Gait Analysis in Prosthetics

Gait Analysis in Prosthetics

James R. Gage, M.D. *
Ramona Hicks, R.P.T., M.A. *

Review

Objective measurement systems which quantify locomotion have been in use for the past century. But not until World War II, when thousands of men returned home to the United States with amputations, was technology really applied to the understanding of prosthetic gait.

Inman and colleagues founded the Biomechanics Laboratory at the University of California to establish fundamental principles of human walking, particularly in relation to problems faced by lower limb amputees. Inman's measurement techniques included motion pictures of coronal and sagittal views, as well as transverse rotations from below using a glass walkway. Using interrupted light photography, the Biomechanics Laboratory team studied the motion of body segments during gait. Force plates measured the subject's ground reaction forces, and muscle activity was recorded using electromyography (EMG), which measures the electrical signals associated with contraction of a muscle. Prior to Inman's fundamental studies prostheses were customized for the individual amputee, without any particular regard to rational structural design. Inman's goal was to provide fundamental data essential for the design of prosthetic limbs. By analyzing normal human walking, he and his colleagues laid the groundwork for biomechanical analysis of amputee gait. Since that time, numerous techniques have been developed to study human locomotion, and numerous studies have been undertaken to evaluate prosthetic gait.

Research Applications

Eberhart, et al. described the locomotor mechanism of the above-knee amputee from kinematic and kinetic data. They compared lateral stick figures of amputees to normal subjects as a means to objectively identify gait deviations in the sagittal plane. Force plate data were used to compare the weight-bearing characteristics of the prosthetic limb and the sound limb. From these comparisons, the authors identified amputees who walked well with their prostheses and those who were less adept. Eberhart believed that ultimately "optimal" patterns of gait could be determined for amputees and used as a reference for evaluating prosthetic gait.

Zuniga, et al. studied gait in 20 above-knee amputees by using electrogoniometers attached to the knee and foot switches. Their data documented asymmetry in the stance and swing phase times between the prosthetic and sound limb.

In similar investigations, James and Oberg and Murray, et al. studied temporal stride parameters and knee flexion-extension angles, and also examined above-knee gait at various speeds. They confirmed the stance and swing phase asymmetry between the prosthetic and sound limb. They also showed that the asymmetry was present regardless of the speed of walking.

The collection of baseline data in above-knee amputees clearly demonstrated some shortcomings in prosthetic gait. One of these, the longer swing time which is required on the prosthetic side, has led to the development of dozens of prosthetic knees. Gait analysis laboratories have been used to evaluate some of these prosthetic designs. Godfrey, et al., in a limited study that compared gait with six cadence-responsive knee units, found no significant differences among them. Murray, et al. compared the gait of above-knee amputees with hydraulic knee units versus constant friction knee units. Temporal and kinematic data, which were collected at slow, free, and fast speeds, showed that the hydraulic knees improved the symmetry between the prosthetic limb and the sound limb, especially at the fast and free speeds. This finding was true for both cadence and the amount of knee-flexion at swing phase.

Hoy and colleagues, in one of the few studies on gait in juvenile amputees, collected kinematic data at various speeds to compare the solid ankle cushioned heel (SACH) foot to a Child Amputee Prosthetic Project (CAPP) experimental foot. The authors found hip range of motion to be closer to normal and significantly less with the CAPP foot than the SACH foot.

Hannah and Morrison studied the effect of alignment of the below-knee prosthesis on gait. Using electrogoniometers to measure hip and knee joint rotations in the coronal, sagittal, and transverse planes, they found that malalignment of the prosthetic foot was the most crucial for gait symmetry.

Grevsten and Stalberg used electromyography to compare muscle activity in below-knee amputees walking with patellar tendon-bearing (PTB) and PTB-suction prostheses. Surface electrodes were placed over the tibialis anterior and gastrocnemius muscles which, in normal gait, usually fire at opposite phases. The data showed that these muscles contracted for longer periods when the PTB prosthesis was used than with the PTB-suction prosthesis, suggesting that the suction mechanism improved the adaptation to the prosthesis.

Thiele, et al. investigated possible neuro-physiological reasons for weakness in above-knee amputees by recording electromyographic activity of the quadriceps during gait. They did not find abnormal recordings and concluded that muscle weakness was secondary to biomechanical, rather than neurophysiological, factors.

Clinical Applications

Until the present, gait analysis has been applied to prosthetics only for research purposes. Routine prosthetic fitting and checkout are still done by means of observational gait analysis. However, observational gait analysis has many disadvantages.

