The first attempts to analyze gait, recorded in the Rig Veda >3,500 years ago, most likely reflect attempts to enhance mobility through early orthotic or prosthetic intervention. This classic prose chronicles the story of Vispala, a fierce female warrior whose leg, lost in battle, was replaced by an iron prosthesis that enabled her return to the front to fight again.1
The “high-tech” side of quantitative gait analysis has traversed a surprisingly long road. In 1995, Braun documented the works of E.J. Marey, who gave birth to the idea of instrumented kinematic, electromyography (EMG), and temporal performance analysis in the 1870s.2 Marey was the first to perform movement analysis of pathologic gait using photography. He also developed the first myograph for measuring the muscle activity and the first footswitch collection system for measuring temporal (time-distance)-related gait events. The footswitch system was an experimental shoe that measured the length, rapidity of the step, and the pressure of the foot exerted on the ground. Muybridge,3 at Stanford University in the 1880s, used synchronized multiple camera photography with a scaled backdrop to capture on film and assess the motion of subjects walking.
Marks, a New York City prosthetist, first characterized amputee gait in the early 1900s, using line drawings to illustrate and analyze eight phases of gait and recommending the use of motion photography for detailed gait analysis (Figure 1). Other major advances in instrumented gait analysis were made by Scherb, who performed hand muscle palpation using a treadmill in 1920, and Adrian, who in 1925 advocated the use of EMG to study the dynamic action of muscles.4
Modern gait technology evolved soon after World War II, when Inman et al. initiated the systematic collection of normal and amputee data in the outdoor gait laboratory at the University of California, Berkeley (Figure 2). In 1957, the Berkeley project was specifically commissioned to reconsider transtibial prosthetic gait and biomechanics. The basic transtibial prosthesis at that time was attached to the limb with a thigh lacer that included articulated knee joints and a foot with an articulated ankle. The long-term contributions of instrumented gait were demonstrated after a detailed review of the normal and transtibial amputee gait data resulted in a totally new approach that led to two developments: the patellar-tendon bearing prosthesis and the solid-ankle, cushion heel foot.
Since then, researchers and clinicians have increasingly used the growing array of gait technologies to measure the parameters of human performance in normal and pathologic gait. The era of the University of California, Berkeley prosthetic project represented the most concentrated period of prosthetic advancement. The fundamental design criteria for biomechanical application of lower-limb amputee gait (transtibial and transfemoral) were established by this basic gait study.5 The project also had the additional depth of considering all three planes of motion, in contrast to previous studies that analyzed only the sagittal plane of gait progression.
In the late 1960s, Dr. Perry and a group of physical therapists from the Ranchos Los Amigos Medical Center Physical Therapy Department developed an organized format for systematically applied observational gait analysis. The individuals at the Rancho laboratory were pioneers in the development of gait technology, advancing knowledge in all areas, particularly dynamic EMG data collection and interpretation. Transferring of modern technology into medical equipment benefits both patient and practitioner.6
Traditionally, full-service gait laboratories have been reserved for research and educational endeavors at hospitals and universities. More recently, as technology has advanced, its applications and availability have advanced to all aspects of the orthotic and prosthetic community. The idea of the gait laboratory has evolved itself into the realm of everyday patient care. Once complex and elaborate systems that filled the basement laboratories of hospitals and institutions of research are now available in space-efficient models, and pricing has come within the means of the common private practice (Figures 3 and 4).
A full-service gait laboratory gathers information on six performance parameters: metabolic, kinematic, kinetic, temporal, EMG, and pressure.
- Metabolic data collection is commonly referred to as “energy cost.” The primary measures of energy cost are oxygen consumption, carbon dioxide generation, and heart rate. Other relevant factors include the volume of air intake by the subject and their respiration rate. All of these factors are viewed in terms of walking velocity and distance relative to the collection period (time).
- Kinematic measurement systems provide joint segment motion of the body in graph form. This information includes sagittal, coronal, and transverse plane motions occurring at the ankle, knee, hip, and pelvis.
