The Effects of Misalignment in Medial/Lateral and Anterior/Posterior Foot X-rays
Patrick Willauer1,2; Bruce Sangeorzan1,2; Eric Whittaker1; William Ledoux 1,3,4
1. VA RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, Seattle, WA, United States
2. School of Medicine, 3. Dept. of Orthopaedics, and 4. Dept. of Mechanical Engineering, University of Washington, Seattle, WA, United States
Results and Discussion
Background
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Radiographs of the foot are an essential tool for physicians to
diagnose common foot pathologies.
• Perspective error, which may lead to inaccuracies in X-ray
measurements, can result from the foot being improperly aligned to
the X-ray source [1].
• The effect of misalignment on common X-ray measures has not
been explored [2].
Objective: To quantify the effect of X-ray misalignment on common
foot measurements in medial/lateral (ML) view and anterior/posterior
(AP) view X-rays using a cadaver foot.
Methods
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Thirteen fresh-frozen foot specimens from seven donors (mean age
81, range 63-92, 4 F, 3 M).
Selected X-ray measures:
o From AP view: talonavicular coverage angle (TNCA) (Fig 1A)
[3], talometatarsal angle (TMA) (Fig 1B) [3].
o From ML view: calcaneal pitch angle (CPA) (Fig 1C) [3], lateral
talometatarsal angle (LTMA) (Fig 1C) [3].
Images captured using a Phillips BV Pulsera C-arm.
Specimens loaded to 25% BW via tibia, nylon rod, and load cell in
an acrylic frame (Fig. 2A&B).
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Misalignment in ML view radiographs
CPA was sensitive to transverse
Misalignment in AP view radiographs
plane misalignment ( p < 0.005)
o Reference position (0˚) mean
[SE] was 29.3° [2.8°], with the
largest change of 8.7° [0.8°] at
misalignment of -20° (Fig 3)
LTMA was not affected by
misalignment (p = 0.073)
o Reference position mean was
5.4° [2.6°], with the largest
change of -2.6° [1.0°] at a
misalignment of -25° (Fig 3)
No association was found between
sagittal plane misalignment and
Figure 3: Effect of transverse plane misalignment
Figure 4: Effect of sagittal plane misalignment on
TNCA angle (p = 0.13) or TMA
on LTMA and CPA (ML radiographs) *p<0.005.
TNCA and TMA (AP radiographs.)
angle (p = 0.12) (Fig 4)
Clinically, transverse misalignment in the ML view likely comes from physician image preferences (i.e. aligned talar domes) and sagittal
misalignment in the AP view is often from limitations in the placement of the X-ray source, due to patient anatomy.
Proper alignment is important for ML radiographs, but there is some leeway for AP radiographs.
Limitations: feet with more extreme angles or pathologies may show different sensitivities; errors in repeatability of loading the feet into the
frame and/or measuring the angles.
Conclusion
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The TNCA and TMA measurements on AP radiographs are
reliable clinical tools, even when sagittal misalignment is
present. Transverse plane misalignment is more of a concern, as
it was shown to affect the CPA, but not the LTMA.
References
A
B
C
1. Tochigi YJ, et al ., Foot and Ankle Int 27(2), 2006: 82-7
2. Brage ME, et al., Foot and Ankle Int 15(9), 1994: 495-7; 2
3. Sangeorzan BJ, et al., Foot and Ankle Int 14(3), 1993: 136-41
Figure 1: Radiographs with measurements of TNCA (A) and TMA (B)
on the AP view and CPA and LTMA on ML view (C).
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Turntable used for transverse plane misalignment (±25˚, 5˚
increments) (Fig 2A), and risers at front of frame used for sagittal
plane misalignment (0-30˚, 5˚ increments) (Fig 2B).
Linear mixed effects regression used to determine the relationship
between X-ray measure and misalignment angle using Bonferroni’s
correction for multiple comparisons.
Acknowledgements
A
B
Figure 2: Specimen in loading frame with externally rotated transverse plane
misalignment (A) and sagittal plane misalignment (B)
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VA RR&D grant A4843C and the University of Washington
MSRTP program.
Larry Raff at Harborview Medical Center
Jane Shoefer, biostatistician