The role of birth trauma of the сervical Spine in the pathogenesis of idiopathis scoliosis: integration of neurological and biomechanical aspects.A review.

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INTRODUCTION

Idiopathic scoliosis (IS) is a polyetiological disorder characterized by complex triplanar spinal deformity and remains one of the most significant problems in pediatric orthopedics. Despite a long history of study, the etiology and pathogenesis of IS in many aspects continue to be the subject of intense scientific debate. The dominant concept today is the multifactorial model, which views IS as the result of the interaction of genetic predisposition, growth disorders, neuromuscular imbalance, and environmental factors [1]. The key role of polymorphisms in the LBX1, GPR126, and other genes regulating the development of the nervous system and musculoskeletal structures has been established [2, 3, 4]. However, genetic predisposition alone does not always lead to the development of the disease, indicating the need for trigger factors that initiate the pathological cascade [1].

In recent years, a hypothesis linking the development of IS with perinatal factors, particularly intrapartum cervical spine trauma, has attracted increasing attention from researchers [5]. The craniovertebral junction (C0-C2) is a unique anatomical zone that provides both stability to protect vital brainstem structures and the mobility necessary for neck and head movements [6, 7, 8]. During childbirth, this area is subject to significant mechanical stress, especially during abnormal birth (breech presentation, shoulder misalignment, and the use of obstetric aids). Theoretically, this could lead to microsubluxations, stretching of dural structures, disruption of blood supply to the brainstem and spinal cord, and damage to the descending motor pathways.

The purpose of this article is to analyze data from domestic and international literature on the etiopathogenesis of idiopathic scoliosis, with an emphasis on data regarding the potential association between complicated births, cervical spine trauma, and the subsequent development of idiopathic scoliosis.

Materials and Methods

This literature review is based on a critical analysis and synthesis of current scientific data on the role of intrapartum cervical spine trauma in the initiation and pathogenesis of idiopathic scoliosis. Such an analysis is highly relevant, as understanding the role of perinatal triggers opens up new opportunities for early preclinical diagnosis, risk stratification, and the development of preventive measures aimed at preventing the development of severe forms of scoliosis in genetically predisposed children.

A search of Russian and English-language publications on the etiology of idiopathic scoliosis was conducted in the electronic databases PubMed, Google Scholar, eLibrary, and CyberLeninka for the period 2010–2024 using the following keywords: idiopathic scoliosis, intrapartum trauma, craniovertebral junction, pathogenesis, and muscle imbalance.

Results

Hypothesis on the influence of intrapartum trauma on the development of idiopathic scoliosis and key questions for discussion.

The hypothesis is that short-term mechanical stress on the cervical spine during childbirth exerts pressure on the spinal cord through its membranes, leading to damage to the neural pathways and centers in the brain responsible for balance and muscle tone. This disruption causes asymmetrical trunk muscle function, which, in our opinion, is the trigger point for the development of idiopathic scoliosis during the child's growth period. Discussion of this hypothesis raises several questions that require clarification.

If perinatal short-term pressure on the spinal cord through its membranes is the trigger for IS, why isn't it much more common? Why do many people with cervical spine dysfunction have no history of scoliosis, and conversely, many with scoliosis have no obvious signs of such birth trauma?

If trauma and neurological impact occurred at birth, why does scoliosis manifest and actively progress years later, especially during growth spurts? How is this early "signal" maintained or activated later? How does this initial "maladjustment" of tone develop into a persistent pathological process leading to progressive spinal deformity over many years, especially with a peak during puberty? Is a constant source of compression or irritation necessary?

How does impact on the high cervical spinal cord levels lead to persistent tone asymmetry in the thoracic and lumbar muscles, which are controlled by the underlying segments? An explanation for the transmission of this "signal" down the central nervous system is needed.

Factors implementing the hypothesis and combined mechanisms

Why do scoliotic deformities or pathological consequences occur only in a certain category of children? This can be explained by several factors. Some children may have congenital or acquired weakness of connective tissue (e.g., in Ehlers-Danlos and Marfan syndromes), which makes the spinal cord membranes more vulnerable [9]. In most children, minor displacements are compensated for by a highly adapted nervous system and musculoskeletal system. In some newborns (e.g., with hypoxic-ischemic CNS damage, prematurity), compensatory mechanisms are weaker, and even minor deformation can lead to clinical manifestations (torticollis, neurological disorders) [10]. In addition, it is necessary to take into account the characteristics of the birth process (breech presentation, rapid/protracted labor, labor stimulation, etc.). Of course, asymmetric muscle tone alone cannot create a three-plane scoliotic deformity with vertebral torsion. This requires the involvement of the osseous-ligamentous apparatus and intervertebral discs. If rotational displacement of the vertebrae occurs during childbirth (for example, due to obstructed passage of the head or shoulders), this can create torsional stress on the ligaments and discs, leading to microsubluxations or fixation of the vertebrae in an abnormal position, which over time causes deformity [11, 12]. The dura mater is also fixed to the sacrum and occipital bone, and mechanical stress on the craniovertebral region can cause asymmetrical tension on the dura mater, creating a rotational component that can progress as the child grows and transmit "torsional loads" to the spine [8, 13]. This explains why, in some children, deformity develops gradually rather than immediately after birth.

