The Lisfranc joint is a complex midfoot articulation that involves several ligaments, joint capsules, and osseous structures. The most clinically significant of these ligaments are found within the first cuneiform-second metatarsal (Lisfranc) interval and are further classified into dorsal, interosseous, and plantar arrangements1,2. The interosseous ligament is thicker and stronger than the capsular ligaments3 (Fig. 1). Injuries to the Lisfranc joint complex typically are differentiated into high- and low-impact traumas, which often have different clinical and radiologic presentations4,5.
An accurate description of Lisfranc joint injury is critical, because undiagnosed injuries may lead to chronic morbidity and long-term sequelae, including chronic pain, functional loss, and posttraumatic arthritis4. Clinical and radiologic diagnosis of Lisfranc injury is challenging, because 20% of all Lisfranc injuries are misdiagnosed clinically and 50% of midfoot sprains are misinterpreted radiographically4,6-9. Non–weight-bearing radiographs may only show subtle diastasis if present, and weight-bearing radiographs may require 6 weeks for diastasis to become radiographically apparent9-11. High-velocity injuries may also blind evaluation of Lisfranc injury in the setting of existing polytrauma9,10.
Classically, magnetic resonance imaging (MRI) is reserved for equivocal cases of Lisfranc injury, but even MRI has its own limitations. In one study that compared MRI interpretations with intraoperative findings, radiologists accurately graded 70% of grade 3 Lisfranc ligament injuries and incorrectly graded 33% of normal Lisfranc ligaments as grade 1 Lisfranc injuries at MRI12. Interobserver variability, level of training, and appropriate MRI protocoling are confounding factors that affect the reliability of MRI interpretations13,14.
Despite these limitations, dynamic stress MRI stands to become a promising advancement in the evaluation of midfoot injury by detecting instability sufficient enough to justify surgery that might not be identified otherwise. Surgery (other than potentially stress x-rays under anesthesia) would not be performed without definitive evidence of instability. To our knowledge, there is only a single publication evaluating the role of dynamic stress MRI, which evaluated ankle joint laxity15. In our institution, we designed, patented, and 3D-printed an MRI-safe foot stressor device that can be used inside any MRI scanner. The foot stressor device is approved by the Institutional Review Board and can apply variable, multidirectional loads to the foot to assess for joint instability (Fig. 2). The MRI stress device is also computed tomography (CT) compatible.
The patient was informed that data concerning the case would be submitted for publication, and he provided consent.
A 26-year-old patient sustained a midfoot injury while ballet dancing. The patient stated that he was attempting to perform a maneuver, which forced his right foot into full plantar flexion, with the full axial load of his body weight directed onto his toes. He then fell, inverting his right foot and ankle. Immediately after the injury, he reported moderate midfoot pain and discomfort while ambulating. He visited an outside urgent care center later that day and had radiographs that reportedly demonstrated no acute abnormalities.
The patient's right midfoot pain persisted, although it demonstrated mild improvement over the next 2 weeks. He then returned to ballet dancing, but he immediately suffered re-injury and reported moderate midfoot pain that persisted up until his appointment with his orthopaedic surgeon. Repeat weight-bearing radiographs demonstrated borderline widening of the Lisfranc interval (Fig. 3). Given continued symptoms, the orthopaedic surgeon ordered a foot dynamic stress MRI examination. Before the MRI examination, the patient signed informed consent for the use of the MRI foot stress device.
As per protocol, nonstressed and stressed images of both feet were obtained, including imaging of the contralateral, noninjured foot as a control. Imaging was performed in a 1.5 Tesla GE Magnet using a head coil. The MRI protocol for the injured foot included multiplanar imaging using T1- and T2-weighted fast spin-echo sequences to evaluate the anatomy of the Lisfranc complex in the nonstressed state. Fluid-sensitive short tau inversion recovery sequences were obtained to evaluate for marrow and soft-tissue edema. The foot stressor screws were then adjusted, so that its movable components placed the foot into dorsiflexion, external rotation, and 25° of inversion. These adjustments generated a 50-pound axial load on the plantar side of the forefoot and a smaller, laterally directed 20-pound load to the forefoot (Fig. 2). These forces are comparable with those applied during physical examination. The asymptomatic foot was then scanned in the axial and coronal planes using T2-weighted fast spin-echo pulse sequences in the stressed and nonstressed states. The stress loads applied to both feet were the same.
The injured Lisfranc ligament in the nonstressed state measured 5.5 mm in length (anteroposterior), 6.0 mm in width (dorsoplantar), and 2.5 mm in thickness (mediolateral). The contralateral, asymptomatic Lisfranc ligament measured 5.5 × 6.0 × 3.0 mm. Nonstressed images of the injured right foot demonstrated minimal widening of the Lisfranc interval without frank ligament avulsion, measuring 3.7 mm. There was mild edema of the interosseous Lisfranc ligament without fibrous avulsion or retraction, representing a mild ligament sprain. The plantar and dorsal capsular Lisfranc ligaments were unremarkable. There was no fracture or joint subluxation. Secondary findings included a small first metatarsophalangeal joint effusion and mild bone bruises of the cuneiforms and second and third metatarsal bases (Fig. 4).
