Certain disorders of motor function manifest themselves most
clearly as impairments of upright stance and locomotion; their evaluation
depends on knowledge of the neural mechanisms underlying these peculiarly
human functions. The analysis of stance, carriage, and gait is a
particularly rewarding medical exercise; with some experience, the
examiner can sometimes reach a neurologic diagnosis merely by noting
the manner in which the patient enters the office. Considering the
frequency of falls that result from gait disorders and their consequences,
such as hip fracture, and the resultant need for hospital and nursing
home care, this is an important subject for all physicians. The
substantial dimensions of this social and economic problem are well
described by Tinetti and Williams.
The normal gait seldom attracts attention but it should be observed
with care if slight deviations from normal are to be appreciated.
The body is erect, the head is straight, and the arms hang loosely
and gracefully at the sides, each moving rhythmically forward with
the opposite leg. The feet are slightly everted, the steps are approximately
equal, and the internal malleoli almost touch as each foot passes
the other. The medial edges of the heels, as they strike the ground
with each step, lie almost along a straight line. As each leg moves
forward, there is coordinated flexion of the hip and knee, dorsiflexion
of the foot, and a barely perceptible elevation of the hip, so that
the foot clears the ground. Also, with each step, the thorax advances
slightly on the side opposite the swinging lower limb. The heel
strikes the ground first, and inspection of the shoes will show
that this part is most subject to wear.
The normal gait cycle, defined as the period
between successive points at which the heel of the same foot strikes
the ground, is illustrated in Fig. 7-1, based
on the studies of Murray and coworkers and of Olsson. In this figure,
the cycle is initiated by the heel strike of the right foot. The stance
phase, during which the foot is in contact with the ground,
occupies 60 to 65 percent of the cycle. The swing phase begins
when the right toes leave the ground. For 20 to 25 percent of the
walking cycle, both feet are in contact with the ground (double-limb
support). In later life, when the steps shorten and the
cadence (the rhythm and number of steps per minute) decreases, the
proportion of double-limb support increases (see further on). Surface
electromyograms show an alternating pattern of activity in the legs,
predominating in the flexors during the swing phase and in the extensors
during the stance phase.
The normal gait cycle, based on the studies of Olsson
and of Murray et al. See text for details.
When analyzed in greater detail, the requirements for locomotion
in an ...