Thus, the hypothesis is realized only in a certain category of children, under a combination of factors: individual anatomical characteristics (hypermobility syndrome, undifferentiated connective tissue dysplasia), the presence of significant mechanical stress during birth, impaired dural tension, and the state of the nervous system and the body's compensatory capabilities. A combined effect on the osseous, ligamentous, and dural structures is necessary in the presence of complex biomechanical disturbances during birth, so that some children develop permanent deformities while others do not.

Supporting Studies, Risk Factors, and Mechanisms of Intranatal Injury

This hypothesis is supported by a number of studies. During the first six months of life, symptomatic asymmetric posture is observed in 12% of all newborns, with positional preference persisting by age 3 in 2.4% of children [14]. The involvement of spinal cord pathways and impaired blood supply to the brain and medulla oblongata is evidenced by the identified correlation between abnormalities in evoked potentials (visual, auditory, and somatosensory) based on EEG data in adolescents with IS and a history of difficult births [15]. A number of scientists have also confirmed the risks of C1-C2 compression in breech presentation using computer modeling using the finite element method [16, 17], where the spine is broken down into small elements with specified elastic properties, bone density, and ligament extensibility, and forces are applied to the resulting model that simulate the birth process. This allows us to determine which tissues are deformed and where critical loads occur that cannot be measured in real-life conditions.

Risk factors for intrapartum injury include: 1) precipitous labor (sharp compression of the fetal head during rapid passage through the birth canal), 2) protracted labor due to weak labor (failure to insert the fetal head into the pelvis, resulting in prolonged pressure on the cervical spine), 3) breech presentation (risk of traction on the torso or pelvis during extraction), 4) cesarean section (especially emergency or complex ones, involving mechanical extraction of the fetus through a small incision with potential impact on the spine), 5) use of obstetric forceps or a vacuum extractor (direct mechanical impact on the head and neck).

The mechanism of intrapartum injury includes:

1. Compression of dural structures or spinal cord. During childbirth, especially when the head or shoulders are obstructed, overstretching or compression of the spinal cord and its membranes can occur, potentially leading to microdamage to the dura mater, which subsequently impacts the biomechanics of the spine. According to several studies, 73% of patients with scoliosis greater than 20° show signs of birth trauma to the neck (based on the anamnesis and radiographs) [5, 18].

2. Microdamage to the vertebral arteries and sympathetic plexuses.

Rotational and tractional forces on the fetal neck can cause brainstem ischemia due to compression of the vertebral arteries, which can trigger autonomic dysfunction (impaired regulation of vascular tone, respiration, and digestion). A. Ya. Tatarinov found hemodynamic disturbances in the vertebral arteries and rotational subluxation of C1 (based on ultrasound and radiography) in 68% of children aged 3-7 years with natal neck trauma, followed by asymmetric muscle tone (76%) and impaired coordination (64%) [19]. According to V. Frymann, rotational forces during childbirth can disrupt blood flow in the vertebral arteries and clinically manifest as an asymmetric Moro reflex and feeding difficulties [20].

3. Craniovertebral junction (CVJ) dysfunction.

Displacement of the occipital bone (e.g., due to vacuum extraction or forceps application) can lead to blocking of the atlantooccipital joint, asymmetric tension of the dura mater, and impaired cerebrospinal fluid flow. According to H. Biedermann, kinematic imbalance due to suboccipital deformity manifests as a persistent head tilt and develops in 16–18% of cases of birth using a vacuum extractor [21]. Fotter et al. found MRI evidence of ligamentous strain in 23% of asymptomatic newborns after normal vaginal delivery, while after instrumental delivery, this figure increased to 61% [22].

