Second Tarsometatarsal Joint: Location, Function, and Clinical Significance

Where is the second tarsometatarsal joint?

The second tarsometatarsal (TMT) joint is located in the midfoot, forming the articulation between the base of the second metatarsal bone and the intermediate cuneiform bone. It is a critical component of the Lisfranc joint complex, renowned for its stability and role as the keystone of the foot's transverse arch.

Introduction to the Tarsometatarsal Joints

The tarsometatarsal (TMT) joints, often collectively referred to as the Lisfranc joint complex, represent a series of articulations in the midfoot where the distal row of tarsal bones meets the bases of the metatarsal bones. These joints are fundamental to the foot's ability to transition from a flexible structure that adapts to uneven surfaces to a rigid lever for propulsion during gait. While all five TMT joints contribute to foot mechanics, the second TMT joint holds a uniquely significant position due to its anatomical configuration and stability.

Precise Anatomical Location of the Second TMT Joint

The second tarsometatarsal joint is situated centrally in the midfoot, acting as a crucial anchor point. Specifically, it is the articulation between:

• The base of the second metatarsal bone: This is the long bone that extends from the midfoot towards the second toe.
• The intermediate cuneiform bone: This is one of the three wedge-shaped cuneiform bones, positioned between the medial (first) cuneiform and the lateral (third) cuneiform.

Unlike the first and third metatarsals, which articulate with a single cuneiform bone, the base of the second metatarsal is uniquely recessed, fitting snugly into a mortise formed by the medial, intermediate, and lateral cuneiforms. This creates a highly stable, "keystone" arrangement that significantly limits its individual motion but enhances overall foot stability.

A key anatomical feature contributing to the stability of this specific joint is the Lisfranc ligament. While there are multiple Lisfranc ligaments, the most clinically significant is the strong plantar ligament that connects the medial cuneiform directly to the base of the second metatarsal. This ligament is unique as it's the only direct ligamentous connection between the medial cuneiform and the second metatarsal, without a corresponding dorsal ligament, making it especially vulnerable to injury.

Structural and Functional Significance

The second TMT joint, by virtue of its position and strong ligamentous attachments, plays a pivotal role in the biomechanics of the foot:

• Keystone of the Foot's Arch: The recessed base of the second metatarsal and its articulation with the intermediate cuneiform is considered the "keystone" of both the transverse and longitudinal arches of the foot. This anatomical configuration provides immense stability to the midfoot, preventing collapse of the arch under load.
• Limited Mobility, High Stability: In contrast to the first TMT joint (which is more mobile to allow for pronation/supination of the first ray) or the fourth and fifth TMT joints (which offer more flexibility to adapt to ground surfaces), the second TMT joint has very limited intrinsic motion. Its primary function is to provide rigidity and act as a stable fulcrum during the push-off phase of gait.
• Weight Bearing and Load Distribution: During standing, walking, and running, the second TMT joint is subjected to significant compressive and shear forces. Its robust structure ensures efficient transfer and distribution of these loads from the lower leg through the midfoot to the forefoot, maintaining the structural integrity of the foot.

Clinical Relevance and Injury Considerations

Given its critical role in foot stability and weight-bearing, the second tarsometatarsal joint is frequently implicated in midfoot injuries, collectively known as Lisfranc injuries.

• Lisfranc Injuries: These injuries involve disruption of the TMT joints, ranging from subtle sprains to complete dislocations and fractures. The second TMT joint and its associated Lisfranc ligament are particularly vulnerable.
• Mechanism of Injury: Lisfranc injuries often result from high-energy trauma, such as direct crushing forces (e.g., a heavy object falling on the foot), or indirect forces involving axial load with a rotational component (e.g., a football player being tackled while their foot is planted and twisted). Even seemingly minor falls or twists can cause significant injury.
• Symptoms: Common symptoms include severe pain in the midfoot, swelling, bruising on the sole of the foot (plantar ecchymosis), and an inability or significant difficulty bearing weight.
• Importance of Diagnosis: Lisfranc injuries are notoriously challenging to diagnose and are often initially misdiagnosed as simple sprains. However, if left untreated or improperly managed, they can lead to chronic pain, midfoot arthritis, arch collapse, and long-term functional disability due to the critical role of the second TMT joint in maintaining foot architecture. Proper diagnosis often requires specialized imaging beyond standard X-rays, such as MRI or CT scans.

Conclusion: A Foundation for Movement

The second tarsometatarsal joint, though small and relatively immobile, is a cornerstone of foot mechanics. Its precise anatomical location, nestled between the intermediate cuneiform and the second metatarsal, and its strong ligamentous attachments, particularly the Lisfranc ligament, render it essential for the stability, load-bearing capacity, and efficient function of the entire foot. Understanding its unique contribution is paramount for clinicians, trainers, and individuals seeking to comprehend the intricate design and resilience of the human foot.