The tarsometatarsal joint, often called the Lisfranc joint, is a complex articulation in the midfoot that bridges the hindfoot and the forefoot. This structure is a group of joints where the small bones of the midfoot meet the long bones leading to the toes. Located centrally, the Lisfranc joint is fundamental for maintaining the foot’s structural integrity. It acts as a stable anchor, allowing the foot to function efficiently during standing and movement.
Anatomical Structure
The Lisfranc joint complex is formed by the articulation of the three cuneiform bones and the cuboid bone (the distal tarsals) with the bases of the five metatarsal bones. The first three metatarsals articulate with the respective cuneiforms, while the fourth and fifth metatarsals connect with the cuboid bone. This arrangement creates three distinct columns—medial, middle, and lateral—that move with varying degrees of flexibility. The second metatarsal base is uniquely wedged into a mortise created by the cuneiforms, making it the least mobile and most structurally stable part of the complex.
Stability is provided by an intricate network of dorsal, plantar, and interosseous ligaments. The strongest stabilizing structure is the Lisfranc ligament, an interosseous band connecting the medial cuneiform to the base of the second metatarsal. Located on the plantar side of the foot, this ligament is the primary restraint against bone separation. The bony and ligamentous configuration creates a stable, arch-like structure where the bones are tightly interlocked.
Role in Foot Biomechanics
The primary function of the tarsometatarsal joints is to convert the foot from a flexible shock-absorber to a rigid lever, necessary for walking and running. The joints have limited movement, allowing only slight gliding motions, which ensures midfoot stability. This rigidity supports the transverse and longitudinal arches of the foot, distributing the body’s weight. The second metatarsal, recessed between the cuneiforms, acts as a keystone, maintaining the integrity of the transverse arch.
During the push-off phase of the gait cycle, the TMT joint complex must lock to create a rigid platform that transfers propulsive force to the ground. The limited motion allows the forefoot to adjust its position relative to the ground surface during weight-bearing. For instance, when the rearfoot supinates, the TMT joints adjust the forefoot’s position to maintain contact and stability. This mechanism ensures efficient propulsion and prevents excessive rotational forces from affecting the lower leg.
Understanding Lisfranc Injuries
A Lisfranc injury is a spectrum of trauma affecting the TMT joint complex, ranging from a mild ligament sprain to severe fracture-dislocations where bones are displaced. These injuries commonly result from high-energy trauma, such as motor vehicle accidents or falls from a height. They can also result from indirect forces, like a twisting fall on a plantar-flexed foot, often seen in athletes. This indirect mechanism involves an axial load applied to a downward-pointed foot, causing a sudden rotation that tears the strong Lisfranc ligament.
Lisfranc injuries are frequently misdiagnosed as simple midfoot sprains, with up to 20% of cases initially missed. Midfoot swelling and bruising on the sole of the foot, known as plantar ecchymosis, is a physical sign highly suggestive of this injury. When the diagnosis is missed, consequences can be severe, including chronic pain, long-term instability, and eventual arch collapse. Untreated instability leads to debilitating post-traumatic arthritis in the joint complex.
Injuries are broadly classified based on the extent of damage, from purely ligamentous injuries to complex fracture-dislocations. The severity determines the stability of the joint, which is the most important factor in deciding treatment. Injuries are categorized by the degree of metatarsal displacement from the tarsal bones. Even subtle instability or displacement on imaging can represent a significant ligamentous tear and requires careful management to prevent long-term functional loss.
Diagnostic Methods and Management
Diagnosis involves a thorough physical examination and standard X-rays of the foot in three views. Since subtle injuries are often missed on standard films, weight-bearing X-rays are necessary if the patient can tolerate them, as this position reveals instability not otherwise visible. A small bone fragment pulled off at the Lisfranc ligament attachment site, known as the “fleck sign,” confirms the diagnosis.
If clinical suspicion remains high despite normal X-rays, advanced imaging is pursued to characterize the injury. Computed Tomography (CT) scans offer superior detail for detecting non-displaced fractures and subtle bony misalignments. Magnetic Resonance Imaging (MRI) is the most accurate method for evaluating soft tissue damage, particularly to the Lisfranc ligament. This detailed imaging helps determine if the injury is stable enough for non-surgical treatment.
Management is based on the stability of the joint complex. Non-surgical treatment is reserved for mild, stable sprains without displacement or fracture, requiring a period of non-weight-bearing immobilization, typically in a cast, for six to eight weeks. Unstable injuries require surgical intervention to restore precise anatomical alignment. The most common approach is open reduction and internal fixation (ORIF), where displaced bones are repositioned and held with screws or plates. For severe joint damage or chronic instability, a primary arthrodesis, which involves surgically fusing the damaged joints, may be performed to ensure long-term stability and reduce the risk of post-traumatic arthritis.