Peroneal tendonitis is not exactly a very common running injury, but it is something I did not use to like seeing as the management always seemed to be difficult; but now I don’t mind as we have learnt more about it and it is really not that difficult to manage. There is also not much, if any, specific research, to guide the understanding of it, except what I have done (and unfortunately not published yet!).
The two peroneal muscles on the outside of the leg have a number of functions. The tendonitis of them usually starts of as an ache just above and/or below the lateral malleolus that gets progressively worse with activity. There may be some swelling.
What Causes Peroneal Tendonitis?
As with any overuse injury the cause is the cumulative load in the tissue is beyond what the tissue can take. This means that there are either/or a combination of activity levels (intensity and/or duration) and/or biomechanical factors that increase the load in the tendons. One of those on their own may not be enough to predispose to the problem, but a combination of both may be enough. To determine the biomechanical factors that may be predisposing them, the thought process to inform the clinical decision making is to consider the function of the muscles that attach to the tendons, specifically in the terms of what joint moments they provide and if there is anything in the biomechanics and gait that is increasing those joint moments (and also importantly, what can be done to reduce those joint moments as part of the management). The peroneal muscles also provide other moments at more distal joints, but will stay away from that to keep it simpler to understand for now.
What biomechanical factors can increase the load in the peroneal tendons? As these tendons provide a plantarflexion moment at the ankle joint (they pass posteriorly to the ankle joint axis), midfoot or forefoot striking is going to increase the load more than heel striking would when running. They also provide an eversion moment at the subtalar joint axis (they pass laterally to the subtalar joint axis), so anything that increases the eversion moment is going to increase the activity of the peroneal muscles and hence the load going through the tendon(s).
The research we did on this was to use the device to measure the force to supinate the foot. I recruited 13 cases of obvious peroneal tendonitis, which took 2 years to find (which indicates just how uncommon this is). The force to supinate these people using our device was a mean of 91 Newtons; whereas the reference group was 138 Newtons. This means that the foot was really easy to supinate in those with peroneal tendonitis, which means that the peroneal muscles are going to be very active trying to counter that. Combine this increased muscle activity with a higher sports activity levels, then this is probably putting the tendon at risk for injury.
What does this mean for the management?
As with any overuse injury the approach is 3-fold:
1. Reduce the load in the damaged tissues: You do this in three ways: One is to reduce the level of activity (intensity and duration) to sensible levels until improved and then extremely slowly progressively increase back up to previous levels of activity. Two is to reduce the joint moments that the muscles provide via the tendons. From the above discussion, we need to reduce the plantarflexion and eversion moments at the rearfoot – you do that by heel striking, (if currently a midfoot or forefoot striker) to reduce the plantarflexion moment and add a lateral wedge under the heel or whole foot to reduce the eversion moment (which you also need to be heel striking for the wedge to work). Minimalism and midfoot or forefoot striking probably increase the risk for peroneal tendonitis (they decrease the risk for other injuries). As to if the heel striking and the lateral wedge are medium to long term interventions will depend on the magnitude of the force that is causing the high joint moments and if the tissues can be adapted to that load (see 2, below). Three is to possibly the use strapping to hold the foot in a more everted position as a very short term measure, but I remained unconvinced it is very effective.
2. Increase the ability of the tissues to take the load: Like with any tendinopthy this is the slow progressive adaption to increasing loads and eccentric muscle activity. Often this is plantarflexion and eversion against resistance. The exact nature of the intervention will depend on the staging of the tendinopathy. This is more of a medium to long term intervention compared to (1) which is more of a short to medium term intervention.
3. Help the tissues heal: I won’t say much here, but this is the usual array of interventions of varying effectiveness that are more aimed at helping the damaged tissues heal rather than reduce the load and increase the ability of the tissues to take the load. This includes things like ICE, NSAID’s, massage, electrotherapeutic modalities etc. In more sever long standing cases, surgical debridement or repair of the damaged tissues may be needed.
What about the strengthening exercises you often see mentioned for this? I am not convinced as I do not see how increasing the strength of the peroneal muscles will help reduce the load or increase the ability of the tendon to take load. I can see how eccentric activity of the muscles will probably help the tendon adapt to the loads, but that is not really dependent on just how strong the muscles are. I actually think that the peroneal muscles in those with peroneal tendonitis are actually quite strong! Paradoxically, if you do inversion and eversion muscle strength testing in those with it, the eversion strength generally feels quite weak; ie the peroneals appear weaker, but are they? We previously showed that about of the third of the variability in the force to supinate the foot is explained by variations in the transverse plane orientation of the clinically palpated putative subtalar joint axis. This means when the force to supinate the foot is low (as it is in those with peroneal tendonitis), the subtalar joint axis is orientated more laterally. This means the peroneal tendons have a relatively short lever arm to the joint axis to evert the foot, so are they really weak or do they just appear weaker due to the short lever arm that they have? It could be that because of that short lever arm the muscle is very strong as it has to work so hard to overcome the short lever arm and the low force needed to supinate the foot (and hence the tendonitis).
I mentioned at the start that I used to not like seeing this condition as it never seemed to respond very well to treatment. In our unpublished study I mentioned above, we also looked at the Foot Posture Index (FPI-8) as a measure of foot alignment; the mean in those with peroneal tendonitis was 5.6; 0-4 is generally considered normal and anything above 4 is pronated (above 10 is pronated a lot); so on average those with peroneal tendonitis have a slightly pronated foot and we all know that overpronation was evil and had to be eliminated at all costs, so what did I use to do to treat it? … when in reality, I needed to be doing the opposite and pronate the foot more. This is a perfect example of thinking more about forces and joint moments and reducing the load in the damaged tissue versus thinking about foot posture and foot alignment and trying to move that to a hypothetical normal. Now I like seeing it, as thinking that way makes it easier to treat.
As always, I go where the evidence takes me until convinced otherwise.