In studying for final comps/orals/boards we have come across many special tests that need knowing. We learn how to do them, where to place hands, what indicates a positive, tissues involved, etc. If we have enough brain capacity after that, we try to remember gold standards in a pathology and how the special tests correlate. And finally… we attempt to know whether a test is Sensitive or Specific for a certain pathology or impairment. Whew!
The last item is what I would like to focus on because it relates to clinical reasoning an differential diagnosis. Sensitivity and Specificity.
To lay down some operational definitions I will define a Specific Test as one that is good at finding nothing wrong, therefore, when something is found, it is important. Example: The Well’s Straight Leg Test for “disc involvement.” (0.97 Spec) Lifting your leg is a really normal activity that is good at not bothering anything… except when it does (a positive!) and now it has meaning.
Likewise a Sensitive Test as one that is superb at finding a problem, therefore, when the results are negative, they become important. An example of a sensitive test is the Ottawa Knee Decision Rule for knee fracture ( 1.00 Sen). It illustrates great characteristics of fracture… if you don’t have the characteristics- no fracture.
Let me make a few statements:
First: A positive result on a sensitive test is worthless. Second: A negative result on a specific test is worthless.
Perhaps the skilled experienced PTs out there are familiar with this concept, but I am finding it to be quite thought provoking and utterly important. I would have previously thought that a positive Ottawa Knee Decision Rule was important. Oh, it’s positive for fracture! But, research says that its a screen (rule out) and that a positive is not powerful. You could read a patient’s chart full of positive findings and still truly not know anything if the special tests used where sensitive by nature. You could also just as easily see a slew of negative results and wrongly assume that there was no issue… it’s all dependent on the test’s abilities.
Now, many of you are saying “I don’t use special tests in my practice any more.” I have heard this a lot and I think you are missing something. You use them every time you listen to a patient tell their story. The patient will describe test positions during ADLs to help you narrow down your objective exam. They will say that when they reach across their body (demonstrating a Hawkins-Kennedy Impingement motion) that it bothers them… so we listen and follow their lead. Hey, did I get you just there? I might have: Hawkins-Kennedy only has 0.66 Specificity (not that good). A positive is not that important…
My point remains the same, however. We listen and our patients tell us what motions and things bother them and what don’t. Think of it as a virtual special test without irritating the patient.
Over clinical internship, Harrison Vaughan PT, DPT taught me about ruling things out first. During all of the Subjective you are ruling out. He has a nice post here on Special Tests as well. I must say that, while the information is taught in school, the importance of knowing what a test is actually able to do is emphasized secondary to their performance. We have a superb professor that likes to say that the Upper Limb Tension Test (for the median nerve for example) is useless because it lights up everybody, no matter what. What he could say is: if it’s negative, you definitely don’t have a neural tension issue. (0.97 Sen)
I leave you with this: add a layer of knowledge on top of those special tests. Know what they are capable of, what they can really tell you. Go forth… and diagnose.
Reference: Wong M. Pocket Orthopaedics: Evidenced-Based Survival Guide. Burlington, MA: Jones & Bartlett; 2010