Change of Radiologic Index of Foot according to Radiation Projection Angle: A Study Using Phantom Foot

Eo Jin Kim; Sang Gyo Seo; Dong Yeon Lee

doi:10.14193/jkfas.2015.19.4.165

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Kim, Seo, and Lee: Change of Radiologic Index of Foot according to Radiation Projection Angle: A Study Using Phantom Foot

Original Article

J Korean Foot Ankle Soc 2015;19(4):165-170.

Published online: 10 January 2015

DOI: https://doi.org/10.14193/jkfas.2015.19.4.165

Change of Radiologic Index of Foot according to Radiation Projection Angle: A Study Using Phantom Foot

Eo Jin Kim, Sang Gyo Seo^*, Dong Yeon Lee

Department of Orthopedic Surgery, Seoul National University Hospital, Seoul, Korea

^*Department of Orthopedic Surgery, Asan Medical Center, Seoul, Korea

Corresponding Author: Dong Yeon Lee Department of Orthopedic Surgery, Seoul National University Hospital, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea Tel: 82-2-2072-2368, Fax: 82-2-764-2718, E-mail: leedy@snu.ac.kr

Received 21 October 2015 Revised 5 November 2015 Accepted 6 November 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

The purpose of this study is to analyze the measurement differences of simple radiographs according to radiation projection angle using a phantom and to propose methods for objective analysis of simple radiographs.

Materials and Methods

We took simple radiographs with different projection angles using a C-arm image intensifier and measured five parameters of the foot on the simple radiographic images. Five parameters include lateral tibiocalcaneal angle, lateral talocalcaneal angle, naviculocuboid overlap, lateral talo-first metatarsal angle, and lateral calcaneo-first metatarsal angle. Intraobserver and interobserver reliability were verified, and then intraclass correlations of parameters were analyzed.

Results

Radiographic parameters of the foot showed high intraobserver and interobserver reliability. Lateral tibiocalcaneal angle has a strong negative linear relationship with rotation and a moderate negative linear relationship with tilt. Lateral talocalcaneal angle has a moderate positive linear relationship with rotation and a strong positive linear relationship with tilt. Naviculocuboid overlap has a strong positive linear relationship with rotation and a moderate positive linear relationship with tilt. Lateral talo-first metatarsal angle does not have a linear relationship with rotation and a moderate negative linear relationship with tilt. Lateral calcaneo-first metatarsal angle has a moderate positive linear relationship with rotation and tilt.

Conclusion

More precise evaluation of the foot with a simple radiograph can be performed by understanding the changes of radiographic parameters according to radiation projection angle.

Keywords: Radiography, Radiographic phantom, Radiation projection, Radiographic parameters, Measurement

References

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Figure 1.

We defined the second metatarsal longitudinal axis as the vertical reference axis (VRA), and the horizontal line perpendicular to the vertical reference axis passing the center of ankle joint as the horizontal reference axis (HRA).

Figure 2.

Both markers on phantom foot should overlap for the radiation projection to be parallel to the horizontal reference axis.

Figure 3.

Angles were measured on plain lateral radiograph. a: Lateral tibiocalcaneal angle was measured to evaluate hindfoot alignment. b: Lateral talocalcaneal angle was measured to evaluate hindfoot alignment. c: Lateral talo-first metatarsal angle was measured to evaluate flatfoot deformity. d: Lateral calcaneo-first metatarsal angle was measured to evaluate cavus deformity.

Figure 4.

Naviculocuboid overlap (a/b) was measured to evaluate midfoot alignment.

Figure 5.

(A) Two markers on phantom foot overlap with radiation projection with 0^o rotation and 0^o tilt. (B) Two markers on phantom foot and alignment were twisted with radiation projection with 30^o external rotation and 15^o medial tilt.

Table 1.

Intraobserver Reliability (Intraclass Correlation Coefficient)

Radiographic parameter	Intraobserver reliability (95% confidence interval)
Lateral tibiocalcaneal angle	0.988 (0.982∼0.994)
Lateral talocalcaneal angle	0.952 (0.910∼0.971)
Naviculocuboid overlap	0.843 (0.736∼0.879)
Lateral talo-first metatarsal angle (Meary angle)	0.865 (0.793∼0.915)
Lateral calcaneo-first metatarsal angle (Hibbs angle)	0.884 (0.804∼0.923)

Table 2.

Interobserver Reliability (Intraclass Correlation Coefficient)

Radiographic parameter	Interobserver reliability (95% confidence interval)
Lateral tibiocalcaneal angle	0.974 (0.961∼0.983)
Lateral talocalcaneal angle	0.849 (0.727∼0.886)
Naviculocuboid overlap	0.664 (0.507∼0.784)
Lateral talo-first metatarsal angle (Meary angle)	0.891 (0.801∼0.937)
Lateral calcaneo-first metatarsal angle (Hibbs angle)	0.823 (0.714∼0.882)

Table 3.

Comparison of Normal Values and Measurement Values

Radiographic parameter	Normal value^*	Measurement value
Lateral tibiocalcaneal angle (^o)	N/A	76.95
Lateral talocalcaneal angle (^o)	46.5±5.45	47.33
Naviculocuboid overlap	N/A	0.21
Lateral talo-first metatarsal angle (Meary angle) (^o)	―2.5±4.6	―6.67
Lateral calcaneo-first metatarsal angle (Hibbs angle) (^o)	44.0±4.5	41.16

Values are presented as mean±standard deviation.

N/A: not available, no normal values in reference paper.

^* Values from the article of Steel et al. (Foot Ankle. 1980;1:151–8).⁶⁾

Table 4.

Changes according to Radiation Projection Angle

Radiographic parameter	Rotation 0^o	External rotation		Internal rotation
Radiographic parameter	Rotation 0^o	5^o	10^o	5^o	10^o
Lateral tibiocalcaneal angle (^o)	76.95	75.81	74.24	76.78	77.36
Lateral talocalcaneal angle (^o)	47.33	47.62	47.42	41.51	40.34
Naviculocuboid overlap	0.21	0.26	0.30	0.16	0.14
Lateral talo-first metatarsal angle (Meary angle) (^o)	―6.67	―6.33	―4.39	―2.03	―1.44
Lateral calcaneo-first metatarsal angle (Hibbs angle) (^o)	41.16	41.54	42.48	38.12	39.35

Table 5.

Correlation between Radiographic Parameters and Radiation Projection Angle

Radiographic parameter	External/internal rotation (p-value)	Medial/lateral tilt (p-value)
Lateral tibiocalcaneal angle	―0.789 (<0.01)	―0.522 (<0.01)
Lateral talocalcaneal angle	0.444 (<0.01)	0.730 (<0.01)
Naviculocuboid overlap	0.920 (<0.01)	0.300 (<0.05)
Lateral talo-first metatarsal angle (Meary angle)	―0.530 (0.714)	―0.504 (<0.01)
Lateral calcaneo-first metatarsal angle (Hibbs angle)	0.509 (<0.01)	0.303 (<0.05)

Statistics by Spearman's rank correlation coefficient.

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