**1. Introduction**

A normal spine alignment including coronal and sagittal balance is essential for optimal biomechanical function [1–7]. The spine, which allows for simultaneous stability and mobility, also has the inherent role of housing and protecting the brain and spinal cord. The alignment of the spine is critical in the context of allowing normal function of the central nervous system (CNS); that is, by not impeding its function by various loading mechanisms (i.e. overstretching the nervous tissues) [8, 9]. Clinical trials [10–16] and case reports [17–25] have demonstrated that corrections in patient posture have resulted in relief of neurological symptoms including for example, cervical spondylotic and discogenic radiculopathy, cervical spondylotic myelopathy (CSM), lumbosacral discogenic radiculopathy, trigeminal neuralgia (TN), dystonia, Parkinson's disease (PD), carpal tunnel syndrome (CTS), and Tourette's syndrome (TS). Although the precise mechanisms underlying improved neurological function in patients having improved postural alignment are not fully understood, they are thought to lie in the biomechanics of the CNS and in normalization of load sharing across tissues innervated by mechanoreceptors which are integral in sensorimotor control through somatosensory potentials.

In 1960, a monograph was published by Alf Breig documenting for the first time, the most comprehensive illustrative demonstrations of the biomechanics of the central nervous system (CNS) [8]. This seminal work laid the groundwork for the comprehensive understanding of how spine movement affects the CNS; that is, how physiologic deformation of the cord and brainstem simultaneously accompanies normal postural movements of the spine (i.e. 'neurodynamics'). In 1978, Breig published a second book expanding on the concepts outlined in 1960, and focused on 'adverse mechanical tension' in the CNS and how this produces common neurological symptoms and signs [9]. An exciting development by Breig was his invention of the 'cervicolordodesis' surgical procedure that increased the cervical lordosis and prevented cervical flexion to relieve tension within the cord, brainstem and nerve roots demonstrating dramatic improvements of neurological disorders including nerve root compression syndromes, TN, multiple sclerosis (MS) and other neuromusculoskeletal conditions [26].

A second prevailing theory on how normalization of spine/posture alignment can dramatically alter patient pain, disability, function, and neurophysiology is through cervical spine sensory afferent input (so called afferentation) and its influence on the motor system termed sensorimotor control. As a result of activation of mechanoreceptors contained in the various ligaments, discs, muscles and skin, changes in spine position-alignment has a major influence on motor control [27]. Intimate connections exist between afferent input (from the proprioceptive, visual and vestibular systems) and stable upright postures of the head and neck [28]. The mechanoreceptors in the cervical spine soft tissues provide necessary neurophysiological input in a feed forward and feedback system for sensorimotor control via connections to the vestibular, visual and central nervous systems [29]. Furthermore, a complex network of neurophysiological connections between cervical spine mechanoreceptors and the sympathetic nervous system exists [30–32]. Though the effects of autonomic system activity on musculoskeletal function has been extensively studied, there is a paucity of research demonstrating that the autonomic nervous system is intimately responsive to changes in the afferent articular input due to spine joint dysfunction [33]. Alterations in afferent articular input driven by spine joint aberrant movement (altered kinematics) and subtle or overt tissue damage is generally referred to as 'dysafferentation' in the literature. The assumption that restoring normal posture and cervical spine alignment is important for a better afferentation process and improved autonomic nervous system function has some preliminary evidence in the recent literature [10, 34].

**49**

*The Influence of Sagittal Plane Spine Alignment on Neurophysiology and Sensorimotor Control…*

Today there are non-surgical evidence-based techniques known to improve posture and spine alignment; in essence to accomplish what Breig was able to do, only without surgery (e.g. increase cervical lordosis). One of these methods is Chiropractic BioPhysics® (CBP®) technique which is a full-spine and posture treatment that utilizes mirror image® (i.e. 'corrective') exercises, adjustments and spinal traction procedures to restore normal spine alignment [35–39]. Due to the implicit interconnectedness of spine alignment and neurologic function, these methods are proving to be particularly effective in treating patients with neurological and sensorimotor control disorders, where perhaps unknowingly, poor spine alignment is a causative factor in patients suffering from neurologic ailments in which their symptoms are exacerbated and/or directly caused by the adverse nerve tensions placed upon them and by dysafferentation caused by spine and postural

This chapter reviews the Harrison normal spinal model [40–47] that is used to assess a patient's spine alignment as compared to the normal/ideal position (i.e. gold standard), how the central nervous system is housed in and biomechanically functions within the skeletal structure under normal and pathologic conditions, including mechanisms for neurologic symptom generation under pathologic biomechanical tensions, and altered sensorimotor control from dysafferentation driven by altered load sharing and spine kinematics. Simultaneously, the CBP structural rehabilitation approach to realigning the spine and postural position in order to treat patients who present with spinal subluxation that is suspected to be pathognomonic for their pain, disability, and generalized neurologic sensorimotor disorders

