Exostosis

What is exostosis?

Exostosis is a localized bone growth developed at the expense of the head of the first metatarsal on its medial side. It appears as a prominent bony protrusion under the skin. Although the exostosis may seem large, it is generally a slight thickening of the bone but causes inflammation and therefore a thickening of the tissues located at its level.

Foot exostosis

Foot exostosis, or bugnon, can develop spontaneously, especially in cases of a broad metatarsal head. A wide forefoot can be squeezed into a narrow shoe or one with stiff leather; this compression encourages a bone reaction with thickening and contributes to the formation of the exostosis. The exostosis may occur in isolation, as part of a hallux valgus, a hallux rigidus, big toe osteoarthritis, or even be mistaken for other bony deformities of the foot like the humped tarsus.

How is it diagnosed?

The diagnosis is clinical; the deformation of the medial border of the forefoot is visible to patients.

• In the case of excessive pressure or rubbing in a shoe where the forefoot is too tight, there may be a bursitis corresponding to an inflammatory red patch in the area of friction.
• If there is significant deformation of the forefoot or a prominent exostosis, the bursitis can become quite severe and form a blister of varying size.
• With bursitis, inflammation can lead to irritation of the adjacent sensory nerve and cause neuropathic pain like electric shocks radiating up and down the big toe.

In the context of hallux valgus, the exostosis is part of the characteristic deformity of the big toe. In hallux rigidus, the exostosis is part of a more global thickening of the metatarsophalangeal joint of the big toe, with the presence of osteophytes, or intra-articular bony blocks due to osteoarthritis.

How is it treated?

The first step in treatment is to adapt the footwear to the morphology of the forefoot. In cases of exostosis, the forefeet are relatively wide and may cause shoe-fitting problems. Some shoe brands offer several forefoot widths for the same shoe size. Certain German or Spanish shoe brands may offer up to 3 widths for the same size: Small, Medium, Large.

Medical treatment can help relieve pain, notably through analgesics and anti-inflammatories. However, to be effective, footwear adaptation is necessary beforehand or at the same time.

If pain persists despite medical treatment and footwear adaptation, surgical treatment can be performed; this is called an exostosectomy.

Exostosis surgery

Isolated exostosis surgery is quite rare; exostosectomy is usually part of the surgical treatment for hallux valgus, along with bone correction of the first metatarsal at the same time. When an isolated exostosectomy is performed for a mild hallux valgus, it is possible to see progressive secondary worsening of the deformity into hallux valgus postoperatively.

Resection of the exostosis, or bugnon, called bugnonectomy, is performed under regional anesthesia, with a tourniquet at the ankle, as an outpatient procedure.

The surgical procedure consists of incising the skin and the medial capsuloligamentous structure to expose the exostosis. The exostosis is then removed, and the capsuloligamentous structure is repaired.

A dressing needs to be applied in the operating room to support the repair of the capsule and the medial collateral ligament, to avoid postoperative loosening and the risk of developing a hallux valgus. The dressing is generally kept in place for three weeks, and walking is protected for a month with a postoperative shoe.