By Steve Kamper
I’m a physiotherapist, as physios (and we’re not alone here) we love to poke and prod our patients with our fingers and ask if it hurts. Anatomical training and experience tells us exactly which part we are poking and the knowing nod of the head followed by a somber and considered ‘aah haa’ lets the patient know we’ve found the source of their pain. But have we? Some clever chaps in Switzerland recently published a nifty little study that speaks to just this question.
The study included people with chronic neck pain caused by a noxious driver in a zygapophyseal joint (z-joint pain). Participants were diagnosed using a fancy method involving carefully-guided anaesthetic injections developed and validated by Dr Bogduk and friends. This technique was used to establish a specific z-joint as the primary driver of their neck pain. The researchers then measured the person’s sensitivity to pressure (the number of kilopascals of pressure it takes to cause pain) at all the z-joints in the neck.
What they found was no difference in the sensitivity measures between the z-joints supposedly responsible for the patients’ pain and those not. So essentially, the researchers had to push just as hard on a symptomatic joint to elicit a painful response as on an asymptomatic joint.
What can we make of this? Well-accepted theories in the manual therapy world assign considerable diagnostic significance to the sensitivity of various tissues to mechanical pressure. Reproduction of pain with passive joint movement (or palpatory pressure) is commonly used to not only provide a specific anatomical diagnosis but also guide treatment. Implicit is the idea that a damaged/injured joint will be more sensitive to pressure than an undamaged one.
As always, there are some limitations associated with the study; the sample was small, pressure-pain threshold measures are inherently quite variable and we don’t know if the same results would hold for acute subjects. An important question also revolves around the reliability of the process used in the study to diagnose z-joint pain. I’m sure the readers of this site don’t need convincing that pain can be a slippery little bugger and nailing it down to one piece of anatomy is no straight-forward matter.
Limitations aside, I think this study nicely frames some ticklish questions regarding manual assessment of musculoskeletal pain and presumed diagnoses. For example we know that sensitivity to pressure is a factor not only of local/peripheral, but also of central processes, how do we incorporate this understanding into a manual assessment? What weight should we apply to findings of specific tenderness when making a diagnosis?
So where does it hurt?
Steve Kamper’s career as an Environmental Scientist was cut short due to an inability to grow dreadlocks or a convincing beard; he changed to Physiotherapy after being told he looked handsome in a polo shirt. He is currently enjoying the fancy restaurants and 4-day weekends that accompany the life of a PhD student at the George Institute for International Health in Sydney. Steve’s research to date has involved investigation into subjective outcome measures and placebo effects, particularly in patients with whiplash and low back pain. Leisure time is spent playing soccer, running and doing push-ups in his Speedos at the beach.
Siegenthaler A, Eichenberger U, Schmidlin K, Arendt-Nielsen L, & Curatolo M (2010). What does local tenderness say about the origin of pain? An investigation of cervical zygapophysial joint pain. Anesthesia and analgesia, 110 (3), 923-7 PMID: 20185669