Any contemporary discussion about the normal/ideal human spinal configuration is regarding its precise orientation (i.e. precise shape of the different spinal regions). Although many research groups have attempted to model the shape of the normal human spine, few have done so as comprehensively and systematically as the Harrison group [40–47]. In a series of studies, elliptical shape modeling of the path of the posterior longitudinal ligament was performed on radiograph samples of asymptomatic subjects. Computer iterations of spine shape modeling was used to determine a best-fit geometric spinal shape by fitting various ellipses of altered minor-to-major axis ratios to the digitized posterior vertebral body corners of the cervical [40–42], thoracic [43, 44], and lumbar spinal regions [45–47] (**Figure 1**). The Harrison normal spine model (**Figure 1**) features a circular cervical lordosis, and portions of an elliptical curve for both the thoracic kyphosis (more curvature cephalad), and lumbar lordosis (more curvature caudad). Consequently, features of the normal human spine reveal that the opposite thoracic and lumbar curves meet together at the thoraco-lumbar junction being essentially straight; the upper, deeper curve of the upper thoracic spine reflects oppositely at the cervico-thoracic junction (between T1 and T2) and continues into the cervical lordosis; the lower lumbar spine increases its lordotic alignment having two-thirds of its curve between L4-S1 as it meets the forward tilted sacral base. The spine is modeled as vertical in the front view. The spine alignment is easily quantified by repeatable and reliable methods from measuring its position from standing X-rays [48–52] (**Figure 2**). The Harrison normal spine model has been validated in several ways. Simple analyses of alignment data of normal asymptomatic populations have been done [40–47, 53]. Comparison studies between normal samples to symptomatic samples [40, 41, 53]; as well as between normal samples to theoretical ideal models have

*DOI: http://dx.doi.org/10.5772/intechopen.95890*

deviations (i.e. adult spinal deformity/subluxation).

will be a main theme.

**2. The Harrison normal spinal model**

*The Influence of Sagittal Plane Spine Alignment on Neurophysiology and Sensorimotor Control… DOI: http://dx.doi.org/10.5772/intechopen.95890*

Today there are non-surgical evidence-based techniques known to improve posture and spine alignment; in essence to accomplish what Breig was able to do, only without surgery (e.g. increase cervical lordosis). One of these methods is Chiropractic BioPhysics® (CBP®) technique which is a full-spine and posture treatment that utilizes mirror image® (i.e. 'corrective') exercises, adjustments and spinal traction procedures to restore normal spine alignment [35–39]. Due to the implicit interconnectedness of spine alignment and neurologic function, these methods are proving to be particularly effective in treating patients with neurological and sensorimotor control disorders, where perhaps unknowingly, poor spine alignment is a causative factor in patients suffering from neurologic ailments in which their symptoms are exacerbated and/or directly caused by the adverse nerve tensions placed upon them and by dysafferentation caused by spine and postural deviations (i.e. adult spinal deformity/subluxation).

This chapter reviews the Harrison normal spinal model [40–47] that is used to assess a patient's spine alignment as compared to the normal/ideal position (i.e. gold standard), how the central nervous system is housed in and biomechanically functions within the skeletal structure under normal and pathologic conditions, including mechanisms for neurologic symptom generation under pathologic biomechanical tensions, and altered sensorimotor control from dysafferentation driven by altered load sharing and spine kinematics. Simultaneously, the CBP structural rehabilitation approach to realigning the spine and postural position in order to treat patients who present with spinal subluxation that is suspected to be pathognomonic for their pain, disability, and generalized neurologic sensorimotor disorders will be a main theme.

## **2. The Harrison normal spinal model**

Any contemporary discussion about the normal/ideal human spinal configuration is regarding its precise orientation (i.e. precise shape of the different spinal regions). Although many research groups have attempted to model the shape of the normal human spine, few have done so as comprehensively and systematically as the Harrison group [40–47]. In a series of studies, elliptical shape modeling of the path of the posterior longitudinal ligament was performed on radiograph samples of asymptomatic subjects. Computer iterations of spine shape modeling was used to determine a best-fit geometric spinal shape by fitting various ellipses of altered minor-to-major axis ratios to the digitized posterior vertebral body corners of the cervical [40–42], thoracic [43, 44], and lumbar spinal regions [45–47] (**Figure 1**).

