Augmented Stress Weightbearing CT for Evaluation of Subtle Lisfranc Injuries in the Elite Athlete

Abstract

Category: Midfoot/Forefoot; Trauma Introduction/Purpose: The Lisfranc joint is the interface between the midfoot and forefoot and forms a strong connection due to its bony architecture and ligamentous attachments in the foot. An unstable Lisfranc injury has traditionally been defined as displacement >2 mm between the 1st and 2nd metatarsal bases or between the medial cuneiform and the second metatarsal base, when compared to the contralateral side on imaging modalities. Classically, Lisfranc injuries have been detected with standard X- ray, stress plain films, standard CT, MRI and ultrasound. We describe an imaging technique that may be used to further assist in the diagnosis and management of subtle Lisfranc injuries, and include a case to demonstrate its use in athletes. Methods: Cone beam weight bearing computed tomography (WBCT) is a well-described imaging modality for evaluation of foot and ankle injuries. We have found it highly beneficial to teach our CT technologists about Lisfranc injuries and the importance of augmented physiologic stress applied across the midfoot (in addition to the standard WBCT) to better demonstrate instability or motion, particularly at the second TMT joint. To perform an augmented stress weight bearing CT, the patient is positioned in the WBCT scanner and initial images are acquired in the standing weight bearing position with feet directed forward and weight distributed equally. A second image acquisition is then performed (augmented stress), where the patient is coached to lift both heels from the scanner platform symmetrically, in a calf-raise type exercise. It is important that the patient distributes weight as evenly as possible between the feet so the affected side is stressed sufficiently. Results: We present here a 22-year-old male collegiate football player who is an offensive lineman. While blocking during a game, his foot was plantarflexed, and he 'felt a pop' in his midfoot. On exam, the player was tender to palpation over the medial midfoot, at the Lisfranc joint. He had pain with forced pronation and abduction as well as axial load through the first webspace. Initial weight bearing radiographs did not show evidence of widening between the medial cuneiform and second metatarsal base. Due to his concerning examination, an MRI was ordered, which revealed a small bony avulsion off the plantar aspect of the second metatarsal base with an otherwise intact Lisfranc ligament. He then underwent weightbearing CT stress views of the foot, which revealed greater than 2 mm of widening between the first and second metatarsals when compared to the contralateral side, indicating instability of the Lisfranc joint. Conclusion: We present the augmented stress weightbearing CT technique of the midfoot to evaluate for subtle Lisfranc injury. The need for this imaging modality has proven useful in the elite athlete with subtle injury to the midfoot, otherwise not found on conventional imaging techniques. Timely diagnosis and treatment is imperiative to these players due to the morbidity associated with missed Lisfranc injuries. We propose this technique for diagnosing otherwise unrecognized, subtle Lisfranc injuries in patients where clinical suspicion persists despite negative imaging because this technique stresses the joint and we believe makes the weightbearing CT more sensitive for this injury.