Background: Up to one-third of Lisfranc injuries (an injury affecting the normal stability, alignment, and congruency of the tarsometatarsal joints) are misdiagnosed. Delayed diagnosis and improper treatment may lead to long-term, irreversible sequela and functional disability. Recently, the employment of three-dimensional (3D) CT demonstrated higher diagnostic reliability, but there is limited evidence on this, and radiologic features of Lisfranc injuries when using this diagnostic modality are not well described.
Question/purpose: What is the diagnostic performance of several novel radiographic signs on 3D CT when evaluating for Lisfranc injury, namely the Mercedes sign, the peeking metatarsal sign, and the peeking cuneiform sign, and what is the interobserver and intraobserver reliability of those diagnostic signs?
Methods: In this retrospective, diagnostic study, video clips of 3D CT reconstructions of 52 feet with intraoperatively confirmed Lisfranc injuries and 50 asymptomatic feet with a normal appearance of the tarsometatarsal joints, as ascertained by a subspecialty-trained foot and ankle surgeon and a musculoskeletal radiologist, were analyzed by two foot and ankle specialists and three orthopaedic residents twice each, with a washout period of 2 weeks. Among the 52 patients with intraoperative evidence of Lisfranc injury, there were 27 male patients and 25 female patients, with a median (IQR) age of 40 years (23 to 58); among the 50 controls, there were 36 male and 14 female patients, with a median age of 38 years (IQR 33 to 49). For each video clip, the presence of all three radiographic signs was documented (each sign was rated in a binary yes/no fashion). Before the evaluations, all observers underwent a short training session by the head of the foot and ankle department. Later, these reading were used to assess for the sensitivity, specificity, and area under the receiver operating characteristic curve in terms of Lisfranc diagnosis against the gold standard of intraoperative testing of tarsometatarsal joint stability. Intraoperatively, the congruency and stability of the second tarsometatarsal joint had been evaluated by direct visualization and by the insertion of a probe into the joint between the base of the second metatarsus and the medial cuneiform and twisting the probe to assess for stability. The individuals evaluating the video clips were unaware of the surgically obtained diagnosis at the time they performed their evaluations.
Results: All 3D radiographic signs that were examined had excellent diagnostic reliability in terms of sensitivity and specificity, ranging from 92% to 97% and from 92% to 93%, respectively. When assessing the association between the suggested 3D radiographic signs and Lisfranc injury diagnosis as a function of the area under the receiver operating characteristic curve, the Mercedes sign demonstrated a higher area under the curve than the other signs did (0.91 versus 0.87 versus 0.8; p < 0.001). The mean intraobserver and interobserver reliability (kappa) values were excellent for all 3D radiographic signs that were evaluated.
Conclusion: The proposed radiographic findings demonstrated excellent diagnostic performance and were repeatable within and among observers. Three-dimensional CT radiographic signs could function as a valuable diagnostic tool for the evaluation and initial screening for Lisfranc injury in the acute injury phase because obtaining AP bilateral standing radiographs of the foot is often impractical in the acute setting. Further research and comparison with AP weightbearing radiographs of the bilateral feet may be warranted.
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