- Kinetic information is obtained from a force platform that collects data on vertical force, fore-aft shear, and medial-lateral shear. Fore-aft shear can be useful to confirm appropriate transtibial prosthetic alignment in the sagittal plane. Combined with kinematic data, kinetic data can be useful in measuring the dynamic stability of a transfemoral amputee throughout stance.
- Temporal data collection systems are useful in measuring stride length, velocity, cadence, percentage of the gait cycle spent in single- or double-limb support, and general stance progression patterns can be measured and assessed. Tendencies toward excessive inversion, eversion, or prolonged heel-only support can be noted. An appropriate modification to component alignment of the prostheses or orthoses is made to normalize these abnormal gait patterns.
- EMG data provide the investigator with knowledge relating to the contraction time and intensity of the subjects' muscles throughout their gait cycle. Appropriate changes to component alignment derived from this feedback can reduce poorly coordinated or prolonged muscle activity.
- Pressure data collection is one of the more recent and clinically promising technologies. This information provides the prosthetist or orthotist and their assessment team an internal eye. Forces and pressures resulting from the device can be measured against the patients' skin.
Traditional metabolic data collection requires the attachment of umbilical devices to the patient, restricting data collection to the use of a treadmill. More recent designs are considerably more self-contained. It would be more preferable for comprehensive energy cost data to be obtained on an open track over a measured distance, allowing the patient to ambulate with a “free walk” gait or natural cadence. The primary limitation of energy cost as an assessment tool is that while it can inform the investigator about body metabolism relative to the patients' gait, it cannot explain why or what specific advantage or disadvantage was present. In the past, the Douglas Bag collection system has been a staple in the gait laboratory. Bizani et al.7 demonstrated the applicability of the Douglas bag method in his resting energy expenditure investigation. Today, with technological advancements, there are many different metabolic measurement systems available. In 2009, Houdijk et al.8 elected to use the Oxycon Champion respirometry system to measure metabolic energy consumption among step-to-step amputee walking. The investigation by Schmalz et al.9 on biomechanical characteristics of lower-limb amputee gait relied on the cardiopulmonary system CPX, by Med Graphics.
Newly introduced to the metabolic corner of the research market is the Cosmed K4b2 mobile cardiopulmonary exercise testing system. This system, like many traditional systems, has the capability to measure Vo2 and Vco2. In addition, the all-in-one mobile Cosmed system delivers telemetry data transmission up to 800 m, indirect calorimetry, integrated GPS system, Spo2, and an integrated 12-lead electrocardiogram, which can be attached directly to an active subject.10
Most kinematic data collection programs display animated or stick figures on a computer screen, representing the actual motions produced by the patient. Typically, the operator can freeze any frame and magnify a specific joint to better examine the gait pattern. The operator can extract raw numbers representing joint placement and motion in space. Advanced motion systems will collect data in combination with other data technologies simultaneously. Common auxiliary systems include force plate and EMG information. Advanced kinematic systems like this are the most expensive component within a gait laboratory. In a full-service gait laboratory, seeking to collect a variety of data about one particular patient, the motion system serves as the technological hub. Kawamura et al.,11 used a Vicon 370 six-camera infrared motion analysis system to document joint movement in patients with spastic diplegic cerebral palsy. In 2007, Kauffman et al.12 demonstrated the usefulness of such a complex system. An EvaRT Motion Analysis Corporation system was used to collect comparative performance samples of mechanical and microprocessor knees in an effort to document the effects on gait and balance in transfemoral users.