An Integrative Model of the Pathogenetic Cascade of Idiopathic Scoliosis Development

Based on a literature review, an integrative model of the pathogenetic cascade for the development of idiopathic scoliosis initiated by intrapartum exposure can be proposed. The proposed pathogenetic cascade may include the following sequential links: 1) the presence of individual anatomical features and genetic predisposition [4, 23], 2) birth mechanical impact as a potential trigger [9, 10], 3) complex damage to the neurovascular and dural structures affects the musculoskeletal, nervous systems and ligamentous apparatus [6, 7, 24, 25], 4) impaired proprioception as a consequence [26, 27], 5) the formation of deformation during growth (depending on the state of the nervous system and the compensatory capabilities of the body, as the child grows from 0 to 5 years, an asymmetric tone (scoliotic posture) or asymmetric dural tension develops with the formation of rotational arcs of spinal curvature during puberty) [28, 29].

Neurological Mechanisms and the Formation of a Vicious Cycle of Structural Changes

A brief mechanical impact on the cervical spine at birth disrupts the delicate balance of neural regulation of muscle tone in the newborn, creating an initial, possibly subclinical, asymmetry. This neurological pathway could theoretically lead to spinal curvature and subsequently cause long-term changes in signal processing by the spinal cord or brainstem, rendering the tone regulation system unstable.

The spinal cord has a distinct segmental structure, with each level receiving signals from specific muscles and joints. Mechanical impact, such as a rotational subluxation of C1-C2, alters the tension of the dura mater, which is connected to the nerve roots, ligaments, and joint capsules. Asymmetrical tension activates nociceptive fibers, causing reflex inhibition of motor neurons [5]. Also, compression of the vertebral artery with ischemia of a spinal cord segment alters motor neuron activity [19]. As a result, spinal interneurons receive different afferentation from both sides, compare them, and generate an asymmetric motor response via the anterior horn motor neurons. This is confirmed by the following studies: after extraction of a newborn with forceps, ultrasound and MRI data revealed signs of spinal cord damage in the craniocervical joint [30], correction of atlas subluxation in infants with torticollis eliminated tone asymmetry in 78% of cases [31]. In addition, the cervical spine is a critical area for the integration of signals from the vestibular system and the brainstem. Damage to cervical proprioceptors disrupts signals to the lateral vestibulospinal tract, which controls extensor tone [32]. Asymmetric tension of the dural structures can activate the reticular formation of the brainstem, which, via the reticulospinal tract, alters the tone of the extensor muscles. Thus, postural dysfunctions caused by a sensory deficit in proprioceptive information coming from the spine have been identified in patients with scoliosis [33]. In another study, during postural exercises in patients with IS, EMG values ​​were higher on the convex than on the concave side of the spinal curvature [27]. 

Thus, the spinal cord can differentiate sides through asymmetric proprioceptive input, segmental reflex arcs, and mechanical effects on dural structures, creating a vicious cycle leading to structural changes.

Mechanical effects at the craniovertebral junction during abnormal births (rapid, prolonged, breech presentation, application of obstetric forceps) can temporarily disrupt cerebrospinal fluid circulation in the newborn and subsequently affect the development of the nervous system and its regulatory functions (although there is no evidence of a direct link to scoliosis). A study showed that patients with IS had a larger anteroposterior surface diameter and area of ​​the foramen magnum, but peak cerebrospinal fluid flow velocities through the foramen magnum did not differ significantly (p>0.05) in patients with low-lying cerebellar tonsils. This may be explained by the compensatory effect of the larger foramen magnum in patients with IS [7].

The Nature of Injuries and the Concept of the Latent Period for the Development of IS

Intranatal exposure may not leave obvious radiographic or clinical signs of rotational subluxation immediately after birth due to the immaturity of bone tissue (cartilaginous structures are radiopaque), but it can potentially cause microdamage, edema, and irritation of the membranes or neural structures. However, transient functional impairments without structural changes (temporary edema without neuronal damage, short-term ischemia with restoration of blood flow, mild irritation of nerve roots without axonal rupture or demyelination) are completely reversible due to the high neuroplasticity of the child's body. Wang et al. noted an improvement in neurological status in 64% of children who survived traumatic spinal cord injury within 19 months of the injury [34]. Partially reversible or latent damage (micro-tears of the dural ligaments with the development of fibrosis and chronic tension, subclinical root ischemia with impaired proprioception and tone asymmetry, irritation of the sympathetic ganglia with the development of autonomic dysfunction) are not detected after birth on MRI or X-ray, but trigger a cascade of pathological reactions with the formation of idiopathic scoliosis or autonomic dysfunction within 5-10 years. According to H. Biedermann, 12% of children with minor birth trauma to the neck developed scoliosis due to dural fibrosis by the age of 10 years [18]. In a study of the consequences of intranal impact on the cervical spine, asymmetry of trunk tone was detected in 85% of children with congenital muscular torticollis, with the development of IS in 15% [35]. In another study, 90.7% of children with IS had cervical pathology confirmed by radiography and 98% of children had cerebral hemodynamic disturbances confirmed by Doppler ultrasound [36].

