![]() Indeed, during gait, bipedal static balance is constantly thwarted by single-foot support while stepping and must be compensated by a muscular tolerance which tends to reestablish this balance by passing through short phases of instability. To understand the conditions necessary for such a balance, it is important to analyse matters both statically and dynamically. The hominids modified their profile by developing cervical curvature and lumbar lordosis to maintain a horizontal gaze and to free the upper limbs that are no longer carriers. Their centre of mass is projected at the centre of their support polygon which is located in front of the footprint of the hind legs. Their spine presents a single thoraco-lumbar curvature in kyphosis. Indeed, the great apes, unlike humans, move on all the four. The human species is characterized by bipedalism, which has the advantage of freeing the upper limbs for other tasks, but this is done at the cost of a more precarious overall balance. It is in this condition that the actions of the agonist and antagonistic muscles of the spine are minimized and therefore most efficient. īalance or equilibrium (from the Latin aequilibrium, from aequus “equal” and libra “balance, weight”) is a concept that describes a situation in which the forces present are equal, or such that none surpasses the sum of the others. These slides can be retrieved under Electronic Supplementary Material. Integration of these parameters into the study of gait is an area still under investigation. Taking these parameters into account also enables us to understand the complications involved in this type of surgery: transitional syndromes or junctional syndromes. Global evaluation of the entire spine and the measurement of the aforementioned parameters allow to determine the extent of the correction to be performed during surgery. Understanding these different data allows for better planning of the surgical management of the patients. Ageing makes it possible to show compensation mechanisms at three levels: spinal, pelvic and lower limbs. The relationship between these different parameters was analysed, and Roussouly proposed his classification of the different spine shape. The average values of these parameters are reported with the new 3D measurements by Le Huec et al. The OD-HA (odontoid hip axis) angle is the most efficient parameter to analyse the global balance. At the thoracic and lumbar level, they are, respectively, kyphosis and lordosis. The cervical parameters are the upper (O–C2) and lower cervical curvatures (C2–C7), the C7 slope, the spino-cranial angle and the vertical cervical offset. The pelvic incidence is constant, and the sacral slope and the pelvic tilt are positional. This analysis involves the study of parameters which are now well defined. During gait, this balance is constantly thwarted by single-foot support. The static sagittal balance of the normal spine is a physiological alignment of the spine in the most efficient manner by the muscular forces.
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