Motion analysis systems are composed of multiple camera angles using high-speed or infrared strobes over filtered lenses that collect and record detailed data. Commonly used motion analysis manufacturers in research include Vicon, Coda, Motion Analysis, and Ariel Dynamics. Data acquired through motion analysis have given better understanding to the mechanics of human movement and ambulatory deviations. In 1996, Gard and Childress relied on the Coda 3 Motion Measurement System to investigate pelvic list and its effect on vertical trunk displacement in normal human locomotion of their subjects. Peak pelvic list was found to be shortly after toe-off and <2° at freely selected gait speeds. With the aid of the Coda system, conjectures regarding the influence of pelvic list on the body's vertical trunk displacement were validated.13
Kinetic data collection of two consecutive steps (or one gait cycle) requires dual force plates. The typical force platform system will record three-dimensional force and torque values. In 2007, Bae et al. used the Kistler Instrument corporation force plates in their dynamic analysis of transfemoral amputee gait. The dynamic analysis conducted revealed weakened hip musculature in the involved side resulting in inadequate torque at the hip joint.14 Some software offers specialized programs for specific purposes, such as stability analysis, which provides information pertinent to the shift in the center of gravity relative to time. This technology has potential for quantitative stability assessment of borderline ambulators. Through investigation of landing mechanics, when stepping down among lower-limb amputees, Kistler force plates were used in this study and yielded data regarding the placement of the ground reaction force aiding the stability of the knee in the involved limb. Jones et al. concluded the ground reaction force was anterior to the knee. This is necessary to ensure that the prosthetic knee does not buckle when loaded during the action of vertical stepping.15
A temporal data collection system may very well be the most cost efficient, clinically meaningful, and affordable technology available to obtain a grasp of the overall quality of a patient's gait. Temporal data are generally collected through the use of pads taped to the bottom of a patient's shoes or feet and keeps track of the amount of time the patient spends on various points of his or her sole over a specified distance, similar to kinetic data. Temporal data can be (and often are) part of a larger system including EMG or motion. Elements of temporal data capture include velocity, cadence, stride length, and information relevant to all phases of the gait cycle.
Temporal data can be collected through the use of footswitches. A footswitch is placed under the insole of a subject's shoes and indicates the total time when each foot and its respective sections are or are not weightbearing. B&L Engineering manufactures the Stride Analyzer portable gait analysis system. The Stride Analyzer was used to quantify temporal and distance aspects of gait in a study by Goldie et al.,16 which looked at the deficit and change in gait velocity during rehabilitation after a stroke. The GAITRite system, an electronic walkway, is the newest technology in the temporal data forum. GAITRite provides traditional data collection, through state-of-the-art equipment that is adjustable and self-contained. The study by Wening et al.17 2008 used the GAITRite system to reinforce the use of ankle-foot orthosis prescription in successful ambulatory rehabilitation among stroke patients. Another option, with lower cost and higher human error potential, is the use of a stop watch and video camera. Differentiated by a wide margin of cost, high-techs and low-tech options record the same parameters with different levels of accuracy and expansion capability.
EMG data may be the most important technology in terms of understanding direct physiological effects of design variation across the devices our patients wear. EMG systems are widely available from numerous manufacturers. Choosing the correct EMG system depends on the needs of your patient population and your professional goals (clinical or research based). Understanding your needs and intentions will dictate which specific EMG features would be of interest to you. EMG systems can provide anything from basic muscle activity feedback to complex crossover compatibility with footswitch technology and motion analysis system software. Depending on the application of the EMG system, electrode channel selection is important when an increase in interface capability is desired, dermal adhesive or intramuscular fine wire sensors are available to ensure measurement precision.
Pressure-sensing technologies are uniquely applicable to the dysvascular patient populations. These products can offer a tremendous insight to the orthotist or prosthetist. The pressure assessment potentially assists in more appropriately custom-designed orthoses, increasing limb salvage efforts. Cavanagh et al.18 maintain that “pressure measurement offers a way to help the clinician break out of the cycle of trial and error that is so often necessary to find the correct solution to a patient's problem.”
Novell Electronics Inc. manufactures many products to aid in the investigation of pressure distribution with a high degree of orthotic and prosthetic influence. Kanade et al. explored the alarming occurrence of bilateral amputation among the diabetic population in 2005. Their study on the risk of ulceration in patients with diabetes with single-leg amputation was conducted using the Novell Pedar system. This system allowed Kanade et al. to quantify the risks in patients with diabetes, showing an increase in mean peak plantar pressures of the sound-side limb. Their interpretation suggests alteration of gait and the duration of walking activity affects the distribution of plantar pressures. Increased pressure on the foot will inevitably heighten the patient's risk of developing ulcerations.19 Biswas et al. investigated the dynamic gait stability index based on plantar pressures. F-Scan insole sensors from Tekscan Inc. were used to document the plantar pressure measurements. The compiled data were used to evaluate dynamic gait stability throughout six different parameters of stability, then changes in sensitivity were indexed across different walking conditions.20 Surface pressure measurement systems exist in a variety of forms: in-shoe, barefoot, seating and positioning, joint, and prosthetic and floor-based analysis are commonly used models in the orthotics and prosthetics (O&P) field. These forms of measurement are available from a variety of manufacturers.
