(2021) 8:90
Szaro et al. J EXP ORTOP
https://doi.org/10.1186/s40634-021-00406-2

Journal of
Experimental Orthopaedics

Open Access

ORIGINAL PAPER

Morphometric relationships
between dimensions the anterior talofibular
ligament and calcaneofibular ligamentin routine magnetic resonance imaging
Pawel Szaro1,2,3* , Khaldun Ghali Gataa1,2, Nektarios Solidakis1,2 and Przemysław Pękala4,5

Abstract
Purpose: This study aimed to test the hypothesis that routine MRI ankle can be used to evaluate dimensions andcorrelations between dimensions of single and double fascicular variants of the ATFL and the CFL.
Methods: We reviewed ankle MRIs for 251 patients. Differences between the length, thickness, width, and length of
the bony attachments were evaluated twice. P < .05 was considered as significant.
Results: For the ATFL, we observed a negative correlation between thickness and width, with a positive correlation
between thickness and length (p < 0.001). The average values for the ATFL were thickness, 2.2 ± 0.05 mm; length,21.5 ± 0.5 mm; and width, 7.6 ± 0.6 mm. The average values for the CFL were thickness, 2.1 ± 0.04 mm; length,27.5 ± 0.5 mm; and width, 5.6 ± 0.3 mm. A negative correlation was found between length and width for the CFL(p < 0.001).
Conclusions: Routine MRI showed that most dimensions of the ATFL and CFL correlate with each other, whichshould be considered when planning new reconstruction techniques and developing a virtual biomechanical modelof the human foot.
Level of evidence: III
Keywords: Ankle, Magnetic resonance imaging, Reconstruction, Graft, Double fascicular ligament
Background
The ankle instability and pain after surgical ligament
reconstruction is seen in about 20% of patients, which
requires further treatment [1]. Due to unsatisfactory
clinical outcomes, there is a need to develop new reconstruction methods and to improve the traditional methods [2, 3]. The graft morphology and morphometry varydepending on the surgical technique but seem to be the*Correspondence: pawel.szaro@gu.se
1
Department of Radiology, Institute of Clinical Sciences, Sahlgrenska
Academy, University of Gothenburg, Göteborgsvägen 31, 431
80 Gothenburg, Sweden
Full list of author information is available at the end of the article

most critical factors that influence the outcome of surgery [2]. To the best of our knowledge, there have been
no studies on how the length, width, or thickness of theanterior talofibular ligament (ATFL) and the calcaneofibular ligament (CFL) correlate with each other in anormal in vivo MRI. Most studies have focused on only
the length and width of these ligaments and have been
performed on cadavers [4–7]. Therefore, comparing theresults of these studies is challenging because the authors
used different measurement techniques, thus obtaining
noteworthy differences, even up to about 10 mm. Sometimes, it is unclear whether the measurements are for asingle fascicular or double fascicular ligament. The lengthof the ATFL has been reported to vary from 12 mm [7] to© The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/.

Szaro et al. J EXP ORTOP(2021) 8:90

21 mm [4]. Based on the published literature, the lengthof the ATFL can be either 13–14 mm or 21–22 mm [4, 6],
which may confirm that the values depend on the methodology and probably variations in fascicular structure.
The length of the CFL is reported to be 15 mm [8] to
25 mm [5]. The width of the ATFL varies between studies
from 6 mm [6] to 11 mm [8], while the width of the CFL
varies from 5 mm [8] to 8 mm [5].
The MRI assessment of the thickness of the ATFL and
the CFL is relevant for radiologists. The thickness may be
a simple and objective factor that reflects the grade of ligament injury. The mean thickness of the ATFL reported
in a previous anatomical study was 2.2 ± 0.6 mm, andthe corresponding value for the CFL was 2.1 ± 0.5 mm[9]. However, there have been no radiological studies onlarger samples. The MRI assessment of ATFL and CFL
dimensions may be relevant for more tailored ankle modeling, virtual surgical planning, or mechanical interpretation of normal or impaired ankle status. Moreover, there
is an ongoing discussion about how to reconstruct theinternal structure of an injured ligament [10, 11], which
is a similar discussion to what occurred for the anterior
cruciate ligament double fascicular reconstruction in thepast. Considering individual variability and the presenceof connections between ligaments [12], finding a correlation between the dimensions of the ATFL and the CFL
will enable the preparation of a more “custom-tailored”
graft [5, 13, 14]. To the best of our knowledge, there havebeen no complex studies on measurements of the ATFL
and the CFL and correlations in vivo, which was the aimof our study.
This study aimed to investigate the clinical anatomyof the ATFL and the CFL and their mutual relationship.
The authors hypothesized that the thickness, length,
and width of single and double fascicular variants of the
ATFL and the CFL would correlate with each other.

