I recommend a full session all over your hands and or feet because other areas might be indirectly involved in helping a particular problem. There are so many interactions among different organs, etc. There are so many natural and necessary chemical reactions in the body. Perhaps some gland affects digestion. This would then affect the supply of nutrition via the blood stream to help the area of concern.
The shoulders can reflex to the hips. Some areas are famous for reflexing back and forth to each other, like the wrists to ankles and the ankles to the wrists; the elbows to knees and the knees to the elbows; and the hips to the shoulders and the shoulders to the hips. This is so both with massage directly on the joint or working with reflexology from the reflex areas.
The spine can help the various organs, the hips and shoulders, etc.
Nerves of the spine go out laterally to assist other parts of the body.
Complementary areas are worked by reflexology to indirectly help the area of immediate concern.
Just don't work directly on a wound on the hands or feet.