SECTION THREE Chapter Two An Overview of the Value of Information Resulting Instrumented Gait Analysis for the Physical Therapist by Sue Ann Sisto, PhD, PT Dr. Sisto is the Director of the Human Performance and Motion Analysis Laboratory at the Kessler Medical Rehabilitation Research and Education Corporation. INTRODUCTION gait analysis technology and goals of the information obtained from QGA is discussed . Groups likely to Instrumented gait analysis is frequently used today benefit from this information are presented . Limitations for clinical applications . Its role has expanded beyond of gait lab data and suggestions for improvement are the area of gait analysis to aid in clinical decision reviewed. making for rehabilitation, surgery, adaptive devices, ergonomics, and athletics . Physical therapists are well Background trained in the area of gait and movement analysis and Over the past 10 years, the clinical application of are, by definition, movement scientists . The evaluation gait analysis has grown rapidly in the United States, as a of gait, locomotion, and balance includes a series of result of several significant changes . The widespread tests described in the Guide to Physical Therapy development of user-friendly software allows the clini- Practice (1). Entry-level didactic requirements include cian to use instrumented gait analysis more easily. normal gait mechanics and pathological gait for nearly Hardware has also been refined to allow faster data all disabilities. Those in physical therapy training acquisition and computing. These two advances have primarily learn observational techniques for clinical gait permitted the clinician to improve his/her understanding analysis. In addition, some academic programs provide and interpretation of information provided by movement an introduction to various forms of instrumented gait analysis technology. analysis and their potential to augment the physical The evaluation of children with spastic paralysis therapist's knowledge of gait . Instrumented gait analysis constitutes the onset of movement analysis for the involves information about temporal and linear param- clinical arena and continues to be a large focus of eters during gait as well as joint angles, ground reaction clinical gait analysis . Orthopedic surgeons frequently forces, and muscle firing patterns. needed objective information about the success of their The purpose of this chapter is to review the scope surgical interventions, compared to a pre-surgical as- of quantitative gait analysis (QGA) as it pertains to the sessment (2) . Other clinical applications of instrumented practice of physical therapy . A brief background about gait analysis include the assessment of persons with quantitative gait analysis is followed by a description of stroke, Parkinson's disease and multiple sclerosis, spinal how physical therapists evaluate gait . An overview of and orthopedic injuries or disease, and amputations. 76 77 Chapter Two : Physical Therapist Clinical use of the gait data takes the form of an gait deviations, instrumented gait analysis may be evaluation, ideally before some intervention, followed warranted. by a summary of the biomechanical and neuromuscular . The intervention influences of gait after an intervention Gait Analysis Terminology may be surgery, orthotic or prosthetic applications, and There are several terms and definitions commonly pharmacological or physical therapeutic treatments . The used when studying gait analysis : Gait kinematics refers physical therapist can then interpret the clinical signifi- to the branch of mechanics that deals with joint angular cance of the change in gait impairment as a result of changes over the gait cycle . Kinematics is evaluated by such intervention. using external markers that can be observed by cameras. Gait kinetics is defined as the forces, moments, and powers that change over the gait cycle . These measure- METHODS ments are captured by the use of force plates embedded in a walkway . Dynamic electromyography (EMG) refers How Physical Therapists Evaluate Gait to the evaluation of muscle activity throughout the gait Observational gait analysis (OGA) is defined as the cycle. This is accomplished through the use of either visual inspection of walking . The identification and surface or needle electrodes. grading of gait deviations depends on the observer's experience and individual bias (3) . The physical thera- pist observer is trained to see a range of gait events . The Gait Measurement Technology gross abnormalities are the most readily observed. Two-Dimensional versus Three-Dimensional Gait Frequently, these are made more pronounced if the Analysis therapist asks the subject to walk at a higher velocity or Most of the current gait analysis systems today removes some physical or mechanical assistance. The convert the two-dimensional (2-D) data from several disadvantage of OGA over QGA is the tendency to cameras into three-dimensional (3-D) data to determine focus the eye on the gross gait deviations while joint centers . This method allows for the measurement overlooking more subtle ones. of gait when there is out-of-plane movement. Two- OGA is a preferable form of gait assessment when dimensional gait analysis is attractive to the clinician considering the ease, time efficiency, and low cost; because there are fewer markers and cameras needed for however, several questions have been raised about its data acquisition and processing time is significantly limitations (4-8). Studies evaluating the reliability and reduced. validity of OGA unanimously point to only a moderate When 2-D motion data reduction methods are level of reliability for intra- and interrater assessments employed for gait analysis, the assumption must be that (9). However, due to certain design differences in these the motion is planar. For example, the knee motion for studies, it is likely too early to eliminate OGA as an the unimpaired person could be considered to move in a important clinical evaluation tool. single axis flexionlextension plane . However, if genu Systematic methods of gait analysis have been valgus, or varus, or femoral, or tibial torsion is present, described by Perry (10) to establish standardization there is a distortion of the data because the joint plane is procedures within the field . Perry describes three steps no longer parallel to the viewing plane. to carry out systematic OGA: 1) organization and Davis et al. (11) evaluated the differences between classification of the essential gait events, 2) anatomic 2-D and 3-D gait analysis, determining that joint angles sequence of observation to sort the multiple events at for the hip and knee were the most consistent, since different joints, and 3) data interpretation for total limb these joints represent the smallest out-of-plane move- function and for gait cycle differentiation. ment during normal gait. The ankle, however, had the Often a physical therapist will start the observation greatest sensitivity between 2-D and 3-D gait analysis. at the foot and assess distally to proximally as the foot This is not surprising since the ankle is oriented out of hits the ground. Interpretation includes the influence of the sagittal plane externally by about 7-10° . Much neuromusculoskeletal and/or behavioral factors that may literature on normal gait over the years must be produce a particular gait pattern, such as spasticity, considered with caution because the conclusions drawn pain, contracture, or lack of motivation . When OGA were based on 2-D gait analysis. Davis and colleagues provides insufficient information about the etiology of also extend this caution to the kinetic analysis . 78 RRDS Gait Analysis in the Science of Rehabilitation Kinematics pressure systems in addition to force platforms . This The evolution of gait analysis technology has technology allows for the determination of how the load enabled the physical therapist to utilize the resultant is distributed on the plantar surface of the foot . This data to aid the interpretation of locomotor performance. information can be useful for individuals with orthope- Since expensive motion analysis equipment is not likely dic pathologies from foot/ankle fractures or those to be present in physical therapy clinics, therapists use relating to disease processes such as diabetic other methods of motion analysis, such as videotaping. neuropathy. Figure 2 is an example of the normal This method creates a permanent record of gait ground reaction force during gait. performance that serves to document progress in Another form of kinetic analysis involves the therapy but still relies on the therapist's ability to evaluation of joint moments and powers . Joint moments observe gait in a reliable way. are the forces produced by muscles and ligaments acting Instrumented gait analysis systems, though not at a distance from the joint center. Joint power is the net present in most physical therapy clinics, constitute the rate of generating (concentric contraction) or absorbing most prevalent method of motion measurement avail- (eccentric contraction) energy by all muscles crossing a able to physical therapists. While electrogoniometers joint, and is the product of the joint moment and its and accelerometers require less instrumentation, these angular velocity . If the calculation of joint moments is devices are more often used in academic or research required, it is necessary to have a system that can have settings, because they are less user-friendly for the both kinetics