Typical Foot Function During Walking
Pelvic and Lower Extremity Movement Patterns During Walking
Human Walking is a highly complex action which requires the integration of enormous amounts of sensory information coordinated with neuromuscular control of the major body segments (Sutherland, 1991). The complex action of bipedal human walking requires movements by tne pelvis and lower extremities in the sagittal, frontal, and transverse planes to provide as energy efficient walking pattern as possible.
Saunders, et al (JBJS, 1952), described the following sfx determinants or events which must occur to achieve as energy efficient as possible walking pattern:
1. Pelvic Rotation in the Transverse Plane
In addition to reducing energy requirements during walking, KNEE FLEXION is also a major mechanism used to attenuate impact forces during early stance phase.
2. Pelvic Rotation in the Frontal Plane
3. Knee Flexion
4. & 5. Foot and Ankle Mechanisms
6. Lateral Displacement of Shift of the Pelvis over the Support Leg
While pelvic rotation in the transverse plane is necessary for energy conservation as well as to faccilitate sagittal plane movements of the lower extremities during the walking cycle, TRANSVERSE PLANE PELVIC ROTATION causes femoral and tibial transverse plane motion (internal and external rotation) while the lower extremity is in contact with the ground (closed kinetic chain). Based on the work of Levens, et al (JBJS, 1948), from heel strike to foot flat the stance side innominate bone is moving in an anterior direction, causing internal femoral and tibial rotation. At the end of foot flat, the stance side innominate bone will begin to move posteriorly, causing external femoral and tibial rotation.
The next step is to determine how the foot functions to permit these pelvic and lower extremity movements to occur.
Functions Provided by the Foot during the Stance Phase of Walking
- Provide a stable base of support throughout stance phase: The joints of the foot must allow the plantar surface of the foot to become plantargrade to the supporting surface as soon as possible after heel strike to provide a stable base of support.
- Provide supple, accommodative structure which adapts to the supporting surface during the contact period: Pronation of the subtalar joint causes the planes of the axes of the midtarsal joints to become parallel so the foot can accommodate to the supportive surface.
- Assist lower extremity in attenuating impact forces curing the contact period of the walking cycle: Subtalar joint pronation assists the popliteus muscle in permiting the knee joint complex to unlock after heel strike so that knee flexion, the primary factor for impact force attenuation, can occur. Also, the role of the plantar heel pad in dampening the initial impact forces at heel strike (20 to 30 ms) cannot be overlooked.
- Convert joint structures into stable, rigid lever to aid in the forward movement of the body during the late stance phase: Supination of the subtalar joint (aided by muscular action, external tibial rotation, and the windlass mechanism) causes the planes of the axes of the midtarsal joints to converge so that the foot can become a more rigid structure prior to toe off.
- Allows transverse plane rotation of the lower extremities during stance phase while the support foot is fixed to the floor by shear and vertical reactive forces: The primary fuction of the subtalar joint is to permit transverse rotation of the support leg femur and tibia during stance phase.
Motion Pattern of the Foot During Walking
Root, et al (1977), proposed the following motion pattern of the foot by describing movement of the subtalar joint throughout stance phase. Prior to heel strike, the subtalar joint is inverted secondary to contraction of the pre-tibial muscle group. From heel strike to foot flat, the subtalar joint undergoes the motion of pronation and remains in a pronated position. From the end of foot flat to toe off, the subtalar joint undergoes the motion of supination.
Root, et al, stated that the subtalar joint and foot would achieve a neutral position at the instant of midstance. It is important to delineate the difference between subtalar joint neutral position and neutral position of the foot.
SUBTALAR JOINT NEUTRAL POSITION is defined as when the subtalar joint is neither pronated or supinated. Neutral position of the subtalar joint can be either palpated or calculated mathematically.
A major point of discussion is whether the subtalar joint and the foot are able to achive a neutral position at the instance of midstance as described by Root, et al. Root, et al, based their description of the normal foot motion on the work of Wright, et al (JBJS, 1964). Wright, et al, used potentiometers aligned to the subtalar and talocrural joints to determine the joint motion patterns in two subjects. An important point of reference in analyzing subtalar joint motion data of Wright, et al, was that they defined subtalar joint neutral position as their subject's relaxed standing foot posture. Thus, it appears that Root, et al, based what they considered to be the normal subtalar joint motion pattern based on the two subjects from the study by Wright, et al.
NEUTRAL POSITION OF THE FOOT is defined as 1) the position of the foot at the point of midstance in the walking cycle and 2) the position of the foot when the subtalar joint is in neutral position (neither pronated or supinated) and the midtarsal joint is locked (pressure under the 4th and 5th metatarsal heads to converge the planes of the midtarsal joint axes).
ADAPTED FROM WRIGHT, et al, JOURNAL OF BONE JOINT SURGERY, 1964
Typical Rearfoot Motion Pattern During Walking
Based on the work conducted in our Gait Research Laboratory at Northern Arizona University, the typical rearfoot motion pattern would be described as follows:
- Rearfoot is slightly inverted prior to heel strike.
- From heel strike to foot flat, the rearfoot undergoes the motion of pronation with the average percent time to maximum pronation approximately 40 percent of stance phase.
- The motion of rearfoot supination is initiated after 50 percent of the stance phase and continues until toe off. In addition to muscular contraction, other factors influencing the initiation of supination would be external tibial rotation which is increased after heel off (approximately 60 percent of stance phase) and the windlass mechanism created by tension placed on the plantar fascia via hallux extension.
- The neutral position for the typical rearfoot motion pattern would be resting calcaneal stance phase (RCSP) rather than neutral calcaneal stance phase (NCSP).