Pronation: Foot pronation is a combination of three joint motions occurring in the three major cardinal planes. Eversion (frontal), abduction (transverse), and dorsiflexion (sagittal) all occur in one motion. i.e. Standing on a street curb with your foot (inside leg) everted.
Supination: Foot supination is a combination of three joint motions occurring in the three major cardinal planes. Inversion (frontal), adduction (transverse), and plantar flexion (sagittal) all occur in one motion. i.e. Standing on a street curb with your right foot (outside leg) inverted.
Due to the extreme difficulty in measuring a triplane motion at the subtalar joint, inversion and eversion movements are used to indirectly signify the amount of pronation and supination.
The foot must be adapt for variance in the terrain (it must be a “mobile adaptor”), which occurs with pronation (the foot is a “loose bag of bones” in pronation). It must also serve as a “rigid lever” to propel the body forward in space. The latter occurring when the foot is supinated, and the foot structure becomes more rigid when supinated (www.footmaxx.com, 2001).
These two-foot motions are very relevant to life. For example, pronation increases the mechanical efficiency of walking and they both provide a greater amount of force dissipation by increasing the time interval of foot contact, thus decreasing the force that is absorbed (impulse = force x time).
More specifically, a normal gait pattern would consist of the foot striking the ground in a supinated position since this provides a rigid lever and it also serves to stabilize then bony architecture of the foot. During the swing phase, the foot pronates first then it supinates. The initial pronation is what provides the biomechanical efficiency by allowing the foot to clear the ground. This requires minimal energy expenditure.
These two-foot motions are key players in the normal gait cycle. This cycle consists of two main components: Stance (contact, midstance, and propulsive) & Swing phase.
Normal gait requires the proper functioning of the musculoskeletal system and the nervous system. The nervous system is responsible for both motor output and sensory input. The basic divisions of the gait cycle are stance and swing. The entire period during which the foot is on the ground is the stance phase. The swing phase begins when the foot is lifted from the floor until the heel is placed down. While walking the thorax rotates in clockwise and counterclockwise directions opposite the pelvic rotations. Some people display more rotation of the thorax, while others display more rotation of the pelvis.
With each step the pelvis drops a few degrees on the side of the non-weightbearing, or swinging, leg. While the leg is swinging, the hip abductors of the weightbearing leg contract in order to prevent the pelvis from falling excessively on the unsupported side. If the abductor muscles are paralyzed the result is Trendelenburg gait in which the pelvis falls on the unsupported side. The degree of lateral pelvic tilt varies greatly with the individual, particularly in females. The walking base, or side to side distance between the two feet, is usually 2-4 inches. The toes normally point laterally 5o-10o.
In humans there is more than one group of muscles responsible for propulsion. As a result it is possible for one to compensate for a defect. For example, when walking across slippery ice there is a transfer from pushing against the ground to lifting the leg up. Although locomotion is still possible using alternative muscle groups, stride length and velocity are often reduced as a result (1997-2000, Molson Medical Informatics Project).
The moment when the red foot just touches the floor. Normally, the heel is the first part of the foot to touch the ground. The hip is flexed, the knee is extended, and the ankle is dorsiflexed to neutral. Meanwhile, the blue leg is at the end of terminal stance (see below).
The double stance period beginning when the foot contacts the floor and continuing until the other foot is lifted for swing. Body weight is transfered onto the red leg. Phase 2 is important for shock absorption, weight-bearing, and forward progression. The blue leg is in the pre-swing phase.
The next task of the gait cycle is single limb support during which one limb must support the entire body weight and provide truncal stability while progression must be continued.
Begins when the red heel rises and continues until the heel of the blue foot hits the ground. Body weight progresses beyond the red foot as increased hip extension puts the leg in a more trailing position.
The second double stance interval in the gait cycle. It begins with the initial contact of the blue foot and ends with red toe-off. Ground contact by the blue leg causes the red leg to increase ankle plantar flexion, increase knee flexion, and decrease hip extension. Transfer of body weight from ipsilateral to opposite limb takes place.
