Gait analysis is all about balance

Gait analysis technology could save the NHS millions.

In the UK, someone over 65 dies every five hours as a result of a fall and 30 per cent of people in this age group suffer a fall each year, with 12 per cent of those falling multiple times. This costs the NHS an estimated £1.7bn per year, and as our population ages the human and financial cost will grow.

For patients it causes lifestyle restriction, loss of confidence, depression, and often leads to other long-term health problems. In the current system, patients are usually not referred to a 'falls clinic' for an exercise programme to strengthen muscles and improve neuromuscular control until after they have already had a fall.

Walking is a skill that we first learn as babies, and requires a good sense of balance, coordination and timing. As people get older it is normal for them to walk more slowly, and often their pattern of walking - or 'gait' - changes due to asymmetry, pain, stiffness or poor balance.

There are only two main variables in human locomotion, stride length and stride frequency, both of which contribute to ultimate walking or running speed. In extreme cases the elderly resort to more of a shuffle, where stride rate increases and stride length decreases, to avoid the need to balance on a single leg for any length of time. Medical professionals long ago recognised that irregularities in gait or poor movement patterns can increase the possibility of a fall, but it has not been easy to identify those most at risk.

Screen and protect

Screening the elderly to predict their likelihood of having a fall can be a complicated and time-consuming process that is mostly done using subjective tests such as the Berg Balance Scale designed to measure an adult's ability to carry out 14 everyday tasks. Now scientists and medical professionals are using modern technology to prevent falls and identify those most at risk. At the high end there are some well known and clinically validated laboratory-based gait analysis systems that use digital optical cameras such as those produced by Vicon. These systems can be coupled with a force plate, EMG (electromyography) and digital video data, depending upon the results required. 

Although extremely accurate and giving a great deal of data, they have a number of limitations. However, it is hard for the patient not to be constrained by the unnatural environment so the results may not accurately reflect a regular gait pattern over an extended period. Add to this the high expense of the equipment, the time taken to gather results, and the need for a large specialised laboratory, and such systems are unsuitable for screening a large number of patients in an NHS setting. What is needed is a system where a person is free to move as naturally as they would in their daily activities, and not be encumbered by wires, cameras or treadmills. 

On-the-body sensors

This is now possible thanks to European Technology for Business Ltd (ETB), based in Hertfordshire. They are developing a range of electronic sensor-based technology to monitor how people really walk. Pegasus is the brainchild of Dr Diana Hodgins, MD.

ETB aim to make the Pegasus gait analysis products simple, portable and affordable so they can be used within the NHS and other clinical settings. Hodgins believes that in five to 10 years this technology will be common place, not only for fall prevention, but in injury rehabilitation, surgical assessment and sports performance.

Advances in technology allow more on-the-body sensors to be used to monitor movement. Initially they were in the form of wired or wireless accelerometers, but more recently inertial measuring units (IMUs). In the case of the Pegasus unit it is all contained in a small lightweight box, which can be quickly attached to any part of the body using a Velcro strap. One of the main advantages of the Pegasus system is that it is simple to use, relatively unobtrusive, and can be left in place for hours or days if necessary. It is simple to compare and contrast results gained at different times, pre- and post-physiotherapy or surgery, or following a programme of rehabilitation. 

The ETB Pegasus sensors were initially designed as part of a four-year European Union Framework 6 Project, aptly named 'Healthy Aims', which developed a range of medical implants and diagnostic equipment to help an aging population and those with disabilities.

ETB recognised the need to develop out-of-the-lab gait analysis systems, and tested their first wired accelerometer unit in 2005. By 2006 they had a unit capable of storing data on three-axis of acceleration. The original units could be linked to a PC via a USB port, and more recently a removable mini-SD memory card. In applications where it is necessary to monitor joint angle, solid-state gyroscopes are integrated to measure rotational rates, producing a full IMU capable of logging data in all six degrees of freedom.

ETB are now working with two key partners: Bath Institute of Medical Engineering Ltd (BIME), a charity with strong associations with the university in Bath, and the London Knee Clinic, a private clinic based at London Bridge Hospital.

Prototype units are currently undergoing testing by Dr Roger Orpwood at BIME. According to Orpwood, fall related injuries are "a big issue in terms of health care and health economics". BIME have done extensive product testing using healthy controls, and are hoping to start work shortly with people who have already had a fall and are referred to a local falls clinic. They will look at their gait behaviour compared to the age-matched controls to see if there is a significant difference between the two, and "the indications from the literature are that we should".

The ultimate aim is to develop the device into a screening tool which could be found in every GP surgery, falls clinic, or physiotherapy practice. 

