Metatarsals: Tarsometatarsal and Metatarsophalangeal Joint Types

What Type of Joint Is the Metatarsals?

The metatarsals themselves are bones, not joints. However, they participate in forming two primary types of synovial joints within the foot: the tarsometatarsal (TMT) joints, which are primarily plane (gliding) joints, and the metatarsophalangeal (MTP) joints, which are condyloid joints.

Understanding the Metatarsals

The metatarsals are a group of five long bones located in the midfoot, connecting the tarsal bones (at the ankle and rearfoot) to the phalanges (toe bones). Numbered I to V from the medial (big toe) side to the lateral (little toe) side, these bones form the main arch of the foot and play a crucial role in weight-bearing, propulsion, and maintaining balance during locomotion. Each metatarsal has a base (proximal end, articulating with the tarsals), a shaft (body), and a head (distal end, articulating with the phalanges).

The Joints Involving the Metatarsals

The metatarsals participate in two distinct sets of joints, each with unique anatomical structures and biomechanical functions:

• Tarsometatarsal (TMT) Joints (Lisfranc Joint Complex): These are the joints formed between the distal row of tarsal bones (medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid) and the bases of the five metatarsal bones. Collectively, these joints are often referred to as the Lisfranc joint complex.
• Metatarsophalangeal (MTP) Joints: These are the joints formed between the heads of the metatarsal bones and the bases of the proximal phalanges of the toes. There are five MTP joints, one for each toe.

Classifying the Metatarsal Joints

Joints are classified based on their structure (e.g., fibrous, cartilaginous, synovial) and the type of movement they permit. Both the TMT and MTP joints are classified as synovial joints, meaning they have a joint capsule, synovial fluid, and articular cartilage, allowing for varying degrees of movement.

• Tarsometatarsal Joints: Plane (Gliding) Synovial Joints The TMT joints are primarily classified as plane (gliding) synovial joints. In these joints, the articular surfaces are relatively flat, allowing for limited gliding or sliding movements between the bones. While individual TMT joints offer only small movements, the cumulative effect across all five TMT joints contributes significantly to the foot's ability to adapt to uneven surfaces, absorb shock, and maintain the arches. The first TMT joint (between the medial cuneiform and the first metatarsal) is generally the most mobile, while the second TMT joint is the least mobile, providing a stable keystone for the transverse arch of the foot.

• Metatarsophalangeal Joints: Condyloid Synovial Joints The MTP joints are classified as condyloid (ellipsoidal) synovial joints. In a condyloid joint, an oval-shaped condyle of one bone fits into an elliptical cavity of another bone. This structure allows for movement in two planes (biaxial movement):

  • Flexion and Extension: Bending the toes downwards (flexion) and straightening them upwards (extension).
  • Abduction and Adduction: Spreading the toes apart (abduction) and bringing them together (adduction). The MTP joints, particularly the first MTP joint (big toe), are critical for the push-off phase of gait, allowing the toes to extend and propel the body forward.

Functional Significance in Foot Biomechanics

The specific joint types involving the metatarsals are fundamental to the foot's multifaceted role in human locomotion and weight-bearing:

• Tarsometatarsal Joints: Their gliding nature allows for subtle adjustments that enable the foot to transition between a rigid lever (for propulsion) and a flexible adapter (for shock absorption and conforming to terrain). This adaptability is crucial for efficient walking, running, and maintaining balance. Instability or injury in this complex (e.g., Lisfranc injury) can severely compromise foot function.
• Metatarsophalangeal Joints: As condyloid joints, the MTP joints provide the necessary mobility for the toes to grip the ground, provide fine balance adjustments, and contribute significantly to the propulsive force during the toe-off phase of gait. The ability to extend the MTP joints, especially the first, is paramount for a smooth and powerful push-off. Restrictions in MTP joint mobility, such as in hallux rigidus (stiff big toe), can profoundly impact gait mechanics and lead to compensatory movements.

Conclusion

While the metatarsals are bones themselves, they are integral components of two distinct types of synovial joints: the tarsometatarsal (TMT) joints, which are primarily plane (gliding) joints, and the metatarsophalangeal (MTP) joints, which are condyloid joints. These classifications directly dictate the range and type of movement available at each location, highlighting their specialized roles in the complex biomechanics of the foot, enabling everything from stable standing to dynamic propulsion during athletic activities. Understanding these joint types is essential for appreciating the intricate design and function of the human foot.