The pes ancerinus (latin for gooses foot due to its odd shape) is where the tendons of the hamstrings join on to the tibia (on the inside of the knee at the top of the shin bone). The tendons, or more commonly an underlying bursa can become inflamed as part of an overuse type phenomenon in sports people. This condition is actually very common in middle aged and elderly active non - sports people too and is mistaken for arthritis.
You will experience pain on the inner aspect at the top of the shin bone, which develops gradually. In sports people it may be initially felt only during exercise, but as the condition progresses it may become a problem with day to day activities. In non sports people it tends to only become apparent once the pain is present with normal walking around.
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. The first thing to do is to reduce the problem activities. Anti-inflammatories and ice are helpful after exercise.
Treatment involves first confirming the diagnosis then establishing the cause. An ultrasound scan or MRI scan can be useful to exclude other problems. Treatment options may include very specific physiotherapy, or injections. Once you have recovered, good physio should be able to prevent this from coming back.