SLR - May 2012 - Diane M. Castro
Reference: Rankine JJ, Nicholas CM, Wells G, Barron DA. The Diagnostic Accuracy of Radiographs in Lisfranc Injury and the Potential Value of a Craniocaudal Projection. AJR 2012; 198: 365-369.
Scientific Literature Review
Reviewed by: Diane M. Castro, DPM
Residency Program: Cambridge Health Alliance; Cambridge, MA.
Podiatric Relevance:
Patients who present to the office with a midfoot injury are commonly screened for a Lisfranc injury. This is done most often with the use of radiography and is usually followed by a CT scan. However, subtle Lisfranc dislocations are routinely missed on radiographs. The purpose of this study was to calculate the diagnostic accuracy of radiographs to diagnose Lisfranc injuries and to come up with the optimum degree of craniocaudal angulation on the AP view to best reveal the second tarsal-metatarsal joint.
Methods:
Radiographic Study: CT reports of patients with an acute foot injury over a one-year period were reviewed, identifying 60 patients aged 11-82 years (33 male, 27 female; mean age 37.4+/- 16.7) with a Lisfranc injury. The initial presenting radiographs were then reviewed on the AP and oblique views independently by two musculoskeletal radiologists, who were blind to the results of the CT. Each case was put into one of three categories: normal, definite evidence of Lisfranc injury, and equivocal for Lisfranc injury; the equivocal category suggested possible Lisfranc injury. Eight months following this, one observer evaluated the CT exams, while blinded to the radiographic exam. The two categories for the CT exams were either normal or positive for Lisfranc injury. The management of patients was as follows: plaster immobilization, examination under anesthesia without surgical fixation if the injury was stable, and open reduction internal fixation if unstable.
Phantom Study: A foot phantom, which consists of anatomically aligned bones of the foot encased in a resin to match the shape of the soft tissues, was evaluated under radiography and CT scan. AP radiographs of the phantom at increments of five degrees of craniocaudal tube angulation up to 35 degrees were obtained. These eight images were reviewed by two observers and by consensus opinion to select the image that best showed the second tarsal-metatarsal joint. Then, a CT of the phantom was obtained and the degree of craniocaudal angulation that would best show the second tarsal-metatarsal joint on AP view of a radiograph was determined. Finally, optimum angle of craniocaudal angulation on patients with midfoot injury was determined by reviewing the CTs of the 60 patients.
Results:
Radiographic Study: The two observers were in agreement in 41 of 60 cases (68 percent). They disagreed between normal and equivocal in 16 of 19 cases (84 percent) and between equivocal and definite in three of 19 cases (16 percent). CT was positive for Lisfranc injury in 45 cases (75 percent) and negative in 15 cases (25 percent). There were in total seven false-negatives and three false-positives based upon CT scans. Twenty of the 45 CT-positive cases were taken to the OR: 18 patients had underwent an ORIF and two were stable under manipulation under anesthesia. The remaining 25 were treated with plaster immobilization. All seven false-negatives were treated with plaster immobilization as well.
Phantom Study: On the phantom foot, one observer chose 15 degrees of craniocaudal angulation as the best angle to view the second tarsal-metatarsal joint, and the other chose 20 degrees. By consensus opinion, 20 degrees was selected. The CT measurement of the phantom also showed 20 degrees. The CT measurement that showed the best angle to view second tarsal-metatarsal joint on patients with a midfoot injury, as demonstrated by the mean measurement of the 60 patients was 28.9 degrees +/- 5.7 degrees.
Conclusions:
With about only 68.9 percent cases identified as Lisfranc injuries on radiographs, these findings suggest that a significant number of Lisfranc injuries go undiagnosed on conventional radiographs. The biggest concern lies with the patient with the subtle injury that goes undiagnosed and continues to bear weight on an unstable joint. Therefore, it is good to be cognizant that a craniocaudal angulation of 28.9 degrees can better visualize the joint on patients with a midfoot injury.