Assessing Lisfranc Instability With Triplanar Weightbearing CT Alignment: Standardized Second Metatarsal Dorsal Offset

Abstract

Background

Subtle Lisfranc injuries may escape detection on conventional imaging. Weightbearing computed tomography (WBCT) offers 3-dimensional assessment under loadbearing conditions and may improve detection of instability. The interval between the medial cuneiform (C1) and the second metatarsal (M2) is commonly measured, but sagittal displacement of M2 relative to the intermediate cuneiform (C2) may provide additional information.

Methods:

We retrospectively analyzed 31 patients with acute Lisfranc injuries who underwent bilateral WBCT. A new standardized measurement of the second metatarsal dorsal offset (M2DO) was performed following triplanar alignment of M2, measuring dorsal cortical offset relative to the second cuneiform. Two foot and ankle surgeons independently obtained measurements; 1 repeated all measurements after 2 weeks. Injured and uninjured sides were compared with paired t tests, and intra- and interobserver agreement was assessed with intraclass correlation coefficients (ICCs).

Results:

The M2DO differed significantly between injured (0.71 ± 1.18 mm) and uninjured feet (−0.74 ± 0.66) (P < .0001). Reliability was almost perfect for intra- and interobserver assessments in injured feet (intrarater 0.92, interrater 0.94) and in the overall cohort (0.93 and 0.92), and substantial in uninjured feet (0.79 and 0.67).

Conclusion:

The M2DO is a reliable WBCT-based parameter for evaluating Lisfranc instability. It may supplement the triplanar C1-M2 method and thereby improve diagnostic accuracy and reproducibility. Future studies should establish thresholds for surgical decision-making and clinical application.

Level of Evidence:

Level III, retrospective diagnostic study.

Introduction

In subtle Lisfranc injuries without clear displacement on conventional imaging, weightbearing studies are used to reveal load-dependent joint space widening or displacement within the Lisfranc joint complex (LJC), aiding surgical decision making. ¹ Bilateral weightbearing radiographs have been widely used for decades.^2,3 More recently, weightbearing computed tomography (WBCT) has emerged as a modality combining weightbearing evaluation with 3-dimensional assessment, enabling distance, area, and volumetric analysis.^{4 -8}

The interval between the medial cuneiform (C1) and the base of the second metatarsal (M2) is commonly assessed, as it follows the interosseous Lisfranc ligament, the primary stabilizer of the LJC. ⁹ Injury to this ligament can cause widening of the C1-M2 interval under loadbearing conditions.^{3 -5} We introduced and validated a WBCT-based triplanar C1-M2 measurement technique, which improved intraclass correlation coefficients (ICCs) and reduced error.^6,8

Ligamentous injury within the LJC may also manifest as bony avulsions from the plantar and dorsal aspects of M2, reflecting ligament attachments. ⁹ Such disruption may cause sagittal shift of the M2 base, accentuated by its dorsally opening, cone-shaped configuration. Attempts to evaluate Lisfranc instability on lateral weightbearing radiographs have been limited by bony superimposition.^2,3

Although dorsal offset of M2 is a characteristic feature of displaced, surgically indicated Lisfranc injuries even on nonweightbearing CT, ¹⁰ WBCT may capture subtle sagittal alterations in the intermediate cuneiform (C2)-M2 relationship under loadbearing conditions, providing an additional parameter to assess LJC stability in subtle variants. However, previous efforts to quantify a second tarsometatarsal (TMT) stepoff on WBCT have been limited by lack of standardized protocols with plane correction, reliance on cadaveric models, or small sample size.^4,5

The aim of this study was to introduce a standardized WBCT measurement of the second metatarsal dorsal offset (M2DO) as a supplement to the previously described triplanar C1-M2 method, incorporating correction of the measurement plane. We sought to evaluate its reliability and compare injured with uninjured sides. We hypothesized that the new measurement would reveal significant side-to-side differences and excellent intraclass correlation coefficients (ICCs).

