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We focus this week on shockwave therapy, inspired by a hot off the press study by Leone et al. 2016. They investigate the effects of shockwave therapy on stem cells derived from tendon. They took cells from healthy semitendinosus tendon (people having an ACL repair) and from ruptured Achilles tendons. They found that shockwave was able to ‘accelerate the in vitro-induced differentiation of human primary cultured Tendon Stem cells’. That’s great, and obviously the methods in this study are very difficult, but the focus is on the holy grail of the tendon world – healing!! The authors admit themselves…’the recovery of a normal function of injured tendons represents an ambitious goal’.
In clinic we are more concerned about treating pain and restoring function – so here is brief guide for clinicians on shockwave therapy mechanisms, effectiveness and application.
Hope you enjoy and see you next time (for more joining the dots)
What does shockwave do?
Shockwave is a common treatment offered to patients who have tendinopathy eg Achilles, gluteal, proximal hamstring, patellar tendinopathies or plantar heel pain. It delivers energy into tissues in waves, and in doing so causes direct mechanical perturbations to the tissue. And an important point is that there are two types of shockwave. Focused shockwave concentrates energy deep in the tissues, whereas radial shockwave disperses in the tissues and becomes less intense the deeper it goes (See figure below).
We don’t really know how it works but there are lot’s of theories. On some manufacturers website you have vague comments like ‘energy promotes regeneration and repair’.
The most common theory talked about is reduced in substance P production (a biochemical involved in pain and sensitisation). In the study often cited, Maier 2003, substance P production actually increased at 6 and 24 hours and then was reduced at 6 weeks – this does not fit with the immediate pain reducing effects of shockwave.
Other common theories are increased cell stimulation and protein synthesis (Bosch 2007), and loss of unmyelinated nerve fibres (Hausdorf 2008). It is important to note that all of these were animal studies, and they used focused shockwave which is much more powerful than radial shockwave.
A rare human study by Waugh 2015 used microdialysis (catheters sampling the peritendinoous environment in vivo) and found increased Il-6 and IL-8 production using radial shockwave. This suggests that even radial shockwave may have some cellular stimulatory effects. Whether this explains the pain effect or is simply a by-product of shockwave is not known.
It is very possible that other mechanisms are at play….
Shockwave is painful, often very painful. This may activate inhibitory pain pathways, in the same as other interventions such as acupuncture. This is often referred to as diffuse noxious inhibitory control or conditioned pain modulation (read about it here). Shockwave is less effective when local anaesthetic is applied during treatment (Klonschinski 2011) to make it more comfortable, which supports this potential mechanism.
The last potential mechanism, certainly not the least, is placebo. As will be discussed below many studies show no benefit over a sham/placebo shockwave machine. There is a buzz about shockwave; patients travel long distances for it, experts (sometimes in white coats) use it, not many people have a machine, etc, etc. The anticipation and expectation build to a crescendo. Many patients hold the belief that a painful intervention will do them good – most likely they have been conditioned to believe this by us clinicians! The patients often say ‘I am happy to sit through the pain if it will do me good’. I have noticed these patients often have a better shockwave outcome, compared to the ones that are fearful/anxious, even though you have explained what they will feel and the likely benefits.
Is it harmful?
This is obviously an important question. We would definitely think twice about using shockwave if there is a chance it could be harmful. Bosch 2009 found that focused shockwave (the more powerful one) applied to ponies did actually damage tendon matrix at 3 and six weeks. Radial shockwave disperses energy so by the time it gets to the tendon it is much less likely to cause tissue damage.
Is it effective?
I use shockwave everyday in clinical practice and if you asked me that question, based on my experience with using it, I would say it has a short term effect on pain and can be a very useful adjunct to exercise. If you look at the evidence, it is very fair to say it is mixed. In a nutshell, good quality studies with adequate placebo control do not always show shockwave performs any better than sham/control. The best evidence for effectiveness of shockwave is in plantar heel pain. These recent lower limb reviews (Mani-Babi 2015 and Aqil 2013) are worth reading.
Who are the best patients to use it on?
Maybe we should avoid shockwave for ‘irritable’ pain, that is pain that flares a lot after activities that involve high load for the tendon e.g. running. There are two assumptions here - a) irritable pain is partly causes by biochemical released by overactive tenocytes, and the stimulatory effects of shockwave (recall the Waugh study above) may make this worse. So clear cases of a recent major flare of pain following a significant increase in load may not be the best time to be ‘hammering’ the tendon with shockwave therapy.
Assumption b) is that the tenocyte proliferation is always the cause of irritable tendon pain. As discussed in last weeks blogs, there may be significant central modulation even when someone presents with what is considered ‘typical’ tendon pain. These people may have great benefit from shockwave, it may be via placebo or other mechanisms, but who cares. So again, keep an open mind regarding irritable ‘tendon’ pain and the mechanisms.
How to best apply shockwave?
There is debate about this. I believe that we are mainly modulating pain, and therefore pain should be our guide. The radial shockwave settings allow you to change pressure (intensity) and frequency. 10 Hz frequency is standard. Increasing power to allow some pain, but within what the patient feels is ‘tolerable’, is a good guide. The key for me is 1) the patients must understand and buy into what you are doing – ie is comfortable; 2) reassess pain during and after the shockwave session with load tests (e.g. hopping in an Achilles patient). If pain on load tests is not immediately and dramatically reduced by shockwave, I would be less likely to offer a follow up session.
In some shockwave studies people are told to refrain from activity, sometimes for weeks, to allow the shockwave to work its tissue magic! This makes no sense to me, particularly given tissue effects that contribute to clinical benefit are really unclear. Harnessing the window of painfree period seems sensible. Many of my patients are running or playing sport during shockwave treatment. Rest is often a bad strategy, and it is not different with shockwave treatment.
Take home messages
1. There is some evidence it is useful
2. It is NOT a miracle cure
3. Mechanisms are unclear and likely involve pain modulation and placebo
4. Tissue effects are unclear,especiallyhow they relate to clinical benefit
5. Radial shockwave is unlikely to cause damage to the matrix
6. Shockwave is an adjunct to GOOD management – ie exercise, education, activity modification, etc, etc
Clinical gems and awesome management models. Your patients will love you for it!