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The fifth metatarsal bone is a bone in the foot that aligns with the fifth toe, also known as the pinky or little toe. It is one of five bones spanning the midfoot between the tarsus, a cluster of bones in front of the heel bone, and the phalanges, which are the bones of the toes. Multiple soft tissues span or attach to this bone, among them the peroneus brevis and tertius muscles, the abductor digiti minimi muscle, the flexor digiti minimi brevis muscle, and the plantar aponeurosis, better known as the plantar fascia. One common injury to the fifth metatarsal bone is a Jones fracture. Plantar fasciitis of the aponeurosis spanning the fifth metatarsal may also afflict this region of the foot.
Palpable along the outer aspect of the foot, the fifth metatarsal bone extends from the base of the pinky toe to approximately midway up the foot. On its far end, it joins with the fifth proximal phalanx, the nearer of two phalanx bones in the toe. The near end of the fifth metatarsal bone connects to two bones: the fourth metatarsal alongside it, and the cuboid bone of the tarsus behind it. While its far end is rounded and convex, its near end features both rounded surfaces and a couple of concave facets where it meets with the fourth metatarsal and cuboid bones.
Attaching to various points along the surface of the fifth metatarsal bone are several muscles, tendons, or other tissues. The peroneus brevis and peroneus tertius muscles, found along the lateral side of the lower leg, send tendons into the outer aspect of the foot that insert along the lateral and dorsal sides of the base of the metatarsal. On the underside of the bone, the tendon of another muscle of the foot, the abductor digiti minimi, crosses the bone’s plantar surface en route to the little toe. Alongside that, the flexor digiti minimi brevis muscle originates near the base of the metatarsal before also extending toward the toe.
An offshoot of the plantar aponeurosis, a layer of connective tissue that covers much of the underside of the foot and supports the arch, attaches to the fifth metatarsal bone as well. Originating on the calcaneus or heel bone, the plantar aponeurosis extends forward into the arch of the foot before dividing into five sections — one for each toe. The fifth section runs along the dorsal aspect of the metatarsal and inserts at the head of the bone just beneath the pinky toe. Inflammation of this tissue as a consequence of overuse is known as plantar fasciitis, a condition that is often felt as pain in the arch. Certain populations, however, may feel this inflammation along the outside of the foot in the fifth section, as well, such as dancers who frequently exhaust the muscles in this part of the foot.
Another injury common in dancers and afflicting the fifth metatarsal bone directly is a Jones fracture. Repeated stress on the outside of the foot can lead to this injury, characterized by a bone break afflicting the near end of the bone toward the arch of the foot. This type of break tends to occur as a result of frequent stress over time rather than a blow or impact on the foot.