Journal List > J Korean Foot Ankle Soc > v.19(4) > 1043356

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

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.

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).
jkfas-19-165f1.tif
Figure 2.
Both markers on phantom foot should overlap for the radiation projection to be parallel to the horizontal reference axis.
jkfas-19-165f2.tif
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.
jkfas-19-165f3.tif
Figure 4.
Naviculocuboid overlap (a/b) was measured to evaluate midfoot alignment.
jkfas-19-165f4.tif
Figure 5.
(A) Two markers on phantom foot overlap with radiation projection with 0o rotation and 0o tilt. (B) Two markers on phantom foot and alignment were twisted with radiation projection with 30o external rotation and 15o medial tilt.
jkfas-19-165f5.tif
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 0o External rotation Internal rotation
5o 10o 5o 10o
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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