Methods
This was a retrospective single center study of 251
clinically indicated MRI scans of the ankle. Our study
included 143 females and 108 males; the age range was
18–62 years, with a mean of 32.7 years. The right ankle
was examined in 132 cases, and the left ankle was examined in 119 cases.
Inclusion criteria

The MRI examinations were performed from January
2018 to May 2020 for non-traumatic indications. The
imaging was performed on 1.5 Tesla (34 cases) and 3.0
Tesla (217 cases) MRI machine (Siemens and Philips). The
inclusion criteria included use of a dedicated ankle coiland the availability of at least the following sequences:
proton density (PD) or T2-weighted sequences without

Page 2 of 12

fat saturation in the sagittal, axial, and coronal planes toassess ligament structure. The other sequences, such as
T1-weighted turbo spin echo (T1-TSE), PD with fat suppression, or short-T1 inversion recovery (STIR), wereused to detect pathology. PD-weighted turbo spin echo(TSE): TE (the echo time) 45 ms, TR (the repetition time)2800–5000 ms. T2-weighted (TSE) TE 60 ms, TR 3000–
5000 ms. T1-weighted: TE 11.5 ms, TR 700–750 ms.
Voxel 0.45 × 0.53 × 3.0 mm, slide thickness 3 mm, field ofview (FOV) 14 cm. No interslice gap was in our protocol.
A dedicated ankle coil was used for MRI acquisition.
Repeatability of position

The patient was in supine position and the location of
the ankle joint was maintained by using a dedicated coil(Fig. 1) which was suited to the shape of the ankle andfoot. Additional elastic wedge-shaped cushions wereused to further secure the ankle and foot position.
Evaluation of the ATFL and CFL

Detailed clinical evaluation of the ankle included in thereferral letter. Uniform thickness, homogeneous signal,
normal adjacent fat tissue, and no marrow edema orbone abnormalities indicate no trauma. MRI evaluationof the examined ligaments was done simultaneously by
two experienced observers. Only normal ATFL and CFL
were included in the study.
The exclusion criteria (Fig. 2) were ankle fracturein the anamnesis (29 cases excluded), the presenceof orthopedic hardware due to possible artefacts (27cases excluded), a history of previous ankle sprain (22cases excluded), ATFL or CFL abnormalities (18 cases
excluded), motion artefacts (13 cases excluded), andobvious abnormalities in the lateral region of the ankle (3cases) (Fig. 2).
In total, 251 MRI examinations of the ankle fulfilled theinclusion and exclusion criteria (Fig. 2). All examinations
were reviewed twice, and the final results were made byconsensus.
Nomenclature

We decided to use the term fascicule to define part ofthe ligament that is distinct and can be visualized on
MRI. However, the appropriate nomenclature is missing
regarding the internal ligament structure [13, 15].
Measurement protocols

First, single, and multi-fascicular ligaments were identified. Then, measurements were assessed following
the same protocol (Fig. 3). The approximate volume of
the ATFL and the CFL was calculated using the cuboid
formula. We used the following equation: volume of a
cuboid = (length [mm] × width [mm] × thickness [mm])Szaro et al. J EXP ORTOP(2021) 8:90

Page 3 of 12

Fig. 1 The coil is dedicated to the ankle and foot examination

Fig. 2 Study flow diagram­mm3. Each MRI examination was reviewed twice by amusculoskeletal radiologist with 5 years of experience,
who performed measurements twice with a minimumof a one-month interval. The mean value between two
measurements was used for each subject. The intersubject mean was used for the study. The other observerwith 3 years of experience in musculoskeletal radiology
performed measurements on one hundred and ten randomly chosen MRI examinations (alfa 0.05, Power 0.95)
to evaluate the inter-observer agreement.

