Forefoot Anatomy: Metatarsals, Phalanges, and Joints

Forefoot Anatomy: Toes and Joints

• The forefoot includes the metatarsals and phalanges (toes).

Metatarsophalangeal (MTP) Joints

• The joint between the metatarsal and proximal phalanx.
• Considered the "knuckle" of the foot.
• Explanation primarily uses the second digit as an example but varies slightly for the hallux (big toe).

Phalanges and Interphalangeal Joints

• Phalanx (singular) refers to an individual bone within the toes.
• Phalanges (plural) refers to multiple toe bones.

Digits Two to Five

• Have three phalanges: proximal, intermediate, and distal.
• Two interphalangeal joints:
  • Proximal Interphalangeal (PIP) Joint: Between the head of the proximal phalanx and the base of the intermediate phalanx.
  • Distal Interphalangeal (DIP) Joint: Between the head of the intermediate phalanx and the base of the distal phalanx.

Hallux (Digit One - Big Toe)

• Has only two phalanges: proximal and distal.
• Only one interphalangeal joint exists; it is simply called the Interphalangeal (IP) Joint.

Joint Movements and Limitations

• MTP joints are condyloid or ellipsoid joints.
  • Allow flexion, extension, abduction, and adduction.

Abduction and Adduction

• Abduction: Movement away from the midline of the foot (splaying toes).
• Adduction: Movement towards the midline of the foot.
• The anteroposterior axis/midline runs down the second digit.
• Abduction and adduction primarily occur at the MTP joints (knuckles).

Limitations of Abduction and Adduction

• Interphalangeal joints (IP, PIP, DIP) are synovial joints, allowing only flexion and extension.
• Factors limiting abduction/adduction at the tarsometatarsal joints:
  • Strong bony sockets deeply position the bases of the metatarsals.
  • Extensive lateral articulation limits side-to-side movement.
  • Deep Transverse Metatarsal Ligament: Connects the metatarsal bones distally, preventing splaying.

Collateral Ligaments

• Present at all toe joints (MTP, PIP, DIP, IP).
• Located on the medial and lateral sides of each joint.
• Provide support, protect the joint, and prevent excessive movements outside the normal planes.

Sesamoid Bones

• Two bony structures located on the plantar aspect (underside) of the foot at the MTP joint of the hallux.
• Support and protect ligaments passing through the toes.

Plantar Plates (or Plantar Ligaments)

• Located on the plantar aspect of each MTP, PIP, DIP, and IP joint.
• Thickened ligamentous structures that:
  • Increase the surface area of the joints.
  • Provide a protective passageway for tendons that plantar flex the toes from the underside of the foot to their distal attachments.

Function of Plantar Plates

• Provide support and structure to the base of the knuckles.
• Protect tendons from being compressed during weight-bearing activities.

Structure and Composition

• Thickened band on the plantar side to withstand weight distribution.
• Dorsal aspect (facing the joint) contains hyaline cartilage to increase articular surface and facilitate smooth movement during flexion and extension.

Clinical Significance

• Damage or inflammation of the plantar plates can cause pain and restrict tendon movement, potentially leading to issues like locked trigger finger (in the hand, analogous condition).