (MMP/ADAMTS), and cell death/senescence. Mechanosensitive ion channels (e.g., Piezo1) provide a mechanistic route linking aberrant mechanical stress to Ca2+-dependent inflammatory cascades. [105,107,108] |
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, Fabrizio Russo2