Measurement of the ATFL

On the sagittal sequence, the length of the fibular
attachment of the ATFL was measured (Fig. 3a). The
length and thickness of the midportion of the ATFL
was assessed on the axial sequence (Fig. 3b). The widthof the ATFL was defined as the longest cranio-caudal
dimension assessed in the midportion on the coronal
section (Fig. 3c). On the coronal sequence, the largest
dimension of the talar insertion was calculated (Fig. 3c).

Szaro et al. J EXP ORTOP(2021) 8:90

Page 4 of 12

Fig. 3 Method of measuring the anterior talofibular ligament and the calcaneofibular in our study. A Sagittal projection, view from the lateral side;b axial section; c and d coronal section. Ant., anterior; post., posterior; med., medial; lat., lateral; 1, the fibula; 2, the tibia; 3, the talus; 4, the calcaneus;
5, the ATFL; 6, the CFL

Measurement of the CFL

Consecutive sagittal slides were used to evaluate the
CFL length and the width and length of the fibular insertion (Fig. 3a). The length of the calcaneal insertion wasassessed on the coronal sequences (Fig. 3d). The thicknessof the midportion of the CFL was assessed on the coronalsequence in the middle part of the ligament (Fig. 3d). In
double fascicular ligaments, the width was measured forboth fascicles together. The CFL angle and the tibiocalcaneal angle (TCA) were measured, as in a previous study[16]. Firstly, we chose the most posterior coronal section
where both the tibia and calcaneus could be identified.
Then, a line along the medial wall of the calcaneus was
drawn (line A). Secondly, a coronal section that showed
the maximum diameter of the tibial shaft was identified.
The long axis of the tibial shaft was called the tibial shaft
line (line B). The intersection angle between line B andthe vertical axis (line C) was assessed to check if lines A
and B were in the same direction or opposing directions.
If lines A and B were in the same direction in relation toline C, then the TCA was between line A and B. If lines A
and B were opposing in relation to line C, then the TCA
was calculated by subtracting the angle between lines B
and C from angle between lines A and C (Fig. 3).
Measurements were made at a dedicated diagnostic
station using radiological software, with measures to
0.1 mm.
Statistical analysis

The Kolmogorov Smirnov test was used to test for normality. A correlation between ligament dimensions andthe TCA was performed using Pearson’s correlation

coefficient. Differences between sex, side, and groups of
single and double fascicular ligament were considered
statistically significant if the p-value was less than .05.
Repeated measures (test–retest) reliability analyses via
interclass correlation coefficients (ICC) (ICC(2,1) andICC(2,2)) and 95% confidence intervals were obtained.
ICC values were interpretated according to Fleiss et al.
[17], where a value of 0.75 or greater indicates excellent
reliability, 0.40 to 0.75 indicates fair to good reliability,and 0.40 or less indicates poor reliability. The standard error of the measurement (SEM) was calculated todetermine the absolute between-trial variability in scores[18]. The data were analyzed using SPSS Statistics software version 22.0. The Swedish Ethical Review Authority approved the study and waived the need for informed
consent (number 2020–06177). Our study was performed in accordance with relevant named guidelines
and regulations.

Results
The anterior talofibular ligament

The intra-observer agreement was measured by ICC
values which ranged from 0.58 to 0.89 for individual
measurements (Table 1) while the inter-observer agreement ranged from 0.41 to 0.70 (Table 2). The SEM
values of the individual measurements are provided
in Table 1. We identified a group of double fascicular ATFL (77%, n = 193) (Figs. 4 and 5) and a group of
single fascicular ATFL (23%, n = 58). No other variations were identified. The average length of the ATFL
was 24.5 ± 3.3 mm, and no significant differences were
found between single and double fascicular ATFL

Szaro et al. J EXP ORTOP(2021) 8:90

Page 5 of 12

Table 1 Dimensions of the anterior talofibular ligament in the general group, single fascicular and double fascicular ligaments
length [mm]GeneralN = 251

single fascicularn = 58

double fascicularn = 193thickness [mm]width [mm]fibula [mm]talus [mm]volume ­[mm3]average

