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2D Video Gait Analysis: Valid and Reliable Measure for PTs

by Kelsey Hattersley SPT

young-woman-doctor-older-man-patient-smilingI recently heard it mentioned that human movement should be considered a vital sign. I found this oddly profound because, without movement, one’s quality of life is greatly reduced. As movement experts, we should always assess movement, treating it as if it is a vital sign. Furthermore, we should continually strive to improve the quality of life for all of our patients across their lifespans by enabling them to keep moving effectively.

As a PT student, I often find myself becoming more observant of human movement as I delve further into my program. When I first learned about normal gait and some common gait deviations, I found myself constantly people watching, analyzing the gait of every person that walked by me.

It was like I had stepped into a different world, noticing excessive hip drop in every person that I walked past.

Now, I realize this was likely an over-exaggeration, but I think it is pretty common to learn a new concept then suddenly become more acutely aware of it in everyday life. My selective attention had kicked in as I was unconsciously looking for abnormal gait patterns. However, looking back I often wonder if I was truly seeing these deviations, or if I was just unconsciously seeking them out.

So, if there truly is this abnormal gait epidemic, then think about many steps are taken each day? For example, consider a 4° abnormality and the increase in loading to a given tissue that occurs with every step taken… it adds up over time!

Eventually, this abnormal gait pattern can lead to some sort of injury that would require treatment by us, the PTs. Nonetheless, before we can treat the problem, we need to be able to identify the problem with an objective measure that is valid and reliable. Once an objective measure is obtained and we can clearly identify the specific impairments related to our patients' dysfunction, we can design and implement an individualized treatment plan.

Objective measurements for gait analysis.

Observational or qualitative gait analysis in real-time is indeed a valid measure, but if the patient has a minor abnormality how confident are you that you can identify this in real-time? Plus, if a PT is implementing a treatment strategy aimed at improving one’s gait pattern, then an objective gait assessment is necessary to prove that meaningful change has occurred.

My main point is, objective measures are one of the best tools for marking meaningful change and improvement. Qualitative, real-time gait analyses may require numerous walking trials which could result in fatigue or symptom exacerbation depending on the patient. As mentioned earlier, gait deviations are oftentimes subtle and difficult to identify in real-time while watching a few trials. So, in the instance where there is only a 4° deviation, the abnormality could potentially be missed during the assessment.

Breunnkreef et al. found that structured visual observation of a patient’s gait using a gait analysis form is only moderately reliable. In this study, 10 raters with varying levels of expertise evaluated previously recorded digital videos of patients’ gait. The raters were allowed to observe each videotape repeatedly before providing the analysis using the previously mentioned gait analysis form. Breunnkreef et al. concluded that this form of gait analysis will supply the observer with indications in a person’s gait, but that in order to evaluate the effect of an intervention, clinicians should use more objective instrumentation that is valid and reliable.

Gait is a complex task, and subtle deviations can be detrimental to one’s function. While we may subjectively observe an unstable antalgic gait pattern characterized by excessive hip drop, trunk lean, etc., it is crucial that we are able to identify something as minor as a couple of degrees of deviations that could be associated with pain and dysfunction.

Later, I will explain how this valid measure can be obtained through 2D video analysis. There are many different ways this can be done, so I will explain a few basic options that are easy enough for anyone with a smartphone or tablet to perform. I mean let’s be honest... just about everyone has a smartphone these days.

Valid and reliable ways to analyze gait.

As I mentioned before, we need a valid and reliable objective measure to use in our initial assessment which can also be used again during reassessments. Additionally, these measures need to be relevant to the patient and their specific gait dysfunction (i.e. painful, unstable, inefficient gait.)

One study by Atkins et al. aimed to establish the reliability and validity of a novel technique that is designed with clinicians in mind, to allow objective assessment of the frontal plane hip kinematics during running. This technique used a commercially available video and a free smartphone inclinometer application. These authors concluded this novel technique was valid and reliable for measuring hip kinematics making it “suitable for broad-based clinical use.”

