Prospective Validation of a Weightbearing CT Stability Threshold for Subtle Lisfranc Injuries

Area of Science:

• Orthopedic surgery
• Medical imaging
• Biomechanics

Background:

• Subtle Lisfranc injuries pose diagnostic challenges.
• Weightbearing computed tomography (WBCT) offers 3D assessment under load but lacks defined diagnostic criteria.
• Optimal WBCT timing, protocols, and stability thresholds for Lisfranc injuries are not established.

Purpose of the Study:

• To define the role of WBCT in diagnosing subtle Lisfranc instability.
• To establish a WBCT measurement protocol and stability threshold.
• To evaluate WBCT's utility in guiding treatment decisions for Lisfranc injuries.

Main Methods:

• Prospective recruitment of patients with subtle Lisfranc injuries (nondisplaced fractures <2mm).
• Bilateral, single-leg WBCT scans to assess Lisfranc joint stability.
• Measurement of medial cuneiform (C1) and second metatarsal (M2) difference scores compared to the contralateral side; instability threshold defined as >3mm C1-M2 difference.

Main Results:

• 38 patients included; 8 (21%) demonstrated instability with a C1-M2 difference >3mm, confirmed by fluoroscopic stress testing.
• 30 patients (79%) showed stable joints (C1-M2 difference <3mm) and received conservative treatment.
• Excellent interrater (ICC 0.95) and intrarater (ICC 0.97) agreement for the measurement method.

Conclusions:

• WBCT can be effectively performed 9 days post-injury for subtle Lisfranc injuries.
• A C1-M2 difference >3mm on WBCT reliably identifies subtle Lisfranc instability.
• This WBCT method provides a standardized approach for diagnosing and managing subtle Lisfranc injuries.