Nonweightbearing Radiographs in Patients With a Subtle Lisfranc Injury.

Background: A midfoot sprain can be easily missed because of minimal findings on initial radiographs, which are almost universally nonweightbearing. We investigated preoperative nonweightbearing plain radiographic images in patients who were found to have unstable subtle Lisfranc injuries.

Methods: We retrospectively reviewed 51 patients who were operated on between February 2004 and March 2015. Abnormal preoperative radiographic findings and intraoperative instability were compared. The relationship was calculated with Fisher's exact test.

Results: Based on intraoperative findings, medial cuneiform (C1)-second metatarsal (M2) instability was observed in 50 cases (98%), which was the most common. Thirty-nine cases (76.4 %) had multiple joint (at least 2) instability. In the preoperative radiologic findings, C1-M2 diastasis was the most common abnormal finding, in 46 cases (90.1%). Specificity and positive predictive value were 1.0 in C1-M2 avulsion, diastasis, and C1-intermediate cuneiform (C2) diastasis. Abnormal findings of C1-C2, C1-M1, and C2-M2 showed a significant relationship with intraoperative instability ( P < .05).

Conclusion: C1-M2 avulsion and diastasis and C1-C2 diastasis were definite preoperative predictors of instability. In unstable subtle Lisfranc injuries, 90% had at least a minor radiographic abnormality at the C1-M2 joint on nonweightbearing radiographs. However, caution should be exercised to identify instability without radiographic abnormality in the C1-M2 joint.

Level Of Evidence: Level IV, retrospective case series.