I’ve just sprained my knee.
It hurts!!
It occasionally clicks!!
It feels unstable!!
Do I need to rush into ER (emergency room), have an x-ray, get an MRI?
Before that… let’s see what the Abbey Mobile Physio has up his sleeve.
Special Tests
Continuing with our MSK physio assessment series, here we introduce the tests a physiotherapist can do to build up to a confident and accurate diagnosis. Surprisingly, or perhaps not, these tests are what we professionals call “special tests”. They fall within the objective assessment so take a look here if you haven’t read about what this is yet. There are many special tests for MSK diagnoses. Normally they are named after the person who created it, but occasionally, named also for the movement or structure it assesses.
To give a better understanding of these special tests, we’ll glance over some that assess the structures of the knee. Here we categorize them by what they assess:
Anterior Cruciate Ligament (ACL) – anterior drawer test, Lachman’s test, pivot shift test, Lelli’s test
Meniscus – Apley’s distraction and compression test, McMurray’s test, Thessaly Test
Patellofemoral Joint – patellar grind test, patellar apprehension sign
These are just some of the few tests out there to assess the knee. Click here to see a whole list of special testing for the knee. This demonstrates the amount and attempt to specifically target certain structures within one area of the body.
To give you a bit of a taster, look at a special test - Lelli’s test in this video.
As demonstrated, the test is done in a particular position (lying face up), the clinician simply puts their fist underneath just below the knee and then pushes on the quadriceps just above the knee. The structure it aims to test is the ACL (anterior cruciate ligament), so theoretically if the ACL is torn, then pushing on the quadriceps won’t make the knee to straighten.
One can quite quickly see why these tests would be beneficial. Examine something accurately at a reasonable cost (depending on how much the physio charges you), and not needing to wait for imaging which can take a long time. But this brings us then to the juicy question – is it accurate?
Tests must be rated on how accurate and precise they are. Anyone can call something a test, what matters is:
1. Whether the thing the test is testing, is truly being tested. We call this Sensitivity.
2. Whether the test is also testing many other things. We call this Specificity.
See this other blog post to understand more about MSK assessments.
With Lelli’s test mentioned above, let’s ask ourselves whether it is a sensitive test, and whether it’s a specific test.
1. What exactly is this trying to test? The ACL integrity. Is it truly being tested? It seems so, but I could imagine that it might not show up if the client had much swelling or stiffening in the knee joint, resulting in the heel lifting off even if the ACL were torn
2. Is this testing many other things? It seems to test the overall joint translation, so it may falsely give the impression that the ACL is torn (false positive) but actually the patient has general joint laxity, or maybe an issue with another structure such as the meniscus.
Even just thinking about it in a theoretical manner, it’s possible that the result from Lelli’s test could be false.
It’s Not Just About the Theory
I’ll create a test and call it the Ben-Flick test. What happens in this test is I flick the patient on the knee cap. A positive result is if it is painful, a negative result is if it isn’t painful. I then make up some elaborate theory that this is testing the cartilage under the kneecap by causing shockwaves through the bone, thus resulting in pain if there is a cartilage issue.
Let’s see how it stands up against the two points mentioned above:
1. What exactly is this trying to test? The cartilage. Is it truly being tested? Sure, how can you prove me wrong?
2. Is this testing many other things? No, according to the theory, the pressure waves released from the flick resonates at a particular frequency which only triggers the cartilage due to this tissue’s particular density.
Just analyzing this theoretically, it seems like I’ve just fluffed up something to say it is both sensitive and specific. That doesn't seem right, but how can we know for sure. To truly be able to know whether a test is sensitive or specific, it must be tested against the best form of measurement. It’s like with measuring distance – if I cut a length of rope and assume it is 1 meter, then use it as a standard of measurement, it could be completely off unless I have measured this rope up against a proper measuring tape. With diagnostic testing, it’s the same. We can only truly understand whether a test works or not when aligning it to the measuring tape of diagnostic testing – here, the gold standard tests.
Gold Standard Tests
Scientific research will always compare a test against its gold standard test to understand how accurate and precise the test is. Unlike measuring tape, when a test is gold standard it doesn’t mean it’s 100% accurate, rather, it’s the most accurate test available and acts as the benchmark to compare other tests with (Versi E). One can imagine that prior to technology, the gold standard tests may have been fairly inaccurate, and as time progressed with technological advances and scientific understanding, gold standard tests were updated with more accurate examination. Within MSK health, gold standard tests largely remain to be medical imaging (MRIs, x-rays, ultrasounds, etc.), blood testing, and nerve conduction tests. Arthroscopy which is keyhole surgical viewing has occasionally overtaken imaging in detecting issues (Oakley et al. 2005).
You must now be thinking, “OK, I thought your whole point was that a physio could accurately diagnose without imaging, now you’re saying the gold standard test is imaging and other non-physio tests?” The point is that gold standard tests allow us to compare how accurate our clinical special tests are. If a test is significantly accurate, there would be a lesser incentive for costly gold standard technological testing. Returning to the measuring tape analogy, if we accurately measured out 5 lengths of rope as 1 meter, then we could use those inexpensive ropes as measuring tapes rather than buying 5 measuring tapes.
