Abstract
Introduction
Lisfranc joint injuries account for only 0.2% of all fractures but early diagnosis improves the chances of a better outcom]. Radiographic signs, such as diastasis (>2mm) of the 1–2 interspace, are subtle and. often missed, leading to a poorer outcome. We present a new radiographic sign, less likely to result in missed diagnoses. Null nypothesis: The intermetarsal angle remains unchanged in Lisfranc injuries.
Method
A series of radiographs demonstrating Lisfranc injury were interspersed with normal and postoperative cases. Evidence of fixation was obscured. A selection of Foundation and Core Trainee medical staff measured the intermetatarsal angle (IMA) on two separate occasions. The measuring technique was demonstrated with no explanation for the reason behind the measurement.
Results
The intra-class correlation (ICC) between observers was 0.96 and a mean 0.86 (range 0.69–0.96) for individual observers. IMA on comparative weight bearing AP views of injured and normal side, using Wilcoxon-signed rank test demonstrated a P< 0.0001 with mean values of 6.6 degrees (normal) versus 4.85 degrees (injured) and standard deviation of 1.97 & 1.91 degrees respectively.
Conclusion
The high ICC value suggests that this radiographic sign is easily taught, reliable and reproducible. Analysis of individual angles suggests that there is a significant difference between the normal and pathological IMA. We therefore reject our null hypothesis. The data supports our proposition that that the IMA becomes more parallel in Lisfranc injuries and that this is an easily recognised sign, which could help reduce the incidence of missed injuries. Elucidation of the exact anatomical pathology responsible is the basis for further, anatomical, studies