The technological surge in the past decade has proven to be one of the most beneficial and baffling occurrences in O&P. The anxiety felt to wisely invest in assessment technology and to choose the correct equipment for your needs is difficult for seasoned laboratory managers and practitioners alike. The wide variety of available technology is endless when examining what equipment should fill your gait laboratory or office on your available budget. There are important things to consider when delving into the commitment of forming a gait laboratory, regardless of its size.
When considering initializing or upgrading your office with gait analysis devices, it is important to think about what you want versus what you need. Ask yourself, “what type of equipment will be most beneficial to both the interests of my patient population and myself?” Factors to consider in determining which equipment combination is the best fit include: cost, interchangeability, diversity in programming, and construction material. A paramount consideration is technical support and user friendliness enabling you and your staff to successfully operate and upkeep the system. There is considerable cost variability in initializing or upgrading a working gait laboratory, whether it is in a clinic or research setting.
Metabolic systems have been around for decades and are still a key player in an effective gait laboratory. Traditionally, the Douglas Bag collection system was used to capture metabolic data. In recent years, this system has been bypassed by technological advancements and availability of portable systems. The K4b2 mobile cardiopulmonary exercise testing system comes equipped with telemetry data communication, such as onboard GPS. Calibration is required on a regular basis to ensure proper operation. The advantage of the system comes primarily from its revolutionary small size. The entire unit is contained in a small, subject-worn pack. Included in the systems purchase is on-site training and installation, as well as a 1-year warranty. Although the Cosmed unit is cutting edge, the Douglas Bag system is still used today and in some instances, it is the best choice for smaller-scale laboratories.
Motion analysis has become an integral part of the motion picture and video gaming industries. The advancements made in these industries have helped advance the research and development of motion systems. The increased demand for more effective and detailed software from other customers has pushed the industry to develop efficient and robust programs. The demand from Hollywood to create films such as Iron Man and Electronic Arts sports to produce video games such as the Tiger Woods Professional Golf Association Tour has funded the continuous research and development of motion capture systems that are readily used in gait laboratories around the world.
There have been always a number of very reliable and extensive systems available, but they were typically reserved for hospitals and research institutions interested in kinematic data collection. Originally, only universities could study gait and motion, but today, it is much more commonplace for the practitioners to feel the need to record and evaluate their patients in the convenience of their office. In recent years, the availability and applicability of these advanced systems have expanded to many realms of the O&P field including the patient clinic and smaller institutions. Motion analysis equipment can vary greatly from system to system. The main types of motion systems available are active-reflective, retroreflective, and video-based systems. Each of these arrangements has its place in studying normal and pathological gait. Although each system has its place in the O&P world, the price ranges of these systems have a strong influence choosing a motion analysis system.
Video-based packages are very useful in smaller or more restrictive settings. The video-based system integrates multiple video cameras into synchronization and analysis software. This program allows for capture, trimming, transformation, filtering, display, analysis, and rendering. Along with the basic capabilities of the video-based software, EMG and force plate integration are an option. The price of this system is much less than other larger systems, which use the reflective marker approach. Ariel Dynamics21 offers the Ariel Performance Analysis System motion analysis system that provides the user with the aforementioned attributes at a fraction of the cost of other more aggressive motion capture programs.
Retroreflective motion analysis programs include multiple high-speed, digital cameras and reflective markers that are placed on key anatomical points of the patient. Integrated with acquisition software, the system allows for simultaneous acquisition of kinematic, kinetic, and EMG data. These systems are a step up from the video camera-based systems in quality and versatility but come at a higher price. Vicon22 and Motion Analysis23 manufacture retroreflective motion analysis systems comprising many versatile features such as integration and synchronization with additional equipment, top-of-the-line frame rates. A plethora of optional product upgrades can personalize and tailor a system to any professional need. A visual input of Vicon display data and simulated cameras is captured in Figure 5.