Idiopathic scoliosis (especially its significant clinical forms greater than 10 degrees) affects 2 to 4% of adolescents [37]. Subluxations of C1-C2 or functional impairments in this area, although occurring, are not universal at birth, and IS may develop as the child grows. IS is characterized by a latent period, as the most common forms of IS (infantile, juvenile, and adolescent) manifest and progress significantly later after birth, not in infancy and childhood, but most often during puberty. Brief mechanical stress on the cervical spine at birth, such as a C1-C2 rotational subluxation, affects the high cervical segments of the spinal cord and can cause microtrauma or compression at this level, leading to the development of dural traction and fibrosis. Impaired proprioception manifests in the child as a primary muscle imbalance in the form of asymmetrical posture. Over the next 5 years, the child's body masks asymmetrical muscle tone through excessive joint mobility (the ligamentous apparatus is more elastic and stretchable), the formation of compensatory muscle chains, creating a "muscle corset" of spasmodic muscles that hold the body in an upright position, and changes in motor patterns, such as an asymmetrical gait and sitting posture. By the age of 7-8 years, hypermobility decreases and the ligamentous apparatus becomes dense and rigid, and in response to chronic instability in the C1-C2 segment and microtrauma, the process of replacing elastic tissue with scar tissue is initiated, disrupting the transmission of nerve impulses and increasing dural tension. A breakdown of compensatory mechanisms occurs during periods of growth spurts, most often at 10-14 years of age, when hormonal status changes, static and dynamic loads increase during the educational process, and against the background of muscle imbalance, accelerated growth of the thoracic vertebrae by 1.5-2 cm per year occurs with an asymmetric load on the growth plates and the irreversible formation of wedge-shaped deformation of the vertebrae (the Huether-Volkmann law - compression inhibits growth, stretching stimulates it) [28], which intensifies the deformation of the spine and the convex side grows faster. In addition, the theory of disproportionate growth between the vertebral column and spinal cord suggests that abnormal tension on the spinal cord (due to faster growth of the spine compared to the spinal cord) may influence neural regulation of vertebral and muscle growth [13, 38]. Stokes' studies revealed that thoracic growth plates are 3 times more sensitive to asymmetric loading in puberty than in childhood (p<0.001) [28]. At the same time, increased estrogen levels increase sensitivity to mechano-dependent signals (TGF-β, YAP/TAZ) [39, 40]. Liu et al. found that TGF-β is activated by mechanical stress and stimulates dural tissue fibrosis [29]. Studies by Nowak R. et al. confirmed a significantly higher content of TGF-β transcripts in samples taken from the concave part of the curve in patients with spinal deformity, and their dependence on the age of onset of idiopathic scoliosis [41]. Thus, the latent period is a time of hidden progression and accumulation of damage that the body "fights" against, and the pubertal spurt is a trigger that aggravates the latent pathological condition. The presence of a latent period is explained by the compensatory capabilities of the child's body and the accumulation of biomechanical imbalance, and for the manifestation of idiopathic scoliosis during puberty, accelerated growth, hormonal background and weakness of the muscular corset are necessary.

Anatomical rationale for signal propagation and the formation of an S-shaped spinal deformity

