- This preliminary study investigated which diagnostic criteria on non-weight-bearing (NWB) and weight-bearing (WB) radiographs correlated with surgically confirmed Lisfranc instability in 26 patients, who were compared with 26 control subjects
- Although key standardized measurements of diastasis were significantly more apparent in both WB and NWB films compared to the control group, WB radiographs showed to be more reliable in detection of the instability in this preliminary study
- WB imaging was more reliable than NWB views when interobserver agreement was calculated
- A majority of patients with Lisfranc instability would have gone undiagnosed if the conventional 2-mm cut-off value for diastasis had been applied to NWB radiographs, therefore revising the cut-off value may be warrented using a larger population study
- Clinical concern for subtle or occult Lisfranc instability in any patient should trigger weightbearing imaging like WB radiographic assessment because this injury can be missed on NWB images
Early recognition of Lisfranc instability is critical for optimizing clinical outcomes, given that surgical delays lead to poorer prognoses. Most research into diagnostic methods has been performed using weight-bearing (WB) X-rays, which are not always available from the emergency room or urgent care clinic.
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Therefore, researchers at Mass General's Foot and Ankle Research and Innovation Laboratory in the Department of Orthopaedic Surgery, including Jan De Brujin, formerly a research intern; foot and ankle surgeons Daniel Guss, MD, MBA, and Gregory Waryasz, MD; and Christopher DiGiovanni, MD, chief of the Foot and Ankle Service, set out to understand diagnostic parameters for non-weight-bearing (NWB) imaging as well. They published their findings in Injury.
The researchers identified 26 patients in the Mass General Brigham patient data registry who presented with a Lisfranc injury between July 1991 and October 2018. Those adults had purely ligamentous Lisfranc injuries, surgically proven instability without complete tarsometatarsal (TMT) joint dislocation, and both preoperative WB and NWB radiographs available.
The team also identified a control group of 26 patients with fifth metatarsal zone I avulsion fractures. Key parameters measured on the radiographs of both groups were:
- C1-M2 distance, the distance between the medial cuneiform and the second metatarsal base
- M1-M2 distance, the distance between the first and second metatarsal bases
- C2-M2 alignment, the lateral displacement of the second metatarsal relative to the intermediate cuneiform
- NWB films—Only C1-M2 distance was more than 1 mm larger (mean difference, 1.35 mm, P<0.001) in the Lisfranc cohort than in the control group; notably, C2-M2 alignment was not significantly different between groups
- WB films—Differences between the groups were magnified and easier to identify than with NWB views; compared with controls, the Lisfranc cohort had significantly larger C1-M2 distance (mean difference, 2.97 mm; P<0.001) and C2-M2 alignment (1.98 mm, P<0.001), although not larger M1-M2 distance
Within the Lisfranc cohort, C1-M2 distance and C2-M2 alignment were significantly larger in WB than in NWB films (mean differences 1.77 and 1.58 mm, respectively; P<0.001 for both).
Supporting the clinical utility of those measurements, their interpretation was more reliable on WB than NWB X-rays:
- NWB films: Intraclass correlation coefficient, 0.79 for C1-M2 distance and 0.72 for C2-M2 alignment (moderate interobserver agreement)
- WB films—0.91 and 0.98 (substantial interobserver agreement)
Relationship to Conventional Threshold
When compared with the cut-off value of 2 mm diastasis that's commonly used to diagnose Lisfranc instability:
- NWB films from the Lisfranc cohort—50% of C1-M2 distance measurements and 96% of C2-M2 alignment measurements were subthreshold
- WB films from the Lisfranc cohort—8% and 50% were subthreshold
Thus, if a surgeon had applied the conventional threshold and used only NWB films, half of the patients with Lisfranc instability would have gone undiagnosed based on C1-M2 diastasis measurements. Virtually none would have been diagnosed based on C2-M2 alignment.
Advice for Surgeons
These findings underscore that when patients are suspected of having subtle or occult Lisfranc instability, it's critical to evaluate the foot using weightbearing imagery like WB radiographs.
Some potential radiographic abnormalities suggested in other research weren't evident in this study—C1-C2 (intercuneiform) distance, C3-M3 and C4-M4 alignment, plantar gapping at the first TMT, arch height loss and dorsal step-off at the second TMT. This could be due to the small study population, and should be clarified through future research, given that abnormalities in these measurements can be associated with Lisfranc instability—especially as injuries become more severe.
In particular, in the senior author's experience, C1-M2 and C1-C2 significant diastasis are often found to require surgical stabilization once directly visualized in the operating room. Additionally, instability is often visible intraoperatively in the sagittal plane that anteroposterior radiography could not have captured. For these reasons, 3D evaluation of the joint might be necessary and should be assessed in future investigations.
Learn more about the Foot and Ankle Research and Innovation Lab
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