Another system based on reflective capture purposes is the Codamotion active-reflective system from Charnwood Dynamics.24 This system uses light-emitting diode markers and unique CX1 units to capture motion. The sensors are precalibrated; making this system simple and convenient to set up almost anywhere. Codamotion has the capability to integrate itself with force plate and EMG technology. The more features a system has or is capable of, the more you are going to pay for that system. A comparison chart has been provided highlighting many of the benefits to each type of system.
Force plates, strain-gauge based or piezoelectric, have proven their importance in recording force data and interpolating kinematic information regarding normal human locomotion. When used alone, force platforms can be used to record acceleration, work, and power of a subject. When force platforms are coupled with other data acquisition systems, kinematic data can be explored and used. AMTI25 and Kistler International26 are lead manufactures of force platforms. AMTI provides the strain-gauge–based system, whereas Kistler International manufactures the piezoelectric-based systems. Both systems are reliable and offer a few different options unique from the other. Both systems are relatively comparable in price and function; determining which system is the best fit for your laboratory is best decided through evaluation of your patients' needs and your laboratories future capacity.
Temporal data collection systems capture velocity, cadence, stride length, and information relevant to all phases within the gait cycle. These areas of information are critical to analyzing human locomotion of normal and pathological gait. Traditionally, the footswitch, a lower tech, yet essential piece of gait laboratory equipment, records contact between sensors. Sensors are strategically placed at the heel, first metatarsal, fifth metatarsal, and greater toe area. The foot-to-floor contact information recorded by the footswitch can be used in a variety of diagnostic ways. This helps to assist the clinician and the patient when developing a customized rehabilitation plan. One manufacturer of reliable footswitches is B&L Engineering.27 B&L Engineering manufactures and supplies many useful and difficult to locate products. One example is their Stride Analyzer—Portable Gait Analysis.
The newest available member to enter the temporal data market is the GAITRite28 system. GAITRite uses either a variable length mat or the interlocking squares to help assess the various aspects of temporal data for your patients. The GAITRite system simultaneously measures temporal and spatial parameters. GAITRite effortlessly provides reliable measurements in real time. Available data include cadence, step length, velocity, and many other temporal gait parameters. Practitioners can now collect real-time data about functional ambulation for each patient and store it through the GAITRite system. GAITRite provides the hardware as well as any required and additional operational software. These additional programs not only increase the price of the system but also increase the versatility and the comprehensiveness of a cutting-edge gait laboratory. Temporal data can be recorded very easily and economically. A video camera and a stopwatch can be used to determine key temporal gait artifacts, which can be used in the same way that the footswitch or GAITRite data are used, but without the large investment that the other systems might require.
EMG data, such as temporal, is and has been an integral part of evaluating gait among various patients. EMG systems help to evaluate the physiological exertion required for the muscles involved with completing activities of daily living as well as recreational. EMG systems can come with a variety of available hardware and software program packages to enhance the function of the system to fit your professional needs. B&L Engineering, Motion Labs,29 and Konigsberg Instruments Inc.30 are all suppliers of quality EMG equipment. Each of which has available optional programs and equipment to accommodate all your EMG needs.
Otto Bock has developed a method of using biofeedback as a form of patient education. The EMG sites on patients with upper-limb differences are used to control an icon of the patient's choice through a computerized course as part of the MyoBoy software. This training tool helps the patient to grasp the idea of coordinated muscle control equipping the patient with better prosthetic control. Biofeedback provides the practitioner with assurance that the patient can properly operate and manipulate the device in a safe and controlled manner.
Tekscan31 and Novel Electronics32 provide a diverse line of pressure mapping and force measurement equipment. Each company provides in-shoe, floor-mat, and socket-based interfaces. Although each company uses different approaches in manufacturing and marketing, each individual product varies in reliable measurement of pressure-specific information. This type of data can be helpful in assisting the practitioner in creating a treatment regimen for the patient, helping alleviate pressure-sensitive areas and reducing the potential for detrimental ulcers and skin breakdown.