Also, to answer the question of how effects on the cervical spinal cord levels lead to persistent tone asymmetry in the thoracic and lumbar muscles, it is necessary to recall the anatomical features. C0-C2 is the zone of nuclei of the proprioceptive pathways, the reticulospinal, vestibulospinal, and corticospinal tracts. Due to the segmental organization of the spinal cord, thoracic and lumbar motor neurons function relatively independently: thoracic muscle tone is controlled by the reticulospinal tract (extensors on the ipsilateral side of the lesion), while lumbar muscle tone is regulated by the vestibulospinal tract (balance and posture on the contralateral side) and corticospinal tracts. At the thoracic level, damage to C1-C2 results in asymmetric activation of the reticulospinal tract, which has a predominantly ipsilateral effect. Its hyperactivation on one side will lead to increased tone in the trunk extensors on the same side (ipsilateral), which will create a pull that will tilt the spine in the opposite direction (contralateral). At the lumbar level, asymmetrical influences on the vestibulospinal tracts (which are also ipsilateral) can increase tone in the ipsilateral extensor muscles, while more complex corticospinal influences (conscious control) and cross-compensatory mechanisms may attempt to "align" the pelvis, creating an opposite tone pattern. The thoracic spine receives the command "pull to the right," while the lumbar spine receives the command "pull to the left" (or vice versa). This is the opposite tone, leading to the formation of an S-shaped deformity (the thoracic curve to one side, the lumbar curve compensatorily to the other) and an attempt to maintain the overall balance of the body under gravity. The underlying segments attempt to autonomously compensate for and restore muscle imbalance through the automatic mechanisms of the spinal cord and brainstem during a latent period. Pathological compensation creates zones of chronic hypertonicity and muscle spasm on one side and hypotonicity on the other. The body is constantly in a state of latent tension and increased energy expenditure, which is gradually depleted with the development of muscle fatigue. Furthermore, asymmetric tone exerts asymmetric pressure on the growth plates of the vertebrae, creating future structural deformity (according to the Huether-Volkmann law). During the pubertal growth spurt, compensatory mechanisms fail to cope with the load, and the deformity rapidly progresses. Thus, compensation is successful in the short term (maintaining balance), but unsuccessful and even harmful in the long term (leading to structural scoliosis). Modern research supports this integrative model. Burwell et al. have described in detail how impaired proprioception at the spinal level triggers a reflex arc leading to muscle asymmetry that the central nervous system attempts, but fails, to compensate for [1]. Other authors have summarized the evidence supporting that dysfunction in the brainstem (the source of the reticulo- and vestibulospinal tracts) is a key factor impairing postural control and leading to compensatory mechanisms that ultimately fail [42]. A systematic review by Paramento et al. shows how asymmetric activation of descending tracts (reticulo- and vestibulospinal) correlates with muscle tone and strain patterns in IS using MRI and EMG data, supporting the incoordination model. [43]. Kong et al. revealed in patients with IS a significant decrease in fractional anisotropy values ​​and an increase in the average diffusion coefficient in the medulla oblongata and segments C1–2, C2–3, C3–4, and C4–5, confirming spinal cord damage above the C5–C6 level [44].

The pathogenetic cascade of the integrative model of IS, initiated by mechanical impact on the cervical spine includes the following links: 1) mechanical impact on C0-C2 [10, 44], 2) dysfunction of the reticulospinal tract (dural tension) [1, 42], 3) disruption of descending control of tone [1, 42], 4) asymmetry of tone of deep back muscles [27, 45], 5) displacement of the center of gravity [46, 47], 6) formation of an arc of curvature (possibly with compensatory pelvic tilt depending on the flexibility of the spine, localization of the arc and biomechanical features) [48]. Modern scientific works confirm that the craniovertebral junction and its dysfunction can be triggers for the development of IS [9, 10, 44]. The central link in this case is the asymmetric activation of the reticulospinal tract, which is a modulator of the tone of the paravertebral muscles. According to MRI and EMG data, asymmetric activation of the brainstem areas associated with the reticulospinal tract was revealed in patients with IS, and this correlates with the electromyographic asymmetry of the paravertebral muscles [1, 42]. Impairment of descending control from the brainstem leads to discoordination of the work of pattern generators at the spinal level, which is manifested by asymmetric activity of the multifidus, intertransverse, and rotator muscles, causing the onset of torsion and the formation of an arc of spinal curvature [43]. In addition, patients with IS have subclinical disorders of vestibular function and visual information processing, which leads to a shift in the center of pressure and the center of gravity [46, 47]. A shifted center of gravity increases the asymmetrical load on the spine, and according to EMG data, this is facilitated by hyperactive muscles on the concave side, creating uneven pressure on the growth plates of the vertebrae, followed by the formation of a wedge-shaped deformation according to the Huether-Wolff law (bone growth slows on the side of compression), and the center of gravity shifts even further. The body attempts to create a new postural balance to maintain equilibrium, forming an arc of spinal curvature [48].

Detailed pathogenetic cascade of IS formation

The location of the curve depends on anatomical features, the nature of the intrapartum injury, and muscle tone. The dura mater has zones of maximum attachment at C1-C2 (odontoid ligaments), T4-T8 (intervertebral foramina), and L1-L2 (conus). With primary injury at the level of the craniovertebral junction, local inflammation develops, leading to fibrosis and a primary attachment point for the dural sac with pathological tension in the caudal direction. The tension is transmitted unevenly, so in thoracic scoliosis the tension is concentrated at the level of C7-T1 (fixation by the odontoid ligaments) with deformation in the thoracic region (T4-T8), and in lumbar and thoracolumbar scoliosis the tension shifts to T12-L1 (the zone of fixation of the dural tube by the conus medullaris) with curvature in the lower regions [49]. Gutmann determined that the localization of the arc depends on the level of maximum dural tension: with fixation in the upper thoracic region - thoracic scoliosis, in the lumbar region - lumbar [5]. A number of authors in their studies also found that 85% of primary IS arcs are localized in the thoracic (T5-T12) or thoracolumbar regions [50]. Burwell et al. confirmed that the thoracic region is a weak link in the spine, where neurogenic imbalance is realized in deformation [51]. Furthermore, the location of the curve depends on muscle imbalance: in thoracic scoliosis, asymmetry of the rotatores and multifidus muscles predominates, while in lumbar scoliosis, it is the quadratus lumborum and iliopsoas muscles that predominate [52]. According to EMG data, asymmetry of muscle activity in IS is maximal at the T7-T9 level [53]. Pelvic rotation is detected in 90% of patients with thoracic scoliosis [54, 55], but some children do not have pelvic rotation in thoracic scoliosis without lumbar involvement, also due to compensatory rotation of the thoracic vertebrae, increased lumbar lordosis, and increased spinal flexibility.

