CHAPTER 38: Foot

JOINTS OF THE DIGITS AND FASCIA OF THE FOOT

BIG PICTURE

The foot is connected to the leg by the ankle (talocrural) joint, which is an articulation between the tibia, fibula, and talus. The foot consists of 7 tarsal bones, 5 metatarsal bones, and 14 phalanges. Motion at the digits for abduction and adduction is defined by an imaginary line along the long axis of the second digit, unlike the hand in which the long axis runs along the third digit. Each digit, with the exception of the great toe, consists of three phalanges (proximal, middle, and distal); the great toe has two phalanges (proximal and distal). The articulations between the bones of the foot create multiple joints. The intrinsic muscles of the foot originate and insert on bones of the foot.

BONES OF THE FOOT

The bones of the foot are as follows (Figure 38-1A):

• Seven tarsal bones. Form the bones of the ankle:

  • Talus. Forms the tibiotalar joint (dorsi and plantar flexion) with the tibia and transmits forces from the tibia to the calcaneus.

  • Calcaneus. The heel bone; possesses attachment with the Achilles (calcaneal) tendon.

  • Navicular. Shaped like a boat.

  • Medial, intermediate, and lateral cuneiform bones. Wedge-shaped bones that help form the transverse arch of the foot.

  • Cuboid. Shaped like a cube; most lateral and distal of the tarsal bones.

• Five metatarsal bones. Forms the bones of the sole of the foot; each of the five metatarsal bones are related to one digit. For example, metatarsal 1 to the great toe and metatarsal 5 to the little toe.

• Fourteen phalanges. Form the bones of the digits:

  • Digit 1 (great toe; hallux). Possesses two digits (a proximal and a distal).

  • Digits 2 to 5 (the lesser toes). Possesses three digits (proximal, middle, and distal).

JOINTS OF THE DIGITS

The several bony articulations within the foot assist in accommodating uneven surfaces during weight-bearing activities. These motions of the foot are accomplished via the following joints (Figure 38-1B):

• Metatarsophalangeal (MTP) joints. Articulations between the metatarsals and the proximal phalanges. The metatarsophalangeal joints allow flexion and extension and abduction and adduction.

• Interphalangeal (IP) joints. Articulations between the phalanges, which allow for flexion and extension.

  • Proximal interphalangeal (PIP) joints. Occur between the proximal and middle phalanges for digits 2 to 5.

  • Distal interphalangeal (DIP) joints. Occur between the middle and distal phalanges for digits 2 to 5.

  • The great toe (digit 1). Has only a proximal and distal phalange and therefore the joint is simply referred to as the IP joint.

FASCIAL STRUCTURES OF THE FOOT