Diagnosis and assessment of subtle Lisfranc injuries: Comparison of computed tomography and weight-bearing radiography.

Background: Subtle Lisfranc injuries cause instability around the Lisfranc joint, leading to loss of foot function without appropriate treatment. The diagnostic accuracy of the commonly used Nunley classification, which is based on weight-bearing radiographs, is controversial. We compared the Nunley classification and computed tomography (CT) findings for subtle Lisfranc injury severity.

Methods: Fifty-one patients diagnosed with subtle Lisfranc injury were retrospectively enrolled. After excluding those without weight-bearing radiography or CT images, the medical histories, weight-bearing radiographs, and CT images of 33 patients were reviewed. We measured the distance between the proximal first and second metatarsals from the anteroposterior radiographs and that between the plantar aspect of the first cuneiform and plantar aspect of the fifth metatarsals from the lateral view and then classified the cases according to the Nunley classification. CT images were evaluated for avulsion fragments at the Lisfranc ligament complex attachment sites.

Results: According to the Nunley classification, seven patients were stage I, 23 were stage II, and three were stage III. Based on weight-bearing radiographs, the C1-M5 distance was 1.29 ± 0.40 cm/1.01 ± 0.36 cm (injured feet/contralateral feet; p < 0.05) overall. On CT images, the avulsion bone fragment location revealed one case of interosseous Lisfranc ligament and five cases of plantar capsular Lisfranc ligament complex in Nunley stage I. In Nunley stage II, three patients had a dorsal capsular Lisfranc ligament complex, 15 had an interosseous Lisfranc ligament, and 18 had a plantar capsular Lisfranc ligament complex. In Nunley stage III, two patients had interosseous Lisfranc ligaments, and three patients had a plantar capsular Lisfranc ligament complex.

Conclusions: Patients in the acute phase of subtle Lisfranc injury did not place weight on their injured foot. In 93.9 % of subtle Lisfranc injury cases, avulsion fragments were present at the ligament attachment site, and severity was different from weight-bearing radiographs.