Gait Analysis

Chapter Outline
Phases of Gait 71
Temporal Parameters 71
Neurologic Control of Gait 72
Function of Gait 72
Gait Energy 72
Kinematics 73
Muscle Activity 74

Observing a child’s gait, whether in a sophisticated computerized laboratory or simply in the hallway of a clinic, is an integral part of the orthopaedic examination. A systematic approach to gait analysis—that is, looking at the trunk and each joint moving in all three planes (sagittal, coronal, and transverse)—can yield valuable information about the patient’s condition and help in establishing a treatment plan. For a child’s gait to be examined properly, the patient needs to be as unclothed as deemed appropriate.

The examination should begin with an assessment of lower extremity passive range of motion and muscle strength. The physician should then observe the child walking from the level of the child—for example, sitting while examining the gait of small children. Whenever possible, the child should also be asked to run. There should be adequate space for the child to walk comfortably and naturally. A thorough evaluation of the head, trunk, upper extremities, hips, knees, and ankles, with the child viewed from the front and side, should be completed. Joint motion during gait can then be compared with passive range of motion and strength.

Phases of Gait

The gait cycle is divided into two phases, stance and swing ( Fig. 5-1 ). Stance phase is defined as the time during which the limb is in contact with the ground and supporting the weight of the body. Conversely, swing phase is the time when the limb is advancing forward off the ground. During swing phase, the advancing limb is not in contact with the ground and body weight is supported by the contralateral limb. Stance phase occupies 60% of the gait cycle and swing phase occupies 40%. Both phases can be subdivided further.

Stance Phase

Stance phase begins when the foot contacts the ground, termed heel strike or initial contact. Next, loading response occurs as the foot plantar-flexes to the ground and weight is accepted. In midstance, the tibia moves forward over the plantigrade foot. Finally, the heel rises at terminal stance.

Stance phase can be divided into single-limb support and double-limb support phases. There are two periods of double-limb support, when both legs are in contact with the ground at the same time. The first period occurs at initial contact. The second period of double-limb support occurs at the end of stance phase just before swing phase as the body weight is shifted onto the other limb and the heel rises from the floor in preparation for push-off.

Swing Phase

Swing phase encompasses three separate periods—initial swing, midswing, and terminal swing. Initial swing begins with toe-off and continues as the foot is raised from the ground and the limb moves forward. Midswing starts as the swing limb advances past the contralateral stance limb, the knee extends, and the foot travels in a forward-swinging arc. Deceleration, or terminal swing, occurs at the end of swing phase as the musculature of the forward-moving swing limb smoothly stops the limb, preparing for initial contact with the ground, and the gait cycle is completed.

Time Spent in Each Phase

The percentage of time spent in each phase of gait is consistent among normal individuals. As the speed at which a person walks increases, the amount of time that is spent in double-limb support decreases. During running, double-limb support disappears and is replaced by double-limb float, a period during which neither leg is in contact with the ground.

Temporal Parameters

Distance and time measurements calculated during gait analysis are referred to as cadence parameters ( Box 5-1 ). Step length is defined as the distance between the two feet during double-limb support and is measured from the heel of one foot to the heel of the contralateral foot. Step length can differ between the right and left sides. Stride length is the distance one limb travels during the stance and swing phases. It is measured from the point of foot contact at the beginning of stance phase to the point of contact by the same foot at the end of swing phase. Step time is the amount of time used to complete one step length. Cadence is the number of steps taken per minute. Walking velocity is the distance traveled per time (usually measured in meters per second). Normal values matched for age are available for these cadence parameters.

Box 5-1

Cadence Parameters

Step length: Distance between two feet during double-limb support
Stride length: Distance one limb travels during stance and swing phases
Step time: Time needed to complete one step length
Cadence: Number of steps per minute
Walking velocity: Distance traveled per time (m/sec)

Small children walk with greater cadence but smaller step and stride lengths, resulting in many quick, small steps. As children grow, their step and stride lengths increase and cadence decreases. Step length increases linearly with increasing leg length. Nomograms have been constructed to determine normal cadence parameters for children based on their height.

Neurologic Control of Gait

The entire neurologic system plays a role in gait. Most of the muscular actions that occur during gait are programmed as involuntary reflex arcs involving all areas of the brain and spinal cord. The extrapyramidal tracts are responsible for most complex, unconscious pathways. Miller and Scott proposed the concept of the “spinal locomotor generator,” designated neurons within the spinal cord that are responsible for reflex stepping movements. Golgi tendon units, muscle spindles, and joint receptors produce neurologic feedback and serve as dampening devices for the coordination of gait. Voluntary modulation of gait (e.g., altering speed, stepping over an obstacle, changing direction) is made possible through interaction of the motor cortex. The cerebellum is important in controlling balance.

A child’s gait changes as the neurologic system matures. Infants normally walk with greater hip and knee flexion, flexed arms, and a wider base of gait than older children. As the neurologic system continues to develop in a cephalocaudal direction, the efficiency and smoothness of gait increase. However, when the neurologic system is abnormal (e.g., in cerebral palsy), the delicate control of gait is disturbed, leading to pathologic reflexes and abnormal movements.

Function of Gait

The simplest function of gait is to travel from one point to another. Normal ambulation is likened to a controlled forward fall. The swing limb comes forward to stop the fall and accept the weight of the body. The joint motions inherent in normal gait serve this purpose. Body weight is transferred from one limb to the other in a smooth fashion, and the forward momentum of the body is sustained.