In a practical sense it will be up to GPs to decide which of the patients coming into their practice would benefit from being tested. According to Orpwood: "Clearly it's not going to work for everybody, but as a screening tool, and given the size of the problem, we feel that it could be a really useful piece of a GP's armoury in trying to reduce the consequences of falls."

It is hoped that the ease of use for GPs, coupled with its non-threatening appearance for patients, will encourage widespread use. Having your gait analysed could become no more unusual than having your blood pressure checked. 

Wider scale trials

There are a number of minor issues that are being resolved before wider scale trials can begin. One is the optimum number of strides or distance which subjects will have to walk to ensure the accuracy of the data. It is neither practical nor desirable for elderly clients to have to walk more than a minimum number of strides, although in a walk of only half a dozen strides there is both an acceleration and deceleration phase which needs to be accounted for.

Another question is exactly how GPs and medical professionals would prefer to see the data displayed, with options ranging from a simple traffic light system (red indicating high risk and green indicating acceptable) to more detailed statistical figures, which can be used to make a judgement. 

Rehabilitation aid

At the London Knee Clinic, orthopaedic surgeons Glyn Evans and Syed Hasan have been using the gait trainer to study the stride patterns of pre- and post-knee-surgery patients, with the hope of demonstrating that it is a clinically accurate tool for measuring the success of surgery and rehabilitation.

Along with stride length and rate, they are particularly interested in the joint angles of the knee when patients are walking on flat ground, and going up stairs, and down stairs, and to achieve this have been using the more detailed IMU-based Pegasus system in their trials.

Unlike the fall prevention application with BIME, the knee clinic work is not a 'once only' gait analysis. Hasan says: "Our plan is to do it before the operation two weeks post operatively, at six weeks, three months, six months, and in some cases two years. This ensures their progress, whether a patient has improved or not, and if they have improved - by how much."

They have currently enrolled around 70 of a predicted 100 patients into their study, 15 of them healthy controls.

Ultimately, they hope to be able to look at their results "to see if one particular operation has given them improved gait pattern or not, and also to see their level of deficiency from the normal gait pattern".

Few capable centres

There are very few centres in the UK that can do comprehensive gait analysis on patients using the optical Vicon or similar systems. Hasan says that, when comparing the Pegasus to these expensive laboratory based systems, "this instrument which we are using from ETB does not give you the same amount of comprehensive data, but it gives you enough, especially for knee problems.

"It is very small and does not require any major setup, all you need is a PC or laptop and the sensors. In most cases we need to do analysis in a clinic and it is not possible do the Vicon gait analysis in that setting as it is definitely not portable and is extremely expensive. I think that the ETB product will have good portability so it can be used in any setting." 

The gait trainer may even help surgeons and physiotherapists to improve their treatment, and pick up details of a person's gait which they would not otherwise notice. "Sometimes you see somebody walking reasonably well six months post-operation, but using the gait analysis you realise that there is a difference between the right and left leg, and that perhaps they need more physiotherapy or treatment," says Hasan.

It is hoped that, eventually, the Pegasus product will have applications in other areas of orthopaedic treatment and not just knees. Another of Hasan's colleagues "has done a small amount of data collection on patients with back pain. If you look at it from foot, to ankle, to knee, to hip, to back, they all affect the gait. So, if the equipment is validated and it is proven to be useful and accurate, then its use will be very widespread in orthopaedics and also in sports".

ETB is now the lead partner in the 'Gait Trainer' project. This is funded by the Technology Strategy Board's (TSB) Assisted Living Programme and designed to meet the demand for independent living from those suffering with chronic health conditions and, in particular, the fast-growing elderly population.

They have received funding to develop a new Gait Trainer, an innovative real-time gait training system for people with abnormal gait. The new system is being designed to be used by the patient inside or outside the clinic. For all applications, the Pegasus sensor module with embedded software will be worn. The simplest application will have the unit on the ankle to measure and record various stride parameters.

The future of pegasus

Dr Hodgins is very excited by the possibilities of other applications for the ETB sensors, and is seeking project partners and investment to take things forwards. There is a need to apply this technology to a number of closely related fields. For instance the effectiveness of many surgical or drug-based therapies could be monitored, like the use of Levodopa medication to improve stride length and reduce hypokinesia (slow body movements) for people with Parkinson's disease.

Feedback may be helpful for people with diabetes, where reduced stride frequency can increase the risk of pressure ulcers on the feet. If the patient could benefit from increasing their stride frequency, they could use a system that has real-time feedback to monitor their progress.

It is hoped that you will soon be seeing systems like the Pegasus becoming commonplace in clinics, and then older patients wearing personal portable units.

Since most of us need to walk in our daily activities and want to avoid falling down, it may only be a matter of time before we all benefit from the technology developed by Hodgins and her colleagues.

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