Begins when the foot is lifted from the floor and ends when the swinging foot is opposite the stance foot. The red leg is advanced by increased hip flexion and increased knee flexion. The ankle only partially dorsiflexes to ensure ground clearance. It is during this phase that a footdrop gait is most apparent. The blue leg is in mid-stance
Continues from the end point of the initial swing and continues until the swinging limb is in front of the body and the tibia is vertical. Advancement of the red leg is accomplished by further hip flexion. The knee is allowed to extend in response to gravity while the ankle continues dorsiflexion to neutral. The blue leg is in late mid-stance.
Begins when the tibia is vertical and ends when the foot touches the floor. Limb advancement is completed by knee extension. The hip maintains its flexion and the ankle remains dorsiflexed to neutral.
Throughout the course of a gait cycle three tasks must be accomplished. Weight acceptance, the most demanding task in the gait cycle, involves the transfer of body weight onto a limb that has just finished swinging forward and has an unstable alignment. Shock absorption and the maintenance of a forward progression are also important components of this phase. The next task of the gait cycle is single limb support during which one limb must support the entire body weight and provide truncal stability while progression must be continued. The final task of the gait cycle is limb advancement, which requires foot clearance from the floor. The limb swings through three positions as it travels to its destination in front of the body.
It is important that the physician be able to distinguish the 'normal' gait changes that occur with age from the abnormal gait changes that occur in disease. Elderly people tend to have decreased muscle bulk, strength, and flexibility, as well as some loss of hearing and vision. The major changes in gait are a reduction in the overall velocity and reduction in the step/stride length. In general, when increasing their velocity the elderly tend to take more steps instead of increasing their stride length. The elderly tend to have more trouble walking in situations that require speed (e.g. crossing the street), agility (e.g. walking on uneven surfaces or in crowds), or in the dark. There is also decreased arm swing, decreased rotation of the pelvis, and a more flat foot approach to both heel strike and push off.
The neural control of gait (i.e. how the nervous system organizes and controls the activation of skeletal muscle and maintains balance) is very complex and not completely understood at this time. It involves complex sensory, motor, and central nervous systems. The effectors include muscles, tendons, ligaments, and skeletal structure. It has been shown that the basic gait rhythm does not require input from the periphery. The spinal cord itself is capable of generating near-normal gait movements, but is not able to provide stability, support body weight, or propagate the body forward. An example of such neural activity is seen when a baby is held upright with its feet just touching the floor. The baby will start moving its legs as if stepping, but is unable to balance or support itself independently. The cerebellum and brainstem must be left intact in order to provide increased inter- and intra-limb coordination, support of body weight, and active propagation.
While walking the body center of mass is outside the base of support 80% of the time. There are two methods for controlling the dynamic equilibrium of the body: reactive and proactive. Reactive control of stability is used for unpredictable upsets to balance, and therefore depends on sensory input. Proactive control is broken down into two subtypes. The first is involved in counteracting perturbations caused by the gait movements themselves. The second is an experience-based system that uses vision to predict potential causes of dysequilibrium and implements appropriate avoidance strategies.
The terms ataxic, antalgic, and apraxic are often a source of confusion in the study of gait disorders because they sound and appear so similar. However, it is important to distinguish these terms because they refer to fundamentally different types of gait disorders. Ataxic gait is an unsteady, uncoordinated walk with a wide base of support and the feet thrown outward. Most of us have experienced this gait after having too much to drink. Antalgic gait consists of a limp adopted so as to avoid pain on weight-bearing structures (as in hip, knee, or ankle injuries), characterized by a very short stance phase on the injured side. Finally, apraxic gait is loss of the ability to carry out familiar, purposeful movements in the absence of paralysis or other motor or sensory impairment(1997-2000, Molson Medical Informatics Project).
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