Peroneal tendonitis is something that that I just used to hate seeing in clinical practice. It’s not a common problem, but my I got the impression that my success rate in treating it seemed to be about 100% failure! Peroneal tendonitis is an overuse injury of the peroneal tendons. It tends to start out as an ache just above or below the lateral malleolus. When those with it are standing, the tendons seem to be very prominent.
As part of the research I was working on we looked at the Foot Posture Index (FPI) (more) and Supination Resistance in a cohort of people with peroneal tendonitis (it took a while to find enough!). The mean Foot Posture Index was 5.6 (+2.7) which indicates that on average they had a moderately pronated foot, so my treatment was to use foot orthotics to deal with that ... then I wondered why they never seemed to be improving.
The startling finding was the supination resistance, this was only 91 (+21) Newtons when the normal or average is around 140N, using the device we used.. This means I could supinate their feet with my little finger. No wonder they got peroneal tendonitis, as the peroneal muscles were having to work so hard as the foot kept wanting to supinate. That was why the tendons were prominent when they were standing - the peroneal muscles were firing when standing in static stance. If they worked that hard during stance, imagine what they were doing during gait!
After the first two subjects in this study (its not published yet), it was clear what was going on. After seeing the these first two subjects, I had a patient clinically with this who had a long history of peroneal tendonitis that had been previously treated by a range of different health professionals and a variety of foot orthotics and other treatments. If I recall correctly her FPI was around 6 or 7, so yes she had a pronated foot. Her supination resistance was as low as it gets. Based on the research resultsat that stage, I took the step of using a lateral wedge in her shoe. When she was standing, her tendons were sticking out and the peroneal muscles were firing. Standing on the lateral wedge, her peroneal tendons disappeared immediately and the muscle were not firing during static stance. For a Podiatrist who had spent most of his professional life treating feet that pronated, it was somewhat traumatic to actually pronate a foot more. She made contact a few days later and years of chronic pain was well on its way to going away!
I got over the psychological trauma of doing it and now comfortabley use lateral wedging on all those with peroneal tendonitis.
I do get often asked about the risk of medial problems from doing that. I respond with the comment that I have never seen any problems develop. The other part of the response is to think in terms of the supination resistance. These people have a very low force that is needed to supinate them, which is why the peroneals are having to work so hard. The posterior tibial muscles does not have to work very hard at all as so little force is needed. If you laterally wedge the rearfoot, the peroneal do not have to work as hard (and the peroneal tendons should get better), but the posterior tibial muscle will have to work harder, but its working at such a low level anyway, that this is not really a problem.
Think forces, not alignment.