As the technological advancement continues and new products are invented, we see improvements to older technology. Not only does technology become more accurate, more affordable, and faster but it also becomes more compact. Today, we see the availability of onboard mini-gait-laboratories. These products track patient activity, and when connected with the prosthetist's computer will upload the pertinent information specific to that patient. In 1991, the Prosthetics Research Study33 in Seattle developed the StepWatch Activity Monitor (SAM) to be used in both orthotics and prosthetics. The article by Boone and Coleman33 discussed the positive applications of this device to the O&P field. SAMs ability to provide information relative to activity improvement and patient compliance were just a couple of documented uses. Evolving from the idea of SAM, Orthocare Innovations34 recently released the Compas system. Compas provides patient-specific onboard gait analysis when paired with the device's software, Smart Pyramid. In just a few short steps, kinematic measurements are calculated and processed. Immediate feedback is provided to the prosthetist with step-by-step instructions on how to align the patient for more optimal gait.
With the introduction of more microprocessor knees, companies have developed software packages unique to their products as part of the competitive marketing process. Today's microprocessor knees from Ossur,35 Otto Bock,36 and Endolite37 internally store steps, odometer distance, and average cadence, plus they have the ability to automatically adapt to external changes in a patient's gait. A primary advantage of modern, onboard, downloadable technology is the incorporation of Bluetooth and other wireless electronic communication technologies. As Arthur Wing once said, “I believe the future is only the past again, entered through another gate.” Technological advancements will only continue to evolve the field of orthotics and prosthetics, incorporating new ideas and expanding on existing traditions and methods. Currently, SensorTech Corporation is developing a “smart polymer” that will have many uses including applications in orthotics and prosthetics.38 The material in development has the ability to map static and dynamic pressures, the force over area, and transmit the data wirelessly for evaluation. The smart plastic, seen in Figure 6, is capable of thermoforming three-dimensional objects just like the contemporary plastics of choice within the O&P field. The current beta product can be developed into load cells and transducers that measure single points of force or pressure distribution sensors which measure multiple points of force. The result is orthoses and prostheses that can explicitly communicate with the practitioner where excessive pressure is—or is not—within a device, removing the guessing game and reliance on patient feedback (Figure 7).
For years, the orthotics and prosthetics discipline has benefited from the advancements in technology that aid in the research and development of new products, ideas, and understanding of human biomechanics. Motion analysis gait laboratories are both historical and future staples in the professional field. With rapidly advancing technology, the tools that help us as practitioners to assess and treat patients have become more widely available in condensed form and at more affordable prices. Laboratory legends such as Coda, Vicon, AMTI, and Kistler are still paving the way. Smaller-scale tools such as Compas, GAITRite, EMG, and metabolic analysis products are finding a niche in the market by targeting and giving an edge to the everyday office. Researching the products and shopping around is important when planning to invest in analysis equipment. Your decision should not be determined based only on who can offer you the best deal but also on which product is most compatible with your goals and needs and which company will offer you the necessary technical assistance to get the most benefit from your purchase.
1.Shastri JL, ed. Hymns of the Rig Veda
. Griffith RT, transl. Varanasi, India: Motilal Banarsidas; 1976:72–80.
2.Braun M. Picturing Time, Work of Etienne-Jules Marey, 1830–1904
. Chicago: University of Chicago Press; 1995:24–84.
3.Muybridge E. Muybridge's Complete Human and Animal Locomotion
. New York: Dover; 1887:20–78.
4.Sutherland DH. Historical perspective of gait analysis (lecture handouts); Interpretation of Gait Analysis Data (instructional course). San Diego: Children's Hospital of San Diego, Oct. 17, 1994;1–2.
5.Ayyappa E. Gait lab technology: measuring the steps of progress. O&P Almanac
6.Perry J. The mechanics of walking: a clinical interpretation. Phys Ther
7.Bizani M, Koletsos K, Matamis D, et al. Comparison of two methods, the thermodilution methods of Fick and Douglas bag method, in estimating the resting energy expenditure. Nutr Res
8.Houdijk H, Pollman E, Groenewold M, et al. The energy cost for the step-to-step transition in amputee walking. Gait Posture
9.Schmalz T, Blumentritt S, Jarasch R. Energy expenditure and biomechanical characteristics of lower limb
amputee gait: the influence of prosthetic alignment and different prosthetic components. Gait Posture
10.Available at: http://www.cosmed.it
. Accessed August 25, 2009.