Measuring Special Tests against Gold Standard Tests
Returning to Lelli’s test for ACL integrity, we theorized about how it could be inaccurate. Let’s see the factual scientific evidence of lining it up against the gold standard test for ACL tears – MRI (magnetic resonance imaging) finding. We see here in Lelli et al (2014) 400 patients with ACL tears of varying degrees having almost 100% specificity and sensitivity. That’s an amazing score, demonstrating this test to be as accurate as MRI. However, we see in a following study by Valsalam et al (2020) the sensitivity being 85.57% and specificity being 25%. As these are quite polarizing results for the specificity, it would be deemed as requiring further investigation.
Things get complicated here with special testing as truthfully, many of the tests are either very specific or very sensitive. Unlike Whiskey, best enjoyed as a single malt than blended, mixing these tests together forms a better and more accurate result. We call these cluster tests which you can find as an example here, the sacroiliac joint cluster tests. Looking at the individual tests, the sensitivity and specificity scores aren’t that high by themselves, but when combined together as a cluster, these values increase. Even so, these tests are never as accurate as the gold standard test.
Diagnosis isn’t Just From the Special Test
I will still insist that this doesn’t mean that we can’t gather an accurate diagnosis without the gold standard test. It just means the clinician (or DIY physio) can’t assume they have an accurate diagnosis just by doing a special test or a cluster of tests. The clinician must take into consideration not only these tests, but the background information they have – such as mechanism of injury, the behaviour of pain, the types of symptoms the patient is having. As a single item, these bits of information may not make a strong case, however with all this information gathered together, a strong argument could be made towards a certain diagnosis giving one confidence in the diagnosis even without the gold standard test.
Risks, Benefits and Final Goal
If that doesn’t yet convince you that you can be safe in a physiotherapist’s hands even without the latest up-to-date technological gadget of a gold standard test, hear this out. The clinician’s brain is working million miles an hour weighing up the risks, the benefits, and the final goal that you want as a client.
Risks: risks for not getting a scan, risks that immediate surgery is required, risk of going down lengthy waiting times and costs when it could be resolved quickly. We professionals use a term Red Flags – when there is a high-level risk for something that requires immediate medical attention.
Benefits: benefits of trialing conservative treatment, benefits of having an exact diagnosis, benefits of avoiding stress and anxiety of complex investigations
Final goal: one person may be to return to upper league football, another recreational park running, walking the ridgeway for another
All these would be considered and discussed with you as the client, so that you can make the best decision going forwards.
So back to where we started:
You’ve just sprained my knee.
It hurts!!
It occasionally clicks!!
It feels unstable!!
Do you need to rush into ER (emergency room), have an x-ray, get an MRI?
NO, not necessarily! Get seen by an expert MSK clinician like the Abbey Mobile Physio first before venturing down that path. Hopefully with this article you will have understood what we have under our sleeves (or rather, under our caps) to ensure you are heading down the right path.
Reference List:
Lelli A, Turi RPD, Spenciner DB, Domini M 2016, The “Lever Sign”: a new clinical test for the diagnosis of anterior cruciate ligament rupture, Knee Surgery, Sports Traumatology, Arthroscopy, vol. 24, pages 2794-2797, Available at: https://link.springer.com/article/10.1007/s00167-014-3490-7 (Accessed: Jan 18 2023)
Oakley SP, Portek I, Szomor Z, Appleyard RC, Ghosh P, Kirkham BW, Murrell GAC, Lassere MN 2005, Arthroscopy – a potential “gold standard” for the diagnosis of the chondropathy of early osteoarthritis, vol. 13, no. 5, page 368-378, Available at: https://pubmed.ncbi.nlm.nih.gov/15882560/#:~:text=These%20results%20suggest%20that%20arthroscopy,video%20footage%20without%20AC%20probing (Accessed Jan 18 2023)
Physiopedia (2023) Category: Knee – Special Tests, Available at: https://www.physio-pedia.com/Category:Knee_-_Special_Tests (Accessed: Jan 18 2023)
Physiopedia (2023) Sacroiliac Joint Special Test Cluster, Available at: https://www.physio-pedia.com/Sacroiliac_Joint_Special_Test_Cluster#:~:text=Test%20Item%20Cluster%20(TIC)%20is,SIJ)%20pain%20is%20clinically%20important(Accessed: Jan 18 2023)
Valsalam P, Sha I, Edwin A 2020, Lever Test: Role of Its Assistance in Diagnosis of Anterior Cruciate Ligament Injury, Journal of Research in Orthopedic Science, vol. 7, no. 3, pages 115-120, Available at: https://jros.iums.ac.ir/article-1-2111-en.pdf (Accessed: Jan 18 2023)
Versi E, 1992, “Gold Standard” is an appropriate term, BMI, vol 305, no. 6846, page 187, Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1883235/?page=1 (Accessed: Jan 18 2023)
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