Nonstressed images of the uninjured left foot were unremarkable. The Lisfranc interval of the left foot measured 3.5 mm. On the stressed images, there was increased widening of the Lisfranc interval in the injured foot from 3.7 mm to 4.7 mm, a net difference of 1.0 mm. Stressed imaging of the asymptomatic left foot did not show any widening of the Lisfranc interval, reflecting a stable joint (Fig. 5).
In summary, these findings indicated a mild sprain of the interosseous Lisfranc ligament with mild fibrous laxity, but no joint subluxation. Given this information, the orthopaedic surgeon decided against surgical fixation and instead prescribed immobilization and physical therapy. At interval follow-up 13 weeks after the initial MR diagnosis and after 8 weeks of physical therapy, the patient reported markedly improved pain with weight bearing and a successful return to his professional level of ballet dancing.
To our knowledge, this is the first case report using dynamic stress MRI of the injured midfoot to demonstrate a mild Lisfranc ligament sprain with direct evidence of ligament laxity in a living person. There are several publications that demonstrated measurable ligament laxity in various joints using cadaveric specimens16-18, but no published literature exists that combines the mechanism of injury with targeted dynamic stress MRI to show functional ligament laxity.
At a histologic level, an acute ligament sprain represents disruption of the longitudinally oriented collagen fibers within the ligament midsubstance and the bone-ligament interface. Disruption of these fibers affects normal mechanical loading and conceivably manifests as ligament laxity and changes in osseous alignment during imaging and physical examination19-23. Anatomic and cadaveric studies have thoroughly described the Lisfranc joint and ultimately ascribed midfoot instability to a combination of Lisfranc ligament injury and additional sites of pathology, including the plantar tarsometatarsal ligaments, supporting plantar forefoot structures, and the intercuneiform ligaments24-26, rather than to isolated Lisfranc ligament pathology.
In our patient, his dynamic stress MRI examination revealed a Lisfranc ligament sprain, based on altered signal abnormality and decreased ligament caliber. The examination also showed mild ligament laxity on the stressed images, which manifested as widening of the Lisfranc interval. Interestingly, there was no widening of the Lisfranc interval in the asymptomatic foot, which reflected an innately stable joint. In the setting of MRI-confirmed acute soft-tissue pathology, we attribute this asymmetric Lisfranc interval widening to the disrupted tensile loading mechanisms in the setting of microtrauma, rather than to benign anatomic variation. These small, but detectable, changes in laxity in the sprained ligament would not be seen radiographically. A stress CT scan would be able to show small fractures or Lisfranc interval widening with similar accuracy to MRI, but it would not show ligament morphology and the more subtle osseous injuries15. Even though our patient had substantial disability after his midfoot injury, he did not fully meet our orthopaedic surgeon's criteria for surgical treatment, which include widening of the Lisfranc interval greater than 3 mm and any Lisfranc joint fracture. He was therefore treated conservatively with good short-term results. To our knowledge, this is the first illustrated case of Lisfranc ligament laxity and microtrauma in a living patient by using dynamic stress MRI.
We therefore propose the routine use of dynamic stress MRI in patients with equivocal midfoot injuries to better evaluate the integrity of the Lisfranc joint and surrounding ligaments. This case report only involves a single patient with a low-impact midfoot injury, so further investigation is warranted and will ideally include a wider spectrum of injury mechanism and pathology. Active patient recruitment is currently ongoing. We also plan to continue imaging the contralateral, noninjured feet in patients who suffer unilateral injury, thereby allowing a valuable intrapersonal control. Future applicability of our dynamic stress MRI will ultimately rely on these research objectives.
As with weight-bearing radiographs, dynamic stress MRI of the foot may offer more realistic information on the osseous and soft-tissue behaviors under near-physiologic loading conditions. We believe that dynamic stress MRI will ultimately allow for improved diagnosis of both Lisfranc injury and midfoot instability. The current criteria for determining midfoot instability, such as Lisfranc interval widening, “fleck” sign, and dorsal tarsometatarsal subluxation, are better measured with cross-sectional examinations. MRI has the added benefit of showing soft-tissue injuries and bone marrow bruises that contribute to the symptomatology and complexity of an injury, which in turn affect the time of healing and length of therapy27. Having the additional information of joint instability and surrounding soft-tissue pathology ultimately has the potential to better guide the foot and ankle specialist in the treatment and management of midfoot injuries through the establishment of new imaging-based criteria.
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