Metatarsals are a group of five long bones found in the human foot, located between the tarsal bones of the midfoot and the phalanges of the toes. These bones form the framework of the forefoot and provide structural support during activities such as walking, running, and standing. Each metatarsal bone is named and numbered from the medial (inner) side of the foot to the lateral (outer) side, corresponding to the five toes.[2]
Location
The metatarsals are located in the foot, specifically between the tarsal bones of the midfoot and the phalanges of the toes. They extend from the arch of the foot to the base of the toes.
Structure and Anatomy
The metatarsals are five elongated bones numbered from medial to lateral, corresponding to the first (big toe) through fifth (little toe). Each metatarsal consists of three main parts: the base, the shaft (body), and the head. These bones contribute to the longitudinal and transverse arches of the foot, aiding in weight distribution.
Individual Metatarsals
1. First Metatarsal
- Size and Shape: The first metatarsal is the shortest but the thickest and strongest of all metatarsals.
- Base: Broad and articulates with the medial cuneiform bone.[3]
- Head: Bears two sesamoid bones on its plantar surface, which help reduce friction and enhance leverage during movement.
- Shaft: Robust, cylindrical, and slightly concave on its dorsal surface.
2. Second Metatarsal
- Size and Shape: The longest of the metatarsals, it is slender and narrower.
- Base: Articulates with all three cuneiform bones, providing stability to the foot.
- Head: Articulates with the proximal phalanx of the second toe.
- Shaft: Thin and tapers slightly as it progresses distally.
3. Third Metatarsal
- Size and Shape: Similar in structure to the second metatarsal but slightly shorter.
- Base: Articulates with the lateral cuneiform bone.[5]
- Head: Connects with the proximal phalanx of the third toe.
- Shaft: Cylindrical and smooth.
4. Fourth Metatarsal
- Size and Shape: Intermediate in length and size between the third and fifth metatarsals.
- Base: Articulates with the cuboid bone and partially with the lateral cuneiform.
- Head: Links with the proximal phalanx of the fourth toe.
- Shaft: Slender and slightly curved.
5. Fifth Metatarsal
- Size and Shape: The most lateral and distinctive due to the prominent tuberosity at its base.
- Base: Articulates with the cuboid bone and provides attachment for the peroneus brevis tendon.
- Head: Connects with the proximal phalanx of the little toe.
- Shaft: Thin and tapered distally.
Articulations
- Proximally: Each metatarsal articulates with tarsal bones.
- First metatarsal with the medial cuneiform.
- Second metatarsal with all three cuneiforms.
- Third metatarsal with the lateral cuneiform.
- Fourth and fifth metatarsals with the cuboid.
- Distally: The heads of the metatarsals articulate with the proximal phalanges of the toes, forming metatarsophalangeal joints.[7]
- Intermetatarsal Articulations: The bases of adjacent metatarsals articulate with each other, stabilized by interosseous ligaments.
Shaft Anatomy
- The shaft of each metatarsal is slightly concave on the plantar surface and convex dorsally. This design aids in forming the longitudinal arch of the foot.
- The plantar surface is rough, providing attachment points for ligaments and muscles.
Vascular Supply
The metatarsals receive blood from branches of the dorsalis pedis and posterior tibial arteries.[8] Nutrient foramina are typically located on the dorsal aspect near the shafts, allowing vascular penetration.
Muscular and Ligamentous Attachments
- Various intrinsic and extrinsic muscles attach to the metatarsals, such as the dorsal and plantar interossei, lumbricals, and the tendons of muscles like tibialis anterior, peroneus longus, and flexor digitorum brevis.
- Ligaments like the plantar ligaments and intermetatarsal ligaments also stabilize the metatarsal bones.
Functions of the Metatarsals
Support and Weight Distribution
The metatarsals play a key role in supporting the body’s weight during standing, walking, and running. They help distribute the weight evenly across the foot, ensuring balance and stability.
Arch Formation
Metatarsals contribute to the formation of both the longitudinal arch and the transverse arch of the foot. These arches act as shock absorbers, reducing stress on the foot and lower limbs during movement.
Facilitation of Movement
The articulation of the metatarsals with the proximal phalanges forms the metatarsophalangeal joints, which enable toe flexion and extension.[1] These movements are essential for activities like walking, running, and jumping.
Force Transmission
The metatarsals transmit forces generated during push-off phases of walking and running from the posterior part of the foot to the toes.
Attachment for Muscles and Ligaments
The metatarsals serve as attachment points for muscles and ligaments that control toe movements and stabilize the foot.[4] These attachments are critical for fine motor control and maintaining foot posture.
Adaptation to Uneven Surfaces
The flexible arrangement of the metatarsals allows the foot to adapt to uneven terrain, maintaining balance and grip during dynamic movements.
Clinical Significance
The metatarsals are prone to various injuries and conditions due to their role in weight-bearing and movement.
- Fractures:
- Stress Fractures: Common in athletes and individuals with repetitive foot stress. The second and third metatarsals are most vulnerable.
- Traumatic Fractures: Result from direct trauma, often affecting the fifth metatarsal’s tuberosity (Jones fracture).
- Metatarsalgia:
- Pain and inflammation in the metatarsal region, often caused by overuse, ill-fitting footwear, or abnormal foot mechanics.
- Bunion (Hallux Valgus):
- Deformity of the first metatarsal, leading to a prominent bump near the base of the big toe.
- Arthritis:
- Degeneration of the metatarsophalangeal joints can lead to stiffness, pain, and reduced mobility.
- Diabetic Foot Ulcers:
- Increased pressure under the metatarsal heads in diabetics can result in ulcer formation, requiring careful management.[6]
- Morton’s Neuroma:
- A painful condition involving nerve compression between the third and fourth metatarsals, often due to tight footwear or high-impact activities.