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

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