Gait analysis, an in-depth observation of how a person walks or performs certain functions, is an important therapist tool in bracing the orthotic or prosthetic patient. Historical work on defining the gait cycle is useful in assessing motion and determining normal versus pathological gait. Today gait is analyzed using a combination of high-tech equipment and trained therapists' observations.
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| From left: Sarah Parsons, MSPO, CO; Chris Hovorka, MS, CPO; an engineering student at Georgia Tech; and David Fritz, MSPO. Photograph courtesy of Georgia Tech |
"Learning the gait cycle is fundamental," explains Chris Hovorka, MS, CPO, director of the Master of Science in Prosthetics and Orthotics (MSPO) degree program at the Georgia Institute of Technology (Georgia Tech), Atlanta. "Understanding how a person moves helps us solve problems. We understand the parameters of normal versus abnormal patterns of movement and use the principles of biomechanics to help individuals use less energy for movement or develop better strategies for movement."
The Georgia Tech MSPO is currently the only entry-level master of science program in prosthetics and orthotics available in the world. Hovorka, a clinical practitioner, says students in the program learn "translational research" or how to connect laboratory research to clinical practice. "Students study body movement (kinesiology and clinical gait analysis) for at least a year," he says. "Then they apply that to a person who has lost a limb or has neuromuscular/skeletal deficits."
The Gait Cycle
The gait cycle describes the pattern of walking, beginning when one foot contacts the ground and ending when the same foot contacts the ground again. The gait cycle comprises two main phases, stance and swing, which account for approximately 60 percent and 40 percent of the cycle, respectively. While the events that occur during these two phases are not universally agreed upon, for the purposes of this article, those events are defined as follows:
The stance phase is divided into loading response, midstance, terminal stance, and pre-swing. Loading response, when the foot makes initial contact with the ground, is labeled pathological when the entire foot or toes hit the ground first rather than the heel. Midstance begins with the contralateral toe-off and ends with the center of gravity over the supporting foot. Terminal stance begins here and ends with the heel of the contralateral foot leaving the ground. Finally, pre-swing corresponds to the cycle's second period of double limb support, contralateral initial contact, and toe-off.
The swing phase consists of initial swing, mid-swing, and terminal swing. Initial swing is the period from toe-off to maximum knee flexion. Mid-swing is from maximum knee flexion until the tibia is perpendicular to the ground, and terminal swing begins there and ends on initial contact.
During the normal gait cycle, the weight-loading period of one leg corresponds with weight-unloading of the trailing foot. In other words, while one foot is accepting the weight of the body, the other foot is rolling off the ground. Throughout the cycle, arm swing corresponds to the contralateral leg to maintain balance.
Gait Analysis
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| Georgia Tech MSPO students learn to use some of the latest gait analysis systems. |
Gait analysis involves an understanding of the gait cycle as well as the measurement of kinematics and kinetics. Kinematics is the science of motion and provides a description of the extent, speed, and direction of the movements of joints or body segments. Kinetics refers to the forces that produce movement such as gravity, inertia, and ground reaction (external forces) and joint motion and muscle activity (internal forces).
Observational gait analysis is the primary clinical tool for therapists and consists of using checklists to note gait deviations as either present or absent. Though useful, these types of analyses are often unreliable. However, orthotists and prosthetists can use a variety of portable and affordable high-tech devices to make kinematic and kinetic measurements. For example, the GAITRite system, manufactured by CIR Systems Inc., Havertown, Pennsylvania, is a portable walkway that can track, report, and graph measurements such as cadence, velocity, and stride length. "This is a 'clinician-friendly' tool," says Hovorka. "It has its limitations, but it does provide some quantification that a therapist can use."
A more sophisticated method of analysis, called Dartfish, is used to optimize athlete performance and aide the judgment of certain subjective events, such as diving, where detailed information about body segment movement is needed. "When used together, the loading information that GAITRite can provide along with the angle measurements Dartfish makes, result in a better understanding of movement," Hovorka comments. "However, the gold standard, which is accepted to be the most reliable, is the Gait Analysis Laboratory (GAL)."
GAL consists of force detection built into the flooring in a walkway and infrared cameras that detect motion of individual body segments via specialized markers strategically placed on the patient. "[These labs] provide detailed information about the way a person moves," says Hovorka. "However, they are expensive, not portable, and require highly trained individuals to operate the equipment, or biomechanists." Biomechanists have extensive knowledge about biological movements; often their education includes a master's degree or doctorate. In addition to digital optical camera and force-plate analysis, GALs may include electromyography (EMG), a study of muscle activity. Though muscle activity varies between individuals and depends on external variables, normal muscle activity during each phase of the gait cycle has been researched and recorded. High-tech devices provide values that are then interpreted by trained gait analysis specialists who translate goniometric, metabolic, and kinetic measurements into appropriate patient care.
