What is an antalgic (painful) gait? Let the sensors have their say.

Falsehood flies, and the truth comes limping after it, so that when men come to be undeceived, it is too late; the jest is over, and the tale hath had his effect.

Jonathan Swift

One of the things we are taught as medical students and doctors is how to recognise various types of gait. This is an imperfect art, particularly for the less observant among us! I remember telling someone that his painful, slow gait was due to his hip arthritis only to see that after successful hip surgery his gait was still just as slow. It turned out that he also had early Parkinson’s disease, and I had missed the early signs of his neurological condition. And if you think you are immune to such lapses of judgement, perhaps you – like me – were fooled by Virgil’s limp in the film ‘Usual Suspects‘ (one of my favourite cinematic endings).

One of the most basic gaits to recognise is someone walking with a single painful hip joint. This is commonly called the ‘antalgic’ gait, and is characterised by someone spending less time putting their weight on the painful leg compared to the other leg.

When surgeons replace hip joints they hope to relieve pain – but they also need to restore a normal gait pattern. Although pain relief happens quickly in most patients, restoration of normal function is more gradual. The best way to study this scientifically is to apply movement sensors to the limbs – accelerometers or more sophisticated triple component inertial movement sensors (IMUs). A 1999 paper by Aminian et al examined this question in a group of patients who had hip surgery for arthritis in a single hip. It turned out that simply measuring gait speed didn’t show the improvements as clearly as the ‘assymetry of double stance’ time. This is the difference between the time you spend on the bad leg vs. the good leg – i.e a scientific measure of the ‘antalgic gait’.

Using sensors to detect improvements in gait after hip replacement
Sensor detection of changes in assymetric (antalgic) gait after hip replacement surgery

In the top left (pre-op) picture you can see a big spread from the identical line (diagonal) – and then as we move to the bottom right (9 months post-op) you can see that the difference between double-stance time on either leg has narrowed except in one patient (circled in the image below).

Sensor detects Gait in Hip Osteoarthritis after surgery
Sensor detection of changes in assymetric (antalgic) gait after hip replacement surgery: spot the one exception!

Now, as it happens, this poor chap still had pain in his hip. I guess you could have found that out a lot easier just by asking him, but the point is that we’ve found that out through a very objective test. Looking at the trace from the motion sensors, an analyst miles away with no video footage could ‘diagnose’ that he still had an antalgic gait. The same sort of analytics can pick out differences that are just not obvious even to the practised eye.

This is just a simple example taken from what is a rapidly expanding area of the scientific literature – how to accurately measure and define human movement. In this case, the use of movement sensors provided objective evidence of improvements we could have discerned by observing the patient’s gait or by asking them to complete a questionnaire. However, movement analysis can be used to perform much more complex assessments that should help the therapist understand why our patients haven’t quite returned to full function at work or at home. Physiotherapists, sports scientists and experts in biomechanics/computer analytics are leading the way. Watch this space!

Reference: Arminian K et al Med Biol Eng Comput 1999 37 686-691

Catching the Wave… Motivating people to get active and exercise

It has been said that ‘inactivity is the new smoking’, and there is no doubt about the medical problems caused by lack of physical activity. This is a growing problem, and one that is particularly difficult for many people with musculoskeletal diseases to deal with.

Historically, there used to be a feeling among doctors that exercise helped inflammation. Once upon a time, people with Ankylosing Spondylitis were put in plaster of paris spinal casts and patients with Rheumatoid arthritis were made to rest in bed for weeks upon weeks. Although the modern Rheumatologist would regard these practices are seriously misguided, it could be argued that our failure to actively promote exercise is also a failure to follow the evidence. If it affects both general and musculoskeletal health we should really be doing more to promote change.

Before the birth of modern Rheumatology, Physical Rehabilitation skills were very much part of the training of a doctor who treated patients with arthritis. Modern training leads us to regard ‘silos’ of physical rehabilitation, medical therapy and surgical therapy as mutually exclusive. We do refer to our physiotherapy colleagues, but is it possible that some patients need a more committed approach from their doctor to get them started? It is clear that a doctor’s advice about smoking is still reasonably effective. And for some patients who just need more general physical activity, perhaps we need to be finding ways for our patients to get involved in local Tai Chi classes, Pool exercise sessions and other ‘Gym Voucher’ schemes to help get people started. The 3 month ‘Gym Voucher’ incentive scheme funded by Public Health in this area is particularly imaginative and effective. The local gym instructors funded to lead these programmes can be a great asset.

From many years of experience in giving advice it has gradually dawned on me that for many people, major behavioural change is not easy. We’ve all seen the person who has just had a heart attack or developed cancer throw their 50cig./day habit in the bin without a second thought. Or the person who has been told by the orthopaedic surgeon that if they don’t lose X amount of weight they won’t get their knee replacement. For some patient it might be getting a dog and starting to walk regularly again. I like to think of this as ‘catching the right wave’ – waiting for a strong motivational push to get them going.

Catching the right wave
Catching the right wave


Clearly Staged Graduated programmes can be very effective. ‘Couch to 5k’ is a great example of this. When we are dealing with people with arthritis we need to be sensitive to the fact that their pain and stiffness will not help them to get started.

couch to 5k

Using technology to motivate. There are now several studies which have shown that simple pedometer devices can be used to help motivate adherence to increased physical activity. These studies usually employ some sort of ‘target’, sometimes using social sharing of our achievements as a further motivator. There are many successful apps such as ‘Runtastic‘ that are helping athletes to improve: perhaps we need more help at the less active end of the scale!

Doctors in Sweden are all trained in the art of issuing an Exercise Prescription. The ‘Doctor’s Handbook’ from Hong Kong (in English) is an excellent booklet which should be required reading for every medical student and doctor.

One useful mnemonic to use when writing an exercise prescription is FITT-VP

—Frequency – sessions per day or week
—Intensity – rate of energy expenditure or force during resistance exercise
—Time (Duration)
—Types of Exercise (Aerobic, Muscle-Strengthening, Stretching, Neuromuscular activity
—Volume – total amount
Progression (advancement)

I would be interested to hear what you think. What motivators work for you? Perhaps you feel that this is not something rheumatologists have time to talk about. Should we just leave it to the physiotherapists? There is no doubt that the latter will give expert advice and this is very necessary with complex rehabilitation programmes, but simple generic advice should be within our remit.