24.5

2.2

5.0

5.7

4.3

250.9

SD

3.3

0.3

0.7

0.9

0.5

50.9

min

16.1

1.3

3.4

3.7

3.1

93.3

max

33.1

3.0

6.9

7.3

5.6

375.7

length [mm]thickness [mm]width [mm]fibula [mm]talus [mm]volume ­[mm3]average

24.2

2.6

4.9

6.2

4.2

297.5

SD

2.8

0.4

0.7

0.7

0.6

47.2

min

19.3

1.9

4.5

4.8

3.5

187

max

27.9

3.0

6.9

6.9

5.2

375

length [mm]thickness [mm]width [mm]fibula [mm]talus [mm]volume ­[mm3]average

24.6

2.1

5.0

5.6

4.3

257.5

SD

3.4

0.2

0.7

0.9

0.5

50.2

min

16.1

1.3

3.4

3.7

3.1

93.3

max

33.1

2.8

6.7

7.3

5.6

375.7

p

> 0.05< 0.001> 0.05< 0.001> 0.05< 0.001

ICC (95% CI)

0.89 (0.88–0.89)

0.82 (0.83–0.86)

0.81 (0.67–0.86)

0.58 (0.56–0.69)

0.60 (0.59–0.76)

0.74 (0.63–0.88)

SEM

0.83

0.08

0.12

0.17

0.08

19.1

Abbreviations: ICC intra-class correlation coefficient, min. Minimum, max. Maximum, SEM standard error of measurement, SD standard deviation. P-value refers todifference between single and double fascicular ligament

Table 2 The Inter-observer agreement
ATFL
ICC
CFL
ICC

length [mm]thickness [mm]width [mm]fibula [mm]talus [mm]volume ­[mm3]

0,7

0,60

0,49

0,46

0,41

0,58

(0,19 - 0,91)(0,00 - 0,88)(−0,07 - 0,83)(−0,23 - 0,84)(−0,13 - 0,80)(0,03 – 0,87)

length [mm]thickness [mm]width [mm]fibula [mm]calcaneus [mm]volume ­[mm3]

0,68

0,77

0,49

0,63

0,69

0,47

(0,17 - 0,91)(0,34 - 0,94)(−0,22 - 0,85)(0,01 - 0,90)(0,13 - 0,91)(0,17 – 0,83)

ATFL the anterior talofibular ligament, CFL the calcaneofibular ligament, ICC intra-class correlation coefficient(Table 1). The average thickness of the ATFL was
2.2 ± 0.3 mm, with a statistically significant difference
between groups. In single fascicular ATFL, the average
thickness was 2.6 ± 0.4 mm, while in double fascicular ATFL, this was 2.1 ± 0.2 mm (Table 1). The averagewidth of the ATFL was 5 ± 0.7 mm, but no statisticallysignificant differences were noted between groupsof single and double fascicular ligaments (Table 1).
The length of the fibular attachment was longer thanthat of the talar attachment, which was, on average,
5.7 ± 0.9 mm, with statistically significant differences
between groups (p < 0.001). No statistically significant
differences were found regarding the length of thetalar attachment. The average volume of the ATFL was
250.9 ­mm3, which corresponds to 0.3 mL, with statistically significant differences between groups (p < 0.001),
as shown in Table 1. There were no statistically significant differences between the ATFL dimensions
obtained on the 1.5 T and 3.0 T machines (p > .05).

Our study revealed very weak but significant negative correlations between the length and thickness in allgroups (Table 3, Fig. 6). There was a significant positive
correlation between the width and length, but there
was a negative correlation between the width and thethickness. This tendency was most prominent in single
fascicular ATFL.
Variable correlation could be seen between thedimensions of the bone attachments and the otherdiameters. A negative correlation between the lengthand the thickness of the ATFL and the length of thefibular attachment in single fascicular ATFL was found(Table 3). The length of the talar attachment of the
ATFL showed a negative correlation with the thickness of single fascicular ATFL. The length of the talar
attachment in double fascicular ATFL showed a strong
positive correlation with the width. The volume of the
ATFL correlated with all diameters, however, mostly
with length (Table 1).