The reticulospinal tracts pass through the cervicoccipital junction and regulate the tone of all paravertebral muscles [56]. Intranatal injury disrupts proprioception, leading to muscle tone asymmetry, but this is most pronounced in areas of greatest biomechanical stress—the thoracic spine as the center of axial load and the "weak link in torsional load" [49]. The thoracic spine contains the largest number of vertebrae and functions as the longest rigid lever in the spine, anchored by the ribs. The weight of the upper body rests on the thoracic vertebrae (especially T6-T8), which have thinner arches and smaller articular processes, offering little protection against torsion. The rib cage rigidly fixes the vertebrae in the frontal plane, preventing lateral displacement, but the joints of the rib heads allow rotation of the vertebrae around the axis without preventing rotation. Results of studies using finite element modeling have shown the crucial role of the thoracic cage in maintaining spinal stability in the frontal plane and vulnerability to torsion (most often in the thoracic region T6-T8), but in patients with IS, a higher sensitivity of the spine to static and vibration loads was revealed [49]. The lumbar vertebrae are more massive with large articular processes, have no ribs, are fixed by a powerful muscular-ligamentous corset, the dura mater is fixed at the level of L2 and the sacrum, which resists lateral displacement and rotation [57].

In addition, an asymmetric signal from C1-C2 (due to subluxation, dural tension, or ischemia) disrupts the balance of excitation or inhibition in the reticulospinal tract, which in the thoracic segments (T4-T12) leads to unilateral hypertonicity (e.g., on the right) [56]. As a result of the forward shift of the center of gravity, kyphosis is compensatorily increased and lordosis is smoothed out, and the tension of the fixed dura mater in the sagittal plane creates multidirectional force vectors [58]. According to Cobb's law, lateral curvature is always accompanied by rotation and changes in the sagittal plane [59]. Depending on the severity of intranatal injury and dural tension, as well as the individual anatomical features and compensatory mechanisms of the child, a spinal curvature is initially formed in the frontal plane with one arc without rotation of the vertebrae in the thoracic region (scoliotic posture). In a pathological course of compensation, the body responds to a signal coming from C1-C2 to the lower segments (lumbar, L1-L5) by compensatorily increasing muscle tone (on the left) to maintain body balance, resulting in the formation of an S-shaped scoliotic posture. Importantly, a single curve initially develops, with compensatory curves only gradually forming [60].

Let's consider a theoretical biomechanical model based on the mechanism of "spiral twisting of the dural tube." Intranatal rotation of C1-C2 results in asymmetric tension on the dura mater, which pulls the nerve roots in one direction in the thoracic region and in the opposite direction in the lumbar region due to attachment to the sacrum. This disrupts proprioception, and the initial impulse goes to the thoracic segments with a command to increase muscle tone on one side, which will manifest as an asymmetric posture in the child during the first year of life. With verticalization, the child will retain unilateral hypertonicity and develop a scoliotic posture. Spiral twisting is transmitted to the ligamentous apparatus, costovertebral joints, and muscular-fascial bands, forming a torsional component of scoliotic deformity [61]. During periods of growth spurts, "dural torsion" intensifies, and compensatory mechanisms are triggered to maintain body balance over the pelvis, sending a signal to increase tone contralaterally in the lumbar region, forming two or three differently directed curves with the development of idiopathic scoliosis. If the primary thoracic curve is long, a third upper thoracic curve may form compensatorily [60]. Chu et al., when studying scoliotic deformity in patients with triple curves, found tension of the dura mater at the C7-Th1 and Th12-L1 levels [7]. In thoracic scoliosis, for example, the curve is to the right, while the pelvis rotates to the left in compensation, regulating the balance of the center of gravity without forming a lumbar curve. Research by Gum et al. has confirmed radiographically that 68% of patients with thoracic scoliosis greater than 25° have a pelvic rotation greater than 5° [55]. The lumbar spine also compensates for the thoracic curve by changing the sagittal profile (increasing lordosis) or increasing the tone of the lumbar muscles without forming a compensatory curve. According to Du et al., thoracic curvatures in children account for 39-47%, thoracolumbar curvatures up to 40%, and double curvatures less than 10% [62]. In S-shaped scoliosis, pelvic rotation and hyperlordosis are often absent, and muscle tone in the lumbar spine is relatively symmetrical. Thus, the multidirectionality of signals is the result of a complex self-regulating system for posture maintenance, where the initial injury triggers a cascade of compensatory responses at various levels of the nervous system.

