Balance

Fig. 1

Man in motion. The line going by inner ear and eye shows the “semi-circular canals” plane which must stay perpendicular to the gravity line during motion

Such a permanent adjustment to motion requires energy which must be controlled for dynamic bipedal harmonious function .

Posture

Upright posture , and by extension sway and destabilizing movement, are specific to the human species. Ideally in the standing position all centers of gravity and centers of body and segment mass are located on the line of gravity which projects at the center of the support surface. This posture of man standing can vary infinitely within the limits of the cone of economy described in Chap. 12 by Jean Dubousset. The variations of posture will then depend on the application of forces, moreover by the perception’s modification induced by individual psychological or emotional status.

Stability

Can be defined as a continuity of anatomical structures between the vertebrae which constitute the vertebral column. This continuity of the structures must be rigorously maintained during the very extreme movements of the elements constituting the whole spine. This stability can be interrupted by accidental or degenerative causes. The consequences are a modification of the global spine alignment and thus affect balance. However, the infinite possibilities offered by the flexibility of the spine whilst retaining the role of protecting the nervous system represent its essential function; stability in motion.

From Alignment to Equilibrium

Evaluated and measured, alignment gives an accurate rendition of the ideal structure of the vertebral column obtained in both posteroanterior and lateral radiographs in the standing position. The criteria for this alignment are clearly presented with their morphological and chronological variations in the in-depth study made by Pierre Roussouly and Jean Dubousset (Chaps. 8 and 12). The hip extension criteria are well illustrated by Istvan Hovorka (Chap. 7). These radiological and clinical criteria are complemented by neuro-muscular studies, which are together implied in the concept of spine alignment. It is possible to define the ideal alignment of an individual’s spine and pelvis in correlation with body’s mass and muscle tone and therefor understand the interactions between the axis of the body and the stays that hold it. Sagittal spine alignment requires full mobility of the hip, including hip extension reserve as a guarantee of functional lumbar lordosis. Pelvis version (pelvic tilt) in correlation with lumbar lordosis induce both thoracic kyphosis and cervical lordosis. As a result, the head’s center of mass is maintained on the body’s line of gravity. Head and neck segments, with specific powerful stays, control horizontal vision, playing an essential role in balance.

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Importance of Spine Anatomy

The Pelvis

When discs, facet joints, and ligaments degenerate causing lumbar lordosis, the pelvis evolves into retroversion. Pelvis retroversion is visible on a lateral spine radiograph, obtained while standing, where the shadow of the femoral head is seen in front of the body’s line of gravity. Such pelvis retroversion combined with maximum hip extension makes the standing upright posture impossible without flexing the knees. Body balance is maintained at the expense of lumbar spine lordosis modification, to the limits imposed by pelvis retroversion. The final result is a cascade of discs, facets, and ligament degeneration, ending up in vertebrae rotatory dislocations and adult spine deformity.

Thoraco-Lumbar Spine

Made up of 17 segments, each individualized , is made up of two zones that operate in a symbiotic mode. The lumbar part, made up of five more voluminous segments presents a sagittal curvature in lordosis. It is also the most mobile while supporting the most important load. Its flexibility, not limited by the rib cage, is much greater than the 12 chest segments with physiological curvature in kyphosis. These two curves compensate each other to such an extent that the increase in the degree of curvature of one corresponds to an increase in the degree of curvature of the other. Let us increase the lumbar lordosis, and we shall see the thoracic kyphosis increase, displacing the head forward increasing stress applied on the cervical spine, affecting the overall spine alignment.

The Cervical Spine

Composed of two complementary segments , it ensures the movement of rotation, lateral flexion, extension, and flexion of the head. The cranial segment is made up of two vertebrae connected to each other, and to the occipital bone, by a complex system of joints constituting three axes of mobility to allow 3 degrees of freedom of the head’s movement. The remainder of the five underlying segments is composed of similar vertebrae, whose articular facets allow a combination of rotation and lateral flexion. Such complexity of movement implies difficulty to adapt to conditions of extreme load, stretching the possibilities of resistance and muscle tone to their limits, in order to control the head’s position.

Spine and Central Nervous System: (CNS) and (PNS)

It may look obvious that standing upright is a given privilege, however, it requires neurological implication of such complexity redefined every year by neuroscience discoveries. Research conducted by Christine Assaiante [1] demonstrated balance control development over years in synchronicity with CNS development. Body balance for a major part is maintained by the cervical action of all neck muscles, ensuring the inner ear’s vestibular stability when acceleration is transmitted to the head by body motion. Head control does not only guarantee good function of the oculo-vestibular reflex, it insures enlarged perception of the environment, and by extension of its specific input at each given moment [2, 3] (Fig. 1). A cervical kyphosis , progressively made permanent by the weakening of the extensors, reduces the visual field and considerably limits the perceptive inputs which are very important to the enrichment of cognition (Fig. 2). Reduction in visual acuity affects not only cognition but also a slowing down of the plasticity of the brain. As a result, other osteo-muscular and tactile perceptions can insidiously compromise the proprioception of the healthy adult. Becoming less engaged, the brain participates less and less in action, and progressive uncertainty creeps in to compromise the feeling of safety. The pattern of behavior is reduced to limit them, and when apprehension becomes fear, the vicious circle is closed.