Szaro et al. J EXP ORTOP(2021) 8:90

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Fig. 4 A double fascicular anterior talofibular ligament. Two asymmetrical fascicles are visible; the bigger one is located in a superior position(arrow), and the smaller one inferior (curved arrow). A T2-weighted sagittal section; b and c T2-weighted axial section; d and e T2-weighted coronal
section. F, fibula; t, talus

The calcaneofibular ligament

The inter-rater ICC values ranged from 0.66 to 0.78 forindividual measurements (Table 4), while the interobserver agreement ranged from 0.47 to 0.77 (Table 2).
The SEM values of the individual measurements are provided in Table 4. A group of double fascicular (69.7%,
n = 175) (Fig. 6) and single fascicular (30.3%, n = 76)
CFLs was identified. The average length of the CFL
was 33.7 ± 4.1 mm. Statistically significant differences(p < 0.001) between the two groups were found (Table 4).
The average thickness of the CFL was 2.1 ± 0.2 mm; however, the differences between groups were not significant.
The average width was 6.6 ± 1.4 mm, without a significant difference between groups. Significant differences(p < 0.001) in volume were revealed, with an average valueof 419.8 ­mm3. The average craniocaudal dimension of thecalcaneal attachment of the CFL was 7.7 ± 1.3 mm, withsignificant difference between groups (p < 0.01) (Table 5).
There were no statistically significant differences between
the CFL dimensions obtained on the 1.5 T and 3.0 T
machines (p > .05).
The inter-rater ICC value for the CFL angle was 0.84
(0.73–0.88, SEM 2.98) (Table 4), while the inter-observer
agreement was 0.43 (0.34–0.65). The average CFL angle
was 113.5 ± 13.1 deg, with no significant differences
between groups (Table 5). The inter-rater ICC value
for the TCA was 0.83 (0.34–0.95, SEM 0.48) (Table 4),
while the inter-observer agreement was 0.39 (0.32–0.52).
The average value of the TCA was 10.9 ± 4.5 deg, withsignificant differences between groups (Tables 4 and 5).
There were no statistically significant differences between
CFL or TCA angles obtained on the 1.5 T and 3.0 T
machines (p > .05).
We revealed some statistically significant correlations between the dimensions of the CFL (Tables 4 and
5, Figs. 7 and 8). Significant negative correlations were
found between the length, thickness, and width. The
most prominent negative correlation between the lengthand thickness was seen in single fascicular CFL. Significant positive correlations between the volume and all
dimensions were noted, with the strongest correlation
with the width; however, these were not significant in single fascicular CFL (Table 5).
The width of the fibular attachment was correlated with
CFL length, thickness, and width (Table 5). Width was
positively correlated with the length of bony attachments,
with significance only in double fascicular CFL (Table 5).
A significant positive correlation between the dimensions of both bony attachments was noted (Table 5). The
strongest significant positive correlation was between
volume and width in double fascicular CFL (Table 5,
Fig. 8). A significantly negative correlation between the
CFL angle and the length of the CFL was seen, mainlyin the group of single fascicular ligaments. The TCA was
negatively correlated with thickness, which was mostprominent in double fascicular CFL.
No statistically significant differences between sex,side, and groups of single and double fascicular ligaments

Szaro et al. J EXP ORTOP(2021) 8:90

Page 7 of 12

Fig. 5 A double fascicular anterior talofibular ligament. Two symmetrical fascicles are visible: a superior fascicle (arrow) and an inferior fascicle(curved arrow). The dashed arrow shows the midportion of the CFL. A T2-weighted axial section; b T2-weighted coronal section; c T2-weighted
sagittal section. F, fibula; t, talus

or dimensions were found (p > .05). We noted two casesof os subfibulare, where the inferior fascicle of the ATFL
had an insertion on the accessory bone and a superiorfascicle on the fibula.

Discussion
Our study revealed the negative correlation between
thickness and width of the ATFL and the positive correlation between thickness and length. The negative correlation was found between length and width for the CFL.
We found significant differences in dimensions between
single and double fascicular ATFL and CFL Significant differences in the midportion thickness, the fibular
attachment length, and the volume between single anddouble fascicular ATFL can be noticed. In the CFL, significant differences were noted in the length of the wholeligament, the length of the calcaneus attachment, and thevolume.
The ligament dimensions may be clinically relevant
because the possibility of injury is more common when
the ligament is wider and longer. More anatomicalreconstruction helps to restore the ligament’s native
geometry and thus helps to restore joint stability [19].
The intercorrelation between the length, the width, andthe thickness of the ATFL and the CFL in relation tofascicular structures has not been studied before. The
ATFL should not be understood as a single ligament but
rather as a component of a biomechanical complex. This
complex, in different positions of the joint and in different directions of force, tenses in different ways, andits extended parts act as stabilizers for post-secondary
movements.
Some differences from previously published results
were noted in the dimensions of the ATFL. This isprobably related to the different methodology and thesmaller groups in previous studies. The length of the
ATFL obtained by us was about 10 mm longer than values reported previously on a smaller number of cases[7, 8, 20–22]. However, when compared with authors
who conducted studies on more extensive sample, ourresults are comparable despite the different methodology [4, 6] (Tables 1 and 3). The reason for our findingSzaro et al. J EXP ORTOP(2021) 8:90

