Background
There are several methods for identification of the insertion site of the distal calcaneofibular ligament (CFL). The purpose of this study was to determine the most accurate radiographic method for finding the true insertion of the CFL when compared to the true insertion as determined by MRI. This method would ideally be easily reproducible intra-operatively and lead to a consistently well-placed location for CFL reconstruction in lateral ankle ligament surgery.
Methods
Ankle MRI’s of 25 patients with lateral ankle sprains and an intact CFL were performed and two surgeons identified the “true” insertion of the CFL on sagittal MRI. The true insertion was marked using a picture archiving and communication system (PACS). The distance between the marked insertion site and three bony landmarks was measured on sagittal MRI using PACS. The measurements included the distance to the posterior 1/3 of the superior surface of the calcaneus, the posterior most aspect of the sinus tarsi, and the distal tip of the fibula. Three proposed methods (Best, Lopes, Taser) for determining the CFL insertion were then applied to lateral ankle radiographs, and the distance from the insertion site as determined by these methods to the three bony landmarks was measured. X and Y coordinate distances on radiographs were recorded for each patient and technique and then compared to the MRI measurements. The average, standard deviation, minimum, and maximum were recorded and compared.
Results
The estimation of the three techniques (Best, Lopes, Taser) was compared to the true insertion based on MRI and findings were recorded as distances from the true insertion with X, Y, and combined XY coordinates. The Best technique was on average X=0.581mm, Y=0.276mm, and XY=3.18mm away. The Lopes technique was on average X=0.288mm, Y=- 2.256mm, and XY=5.86mm away. The Taser technique was on average X=1.668mm, Y=-0.916mm, and XY=3.84mm away. For distance in the X direction, there was no significant difference between techniques (P=0.264). For distance in the Y direction, there was a significant difference between techniques (P=0.015). For distance in the combined XY direction, there was a significant difference between techniques (P=0.001). The CFL insertion as determined by the Best method was significantly closer to the true insertion compared to the Lopes method in the Y (P=0.042) and XY (P=0.004) directions. The CFL insertion as determined by the Taser method was significantly closer to the true insertion compared to the Lopes method in the XY direction (P=0.017). There was no significant difference between the Best and Taser methods.
Conclusion
Overall, the Best and Taser techniques were found to be closest to the true CFL insertion when combining X and Y distances. If the Best and Taser techniques can be readily used in the operating room, they would likely prove the most reliable for finding the true CFL insertion for lateral ankle ligament reconstruction.