Student Physiotherapists learn a broad selection of orthopaedic “special tests” during their university study.
These special tests are designed to test a specific structure, like an ACL or ATFL, to determine if it’s injured, compromised or a source of symptoms.
They’re often backed by a research paper on the sensitivity and specificity of the test, and you can’t argue with research, right? (<— insert eye roll here…)
Issues with overlapping structures and force dissipation
Think about what actually gets loaded during a “special test”.
Sure, the target structure will be loaded as intended. But it’s very rare in the design of the human body that one structure and only that structure will take the full force on its own.
The way the body has evolved is that multiple structures will take the load to help dissipate the force.
In some cases, the primary structure takes the load but secondary structures will kick in to assist as the force increases.
Whichever the case, it’s very rare to be able to “isolate” a structure and selectively load it during a special test.
This presents two issues:
Firstly, an intact secondary restraint may disguise an injury to the primary restraint.
Secondly, a positive special test may actually indicate multiple injuries to numerous structures rather than just the primary structure.
Issues with other causes of laxity, pain and more
If you perform a Lachman’s special test for ACL injury, you’re looking for laxity and a lack of an end feel.
But what if other factors could affect the results?
It seems logical that laxity would be due to a damaged or ruptured ACL.
But perceived laxity will also occur with a moderate amount of joint swelling, as the overinflated joint capsule allows more translation of the tib-fib joint.
You’ll also get more perceived laxity with a ruptured PCL, as the joint is starting from a more posterior position and therefore seems to move further as your shift the tibia anteriorly.
Then there’s the end feel of the special test – we’re looking for the absence of that firm stop at the end of the movement.
Joint swelling will obscure that feel, as well any hamstrings guarding, making it a difficult test to interpret.
(Side note: pay particular attention to the state of the individuals in research papers for special tests – testing end feel in an anaesthetised patient would be far clearer/easier than in a patient who’s alert and apprehensive!)
Issues with an inability to selectively load a structure
Our last issue with special tests is the inability of most tests to isolate force or pressure on a specific structure.
Any shoulder rotator cuff test will generally be a “special test” for one of the muscles – it identifies Subscapularis or Supraspinatus injuries.
But the cuff works together as a unit, not in isolation, so getting one muscle to work while avoiding the others just isn’t possible.
McMurray’s test will load each meniscus to identify a meniscal lesion, looking for a painful click as the force passes over the lesion.
You’ll get a similar result with acute osteochondral lesions and even smaller tibial plateau fractures.
So if the test can’t differentiate between these pathologies, is it useful for us?
Approaching special tests in a different way
What if we took the “special” out of special tests?
What if special tests were named after their loading patterns, rather than being associated with a structure?
Lachman’s test would become the “Anterior Tibial translation test”, rather than an ACL test.
Seems like a minor point but a positive test would indicate an increased amplitude of anterior Tibial movement and a lack of anterior translation end feel.
It would take out the assumption of a positive test = ACL tear.
It would start the clinical reasoning thought process of “what could cause an increased translation and loss of end feel?”
It would give the clinician the ability to use their knowledge of biomechanics and anatomy, rather than just providing simplified and often inaccurate outcomes for special tests with “this test = this diagnosis”.