Page 8 of 12

Table 3 Correlation of the anterior talofibular ligament’s dimensions

GeneralN = 252

lengthlengththicknesswidth

fibulartalar

volumex−0.02***

0.20***

0.15***

0.05***

0.67***−0.13***

0.21***−0.15***

0.45***

0.49***

0.62***

0.05***

0.17***

x

0.20***

thickness

x

width

x

fibula−0.02**
x

talus
volumeSingle fascicularn = 58lengthxx

thickness− 0.01***xwidth

0.39***− 0.49***x

fibula−0.07***

0.01***

0.86***−0.19***

0.43***

0.01*− 0.60***0.45***

x−0.04−0.08***
x− 0.16***−0.4***

talus
volumeDouble fascicularn = 193

lengththicknessxx−0.003***x

width
fibulatalus
volume0.14***

0.25***

0.06***

0.65***−0.01***

0.27***

0.05***

0.44***−0.03*

0.67***

0.68***

0.03***

0.43***

x

0.43***xxx* p < 0.05, ** p < 0.01, *** p < 0.001

Fig. 6 Examples of correlations between the dimensions of the anterior talofibular ligament. A, c, and e transverse section; b, d, and f view
from the lateral side. Ant., anterior; post., posterior; 1, talus; 2, fibula. C and d the increased length of the anterior talofibular ligament is positively
correlated with width and negatively correlated with thickness. E and f the increased thickness of the ATFL is positively correlated with the length of
the fibular insertion and negatively correlated with the width and length of the talar insertion, and there is a very weak positive correlation with thelength of the whole ligamentof a longer ATFL than other authors may be due to thefact that we measured the entire ligament, including
its bony attachments, while some authors measured
from the midpoint of the attachment. It is also possible that MRI can better differentiate the structure of
the ligament from its bony attachment [7, 23]. In future

research, the methodology of the research on ankle
ligaments should be standardized. From a clinical pointof view, it is better to use our method because it refers
to a functional ligament complex, which the surgeon
also sees during the procedure. The dimensions of the
ATFL may have a developmental context because it isSzaro et al. J EXP ORTOP(2021) 8:90

Page 9 of 12

Table 4 Dimensions of the calcaneofibular ligament in the general group, single fascicular and double fascicular ligaments
length [mm]thickness[mm]

width [mm]fibula [mm]calcaneus[mm]volume­[mm3]

CFL angle[deg]

TCA [deg]

average

33.7

2.1

6.6

5.2

7.7

419.8

113.5

10.9

SD

4.1

0.2

1.4

1.0

1.3

98.2

13.1

4.5

min

24.2

1.3

3.8

2.7

4.9

248.8

80.2

2.2

max

42.7

2.5

10.1

7.1

10.1

656.6

133.4

16.7

length [mm]thickness[mm]

width [mm]fibula [mm]calcaneus[mm]volume­[mm3]

CFL angle[deg]

TCA [deg]

average

31.4

2.0

6.2

5.4

7.1

383.8

116.1

12.4

SD

3.5

0.1

1.7

0.9

1.3

99.0

12.6

5.3

min

24.7

1.8

3.8

3.1

4.9

248.8

90.0

2.0

max

42.7

2.1

9.2

6.4

8.9

290.3

133.0

23.0

length [mm]thickness[mm]

width [mm]fibula [mm]calcaneus[mm]volume­[mm3]

CFL angle[deg]

TCA [deg]

average

33.2

2.1

6.5

5.2

7.6

437.0

113.1

10.3

SD

4.3

0.3

1.3

1.1

1.3

93.7

13.2

3.8

min.

