lecture 4 (5).pdf

Frontal Plane kinematics Pelvis The pelvis tilts laterally in the frontal plane about 8° on each side. In unilateral stance, the pelvis of the swing leg tilts laterally downward about 8°. This lateral drop occurs on the swing leg since the stance leg adducts. This small but important motion serves...

Frontal Plane kinematics Pelvis The pelvis tilts laterally in the frontal plane about 8° on each side. In unilateral stance, the pelvis of the swing leg tilts laterally downward about 8°. This lateral drop occurs on the swing leg since the stance leg adducts. This small but important motion serves two purposes: 1-It puts the hip abductor muscles of the stance leg on a slight stretch, thereby putting them at an improved length tension advantage 2-It reduces the rise of the center of mass of the swing leg. This reduction in the limb’s COM elevation was initially thought to be important in decreasing energy expenditure. Hip joint: Hip motions in the frontal plane directly impact pelvic motion. Frontal plane hip motions offer crucial contributions to stability and efficiency during gait. At initial contact, the hip is adducted to about 10° and continues to adduct another 5° during loading response, serving to put the gluteus medius on the stance side on a slight stretch. This position places the gluteus medius on stretch so it may generate the forces needed to stabilize and hold the contralateral pelvis level during a unilateral stance. From midstance through terminal stance, the thigh moves into a relatively neutral position. The hip abducts about 5° during the swing phase to assist in clearing the foot from the floor and returns to neutral as it approaches the end of the terminal swing. Knee joint: At initial contact, the knee is in slight abduction and moves to its maximum of about 3° of abduction during initial contact. During the swing phase, the knee moves into adduction to a maximum of about 8° N.B: Total abduction-adduction motion of the knee is minimal because of the stable collateral ligaments supporting the joint. Ankle joint and Foot Subtalar Joint Subtalar joint motions of inversion and eversion occur during gait. The subtalar joint is in slight inversion at initial contact and immediately moves into eversion after making contact with the ground. The subtalar joint rapidly moves through to its maximum range of eversion, about 5°, after loading response and by the time the limb is in early midstance. At midstance, the subtalar joint begins moving toward inversion. By preswing, it is at its maximum inversion position, approximately 8° to 11°. During the swing phase, the subtalar joint returns to neutral and is in slight inversion by the time the limb is in terminal swing. Midtarsal Joint As does the rest of the foot, the midtarsal joint follows the motions of the subtalar joint during all phases of gait. The two joints comprising the midtarsal joint, the talonavicular, and calcaneocuboid joints, each have approximately 11° to 15° of total motion in the frontal plane during the normal gait cycle. Immediately after initial contact, the midtarsal joint flattens to absorb impact forces and allow the entire foot to touch the ground. Once in midstance, the arch elevates, following the inversion movements of the midtarsal and subtalar joints, to move the forefoot joints into more congruent positions in preparation for terminal stance and preswing.