Overload of Metatarsal Heads
Each toes sits on the end of a long metatarsal bone. Each metatarsal ends in a drumstick-like expansion called the metatarsal head. The row of metatarsal heads forms the ball of the forefoot. The skin and fat below the metatarsal heads is highly specialised to withstand the pressure and friction of the ground. The ball of the big toe normally takes a large portion of the pressure. If it takes less (such as with bunions or arthritis), the pressure is passed over to the ball of the lesser toes
If any of the metatarsal heads begins to press down on the ground too hard, a callosity or corn will develop below those metatarsal heads. If the pressure worsens, the tissue becomes inflamed and sore. This is one type of metatarsalgia and can feel like walking on a stone or pebble. With deterioration, the joint at the base of the toe inflames. The whole forefoot can swell and the toe joint loses its shape so that the toe becomes angled or clawed.
Some people have feet vulnerable to this problem because their second and third toes' metatarsals are longer than the big toe's. This is called a Morton's or "grecian" foot. Use of a shoe heel with any height will force the weight onto these long second and third metatarsals, overloading them. Therefore, treatment always involves attention to footwear and often succeeds when pressure is evened out using custom insoles. Tight calf muscles worsen the problem so physiotherapy has an important role here. When these treatments fail, surgery can realign the weight-bearing metatarsal ends (weil's osteotomy, BRT osteotomy), straighten clawed toes (excision arthroplasty of PIP joint) and correct the underlying causes when present (e.g., scarf osteotomy or chevron osteotomy for a bunion).