The Harrison normal spine model (**Figure 1**) features a circular cervical lordosis, and portions of an elliptical curve for both the thoracic kyphosis (more curvature cephalad), and lumbar lordosis (more curvature caudad). Consequently, features of the normal human spine reveal that the opposite thoracic and lumbar curves meet together at the thoraco-lumbar junction being essentially straight; the upper, deeper curve of the upper thoracic spine reflects oppositely at the cervico-thoracic junction (between T1 and T2) and continues into the cervical lordosis; the lower lumbar spine increases its lordotic alignment having two-thirds of its curve between L4-S1 as it meets the forward tilted sacral base. The spine is modeled as vertical in the front view. The spine alignment is easily quantified by repeatable and reliable methods from measuring its position from standing X-rays [48–52] (**Figure 2**).

The Harrison normal spine model has been validated in several ways. Simple analyses of alignment data of normal asymptomatic populations have been done [40–47, 53]. Comparison studies between normal samples to symptomatic samples [40, 41, 53]; as well as between normal samples to theoretical ideal models have

*Therapy Approaches in Neurological Disorders*

musculoskeletal conditions [26].

A normal spine alignment including coronal and sagittal balance is essential for optimal biomechanical function [1–7]. The spine, which allows for simultaneous stability and mobility, also has the inherent role of housing and protecting the brain and spinal cord. The alignment of the spine is critical in the context of allowing normal function of the central nervous system (CNS); that is, by not impeding its function by various loading mechanisms (i.e. overstretching the nervous tissues) [8, 9]. Clinical trials [10–16] and case reports [17–25] have demonstrated that corrections in patient posture have resulted in relief of neurological symptoms including for example, cervical spondylotic and discogenic radiculopathy, cervical spondylotic myelopathy (CSM), lumbosacral discogenic radiculopathy, trigeminal neuralgia (TN), dystonia, Parkinson's disease (PD), carpal tunnel syndrome (CTS), and Tourette's syndrome (TS). Although the precise mechanisms underlying improved neurological function in patients having improved postural alignment are not fully understood, they are thought to lie in the biomechanics of the CNS and in normalization of load sharing across tissues innervated by mechanoreceptors which

are integral in sensorimotor control through somatosensory potentials.

In 1960, a monograph was published by Alf Breig documenting for the first time, the most comprehensive illustrative demonstrations of the biomechanics of the central nervous system (CNS) [8]. This seminal work laid the groundwork for the comprehensive understanding of how spine movement affects the CNS; that is, how physiologic deformation of the cord and brainstem simultaneously accompanies normal postural movements of the spine (i.e. 'neurodynamics'). In 1978, Breig published a second book expanding on the concepts outlined in 1960, and focused on 'adverse mechanical tension' in the CNS and how this produces common neurological symptoms and signs [9]. An exciting development by Breig was his invention of the 'cervicolordodesis' surgical procedure that increased the cervical lordosis and prevented cervical flexion to relieve tension within the cord, brainstem and nerve roots demonstrating dramatic improvements of neurological disorders including nerve root compression syndromes, TN, multiple sclerosis (MS) and other neuro-

A second prevailing theory on how normalization of spine/posture alignment can dramatically alter patient pain, disability, function, and neurophysiology is through cervical spine sensory afferent input (so called afferentation) and its influence on the motor system termed sensorimotor control. As a result of activation of mechanoreceptors contained in the various ligaments, discs, muscles and skin, changes in spine position-alignment has a major influence on motor control [27]. Intimate connections exist between afferent input (from the proprioceptive, visual and vestibular systems) and stable upright postures of the head and neck [28]. The mechanoreceptors in the cervical spine soft tissues provide necessary neurophysiological input in a feed forward and feedback system for sensorimotor control via connections to the vestibular, visual and central nervous systems [29]. Furthermore, a complex network of neurophysiological connections between cervical spine mechanoreceptors and the sympathetic nervous system exists [30–32]. Though the effects of autonomic system activity on musculoskeletal function has been extensively studied, there is a paucity of research demonstrating that the autonomic nervous system is intimately responsive to changes in the afferent articular input due to spine joint dysfunction [33]. Alterations in afferent articular input driven by spine joint aberrant movement (altered kinematics) and subtle or overt tissue damage is generally referred to as 'dysafferentation' in the literature. The assumption that restoring normal posture and cervical spine alignment is important for a better afferentation process and improved autonomic nervous system function has some preliminary evidence in the recent literature [10, 34].

