A Problem with Musculoskeletal Diagnosis
The patho-anatomical medical model, searching for the tissue at fault and aiming the therapy at that fault, has served us well. It works very effectively in much of medicine, in cancer, infection, heart disease and a myriad other conditions.
It’s primarily in musculoskeletal diagnosis where this link breaks down, that the diagnosis becomes less relevant, that the treatment does not fit the crime, so to speak.
There is a spectrum in MSK disorders, from where the diagnosis is vital and accurate to where the diagnosis is speculative and arguably spurious.
Unfortunately, this spectrum is not well recognised in the management of these disorders and musculoskeletal diagnosis continues to be pursued in cases where it is unnecessary or potentially harmful.
Diagnosis must serve the purpose of identifying a potential tissue target for intervention and indicating which intervention would be most appropriate. If it cannot identify the tissue at fault with reasonable probability, or does not point us towards the treatment, it does not have a use.
Trauma – High Certainty, Clear Treatment
A man mis-steps on the edge of a kerb, going over on his ankle. He hears the crack, the foot swells and he can’t bear weight on it. The pain is significant and immediate. Tissue damage has occurred.
The x-ray shows a fracture of the lateral malleolus, the bony prominence on the outside of the ankle. The ankle ligaments have held against the force of the fall, but the lower part of the fibula has parted from the upper, removing the stabilising mortise from the ankle joint.
The bones must now be held in position and in close proximity for long enough so that they knit sufficiently. Five or six weeks in a cast, usually with weight bearing allowed at some point, restore the stability of the ankle and allow normality to return.
Trauma – Moderate Certainty, Clear Treatment
A young woman pivots as she runs towards the ball. She feels her knee give way with pain and collapses onto the pitch. Her knee swells quickly and she finds bearing weight difficult.
Initial diagnosis is an anterior cruciate ligament (ACL) injury. The knee is treated with ice, compression and rest for a few days, progressing to the restoration of muscle control and knee bending as the swelling and pain ease.
An examination from a knee specialist two weeks after the injury shows some laxity of the anterior cruciate ligament. The provisional diagnosis is an ACL strain and an MRI shows some changes that support that hypothesis.
?Trauma – Low Certainty, Unclear Treatment
A man bends over to pick something up. It’s very light and he has a job where he does quite a bit of heavy work so it should be easy. He gets severe back pain. GP consultations and local physiotherapy make no progress.
A spinal opinion diagnoses low back pain and an MRI scan shows degenerative changes in the lower two lumbar segments.
It is now three months since he worked. Spinal injections are suggested or a discectomy to deal with one of the minor bulges seen on the scan. He is heading for long term pain and disability.
Back Pain Diagnosis
10-15% of back pain patients have a substantive diagnosis, either of a serious medical condition or a specific back pain condition such as a nerve root compression or spinal stenosis.
All the rest are left with nothing.
By nothing I mean that we know they are not seriously ill and they don’t have a particular condition we can pin down. A diagnosis by exclusion is not really a diagnosis at all. It’s a description – “You have low back pain”.
And that’s 85% of all back pain sufferers! 85% for whom the diagnosis has no relevance as it never points to a particular treatment with good evidence of effectiveness. I’ll go over the plethora of back pain treatments another time.
Concentrating on diagnosing, on imaging, on investigating in this group of people seems to have little validity. And if we do come up with a diagnosis, if it doesn’t change the treatment or outcome for the better then it’s an example of spurious diagnostic accuracy.
The gold standard of imaging, the MRI scan, doesn’t show what’s wrong in low back pain. It shows a lot of things, but we have no way of knowing which are relevant to the person’s pain in most cases.
Normal people, by which I mean people who have never had low back pain, show what we typically call significant spinal changes on MRI scanning. As these are not painful by definition, how are we to decide on the relevance of such changes in people with low back pain?
For the vast majority of back pain sufferers, chasing a patho-anatomical musculoskeletal diagnosis, either as a surgeon or as a physiotherapist, seems to be a losing play.
Patients need a functional diagnosis and to have attention paid to the characteristics which define how they are and how they will be. Those characteristics are mostly psychosocial and they take time to unravel.
Another time I’ll talk about time and how we might improve back pain assessment and management.