In another study by Munro et al., they tested the reliability of 2D video analysis and the associated measurement of error in the analysis of lower limb dynamic valgus. Based on the results of this study these authors concluded that the frontal plane projection angle assessed using 2D video analysis is a reliable measure of lower extremity dynamic knee valgus. This study provides clinicians with a tool for assessing individual performance and changes in performance resulting from interventions.

These are just two studies from a growing body of literature that have investigated the validity and reliability of 2D video analysis during activity. For many patients, PTs can get by using 2D video to assess sagittal and frontal plane movement because many movement abnormalities occur in these planes during gait. Similar to subjective real-time gait analysis, analyzing 2D video is valid and reliable.

Utilize the analysis for feedback to the patient.

2D video analysis is not only useful to the clinician, but it is also useful for educating patients. It can provide a form of visual feedback to the patient as well. Using video as an educational tool opens the floor for different approaches to treatment. The clinician can use this to point out abnormalities to the patient. For example, as PTs, we know what someone means by hip drop, but patients may need to see for themselves with someone telling them “look right here, this is what hip drop looks like in your gait”.

You can also have the patient analyze their own gait to point out abnormalities they see, then you can confirm this and expand upon it or explain that what they see as abnormal is actually normal. Education and feedback in this way can be invaluable because it provides the clinician with various options that he or she can adapt to the individual patient and their unique learning style.

Video analysis options in the clinic.

There are many options available to clinicians interested in 2D video analysis of the gait. For tech-savvy individuals interested in more advanced gait analyses, there are several motion analysis programs available for computers.

Hudl Technique is a commercially available, free application available to download on smartphones and tablets. This application offers more than just using the video feature of your smartphone because it allows for a more in-depth analysis of the video. The user can view the video in slow motion, advance the video frame-by-frame, draw directly on the screen, measure joint angles with the protractor feature, and make a side-by-side video with two separate videos.

This is an awesome feature because the clinician can have the original video and the reassessment video side by side. Once comfortable using simple 2D video through a smartphone, you may consider looking into different computer programs and special cameras that will allow you to go further in-depth.

Final thoughts on gait analysis.

1. Know normal gait.

Before identifying a gait you think may be abnormal, it is important to be aware of what a normal gait looks like. Just like anything else, you have to know what normal is before you can say something is abnormal. I use Observational Gait Analysis by Ranchos Los Amigos National Rehab Center as my reference for normal gait. Another, more in-depth reference text is Gait Analysis: Normal and Pathological Function by Jacquelin Perry and Judith Burnfield.

2. Use additional objective measures to support your findings as a 2D video analysis of gait is only one piece to the puzzle.

For example, if a patient’s gait abnormality is consistent with hip muscle weakness, then you can confirm that hip weakness (i.e. an impairment) is contributing to the gait abnormality (functional limitation). A handheld dynamometer can be useful for objectively measuring muscle strength deficits and highlighting imbalances. Remember, human movement is complex and oftentimes there are many factors that contribute to abnormal movement.

3. Start simple.

Like I mentioned before, begin with a smartphone or tablet, and then consider investing in a video camera and motion analysis software if/when you feel that it is worth your time and money.

4. Movement is life.

As PTs, our goal should be focused on keeping people moving to improve their quality of life!

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  1. Atkins LT, James CR, Sizer PS, Jonely H, Brismee JM. Reliability and concurrent criterion validity of a novel technique for analyzing hip kinematics during running. Physiother Theory Pract. 2014 Apr;30(3):210-7. doi: 10.3109/09593985.2013.830349. Epub 2013 Sep 11. PubMed PMID: 24020985
  2. Munro A, Herrington L, Carolan M. Reliability of 2-dimensional video assessment of frontal-plane dynamic knee valgus during common athletic screening tasks. J Sport Rehabil. 2012. Feb;21(1):7-11. Epub 2011 Nov 15. PubMed PMID: 22104115.
  3. Brunnekreef JJ, can Uden CJ, can Moorsel S, Kooloos JG. Reliability of videotaped observational gait analysis in patients with orthopedic impairments. BMC Musculoskelet Disord. 2005 Mar 17;6: 17. PubMed PMID: 15774012; PubMed Central PMCID: PMC555760.


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