Background: There are two primary radiographic patterns of Lisfranc instability, transverse and longitudinal. There is no single diagnostic method with which to consistently confirm the diagnosis of an unstable injury. Our purpose was to define which ligament disruptions produce these two injury patterns and to compare the utility of weight-bearing and stress radiographs for detecting each pattern of instability.

Methods: Ten fresh-frozen cadaveric lower extremities were dissected to expose the dorsal aspect of the midfoot. Radiographic markers were placed at the base of the second metatarsal and the distal borders of the first and second cuneiforms. The specimens underwent sectioning of the interosseous first cuneiform-second metatarsal (Lisfranc) ligament and were then divided into two groups. The transverse group underwent sectioning of the plantar ligament between the first cuneiform and the second and third metatarsals at the plantar aspect of the second cuneiform-second metatarsal joint, whereas the longitudinal group underwent sectioning of the interosseous ligament between the first and second cuneiforms. Weight-bearing, adduction, and abduction stress radiographs were made before and after each ligament was sectioned. The radiographs were digitized, and displacement was recorded. Instability was defined as =2 mm of displacement.

Results: Weight-bearing radiographs made after the Lisfranc (first cuneiform-second metatarsal) ligament alone was sectioned were diagnostic (showed instability) for one of ten specimens. Abduction stress radiographs were diagnostic for two of five specimens, and adduction stress radiographs were diagnostic for zero of five specimens. In the transverse group (sectioning of the plantar ligament between the first cuneiform and the second and third metatarsals), weight-bearing radiographs were diagnostic on the basis of first cuneiform-second metatarsal displacement for one of five specimens but were not diagnostic on the basis of second cuneiform-second metatarsal displacement for any of five specimens. Abduction stress radiographs were diagnostic on the basis of displacement of both the first cuneiform-second metatarsal and the second cuneiform-second metatarsal joints for five of five specimens. In the longitudinal group (sectioning of the interosseous ligament between the first and second cuneiforms), weight-bearing radiographs were diagnostic on the basis of first cuneiform-second metatarsal displacement for one of five specimens and were diagnostic on the basis of displacement between the first and second cuneiforms for one of five specimens. Adduction stress radiographs were diagnostic on the basis of first cuneiform-second metatarsal displacement for one of five specimens and were diagnostic on the basis of displacement between the first and second cuneiforms for four of five specimens.

Conclusions: Transverse instability required sectioning of both the interosseous first cuneiform-second metatarsal ligament and the plantar ligament between the first cuneiform and the second and third metatarsals. Longitudinal instability required sectioning of both the interosseous first cuneiform-second metatarsal ligament and the interosseous ligament between the first and second cuneiforms. Compared with weight-bearing radiographs, injury-specific manual stress radiographs showed qualitatively greater displacement when used to evaluate both patterns of instability.

Clinical Relevance: We recommend further evaluation of the effectiveness of making injury-specific manual stress radiographs with fluoroscopy for patients with suspected Lisfranc instability to determine both the presence of instability and its pattern.