11.Kawamura CM, Filho MC, Brreto MM, et al. Comparison between visual and three-dimensional gait analysis in patients with spastic diplegic cerebral palsy. Gait Posture
12.Kauffman KR, Levine JA, Brey RH, et al. Gait and balance of transfemoral amputees using passive mechanical and microprocessor-controlled prosthetic knees. Gait Posture
13.Gard SA, Childress DS. The effect of pelvic list on the vertical displacement of the trunk during normal walking. Gait Posture
14.Bae TS, Choi K, Hong D, Mun M. Dynamic analysis of above-knee amputee gait. Clin Biomech
15.Jones SF, Twigg PC, Scally AJ, Buckley JG. The mechanics of landing when stepping down in unilateral lower-limb amputees. Clin Biomech
16.Goldie P, Mapp SC, Matyas T, Evans O. Deficit and change in gait velocity during rehabilitation after stroke. Arch Phys Med Rehabil
17.Wening J, Huskey M, Hasso D, et al. The effect of an ankle-foot orthosis on gait parameters of acute and chronic hemiplegic subjects. AAOP Academy Annual Meeting, Thranhardt Lecture Series Presentation 2008.
18.Cavanagh PR, Ulbrecht JS, Caputo GM, Lemmon D. Gait analysis and diabetic footwear prescriptions: is there a marriage on the horizon? Biomechanics Magazine Annual Desk Reference
19.Kanade RV, Van Deursen RW, Price P, et al. Risk of plantar ulceration in diabetic patients with single-leg amputations. Clin Biomech
20.Biswas A, Lemaire ED, Kofman J. Dynamic gait stability index based on plantar pressures and fuzzy logic. J Biomech
21.Ariel Dynamics, Inc: San Diego, CA. Available at: www.arielnet.com
. Accessed September 22, 2009.
22.Vicon: CO. Available at: www.vicon.com
. Accessed September 17, 2009.
23.Motion Analysis: Santa Rosa, CA. Available at: www.motionanalysis.com
. Accessed September 22, 2009.
24.Charnwood dynamics Ltd.: Leicestershire, United Kingdom. Available at: www.codamotion.com
. Accessed September 19, 2009.
25.Advanced Medical Technologies, Inc. (AMTI): Watertown, MA. Available at: www.amti.biz
. Accessed September 20, 2009.
26.Kistler Instrument Corp.: Amherst, NY. Available at: www.kistler.com
. Accessed September 22, 2009.
27.B & L Engineering: Santa Ana, CA. Available at: www.bleng.com
. Accessed September 21, 2009.
28.CIR Systems, Inc.: Havertown, PA. Available at: www.gaitrite.com
. Accessed September 22, 2009.
29.Motion Laboratories, Inc.: Cortlandt Manor, NY. Available at: www.motionlabs.com
. Accessed September 22, 2009
30.Konigsberg Instruments Inc.: Pasadena, CA. Available at: www.konigsberginc.com
. Accessed September 17, 2009.
31.Tekscan, Inc.: South Boston, MA. Available at: www.tekscan.com
. Accessed September 18, 2009.
32.Novel North America: St. Paul, MN. Available at: www.novelusa.com
. Accessed September 20, 2009.
33.Boone DA, Coleman KL. Use of a step activity monitor in determining outcomes. J Prosthet Orthot
34.Orthocare Innovations: Mountlake Terrace, WA. Available at: www.orthocareinnovations.com
. Accessed September 19, 2009.
35.Ossur Americas: Aliso Viejo, CA. Available at: www.ossur.com
. Accessed September 20, 2009.
36.Otto Bock, Science Center Medical Technology: Berlin. Available at: www.ottobock.com
. Accessed September 17, 2009.
37.Endolite Corporate Headquarters; Centerville, Ohio. Available at: www.endolite.com
. Accessed September 19, 2009.
38.Sensor Tech Corporation, Department of Naval Research, Office of Naval Research, One Liberty Center: Arlington, VA. Available at: www.sensortechcorp.com
. Accessed September 22, 2009.