Interphalangeal Joints of the Toes
Similar to the structure of the fingers, each toe contains two key interphalangeal joints:
- Proximal interphalangeal (PIP) joint
- Distal interphalangeal (DIP) joint
However, like the thumb in the hand, the big toe (hallux) has only one interphalangeal joint, distinguishing it from the other toes.
All interphalangeal joints in the foot share similar anatomical characteristics. These joints primarily consist of:
- A convex proximal phalanx head
- A concave distal phalanx base, which articulates with it
A clear view of the concave surface of the proximal interphalangeal joint can be seen when the proximal phalanx of the second toe is removed. The structural and functional characteristics of the connective tissues within the interphalangeal joints closely resemble those found in the metatarsophalangeal (MTP) joints.
These joints are stabilized by:
- Collateral ligaments
- Plantar plates
- Joint capsules
However, compared to MTP joints, the interphalangeal joints are smaller in scale and less distinctly defined.
The primary movements at these joints are flexion and extension, with minimal movement in other directions. Flexion has a greater range of motion than extension, and the proximal interphalangeal joints generally have more mobility than the distal interphalangeal joints. Extension is further restricted by passive tension from the flexor tendons and plantar ligaments.
Function of Forefoot Joints During Late Stance Phase of Gait
As the stance phase nears its end, the midfoot and forefoot must generate sufficient stability to absorb and transmit forces effectively during push-off. This stability is achieved through:
- Coordinated activation of intrinsic and extrinsic foot muscles
- Elevation of the medial longitudinal arch, which further reinforces foot stability
Due to the attachment of the plantar fascia at the proximal phalanges, full extension of the metatarsophalangeal joints increases tension within the medial longitudinal arch. This heightened tension enhances both the elevation and stabilization of the arch, ensuring greater foot rigidity as body weight transitions forward.
As the heel and most of the foot lift off the ground, the center of mass gradually shifts toward the medial metatarsal heads. Several specialized anatomical structures help in managing load distribution at this stage:
- Fat pads absorb and distribute stress, reducing potential damage to bony structures
- Sesamoid bones protect the flexor tendons of the hallux from excessive mechanical stress