Subtle Lisfranc: When is minimal displacement equal to stability,and does it matter?

The Scandinavian Journal of Surgery recently presented the study: “Operative versus nonoperative treatment for non-displaced Lisfranc injuries: a multicenter randomized controlled trial” by Ponkilainen et al. ¹

The authors are to be commended for their effort in randomizing this rare injury. Unfortunately, the required number of patients could not be reached during approximately 10 years of accrual. The primary outcome showed a statistically non-significantly different mean Foot-Ankle Visual Analogue Scale (VAS-FA), in the non-operative group of 96.1 [CI = 91.5–100] and 91.8 [86.9–96.7] in the operative group at 24-month follow-up. In addition, none of the secondary outcome measures differed between the groups.

This study is important because it raises awareness that not all Lisfranc injuries are created equally and should not be treated as such. Determining which subtle Lisfranc fractures may be treated non-operatively remains a challenge. The current study set the criteria of minimal fracture displacement of the tarsometatarsal (TMT) joints at less than 2 mm, the minimal displacement between the medial cuneiform and the base of second metatarsal at less than 5 mm, and the absence of fractures at the TMT joints 4 and 5. Weight-bearing radiographs were not employed.

One of the major issues with this study lies here. Are those, as mentioned above, the correct criteria for minimal displacement (as normal values range between 2 and 2.5 mm), ² and does minimal displacement imply stability? Weight-bearing radiographs (or computed tomography (CT)) may determine stability in subtle Lisfranc injuries. ³ Guerreiro et al. ⁴ recently systematically reviewed outcomes of Lisfranc injuries treated non-operatively. They highlighted the wide variety of criteria used in the literature to consider non-operative management, with five out of eight studies using less than 2 mm displacement (M1-M2, C1-C2, or C1-M2). The lack of definition of subtle Lisfranc injuries probably led to significant discrepancies in functional outcomes reported. The best outcomes (The American Orthopaedic Foot and Ankle Society (AOFAS) > 90) were reported by authors who routinely used CT to assess all midfoot injuries, set criteria at less than 2 mm displacement (M1-M2, C1-M2) and applied (fluoroscopic) stress views to rule out dynamic instability.^4,5

In light of the aforementioned, in order to maximize the results of research per time spent, one may need to look at other study designs than randomized controlled trial (RCT), such as pragmatic clinical trials and prospective (inter-)national database studies. One other example is the adaptive platform trial, ⁶ which may solve some of the shortcomings for studies in the rarest of entities and may bypass complex study designs and draconian regulations.