Brachymetatarsia is a condition in which one of the long bones of the foot (the metatarsal) is significantly shorter than normal. The metatarsal bones run five in number, from the middle of the foot to each corresponding toe. The metatarsal shortening is usually due to premature closure of the growth plate of that bone, although it can also be linked to a number of genetic diseases as well. Other less common causes could include injury and infection of the bone resulting in a much shorter metatarsal than those around it. The most commonly involved metatarsal is the 4th metatarsal, which is at the base of the toe next to the little toe. It is seen twenty-five times more frequently in women than men.
The main external symptom of this condition is a sunken, short toe, or a toe that appears to 'float' above the others, at the site of the short metatarsal. It usually becomes apparent during adolescence when the full growth of the toes is completed. The toes next to the short toe can dive underneath it, and calluses can form under the ball of the foot on either side of the shortened metatarsal due to its lack of 'pulling its weight when it comes to distributing the pressure of the ground along the skin. This condition is often only a cosmetic one, except when shoes irritate the floating, short toe, and calluses underneath the foot become painful.
Treatment can include the use of deeper shoes to avoid toe irritation or prescription orthotics shoe inserts to help redistribute pressure under the ball of the foot. Surgical lengthening of the bone is a good option to provide permanent correction of this deformity. Since instant lengthening can overstretch short arteries, veins, and nerves and cause tissue death, a gradual lengthening process is employed to safely lengthen the metatarsal. Using a process called callus distraction, a cut is made in the bone and the ends are pulled apart using a device that stays outside of the foot, at a rate just slightly faster than the bone can mend. By pulling apart the mending bone, the calcification of the new elongating bone takes long enough to safely stretch the fragile soft tissue without causing damage. The result of this process is a new, full-length bone that pushes the toe out to proper length.