Peroneal Tendonitis is an rare problem with the tendons on the outside of the rearfoot. The problem in most cases happens in runners in which the strains on these tendons are so higher. There are 2 peroneal muscles on the lateral side of the leg whose tendons pass round the outside of the ankle joint with one tendon attaching on the lateral side of the foot at the bottom of the fifth metatarsal. The other tendon passes under the foot to attach to an region close to the center of the arch of the foot. The peroneal muscles have several different functions, but a major one is to prevent the rearfoot rolling laterally and winding up having a ankle sprain. Because they work hard at that task, the load on the tendons could be too much for the tissue to take and they end up with a peroneal tendonitis.
Commonly the problem starts off with discomfort either over or just below the lateral ankle bone without or with some inflammation. In some the swelling develops later. With continued exercise the symptoms gets more constant and gradually worse. A common feature in those with peroneal tendinopathy is a decreased supination resistance. Because of this it's easy for the ankle to supinate or roll outwards. This makes the peroneal tendons to be really active, so if you then combine it with higher level of sporting activity, then the tendon is at high risk for an injury.
The treating of peroneal tendonitis almost always begins with minimizing the strain by lowering activity levels and the use of shoe wedging or foot inserts to pronate or tip the foot inwards so the muscle does not have to work as hard. Ice and anti-inflammatory drugs could also help decrease the pain and swelling. Over the medium to long term raising stress by the way of exercise ought to be put on the tendon so that it can get accustomed to the strains placed on it. In a few situations, surgery is indicated.