Patients and Methods

This retrospective study was approved by the institutional review board (IRB Pro00113556). The same patient sample as in the previous study on C1-M2 measurement precision after triplanar alignment of M2 was used. ⁸ It included individuals with acute Lisfranc injuries who underwent bilateral WBCT (CurveBeamAI) as part of clinical assessment. Lisfranc injuries were defined on WBCT by morphologic evidence of involvement of the first, second, or third TMT joints and/or the C1-M2 interval, including avulsion fractures at ligamentous attachment sites of the dorsal, interosseous, or plantar ligaments. No patients with dorsal comminution of the TMT2 joint were included in this study. A flow chart illustrating inclusion and exclusion appears in Figure 1.

Figure 1.

Study inclusion flowchart.

Manual measurements were independently performed by 2 fellowship-trained foot and ankle surgeons using CubeVue version 4.2.0.1 (CurveBeamAI). For intraobserver reliability, 1 observer repeated measurements after 2 weeks. Both observers were masked to each other’s results and to their own prior measurements.

Triplanar Alignment and M2DO Measurement

Axial alignment began with a slab view, marking midpoints of the proximal and distal M2 diaphysis and rotating accordingly. The coronal plane was aligned by drawing a tangential line along the dorsal M2 base and adjusting M2 perpendicular. Sagittal alignment was achieved by marking midpoints of the M2 diaphysis and adjusting the reference line just plantar to the plantar cortex of M2. For M2DO, the axial plane was corrected perpendicular to the C2 articular surface. The sagittal slice at the TMT2 joint center was selected, and a line is drawn along the dorsal cortex of C2. A parallel line was placed at the most dorsal point of M2; their vertical distance defines the M2DO. Positive values indicate dorsal displacement of M2 relative to C2, negative values plantar positioning (Figure 2).

Figure 2.

Standardized measurement of the second metatarsal dorsal offset (M2DO). Before measuring M2DO, triplanar adjustment of the measurement plane is performed according to the axial, coronal, and sagittal axis of the second metatarsal (M2) (red line in panels 1, 2b, and 3a). Initial axial plane alignment starts by creating a slab view, marking the midpoints of the proximal and distal diaphysis of M2, and rotating the bone accordingly (1). The coronal plane is aligned by drawing a tangential line along the dorsal surface of the M2 base (2a) and adjusting M2 perpendicular to this line (2b). Finally, sagittal alignment is achieved by marking midpoints of the proximal and distal M2 diaphysis in a sagittal slab view, aligning rotation by them (3a), and adjusting the reference line in the sagittal view just plantar to the plantar cortex of M2 (3b). For the M2DO measurement, the axial plane is corrected perpendicular to the articular surface of C2 (4). The sagittal slide centered at the TMT 2 joint is selected and a reference line is drawn along the dorsal cortex of C2 (yellow line; 5a healthy side, 5b injured side). A second line, parallel to the first, is drawn at the most dorsal point of M2 (orange line). The vertical distance between these 2 lines represents the M2DO (red marker in panels 5a and 5b). Positive values indicate dorsal displacement of M2 relative to C2, whereas negative values indicate that the dorsal cortex of M2 lies plantar to that of C2. In the illustrated case, the M2DO was −0.9 mm on the uninjured side and 1.51 mm on the injured side.

Statistics

Normality of the continuous variable was confirmed using the Shapiro-Wilk test. Injured vs uninjured sides were compared with paired t tests. Interobserver agreement was assessed with ICCs using a 2-way mixed-effects model for absolute agreement. ICCs were interpreted as follows: 0.81 to 0.99, almost perfect; 0.61 to 0.80, substantial; 0.41 to 0.60, moderate; 0.21 to 0.40, fair; and ≤0.20, slight reliability. ⁴ A P value <.05 was considered significant. Analyses were performed using Stata 18.0 (StataCorp, College Station, TX, USA).

