This refers to inflammation in the peroneus longus and brevis tendons that run behind the lateral malleolus (the bony lump on the outside of the ankle) and are responsible for flexing and everting the foot and ankle and stabilizing the ankle. Peroneal tendonitis is usually an overuse injury.
You will experience pain at the bottom of the lateral malleolus and along the outside edge of the foot. It usually starts gradually and may initially only be painful after exercise (often the following morning). As the condition gets worse the symptoms become more intrusive and may start to interfere with sport and cause pain with day to day activities. You may notice swelling in the tendon at the bottom of the malleolus.
If you think you have this condition it is well worth getting it checked out by Mr Willis-Owen. In the mean time you should avoid any aggravating activities which may prolong the problem. It generally won't get better on its own. Anti-inflammatories and ice are helpful after exercise.
Treatment involves first confirming the diagnosis then establishing the cause. An MRI scan or an ultrasound scan can be useful to exclude other problems and confirm the diagnosis. Treatment options may include specific physiotherapy, orthotics, and injections. Once you are recovered it is important to address any biomechanical problems or other underlying factors in order to prevent recurrence.