In the first place, even normal human walking is extremely complex. With each step, more than 30 major muscles have to contract and/or relax synchronously in each lower extremity. Also, normal human gait is rapid (approximately 105 steps per minute), and the human eye is not fast enough to separate the various components of gait at this speed. Krebs, et al. have shown that data vary widely when different examiners have observed a person's gait and that observational analysis is only a moderately reliable technique. The variations between observers may be due to the preconceptions of individual observers, to limitations of human perception, or to problems in transmitting the information or data to colleagues. In light of these findings, it is not surprising that the fit and quality of the limbs fabricated by different prosthetists vary greatly.

Technology has now progressed to the point where automated gait laboratories can be built. Their capabilities vary, but most labs monitor one or more of the following parameters:

1. kinematics or movement measurements through a motion analysis system,

2. evaluation of ground reaction forces via force plates or pressure sensitive switches, and

3. dynamic electromyography (monitoring the electrical activity of contracting muscles).

The advantage of an automated motion measurement system is that automated data entry and rapid processing allow routine clinical use at a reasonable cost. Since the sampling rate of most automated motion systems is in excess of 50 Hz (50 samples/second), all movement in the lower extremities during walking can be examined in detail and with excellent reproducibility.

Thus, the analysis of walking becomes objective, rather than subjective, and a record of this objective analysis is produced by the computer in such a fashion that preconceived biases and communication errors between observers are minimized. Furthermore, some of the more modern gait analysis facilities have the ability to compare records, for example, of a patient's gait pre- and post-operatively, or of an amputee's gait with two different prosthetic devices or components. Through comparisons like these, the presence or absence of benefit can be determined objectively.

Kinesiology

The field of prosthetics can make use of the new science of kinesiology, or the study of movement. Kinesiology consists of two major fields:

1. kinematics, the study of motion exclusive of the influences of mass or forces, i.e., without regard to the underlying cause of the motion; and

2. kinetics, which deals with the forces that produce motion.

Kinematic Data

Kinematic data can be gathered in a variety of ways—through interrupted light photography, cinefilm, video systems, and/or electro-goniometers—and it can be displayed in many ways. Stick figures provide a visual display of the subject walking.

Fig. 1 is a stick figure representation of an 11 year old girl with a right knee disarticulation. The stick figures facilitate the identification of gait deviations, e.g., knee hyperextension on the prosthetic side at stance phase. With observational gait analysis, this gait deviation might be missed, or two examiners might argue about its presence. With objective gait analysis, we can prove the deviation's existence by viewing the stick figures, and we can identify the cause of the deviation by reviewing the graphs that depict motion. These graphs display motions of each joint of the lower extremities in all three planes during a representative gait cycle.

Fig. 2 is a graph showing knee flexion-extension of the same child with a knee disarticulation. The child's sagittal knee motion is compared with the mean or average flexion-extension of seven other above-knee amputees.

Although all above-knee amputees hyperextend their knees slightly during stance phase, this patient has 10 degrees more hyperextension than average. Following the gait analysis, it was discovered that the knee extension bumper was too soft, and it was replaced with a suffer one.

Kinematic data can also be used to compute temporal data, such as stride length, cadence, and walking velocity. Fig. 3 compares the temporal data of the child with knee disarticulation with "normal" children the same age. Notice that the stride length is normal but that the walking velocity and cadence are less than normal.

Kinetic Data

The forces that cause movement are usually collected through pressure sensitive switches or paper, or with commercial force plates, which are designed to break down the ground reaction forces into their components (X,Y,Z force, and X,Y,Z moment). The software of a modern gait analysis laboratory is able to combine force plate data with motion analysis data to produce meaningful graphic outputs.

Fig. 4 shows the vertical ground reaction force (Z force) for walking barefoot compared with walking with shoes in a 9 year old boy with a Symes prosthesis. Notice the improved symmetry at push-off between the prosthetic and sound limb when shoes are worn.

Force plates can also be used to compute the location of the center of pressure on the foot. Fig. 5 compares the foot force progression pattern of a SACH foot to a multi-axis foot in a 27 year old male with a below-knee amputation. From these data, one can see that the foot force progression pattern is more lateral with the multi-axis foot than with the SACH foot. Also, notice with the SACH foot how the initial forces move from an anterior to posterior direction as the heel compresses. This pattern is not seen in the multi-axis foot.

Dynamic Electromyography

Dynamic electromyography is a valuable tool for measuring the time duration of muscle activity, which is recorded through electrodes, either surface or indwelling. However, since voluntary muscle activity results in an electromyographic recording that increases in magnitude with the tension, other variables can also influence the signal, limiting the accuracy of EMG as a predictor of muscle tension.

