Abscesses of the sole of the foot are usually caused by infected punctured wounds, or by the extension of infection from wounds of the toes, etc.

The plantar fascia lies on the flexor brevis digitorum while the long flexor tendons lie beneath it. A punctured wound may perforate the plantar fascia and penetrate the flexor brevis which arises from its under surface, yet if this muscle is not entirely traversed by the wound the tendons of the long flexors beneath escape infection and the pus accumulates beneath the plantar fascia.

Superficial Plantar Abscess

In the superficial form of plantar abscess the pus tends to point in four directions: (1) it may come directly up through gaps between the fibres of the plantar fascia and make an hour-glass abscess, a small amount of pus being above the plantar fascia, between it and the skin, while a larger collection is beneath the fascia in the substance of the muscle; (2) it may burrow its way forward showing between the tendons in the direction of the webs of the toes; (3) it may appear in the groove on the outer side of the foot between the flexor brevis and abductor minimi digiti; (4) it may appear on the inner side of the foot between the abductor hallucis and flexor brevis (Fig. 594).

Deep Plantar Abscess

Indeep infection the pus accumulates around the deep flexor tendons and beneath the flexor brevis muscle. Its greatest tendency is to extend up the leg by following the flexor tendons behind the internal malleolus. It may also show itself in the grooves on either side of the flexor brevis, or between the tendons at the webs of the toes.

Incision Of Plantar Abscess

The safest way to open these abscesses is by the method of Hilton. The skin is first incised and the abscess opened by inserting a pointed haemostatic forceps and opening its blades, or using some similar blunt instrument. This is done to avoid wounding the arteries. If necessary the whole thickness of the foot may be traversed by this means and a drainage-tube passed through from one side to the other.

Fig. 594.   Diagram showing the points of exit of suppuration beneath the plantar fascia.

Fig. 594. - Diagram showing the points of exit of suppuration beneath the plantar fascia.

Incisions should not be made over bony points where they would be subjected to pressure. Hence the heads of the metatarsal bones and the prominent outer edge of the foot are avoided. Incisions in the hollow of the foot and between the forward ends of the metatarsal bones are to be preferred. In opening a subcutaneous collection one should not be satisfied with simply incising the skin, but the fascia should be widely split to guard against a larger collection of pus beneath.

Collections which present to the outer side of the flexor brevis are to be opened a little distance behind the base of the fifth metatarsal bone because the external plantar artery becomes somewhat superficial at its inner side.