There has been a lot of discussion in research and on social media regarding central sensitization. A feature of this phenomena is allodynia. This week’s post takes an in-depth look at the many features of sensation and how to use these to enhance your clinical reasoning.
Anatomy Doesn’t Lie
If you get a chance to read Abraria and Ginty’s article, “The Sensory Neurons of Touch” you won’t be disappointed. It is one of the best articles I have read regarding the somatosensory system. One of many, many, anatomical nuggets in this publication is the description of the Meissner corpuscles. They are a rapidly adapting receptor, which respond on contact and then again on release. Juxtaposed with the slowly adapting Merkel cell complex, these receptors paint a picture in the brain of an object being grasped (stereognosis), comparable to how rods and cones are utilized by the eye to paint a picture. When testing sensation, it is important to distinguish between these two receptors and appreciate all aspects of touch (vibration, hot, cold). In a busy clinic day, most therapists skip sensory testing or default to a quick “Kleenex” test through the dermatomes. Take the time to revisit sensory testing.
The Body Heals in a Predictable Manner
It is important to review the research on how long it takes for nerves to heal, the chart below is a good template. This will help you set goals for your patients and reflect/predict recovery times and expectations.
|Degree of Nerve Injury||Spontaneous Recovery||Rate of Recovery||Surgery|
|Full||Occurs in Days or 3 months following injury||None|
|Full||Regenerates at the rate of 1” per month.||None|
|Third||Partial||Regenerates at the rate of 1” per month.||None or neurolysis|
|Fourth||None||Following surgery regenerates at 1” per month||Nerve repair, graft or transfer.|
|None||Following surgery regenerates at 1” per month||Nerve repair, graft or transfer.|
|Recovery and type of surgery will depend on the injury and the cementation of degrees of nerve injury.|
*Reproduced from Susan E. Mackinnon, MD & Christine B. Novak, PT, MS
Pain is in the Brain
I have always been fascinated by the representation of the hand in the brain. The hands, fingers and wrist have the largest cortical representations, larger than the whole arm itself. The emotional connection to the hand adds a layer of complexity as well, for it will heighten the pain response through apprehension and fear. The limbic system modulates the pain response to a noxious stimulus (Hansen, Streltzer 2005) and is a significant contributor to this heightened pain response. Remember, pain is always in relation to the context in which it occurs.
We are Prone to Clinical Reasoning Errors During a Busy Clinic Day
This week we can briefly discus the argument from ignorance (also, Argumentum ad Ignorantiam): The fallacy that since we don’t know (or can never know, or cannot prove) whether a claim is true or false, it must be false (or that it must be true). This happened with phantom limb pain. The AMA initially ignored phantom limb pain, stating that if the nerve is not there, painful stimuli cannot be transferred to the CNS. Herman Melville recognized phantom limb pain before more physicians. Captain Ahab says, “put thy live leg here in the place where mine was; so, now, here is only one distinct leg to the eye, yet two to the soul. Where thou feelest tingling life; there, exactly there, there to a hair, do I. Is’t a riddle?” This week ask yourself the question “what am I not seeing or ignoring?” and you may be surprised.
Treat the Person and You Win Every Time
I love this quite from Brand in his book “Clinical Mechanics of the Hand, 2nd Ed.”
Video of the Week
Take a look at this video, it explains an alternative approach to testing sensation instead of using a monofilament.
The is a non-PT article, but is an interesting and in depth look at the psycholgy of pain: The Psychology of Pain
For a deeper dive into some of these issues and much more, including hands-on manual therapy, find a NAIOMT course in your area! And if interested in receiving weekly MSK Monday posts, subscribe to the left to get them delivered to your inbox. Enjoy your week!