Because idiopathic scoliosis is a multifactorial disease with numerous theories regarding its origin, the underlying cause remains unknown. Therefore, we can consider the C0-C2 craniovertebral junction not as an isolated structure, but as a key integrative center that can be both a source of primary dysfunction and a target for systemic disorders that exacerbate the deformity. Melatonin, whose receptors are found in the paravertebral muscles, has a muscle relaxant effect. Its deficiency or signaling disruption leads to asymmetric muscle tone [63]. The craniovertebral junction is richly innervated and contains structures that influence autonomic balance. Dysfunction at the C1-C2 level can impair sympathetic innervation (via the superior cervical ganglion) and blood supply to the pineal gland (from the vertebral arteries), potentially affecting the production and effectiveness of melatonin. This creates a vicious cycle: cervical dysfunction causes dysregulation of melatonin, the deficiency of which leads to muscle imbalance and the progression of scoliosis [63].

Impaired intracellular calcium metabolism in platelets and osteoblasts mirrors similar dysfunction in neurons and muscle cells. The calcium-calmodulin complex is critical for neuromuscular transmission. Dysfunction at the level of the brainstem and upper cervical segments (e.g., due to mechanical effects on C1-C2) may disrupt calcium signaling in motor neurons that control paravertebral muscle tone. Thus, the cervical spine may be the site of a primary neurological defect that is mediated by impaired calcium metabolism [64]. High leptin levels in girls with IS overstimulate the sympathetic nervous system (SNS), leading to asymmetric bone growth and muscle tone. The superior cervical ganglion, a key SNS node, is located in close proximity to the C1-C3 segments. Its activation by leptin can directly influence: 1) the tone of the vertebral arteries, altering the blood supply to the brainstem and cerebellum, 2) neurovascular transmission in the structures of the posterior cranial fossa, and 3) proprioceptive input from the upper cervical muscles [65, 66]. This directly links a systemic hormonal factor (leptin) to cervical spine function and explains why its dysfunction can be a trigger.

When analyzing this hypothesis, the question arises: why does short-term impact on the cervical spine not always manifest itself in pathology detected by diagnostic methods? The cervical spine is anatomically quite stable and simultaneously mobile. Stability is ensured by the unique structure of the C1-C2 joints, the ligament system (strong cruciate and alar ligaments), and the muscular corset (deep flexors and multifidus muscles). Mobility is determined by the characteristics of the joints: flat articular surfaces (except C1-C2), large intervertebral discs (relative to the size of the vertebrae), and the absence of a costal framework. The upper cervical spine (C0-C2) specializes in a specific type of movement (rotation) and, along with maximum stability to protect the brainstem, is most susceptible to rotational (subluxations) and whiplash injuries, chronic dysfunctions due to muscle imbalance, while the lower cervical spine (C3-C7) is more mobile and provides a greater range of motion (flexion/extension and lateroflexion) [11]. In children, the ligaments contain more elastic fibers and are more extensible, muscle tone of the neck is reduced, but when in a supine position, the cervical spine of a newborn remains stable. Stability is impaired intrapartum by axial traction on the head, leading to overstretching of the C1-C2 ligaments (risk up to 15% in breech presentation) [67], by sudden head tilt, and by congenital developmental anomalies (hypoplasia of the odontoid process). Cervical instability can be diagnosed by the non-specific sign of asymmetry of the skin folds on the neck, but more reliable are ultrasound signs of divergence of the articular surfaces of more than 4 mm and radiography with functional tests [12].

Although the etiologic core of IS is a genetic predisposition, intrapartum trauma to the craniovertebral junction is considered a significant precipitating factor capable of initiating a cascade of pathological changes in susceptible patients. This review focuses on the role of this factor in the pathogenesis of IS, without excluding the importance of other triggers. The LBX1 gene is expressed in the dorsal horn of the spinal cord [68] and regulates the development of interneurons that control the symmetry of tone of the rotator cuff muscles. Mutations in LBX1 cause hypertonicity on one side, followed by twisting of the vertebrae [69]. We believe that damage to the C0-C2 region may trigger pathological LBX1 activity, leading to muscle imbalance.