**1. Introduction**

**48**

### **Figure 1.**

*The Harrison normal sagittal spine model as the path of the posterior longitudinal ligament. The cervical, thoracic and lumbar curves are all portions of an elliptical curve having a unique minor-to-major axis ratio. The cervical curve is circular meaning the minor and major axes are equal.*

**51**

**Figure 2.**

*within about 2° (Courtesy CBP seminars).*

*The Influence of Sagittal Plane Spine Alignment on Neurophysiology and Sensorimotor Control…*

been done [40, 41, 43–46]. The statistical differentiation of asymptomatic subjects from symptomatic pain group patients based on alignment data have been performed [42, 47]. The demonstration of paralleled spine alignment improvements with reduction in pain and disability, versus no change in untreated control groups in pre-post clinical trials have been performed [54–59]. The demonstration in randomized clinical trials that only patient groups achieving lordosis improvement (lumbar or cervical) and hyper-kyphosis (thoracic) reduction achieve long-term improvements in various outcome measures versus comparative treatment control groups not getting spine alignment improvement who experience regression in multiple outcome measures at follow-up have also been done [10–16, 60–64].

*Harrison posterior tangent method involves lines drawn contiguous with the posterior vertebral body margins. Intersegmental as well as regional sagittal curves are easily quantified having a standard error of measurement* 

Chiropractors practicing Chiropractic BioPhysics® (CBP®) structural rehabilitation techniques have used this spine model as the goal of care for over 20 years; and more recently physical therapists and other manual medicine rehabilitation specialists have adopted components of this system as well. It is noted that this model serves as the baseline for patient comparison; specific patient comparisons, however, must include patient-specific considerations related to thoracic inlet parameters [65] as well as pelvic morphology [66] as these may dictate a structural modification to the model for a given patient. There are software programs (i.e. PostureRay Inc., Trinity FL, USA) that aid in the ability for practitioners to assess spine alignment quickly in daily practice (**Figure 3**). It must also be mentioned

*DOI: http://dx.doi.org/10.5772/intechopen.95890*

*The Influence of Sagittal Plane Spine Alignment on Neurophysiology and Sensorimotor Control… DOI: http://dx.doi.org/10.5772/intechopen.95890*

### **Figure 2.**

*Therapy Approaches in Neurological Disorders*

**50**

**Figure 1.**

*The Harrison normal sagittal spine model as the path of the posterior longitudinal ligament. The cervical, thoracic and lumbar curves are all portions of an elliptical curve having a unique minor-to-major axis ratio.* 

*The cervical curve is circular meaning the minor and major axes are equal.*

*Harrison posterior tangent method involves lines drawn contiguous with the posterior vertebral body margins. Intersegmental as well as regional sagittal curves are easily quantified having a standard error of measurement within about 2° (Courtesy CBP seminars).*

been done [40, 41, 43–46]. The statistical differentiation of asymptomatic subjects from symptomatic pain group patients based on alignment data have been performed [42, 47]. The demonstration of paralleled spine alignment improvements with reduction in pain and disability, versus no change in untreated control groups in pre-post clinical trials have been performed [54–59]. The demonstration in randomized clinical trials that only patient groups achieving lordosis improvement (lumbar or cervical) and hyper-kyphosis (thoracic) reduction achieve long-term improvements in various outcome measures versus comparative treatment control groups not getting spine alignment improvement who experience regression in multiple outcome measures at follow-up have also been done [10–16, 60–64].

Chiropractors practicing Chiropractic BioPhysics® (CBP®) structural rehabilitation techniques have used this spine model as the goal of care for over 20 years; and more recently physical therapists and other manual medicine rehabilitation specialists have adopted components of this system as well. It is noted that this model serves as the baseline for patient comparison; specific patient comparisons, however, must include patient-specific considerations related to thoracic inlet parameters [65] as well as pelvic morphology [66] as these may dictate a structural modification to the model for a given patient. There are software programs (i.e. PostureRay Inc., Trinity FL, USA) that aid in the ability for practitioners to assess spine alignment quickly in daily practice (**Figure 3**). It must also be mentioned

### **Figure 3.**

*Three patients demonstrating dramatically different spine alignment patterns. Left: Excessive lumbar hyperlordosis, L4 anterolisthesis, and excessive anterior sagittal balance in a mid-aged female with disabling low back pain; Middle: Excessive thoracolumbar kyphosis and early degenerative changes in a mid-aged male; Right: Excessive thoracic hyperkyphosis in a young male with Scheuermann's disease. Red line is contiguous with posterior vertebral body margins; green line represents Harrison normal spinal model (Courtesy PAO).*

that proper assessment of the spine includes the whole spine, that is, the cervical, thoracic and lumbar regions and femur heads. This is because spine balance and compensation mechanisms involve the whole spine; thus, regional X-rays to the 'problem area' can mislead treatment and not account for distal spinopelvic compensations that need to be considered prior to initiating a trial of spine care by these methods.