Gait Energy

Although gait is designed to be energy-efficient, bipedal gait is inherently unstable and inefficient. Quadrupeds (e.g., dogs) run faster than humans, regardless of size. Their center of gravity is suspended between the four limbs on the ground, and the vertebral and trunk muscles act to augment stride. In human gait, the center of gravity is not balanced between the limbs, nor do the trunk and spinal muscles play a significant role in walking.

To conserve energy, coordinated movements of the joints of the lower extremities minimize the rise and fall of the center of gravity, located just anterior to the second sacral vertebra. Muscular activity during gait is precisely timed, and very few concentric contractions of the muscles are required during normal ambulation. Inertia is used to its fullest advantage to lessen the work of walking.

Abnormal deviations in gait can have significant physiologic costs and substantially increase the energy required to walk. Deviations such as a weak muscle, contracted joint, or impediment of a cast may change gait enough to increase the metabolic requirements, thereby causing the individual to tire easily. The amount of energy required to walk can be measured by quantifying oxygen consumption and oxygen cost. Oxygen uptake and oxygen cost during walking are greater in children younger than 12 years than in teenagers. An indirect measure of energy expenditure is the heart rate, which rises as oxygen consumption increases. The physiologic cost index (PCI) is calculated using the child’s heart rate and walking speed. Repeatability in PCI data ranges in the literature from high to low.

In 1953, Saunders and colleagues described the six determinants of gait whereby the body reduces the amount of energy required to ambulate ( Table 5-1 ). These six strategies work in harmony to minimize the rise and fall of the center of gravity (vertical displacement) and the side to side motion of the pelvis (horizontal displacement). The end result is the establishment of a smooth pathway for the forward progression of the body’s center of gravity during gait. The center of gravity displaces an average of ⅛-inch during gait, with the lowest point at 50% of the gait cycle during double-limb support.

Table 5-1

Six Determinants of Gait

Determinant	Strategy
Pelvic rotation	Decreases angle between limbs and ground, flattens arc of pathway of center of gravity, allowing stride to lengthen without increasing drop of center of gravity at point of initial contact
Pelvic tilt	Decreases vertical displacement of center of gravity by approximately 50% and shortens pendulum of limb by knee flexion in swing phase
Knee flexion after initial contact in stance phase	Reduces vertical displacement of center of gravity as weight of body is carried forward over stance limb
Foot and ankle motion	Smooths out path of center of gravity when coupled with knee motion
Knee motion	Smooths out path of center of gravity when coupled with foot and ankle motion
Lateral displacement of pelvis	Reduces lateral movement of center of gravity toward stance foot during gait cycle

An example of these determinants in action is flexion of the knee coupled to ankle joint motion in stance phase. If one imagines how much rise and fall is felt when walking with a cylinder cast with knee extension, the contribution of knee flexion in stance phase (the third determinant) to minimizing energy required for walking is easily appreciated.

Kinematics

Kinematics is defined as the study of the angular rotations of each joint during movement. In simpler terms, kinematics denotes the motions observed and measured at the pelvis, hip, knee, and ankle during the stance and swing phases of gait ( Fig. 5-2 ). Kinematics can be observed in three planes—the sagittal plane (flexion and extension), coronal plane (hip abduction and adduction), and transverse plane (rotation of the hips, tibiae, or feet). The data are collected by the three-dimensional tracking of markers placed over bony landmarks by infrared cameras positioned in the gait laboratory. Normal kinematics for each plane are briefly described in the following sections.

Sagittal Plane

In the sagittal plane, the pelvis is tilted anteriorly approximately 15 degrees (see Fig. 5-2, A ). There is minimal motion of the anterior tilt as each leg is advanced forward. Alterations in pelvic tilt can occur when there are contractures of muscles around the hip. For example, if the hamstrings are tight, the pelvis typically assumes a more posterior tilt.

The hip is flexed at initial contact and then extends fully during stance phase as the body advances over the planted foot (see Fig. 5-2, B ). At heel rise and push-off, the hip flexes rapidly to pull the stance phase limb off the ground. The hip continues to flex during swing phase.

The knee exhibits a more complex pattern (see Fig. 5-2, C ). At initial contact, the knee flexes approximately 15 degrees, buffering the acceptance of body weight through knee flexion. The knee then extends during stance phase to neutral position or minimal flexion. At heel rise, the knee begins to flex again, reaching maximal flexion in early swing phase to allow the foot to clear the ground as the limb advances. During the remainder of swing phase, the knee extends passively, using forward momentum. The normal kinematics of the knee is disturbed in gait secondary to spasticity from cerebral palsy. Deviations range from hyperextension of the knee in stance phase if the heel cord is tight, to crouch gait, resulting in flexion in stance phase caused by tight hamstrings, to inability to flex the knee in swing phase caused by inappropriate rectus femoris action.

Ankle sagittal plane kinematics starts with a neutral ankle at initial contact, when the heel normally strikes the ground (see Fig. 5-2, D ). The ankle then plantar-flexes 5 to 10 degrees as the forefoot comes to rest on the ground. This plantar flexion is known as first rocker. The ankle dorsiflexes throughout midstance as the tibia moves forward over the plantigrade foot (second rocker). During third rocker, the ankle plantar-flexes and the heel rises to prepare for push-off ( Fig. 5-3 ). Dorsiflexion of the ankle back to a neutral position is seen during swing phase to allow for clearing of the foot. In patients with peroneal nerve palsy and foot drop, dorsiflexion during swing phase is impaired. The individual compensates by hyperflexing the knee and hip in swing phase to avoid dragging the toes, a pattern termed steppage gait.