Electromyographic data can be displayed in several ways. When used to analyze a gait cycle, the data show which muscles are active during each phase of gait. Fig. 6 compares muscle activity during gait of the subject walking with the SACH foot compared with the multi-axis foot. The hamstrings and quadriceps muscle groups were sampled and show the same firing patterns regardless of the type of foot that is worn. What is interesting is that the hamstrings are firing just before toe-off when they are usually silent and the quadriceps are inactive at this time when normally they fire to restrain knee flexion and prevent excessive heel rise. As might be expected, this patient walks with exaggerated knee flexion at swing phase.

Summary

Gait analysis is useful in evaluating an amputee's prosthesis by providing objective measurements and a permanent record of the patient's status. Kinematic, kinetic, and EMG data assist the clinician and prosthetist in identifying specific problems encountered by the amputee and in identifying the causes. Gait analysis also allows comparison of different prosthetic designs or different alignments of the same prothesis. Most importantly, however, the record provided allows examiners to objectively discuss the problems and their potential solutions.

Future Applications

The field of prosthetics will begin to change rapidly with the application of kinesiology. Soon, optimal standards of gait will be established for each prosthetic level. With the widespread availability of low-cost motion analysis, kinematic analysis will be routinely incorporated into dynamic alignment of each new prosthesis, helping to insure appropriate alignment and fit. Finally, prosthetic research, using both kinematics and kinetics, will continue as we seek to identify and rectify the problems created by loss of the body's normal limb. The ultimate outcome of this research will be the development of components that will be stronger, lighter in weight, and much more functional than those used now.

References:

1. Fundamental Studies of Human Locomotion and Other Information Relating to Design of Artificial Limbs. Subcontractor's Report to the Committee on Artificial Limbs. National Research Council. Prosthetic Devices Research Project, College of Engineering, University of California, Berkeley. Serial No. CAL 5. 2 vols. The Project, Berkeley, 1947.
2. Radcliffe, C.W., "Functional considerations in the fitting of above-knee prostheses," Selected Articles From Artificial Limbs, Huntington, NY, Kreiger Publishing Co, Inc, 1970, p.p. 5-30.
3. Winter, D.A., Biomechanics of Human Movement, New York, John Wiley & Sons, 1979, p.p. 9-46.
4. Eberhart, H.D.; Elftman, H.; and Inman, V.T., "The locomotor mechanism of the amputee," Klopsteg PE, Wilson PD, et al (eds): Human Limbs and Their Substitutes, New York, Hafner Publishing Co, 1968, p.p. 472-480.
5. Zuniga, E.N.; Leavitt, L.A.; Calvert, J.C.; Canzoneri, J.; and Peterson, C.R., "Gait patterns in above-knee amputees," Arch Phys Med Rehabilitation, 53:373-382, 1972.
6. James, U. and Oberg, K., "Prosthetic gait pattern in unilateral above-knee amputees," Scand J Rehabil Med, 5:35-50, 1973.
7. Murrary, M.P.; Sepic, S.B.; Gardner, G.M.; and Mollinger, L.A., "Gait patterns of above-knee amputees using constant-friction knee components," Bull Prosthet Res, 17(2):35-45, 1980.
8. Godfrey, C.M.; Jousse, A.T.; Brett, R.; and Butler, J.F., "A comparison of some gait characteristics with six knee joints," Orthotics and Prosthetics, 29(3):33-38, 1975.
9. Murray, M.P.; Mollinger, L.A.; Sepic, S.B.; Gardner, G.M.; and Linder, M.T., "Gait patterns in above-knee amputee patients: Hydraulic swing control vs constant-friction knee components," Arch Phys Med Rehabil, 64:339-345, 1983.
10. Hoy, M.G.; Whiting, W.C.; and Zernicke, R.F., "Stride kinematics and knee joint kinetics of child amputee gait," Arch Phys Med Rehabilitation, 63:74-82, 1982.
11. Hannah, R.E. and Morrison, J.B., "Prostheses alignment: Effect on gait of persons with below-knee amputations," Arch Phys Med Rehabil 65:159-162, 1984.
12. Grevsten, S. and Stalberg, E., "Electromyographic study of muscular activity in the amputation stump while walking with PTB- and PTB-suction prosthesis," Ups J Med Sci, 80:103-112, 1975.
13. Thiele, B.; James, U.; and Stalberg, E., "Neuro-physiological studies on muscle function in the stump of above-knee amputees," Scand J Rehabil Med, 5:67-70, 1973.
14. Krebs, D.E.; Edelstein, J.E.; and Fishman, S., "Reliability of observational kinematic gait analysis," Accepted for publication in J Phys Ther, 1985.