24.2

1.3

4.1

2.7

5.1

277.2

80.0

3.0

max

42.7

2.5

10.1

7.1

10.1

656.6

140.0

17.0

P

< 0.001> 0.05> 0.05> 0.05< 0.01< 0.001> 0.05< 0.05ICC (95% CI)

0.78(0.74–0.79)

0.66(0.39–0.75)

0.78(0.66–0.89)

0.74(0.63–0.88)

0.72(0.60–0.77)

0.74(0.67–0.78)

0.84(0.73–0.88)

0.83(0.34–0.95)

SEM

0.90

0.06

0.24

0.21

0.18

27.8

2.98

0.48

GeneralN = 251

Single fascicularn = 76

doublefascicularn = 175

Abbreviations: CFL the calcaneofibular ligament, deg. degrees, ICC intra-class correlation coefficient, min. Minimum, max. Maximum, SEM standard error ofmeasurement, SD standard deviation, TCA​the tibiocalcaneal angle. P-value refers to difference between single and double fascicular ligament

Table 5 Correlations of the calcaneofibular ligament’s dimensions

GeneralN = 251

lengthlengththicknesswidth

fibulacalcaneus

volume

CFL angle

TCA​x- 0.19***- 0.13***- 0.23***- 0.09***0.22***- 0.18***- 0.17***

0.21***

x

0.48***−0.08***−0.44***

0.13***

x

0.56*

0.73***

0.33**

0.56***

0.21***

0.21***−0.20***

x

0.57***

0.22***

x

0.25***−0.02***

0.01***

0.14***

0.06***−.67***

thicknesswidth
fibulax

calcaneus
volumeSingle fascicularn = 76

lengthx

thickness- 0.51***- 0.16***- 0.42***x- 0.10***0.4***

x

0.51

0.57

x

width
fibulacalcaneus
lengththicknesswidth
fibulacalcaneusx

0.01***−0.27***−0.28***
0.19***

0.13***

0.51

0.42***

0.56**

0.52***

0.29***−0.29**

x

0.78***

0.24**

x

0.16***−0.22***- 0.03***- 0.11***- 0.13***- 0.12***0.21***

x- 0.24***- 0.33***0.29***

x

0.47**−0.2***
0.52*

0.47*

0.29***

0.58***

0.13***

0.20***

x

0.44***

0.26***

x

0.41***

x−0.23***

0.13***

volumeDouble fascicularn = 175

0.26***

volumeAbbreviations: CFL the calcaneofibular ligament, TCA​the tibiocalcaneal angle. * p < 0.05, ** p < 0.01, *** p < 0.001

0.36***

0.12***−0.31***−0.21***
0.17***−0.44***−0.09***−0.10*−0.23***−0.32***

Szaro et al. J EXP ORTOP(2021) 8:90

Page 10 of 12

Fig. 7 The double fascicular calcaneofibular ligament. The medial (arrow) and lateral fascicle (curved arrow) are visible. A and b T2-weighted
coronal section; c T2-weighted axial section. Cal, calcaneus; f, fibula; t, talus

Fig. 8 Examples of correlations between the dimensions of the calcaneofibular ligament. A, c, and e lateral view; b, d, and f coronal section. Ant.,anterior; post., posterior; med., medial; lat., lateral. C and d the increased length is negatively correlated with the width, thickness, and length of thefibular attachment and the CFL angle. E and f the increased thickness is positively correlated with the CFL angle and negatively correlated with thelength of the fibular insertion and the width and length of the whole ligament, and there is a very weak negative correlation with length of thecalcaneal attachment

significantly wider in clubfoot than in the general population [24, 25].
The thickness of the ATFL and the CFL has not beenstudied as much as the length or width. The focus onlength and width is related to the fact that these dimensions are most relevant for orthopedists in the context

of surgical reconstruction. The normal thickness of astructure has importance to the radiologist during theevaluation of MRI after trauma and chronic injuries.
A partial injury to a ligament may preserve a narrow
ligamentous band that has no mechanical properties or
may affect only a small part of the ligament, which may

