The LiLiPUT for Ligamentous Lisfranc Injury

Abstract

Category: Trauma Introduction/Purpose: The Lisfranc ligament complex is integral to the stability of the 2nd tarsometarsal joint (TMTJ). Injury causes the 2nd metatarsal to displace dorsally and laterally. Injuries are often missed acutely because of subtle findings that are not always apparent on both weight bearing and non-weight bearing radiographs. The concept of the LiLiPUT (Ligamentous Lisfranc Push Up Test) originated from observations during operative cases that dorsal displacement appeared to be the major direction of instability. A sensitive and reproducible out-patient ‘stress test’ for occult Lisfranc injury is, as yet, elusive. The aims of the study were to assess the ability of the LiLiPUT (a raised block beneath the 2nd metatarsal) to reveal an occult ligamentous Lisfranc injury. Methods: Ten fresh frozen cadaveric lower limbs were used. Postero-anterior and lateral foot radiographs were obtained prior to simulation of a ligamentous Lisfranc injury via a dorsal approach incising the dorsal and plantar ligaments of the 2nd TMTJ. Radiographs were obtained with: Blocks of increasing size placed underneath the 2nd metatarsal. The foot in 3 different positions of increasing dorsiflexion over the blocks. 10Kg load applied skeletally to the leg over the same blocks and positions. A pressure sensor was at the interface between the 2nd TMTJ and block obtaining pressure maps with maximal load readings for each test. Results: The introduction of a 2 x 1 cm block beneath the 2nd metatarsal, with downward force coming from the weight of the amputated limb, revealed an occult injury on the lateral radiographs in 8 of the 10 specimens. A positive test was taken as any discernible dorsal displacement. An increase in block size did not change the force transmitted through the 2nd TMTJ (p=0.32 to 0.42) and had no significant effect on diagnostic yield. Increasing dorsiflexion and increasing load also had no effect on the diagnostic yield. The two specimens without displacement had cavus type foot deformities. Conclusion: A small raised block beneath the 2nd metatarsal in a non weight-bearing patient with the foot in a neutral position may be an adequate means of identifying occult ligamentous Lisfranc injuries on lateral radiographs. Further evaluation in the clinical setting is required as this test may not demonstrate instability in the cavus foot variant.