Results

Thirty-one patients were included (11 men, 20 women; mean age 46.8 ± 16.5 years; mean BMI 29.4 ± 5.6). Injuries involved the right foot in 18 and the left in 13. WBCT was obtained a mean of 17 ± 11 days after injury.

Measurement results and ICCs are summarized in Table 1. A highly significant difference was found between injured and uninjured sides (0.71 vs −0.74 mm, P < .0001). The method demonstrated almost perfect intra- and inter-rater reliability in injured feet and the overall cohort, and substantial reliability in uninjured feet.

Table 1.

Measurement Results (in Millimeters) Comparing the Injured Side With the Uninjured, Contralateral Side (First Row). ^a

	Injured side	Contralateral Side	Difference	P Value
M2DO, mean (SD)	0.71 (1.18)	−0.74 (0.66)	1.45 (1.17)	<.0001
			All Feet
Intrarater, ICC (95% CI)	0.9199 (0.8409, 0.9606)	0.7918 (0.6145, 0.8935)	0.9269 (0.8816, 0.9553)
Interrater, ICC (95% CI)	0.9412 (0.8818, 0.9712)	0.6742 (0.4249, 0.8285)	0.9197 (0.8705, 0.9508)

Abbreviations: ICC, intraclass correlation coefficient; M2DO, second metatarsal dorsal offset.

^aICCs for intra- and interrater reliability (last two rows).

Discussion

This study introduces a standardized technique for measuring the M2DO with triplanar alignment as a supplemental WBCT tool for assessing Lisfranc injuries, demonstrating significant side-to-side differences and high ICCs.

The method builds on the previously described triplanar C1-M2 measurement technique but modifies axial alignment by orienting the plane perpendicular to the TMT2 joint surface of C2. This ensures correct sagittal positioning and reference at C2, as M2 typically displaces relative to C2. Coronal correction further centers the sagittal slice and clarifies the dorsal cortex of C2: crucial for drawing the measurement reference line (Figure 2[5a and 5b]).

Both intra- and interrater ICCs for the uninjured side were lower than in the injured feet (Table 1), likely reflecting the narrower normal range, where small discrepancies weigh more heavily, and a ceiling effect in which subtle deviations within a tight interval reduce agreement.

Previous attempts to measure M2DO on WBCT have been reported. ⁵ Bhimani et al ⁵ assessed TMT2 stepoff in 14 bilateral scans with intraoperatively confirmed Lisfranc instability, measuring at the midportion of the joint, and reported interrater ICCs of 0.90 with mean values of –1.2 mm for healthy and 0.6 mm for injured feet. Our corresponding values were –0.74 mm and 0.71 mm. Differences in uninjured values may reflect measurement technique, although their wider injured range likely reflects inclusion of only surgically unstable injuries. In contrast to their preset sagittal slice without realignment, our method standardizes alignment to the coronal M2 axis and C2 joint surface, reducing susceptibility to oblique slicing. Additionally, their ICCs were derived from only 4 patients and intrarater reliability was not reported, whereas our study assessed reproducibility on a larger cohort with repeated reads, improving generalizability.

We consider this method clinically applicable, as it captures sagittal changes in Lisfranc injuries that are difficult to assess on weightbearing radiographs. It can be performed using any imaging software supporting multiplanar CT reconstruction.

This study has limitations. Full weightbearing during WBCT was not verified, and patient posture may have influenced the M2DO. Moreover, we assessed reproducibility but not diagnostic accuracy, and variability in uninjured feet may affect interpretation.

Conclusion

In this study, we report excellent intra- and interobserver reliability of a novel method of measuring the M2DO as an additional WBCT approach for assessing Lisfranc injuries. Future studies should clinically validate the M2DO by correlating it with surgical findings and outcomes, define diagnostic thresholds to guide treatment, and assess whether combining it with the triplanar C1-M2 technique improves accuracy in unstable Lisfranc injuries.