Identifying early genetic markers (especially PRS - Polygenic Risk Scores) in combination with family and intranatal history can be a powerful tool for identifying children at high risk for preclinical IS. The intranatal trigger hypothesis fits perfectly with the genetic model:

1. Genetic predisposition (LBX1, GPR126, etc.) creates a "vulnerable" phenotype: impaired neuromuscular control (proprioception, tone), abnormalities in connective tissue development and bone metabolism.

2. Intranatal exposure (C1-C2 subluxation, microdamage to the brainstem/spinal cord) acts as a trigger, initiating dysregulation of muscle tone with asymmetric loading on the growing vertebrae, leading to spinal curvature.

3. The pubertal hormonal surge (IGF-1, estrogens) accelerates progression against the background of an existing imbalance.

Genetic markers are a scientific tool for risk stratification. Their power is revealed when integrated with clinical data, anamnesis (including triggers), and functional markers. They also provide a path to early diagnosis and personalized prevention of idiopathic scoliosis.

Then the question arises: why does scoliotic deformity develop in children with normal pregnancies and births? The development of scoliosis in children born without complications is explained by a complex interaction of genetic, biomechanical, and environmental factors. First, the most fundamental factor is genetic predisposition. Polymorphisms in the LBX1, GPR126, and other genes are detected in 80% of patients with idiopathic scoliosis (IS) [69, 70], and the heritability of IS reaches 38-80% [4]. Even in the absence of birth trauma, genes can disrupt the formation of spinal cord interneurons, reduce the resistance of connective tissue to stress, and alter the mechanosensitivity of vertebral growth plates. Secondly, postnatal biomechanical factors play a significant role in the era of scientific and technological progress. During school, prolonged sitting at a desk in an incorrect posture, carrying heavy backpacks, and physical inactivity lead to increased axial loads and weakness of the muscular corset. Thirdly, neurohormonal imbalance during puberty manifests itself in accelerated growth, melatonin and calmodulin imbalances, estrogen-dependent ligament hypermobility in girls, etc. Furthermore, increased athletic activity and abrupt or abnormal movements in children lead to microtrauma and latent dysfunctions (subclinical subluxations of C1-C2, latent instability of the dural attachments). Thus, even in the absence of birth trauma, genetic predisposition, combined with postnatal factors, can trigger a pathological cascade. This explains cases of "spontaneous" development of IS in children from the low-risk group.

Conclusion

This review demonstrates that intrapartum cervical spine trauma is a significant precipitating factor in the pathogenesis of idiopathic scoliosis (IS), but its role is realized solely in the context of genetic predisposition and within the framework of a multifactorial model. Microdamage at the C0-C2 level acts as a trigger, disrupting descending neuromuscular control (reticulo- and vestibulospinal tracts) and initiating a cascade leading to asymmetry in paravertebral muscle tone, as confirmed by EMG studies and biomechanical modeling. This mechanism explains the presence of a latent period and subsequent progression of deformity during puberty: the initial muscular imbalance, masked by hypermobility, is transformed into structural deformity under the influence of a growth spurt and hormonal changes according to the Huether-Wolff law. The hypothesis fits perfectly into the current model, where gene polymorphisms (LBX1, GPR126) create a "vulnerable phenotype"—impaired proprioception and connective tissue weakness. The combination of intrapartum history analysis (complicated births) with early genetic screening (PRS—polygenic risk scores) and ultrasound monitoring of the craniovertebral junction in children at risk opens the way to preclinical risk stratification and early prevention.

Thus, intrapartum trauma to the cervical spine is not the only, but an important and potentially modifiable component in the complex etiology of idiopathic scoliosis, which justifies the advisability of an interdisciplinary approach (orthopedics, neurology, neonatology) to identifying target groups for early diagnosis and prevention of IS.

 

 

 

 

 

 

 

 

About the authors

Marina E. Vinderlih

Mari State University

Author for correspondence.
Email: vinderlikh@yandex.ru
ORCID iD: 0000-0002-9855-548X
SPIN-code: 9943-2150

Associate Professor, Candidate of Medical Sciences, Department of Surgical Diseases

Russian Federation, 1 Lenin Square,424000 Yoshkar-Ola, Mari El Republic, Russia;

Sergey V. Vissarionov

H. Turner National Medical Research Center for Children’s Orthopedics and Trauma Surgery

Email: vissarionovs@gmail.com
ORCID iD: 0000-0003-4235-5048
SPIN-code: 7125-4930

MD, PhD, Dr. Sci. (Med.), Professor, Corresponding Member of RAS

Russian Federation, 64-68 Parkovaya str., Pushkin, Saint Petersburg, 196603

References

Supplementary files