Metatarsalgia
A generalized term for pain or irritation in the ball of the foot especially at the base of the toes around the 'knuckles'.
Breaking it down into its components:
The metatarsals are the long bones in the foot that run from about the midpoint of the arch up to the base of the toes. There are five of them in each foot, one for each toe. The ends of these bones are a little knobby and larger than the shafts that make up the majority of the length, quite a lot like a typical cartoon bone. These thicker ends are called the metatarsal heads and are where a lot of issues tend to congregate.
The metatarsal shafts are highlighted in red, the metatarsal heads are highlighted in blue.
‘Algia’ is a common medical suffix that gets slapped onto a word. It means painful, irritation, or just not feeling so great.
Putting them together we get metatarsalgia. Pain in the metatarsals, particularly out at the heads by the base of the toes.
Metatarsalgia isn't descriptive of why that area hurts. There can be a couple of underlying causes.
A big one, is that everyone has fat pads underneath their heels and under the balls of their foot. These pads act like the tabs that you would use on the leg of a chair to stop it from scraping against a hard floor. They do the same thing in our feet, preventing the heads of the metatarsals from clacking uncomfortably against the floor. As we get older or use our feet more and more these pads can get worn down or shift out of place, exposing our metatarsal heads to the ground without any padding. And that can hurt, especially when walking or standing barefoot.
Second is the way that the heads of the metatarsals line up next to each other. Usually while unloaded they form a bit of an arch, with the middle three heads kind of elevated up away from the ground. This is called the transverse arch of the foot. I tend of think of this as a transient arch as it pretty much flattens out upon weight bearing, but that is an aside. Sometimes one or more of the heads of the metatarsals will sit lower than the others. It drops down out of line and ends up taking more of the body’s weight as a result. This excess pressure can start to hurt after a while.
Similar to the point above is that some metatarsals are longer than others. One of the bones may be notably longer than the others; this is especially common with the second bone from the inside, so common in fact that a foot that presents with a really long second metatarsal has a fancy name: Morton's foot. When you progress over your foot while walking (going up onto your toes just as your opposite heel first hits the ground) a long metatarsal will end up taking on extra weight. It sticks out more, so it gets hammered more.
Finally, the joints themselves at the base of the toes may be irritated for a whole host of reasons. Tightened or torn soft tissue, osteoarthritic roughening of the joint surfaces, rheumatoid irritation of the joint capsule, a ton of things can make motion at these joints painful.
So, what can a pedorthist do to help?
A lack of padding under the ball of the foot can be fixed with the simple act of putting some padding under there, either with an orthotic or with a cushioned shoe.
A metatarsal pad can be installed on custom orthotics, insoles, or into the shoes themselves. This pad is shaped kind of like a pyramid or teardrop. It doesn't sit directly under the metatarsal heads, rather a bit further back under the shafts. It acts to lift up on the shafts at a non-painful point and take some pressure off the tips of the bones where they have been overloaded.
The area where a metatarsal pad tends to sit is highlighted in red. Note how it is not placed directly under the the heads of the metatarsals. Typically we want to move pressure away from the metatarsal heads and the shafts of those bones are a often an ideal place to put it.
Rocker bottomed shoes can help minimize the amount that painful joints must move during walking. There are two components to rocker toed shoes:
1) They must be stiff and sturdy through the sole up front by the ball of the foot
2) When you push down on the toe you want it to smoothly roll up onto the toe tip like it's an old rocking chair
This will keep the joints at the base of the toes from having to flex too much by instead having the forefoot stay more static while the entire shoe kind of rotates through the motion instead. It essentially does away with that 'break point' in the shoes where they want to flex a lot right where the ball of the foot is located. That flex point can irritate certain types of metatarsalgia.
