There are many different causes of lumps and bumps on the inside of the foot. Starting from the big toe and working back to the heel:
A swelling along the margin of the big toenail is likely to be due to the formation of an ingrown toenail. At times this swelling can produce open, weeping flesh. Treatment consists of removing the ingrown toenail (See treatment for ingrown toenails).
A swelling often associated with a hard, callused area may form on the side of the big toe. This is due to an enlargement of the bone in this area. It is usually associated with a deviation at the joint in the big toe. Treatment consists of using a functional foot orthotic to redirect the pressure from the area. Surgical removal of the underlying bony prominence or surgical straightening of the toe may be recommended. People who have diabetes must watch this area because over time the excessive pressure to the area from walking can cause the skin beneath the callused area to break down forming an ulceration that can become infected. Left untreated, the bone can become infected and in severe cases amputation of the toe may be necessary.
Another area on the big toe, which can demonstrate a lump or bump, is the top outside portion of the toe at the level of the joint in the toe. This is usually seen in association with a contracture of the big toe making the joint more prominent. This prominence can become irritated due to shoe pressure. The condition is called a Hallux hammertoe. The word Hallux is the medical term for the big toe. If the deformity is flexible and the toe can be manually straightened, the condition can be corrected by a simple surgery that releases the tendon in the bottom of the toe. If the condition is rigid and the toe cannot be manually straightened, then a fusion of the joint may be necessary (See surgical correction of hallux hammertoe). Treatment should also include determining what caused the condition. Quite often it is due to some underlying functional problem in the foot and treatment of this condition with a functional foot orthotic should be considered. Other causes of a hallux hammertoe are previous surgery in the area, nerve damage or a neurological condition.
A painful lump may also be found on the bottom of the big toe. This condition often presents as a hard callused area. Sometimes a hard lump may be felt beneath the callused area. The most common cause of this condition is a limitation of movement at the big toe joint while walking. If there is limitation of movement at this joint, then the big toe cannot bend upward as the heel comes off the ground while walking. As a consequence, there is excessive force placed on the bottom of the big toe and an enlargement of the bone in this area will occur secondary to the pressure. Another cause is the presence of an extra bone or piece of cartilage in the area. However, it is the limitation of movement in the big toe joint that causes the area to become enlarged and painful. People who have diabetes must watch these areas closely. Over time, the excessive pressure can cause this area to break down and ulcerate. As in the previous condition this can lead to infection and possible amputation. One way to check to see if there is a limitation of movement of the big toe joint is to perform the following test. While standing on a flat surface have another person try to bend the big toe upward. The joint that must move is the joint where the toe attaches to the foot. There is a joint in the middle of the big toe and this is not the one you are checking. If the big toe joint cannot be bent upward then a limitation of motion exists. Testing the movement at the joint without putting weight on the foot will give a false impression as to the available movement at the joint while you are walking. The limitation of movement of the big toe while walking can, over time create an arthritic condition in the joint. A bony mass may then form on the top of this joint as a result of jamming in the joint. This condition is called hallux limitus or hallux rigidus. Treatment for the painful lesion in the bottom of the big toe joint consists of using functional foot orthosis to correct the functional limitation of the big toe joint motion or may consist of surgical correction of the hallux limitus. Rarely is surgery to remove only the lesion on the bottom of the toe alone successful, because the cause of the initial problem still exists.
Yet another area of bony prominence about the big toe joint is on the outside of the joint. The most common cause of this condition is called hallux abductovalgus or bunion. This is a common condition associated with deviation of the big toe towards the second toe. Treatment consists of padding the area to reduce shoe pressure, bigger shoes, orthotics and surgery (See surgical correction of bunion deformity). A sudden onset of pain in the area with or without a bunion may be due to gout. Gout is a metabolic condition that results in an elevation of the uric acid in the blood stream. Once the uric acid level reaches a certain point it will crystallize and leave the blood stream and deposit itself in a joint or other soft tissue location. Gout rarely occurs in women until after menopause or if they have had a hysterectomy. A sudden onset of pain in this area in women is usually associated with the formation of a bursa secondary to wearing a tight shoe. Treatment consists of wearing looser fitting shoes and taking an oral anti-inflammatory medication. Occasionally, a cortisone injection may be advised.
Moving back towards the heel, another area of a common lump or bump is just in front of the weight-bearing portion of the heel. This prominence is usually a hard bony mass that protrudes outward. It is due to a bony enlargement of the Navicular bone. Some people have a natural enlargement in this area while other people have an extra bone in this area. This condition is often referred to as Os Navicularis. This condition is often associated with a flat foot deformity. A very powerful tendon from a muscle in the leg called the posterior tibial tendon partially attaches into this area. If the navicular bone is naturally enlarged or there is a second bone present then the tendon dose not function properly and cannot support the arch of the foot adequately. Over time, this will cause a weakening of the tendon causing an entire collapse of the arch of the foot. This condition called Posterior Tibial Tendon Dysfunction is a very serious condition that should be treated promptly and aggressively. The bony prominence of the navicular bone may cause secondary pressure in shoes resulting in pain. Treatment of the prominence of the navicular bone consists of padding to reduce shoe pressure, functional foot orthosis to treat the associated flat foot deformity and the possible onset of posterior tibial tendon dysfunction, or surgery. Following any surgical intervention in this area, the patient should be placed in a functional foot orthosis. The surgical removal of the bony prominence does not correct a flat foot or prevent the occurrence of posterior tibial tendon dysfunction.