In this chapter, the focus is on how the various body structures are integrated into a system that enables the body as a whole to maintain a particular posture. We will use our knowledge of individual joint and muscle structure and function as the basis for determining how each structure contributes to the equilibrium and stability of the body in the optimal standing posture We will consider the internal and external forces acting on the body in relation to standing, sitting, and lying postures, and we will explore how these forces will affect the patient in Patient Case 13-1. Throughout the chapter, we will include discussions, in the form of Case Applications, related to our patient's ability to function without many of the normal postural control mechanisms and the internal lower extremity forces necessary to maintain his body in the standing posture, as well as potential problems that he might have in the sitting and lying postures.
Case 13-1: Patient Case
Dave Nguyen, a 19-year-old college varsity ice hockey player, was injured during a game when two members of the opposing team checked him against the boards. The impact of the collision knocked all three players down onto the ice, with Dave on the bottom and the other players on top. Dave sustained fractures of two thoracic vertebrae (T9 and T10) and a complete spinal cord injury, which resulted in paraplegia (muscle paralysis in both lower extremities). He has functioning lower abdominal and lower erector spinae muscles but no function in his hip or lower extremity muscles.
When we first meet Dave, his surgically repaired vertebral fractures have healed, and he is medically cleared to begin an aggressive rehabilitation program.
Dave's main goal at this point is to become independent as soon as possible, including being able to walk again. He admits that his legs probably will not regain their function, but he is determined to be able to get around with crutches.
His youth, his good physical condition, and the fact that he is used to the discipline required for participation in a varsity sport should be helpful in the rehabilitation process.
STATIC AND DYNAMIC POSTURES
Posture can be either static or dynamic. In static posture, the body and its segments are aligned and maintained in certain positions. Examples of static postures include standing, sitting, lying, and kneeling. Dynamic posture refers to postures in which the body or its segments are moving—walking, running, jumping, throwing, and lifting. An understanding of static posture forms the basis for understanding dynamic posture. Therefore, the static postures of standing and sitting are emphasized in this chapter. The dynamic postures of walking and running are discussed in Chapter 14.
The study of any particular posture includes kinetic and kinematic analyses of all body segments. Humans and other living creatures have the ability to arrange and rearrange body segments to form ...