"[In using these tools] our main goal is to problem-solve," says Hovorka. "Whether it's teaching a child to stand for the first time using an orthosis or helping someone to move using less energy, getting a better understanding of how the person moves can help us solve those problems."
When normal gait cycle biomechanics are understood and tools have been used to analyze a patient's movement and compare it to "normal," then the orthotist and prosthetist can develop devices to help the patient move more naturally while using less energy.
Making Movement More Efficient
"Movement science involves understanding a movement problem, developing a solution, and helping a person create a new movement strategy," summarizes Hovorka. "We design bracing to position the joints in a different alignment. The more joints an orthotic or prosthetic device crosses, the greater the limitation of motion will be at those joints and the more energy a person will have to use to move. There's a fine line for how much bracing to use."
Because pathological gait results in excessive energy expenditure, many disabled children abandon walking from the beginning, and adults dealing with new circumstances, such as amputation, find basic movements exhausting. The most common gait disturbances seen in amputees involve abnormal load acceptance, load relief, and swing phase clearance, though the level of amputation determines the extent. Pathological gait is also found in spinal and neuromuscular impaired patients.
An energy efficient gait pattern is one that moves a person's center of gravity (COG) forward with minimal vertical and lateral displacement. Pelvic rotation, knee-ankle-foot interactions, lateral pelvic drop, and knee flexion affect vertical displacement. Lateral displacement of COG is limited by the genu valgus, a structural feature of the knee. Appropriate bracing across the genu valgus, hip, and ankle can lesson energy demands by addressing COG displacements.
Orthotic Management
An orthosis can support a structural deformity of the ankle and/or foot to help alleviate predictable gait deviations. The five most common foot pathologies are rearfoot varus, forefoot varus, equinus, plantarflexed first ray, and forefoot valgus and rearfoot valgus. Each involves some degree of inversion or eversion of the foot or ankle. Orthotic management of these conditions includes supporting the foot with a medial heel, lateral forefoot, or medial forefoot wedge. The three primary types of orthoticsrigid, semi-rigid, and softprovide the appropriate bracing to influence function, dynamic balancing, and shock absorption, while minimizing pressure sores.
Because an AFO can substitute for weak dorsiflexor muscles during swing phase and weak plantarflexors during stance phase, they are often recommended for patients with gait deviations from muscle weakness. By supporting the forefoot, an AFO can prevent the common problem of foot drop in swing phase. The orthotist aligns the AFO in dorsiflexion or plantarflexion depending on the specific gait displacement. Because proper foot and ankle biomechanics contribute to normal gait, creating proper alignment between the foot and the ground using foot orthoses and controlling the motion of the ankle, rearfoot, and forefoot reduces the risk for abnormal mechanical strain on the knees, hips, and spine.
Some types of AFOs and other bracing store and release energy when needed for normal gait, preventing premature foot drop as well as providing stability at midstance and propulsion during toe-off. The energy released by the orthosis at terminal stance propels the leg up and forward, and the swinging limb helps the body, or center of gravity, to move forward. The appropriate ratio of stance and swing phase (60:40) allows the energy from one step to transfer to the next so the patient experiences less fatigue. In addition, in the absence of normal muscle function, the orthosis counteracts the forces tending to buckle the limb in stance. Therefore, an orthotic device is judged on how well it can control limb movement during the swing phase and load bearing during stance phase.
By correcting and stabilizing the deviations in joint alignment, proper bracing can help patients establish a more stable and energy efficient gait. KAFOs and HKAFOs improve gait just as AFOs do, by providing joint stability and alignment over more joints. Because more energy is expended when a brace encompasses more joints, the reciprocating gait orthosis (RGO) couples the left and right orthoses so that hip extension in either one tends to force the other hip joint into flexion, providing coordinated motion between the legs and less energy expenditure.
"Using the normal gait cycle as the benchmark, we can breakdown a person's movements into measurements," concludes Hovorka. "We can take those measurements and offer treatments that will improve the person's movement strategy; making movement [more natural] and less fatiguing."
Sherry Metzger, MS, is a freelance writer with degrees in anatomy and neurobiology. She is based in Westminster, Colorado, and can be reached at sherry@opedge.com .
