Lisfranc fracture-dislocation of the tarsometatarsal joint complex is a diagnostic pitfall. The radiographic finding on weight-bearing AP foot X-ray that confirms significant Lisfranc instability is:
- A Diastasis >2 mm between the first and second metatarsal bases ✓
- B Stress fracture at the base of the fifth metatarsal
- C Subluxation of the first tarsometatarsal joint alone
- D Dorsal cortex discontinuity of medial cuneiform
Correct answer: A. Diastasis >2 mm between the first and second metatarsal bases
Explanation
The Lisfranc ligament runs from the medial cuneiform to the base of the second metatarsal. Disruption is diagnosed by >2 mm diastasis between the first and second metatarsal bases on stress or weight-bearing AP radiograph (the fleck sign — avulsion of the Lisfranc ligament insertion from the second metatarsal base — is pathognomonic). Normal alignment requires the medial border of the second metatarsal to align with the medial border of the intermediate cuneiform. Missed Lisfranc injuries cause chronic midfoot instability and post-traumatic arthritis requiring arthrodesis.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.