Do shoulder impingement physical tests work? - Upright Health

Do shoulder impingement physical tests work?

Why think about special tests for the shoulder?

When people are told they have shoulder impingement, there are a number of physical maneuvers or "special tests" that doctors will use to investigate their problem.

These special tests are supposed to provide useful information that tells you whether you have true "impingement." These special tests, however, are extremely problematic. Based on the available research, these tests don't actually tell you anything of value!

A primer on sensitivity and specificity

There are two concepts you need to understand here. Sensitivity is how good a test is at spotting true positives. Specificity is how good a test is at spotting a true negative.

Sensitivity is how good a test is at spotting true positives. Specificity is how good a test is at spotting a true negative.

A metal detector is a great illustration of sensitivity and specificity. If you send 100 people with metal in their pockets through the metal detector, you want it to give you a positive response 100 timesIf the metal detector gives you 100 positive responses, it has a sensitivity of 100%. Its specificity, however, would be unknown.

To know the specificity, you have to have some negative cases. Let's say we send 100 people through a metal detector with no metal in their pockets. We want the metal detector to give us 100 negative responses. If it gives us 100 negatives, then it has specificity of 100%! What's the sensitivity? We don't know unless we have positive cases.

So now we send 100 people through. This time 90 people do not have metal in their pockets, and 10 people have metal in their pockets. If the metal detector gives us 90 positives and 10 negatives on all the right people, it has a sensitivity of 100% and a specificity of 100%!

If, however, the metal detector gives us 100 positives, that means its sensitivity is 100% (it caught ALL the 10 people with metal), and its specificity was 0% (because it missed ALL the people who had no metal in their pockets).

If the metal detector gives us 100 negatives, its sensitivity is 0% (it didn't catch ANY of the 10 people with metal), and its specificity is 100% (it caught all the 90 people without metal). 

The point is this: you need to have high sensitivity AND high specificity for a test to be of much use. If it has high sensitivity and low specificity, it has a very high risk of giving you false positives.

The point is this: you need to have high sensitivity AND high specificity for a test to be of much use. If it has high sensitivity and low specificity, it has a very high risk of giving you false positives.

How do special tests for shoulder impingement measure up?

There are a number of different shoulder tests that are supposed to tell you whether you have true "shoulder impingement." In 2000, Calis et al examined a number of tests.

Test name

Sensitivity %

Specificity %

Accuracy %

Hawkins

92.1

25

72.8

Neer

88.7

30.5

72

Horizontal Adduction

82

27.7

66.4

Speed

68.5

55.5

64.8

Yergason

37

86.1

51.2

Painful arc

32.5

80.5

46.4

Drop Arm

7.8

97.2

33.6

As you can see, the accuracy numbers for all these tests tops out at 72.8%. But that's not the full story. For the most "accurate" tests, you can see abysmally low specificity numbers. 

The Hawkins and Neer tests have the highest accuracy percentages, and their specificities are at 25% and 30.5% respectively. That means these tests are worse than a coin toss at finding true negatives. A coin toss would call a true negative at approximately 50%. These tests are biased to give a positive response - which means they are like our bad metal detector that has low specificity (remember, low specificity = high likelihood you're getting false positives).

The only test that has a specificity rate above 90% is the Drop Arm, and that has sensitivity of 7.8% - which means it's pretty bad at finding true positives! 

What if you combine these tests together?

There is a common misconception that by putting a bunch of tests together, you can increase the accuracy and certainty of your conclusions. Especially when dealing with tests that have such bad specificity ratings, this is simply not the case. 

There is a common misconception that by putting a bunch of tests together, you can increase the accuracy and certainty of your conclusions. Especially when dealing with tests that have such bad specificity ratings, this is simply not the case.

If you have a test that is highly sensitive and has poor specificity, you actually increase the likelihood that you'll get a "positive." This is very intuitive when you think about it. High sensitivity and low specificity means you have a high risk of false positives.

If you take a bunch of tests with a high risk of false positives and put their results together, you don't get more accurate information. You get the opposite. You get an increasingly certain outcome: a false positive!

So what good are these special tests for the shoulder?

"The highly sensitive tests seem to have low specificity values and the highly specific ones to have low sensitivity values. Although this finding suggests that these diagnostic tests are insufficient for certain diagnosis, it is suggested they play an important part in clinical evaluation."

If you have tests that do not give you reliable information, they're not all that useful. Tests that hover around the level of 50/50 should not at all be considered reliable and likely should not be used to make important decisions. Tests that have wildly unbalanced sensitivity and specificity should also be considered unreliable since they probably aren't giving us information that's relevant (high false positive or high false negative risks). 

If we invented a totally new test that was simple - let's say tapping on the shoulder with a hammer - that had sensitivity and specificity numbers as bad as these existing physical tests, we would not consider using the test. It'd be silly. 

These physical tests only seem to be considered useful and informative because they had been considered useful as a matter of faith. Now that there is research into their reliability, people need to seriously consider whether these tests actually do anything to clarify shoulder problems at all.
Based on the evidence, these tests do not.

These physical tests only seem to be considered useful and informative because they had been considered useful as a matter of faith. Now that there is research into their reliability, people need to seriously consider whether these tests actually do anything to clarify shoulder problems at all.

Based on the evidence, these tests do not.

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About the Author

Matt Hsu is a trainer and orthopedic massage therapist. He fought a long battle with chronic pain all over his body and won. He blends the principles he learned in his journey, empirical observations with clients, and relevant research to help others get their lives back.

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