The Effects of Misalignment in Medial/Lateral and Anterior/Posterior Foot X-raysPatrick 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 States2. School of Medicine, 3. Dept. of Orthopaedics, and 4. Dept. of Mechanical Engineering, University of Washington, Seattle, WA, United States

Background

• 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

• 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).

Figure 3: Effect of transverse plane misalignment on LTMA and CPA (ML radiographs) *p<0.005.

Figure 4: Effect of sagittal plane misalignment on TNCA and TMA (AP radiographs.)

Conclusion

Acknowledgements

References

• 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.

• CPA was sensitive to transverse 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 TNCA angle (p = 0.13) or TMA angle (p = 0.12) (Fig 4)

Results and Discussion

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

• VA RR&D grant A4843C and the University of Washington MSRTP program.

• Larry Raff at Harborview Medical Center• Jane Shoefer, biostatistician

• 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.

Figure 2: Specimen in loading frame with externally rotated transverse plane misalignment (A) and sagittal plane misalignment (B)

A B

Figure 1: Radiographs with measurements of TNCA (A) and TMA (B) on the AP view and CPA and LTMA on ML view (C).

A B C

• 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.

Misalignment in ML view radiographs Misalignment in AP view radiographs