T he anatomy of the mortise of the Lisfranc joint between the medial and lateral cuneiforms was studied in detail, with particular reference to features which may predispose to injury.In 33 consecutive patients with Lisfranc injuries we measured, from conventional radiographs, the medial depth of the mortise (A), the lateral depth (B) and the length of the second metatarsal (C). MRI was used to confirm the diagnosis. We calculated the mean depth of the mortise (A+B)/2, and the variables of the lever arm as follows: C/A, C/B and C/mean depth. The data were compared with those obtained in 84 cadaver feet with no previous injury of the Lisfranc joint complex. Statistical analysis used Student's two-sample t-test at the 5% error level and forward stepwise logistic regression.The mean medial depth of the mortise was found to be significantly less in patients with Lisfranc injuries than in the control group. Stepwise logistic regression identified only this depth as a significant risk factor for Lisfranc injuries. The odds of being in the injury group is 0.52 (approximately half) that of being a control if the medial depth of the mortise is increased by 1 mm, after adjusting for the other variables in the model. Our findings show that the mortise in patients with injuries to the Lisfranc joint is shallower than in the control group and the shallower it is the greater is the risk of injury. The tarsometatarsal joint of the foot (Lisfranc joint) consists of the distal row of tarsal bones, the medial, intermediate, and lateral cuneiforms and the cuboid, which articulate with the bases of the five metatarsals. It is Sshaped and is divided into three columns, with three distinct arches.1,2 Of the three arches, the horizontal arch is anchored by the base of the second metatarsal, which is recessed into a 'mortise' between the medial and lateral cuneiforms (Fig. 1), and stabilises the joint.
2,3Intermetatarsal and thin dorsal ligaments connect the second, third, fourth and fifth metatarsals, and the tarsometatarsal joint is further stabilised by the strongest of the ligamentous structures, the plantar tarsometatarsal ligaments. There is no intermetatarsal ligament between the bases of the first and second metatarsals. The main stabilising structure of the tarsometatarsal joint is a Y-shaped interosseous ligament (Lisfranc's ligament). This extends on the plantar surface from the lateral aspect of the medial cuneiform to the medial aspect of the base of the second Fig. 1 Anatomical specimen of a left foot. It was dissected in an oblique axial plane showing the position of the second metatarsal base in the mortise between the medial and lateral cuneiform.