Szaro et al. J EXP ORTOP(2021) 8:90

still have good function. Both are anatomically classified as grade two injuries; although, they are functionally very different. The amount of ligament defect after
trauma should be specified in the radiological report.
Thus, the thickness of the torn ligament at grade twoshould be compared to a normal cut-off value. However, this value is not specified in the literature. Our
results are comparable to the sparse papers available [6,26, 27]. In our opinion, the use of MRI enables an accurate assessment of the degree of ligament injury, whichallows for planning possible surgical treatment.
No significant differences were noted between the
thickness of the CFL revealed by us compared withpreviously reported values [9]. As with the ATFL, thelength and width of the CFL revealed by us differedfrom the previously published results of anatomical
studies on cadavers. The difference in the length of the
CFL was about 10 mm, and the difference in the width
was about 4 mm [5, 6, 8]. The differences probably arise
from different methodologies and the smaller numberof cases in previously published studies.
A CFL angle lower than 119 deg measured on MRI
may indicate valgus hindfoot [28]. This is due to thefact that a decreased CFL angle is associated withan increased TCA, which may correspond to valgus deformity [28]. Quite prominent correlations
were visible between CFL diameters, CFL angle, andTCA values. The orientation of the CFL in relation
to its thickness can be a valuable factor during surgical reconstruction. A confirmation of this opinion canbe the observation that a horizontally orientated CFL
angle may indicate hindfoot [28]. Conventionally, thehindfoot assessment has been performed on standardized X-ray, and values of more than 10 deg are considered abnormal [29]. The values obtained by us are
somewhat difficult to compare with the values reportedon X-ray because the patient’s position during MRI
and X-ray is different [28, 29]. However, there is a correlation between CFL angle and the TCA [28]. This isessential to avoid possible overloading of the reconstructed CFL by hindfoot deformation.
We acknowledge the limitations of our study. Only thelongest dimension of the bony attachments was measured.
We believe that a special protocol with ultra-thin layers or
3D sequences should be used to improve measurement
accuracy. It will enable reformatting at the plane along or
perpendicular to the measured ligament. Measurement
errors may be related to slide thickness and the angle ofthe section. The retrospective character and the lack ofsurgical correlation may also be limitations of this study.
Another limitation is the lack of information about the subjects’ height, weight, and body mass index (BMI). Only one

Page 11 of 12

operator performed the measurements. MRI examinations
were performed on two different MRI machines.

Conclusion
Most dimensions of the ATFL and the CFL correlated witheach other. There are significant differences in dimensions
between single and double fascicular ligaments. Routine
MRI may be used to assess ATFL and CFL correlationsof dimensions. The data from this study may be used forthe development of a virtual biomechanical model of thehuman foot.
Abbreviations
ATFL: Anterior talofibular ligament; BMI: Body Mass Index; CFL: Calcaneofibular ligament; FOV: Field-of-view; ICC: Intraclass correlation coefficient; MRI:
Magnetic resonance imaging; PD: Proton density; SEM: Standard error of themeasurement; STIR: Short-T1 inversion recovery; T1-TSE: T1-weighted turbo
spin echo; TCA​: The tibiocalcaneal angle; TE: Echo time; TR: Repetition time;
TSE: Turbo spin echo.
Acknowledgements
Not applicable.
Authors’ contributionsFirst authors: conception, design and supervision of the study, acquisitionof data, analysis and interpretation of data, figures preparation, drafting thearticle. Second author acquisition of data, analysis, and interpretation ofdata. Third and fourth authors analysis and interpretation of data, revisingmanuscript critically for important intellectual content. All authors read andapproved the final manuscript.
Funding
Open access funding provided by University of Gothenburg.
Availability of data and materials
The datasets used and/or analyzed during the current study are available fromthe corresponding author upon reasonable request.

Declarations
Ethics approval and consent to participate
The Ethical Review Authority approved this study and waived the need for
informed consent (number 2020–06177).
Consent for publication
The Ethical Review Authority approved this study and waived the need for
informed consent (number 2020–06177).
Competing interests
The authors declare that they have no competing interests.
Author details
1
Department of Radiology, Institute of Clinical Sciences, Sahlgrenska Academy,
University of Gothenburg, Göteborgsvägen 31, 431 80 Gothenburg, Sweden.
2
Department of Musculoskeletal Radiology, Sahlgrenska University Hospital,
Gothenburg, Sweden. 3 Department of Descriptive and Clinical Anatomy, Medical University of Warsaw, Warsaw, Poland. 4 Faculty of Medicine, Jagiellonian
University Medical College, Krakow, Poland. 5 Faculty of Medicine and Health
Sciences, Andrzej Frycz Modrzewski Kraków University, Kraków, Poland.
Received: 25 June 2021 Accepted: 17 September 2021

Szaro et al. J EXP ORTOP(2021) 8:90

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