Comparison of 2D-3D measurements of hallux and first ray sagittal motion in patients with and without hallux valgus

Background: Clinicians base treatment decisions on measures of hallux and first ray motion in the management of first metatarsophalangeal joint disorders. Women account for a majority of the patients. This study assessed the reliability of a 2D approach for the measurements of sagittal motion, and compared the result to a Cardan (3D) angle criterion standard and evaluated how hallux valgus (bunion) deformity affected the comparisons. Methods: Twenty-nine women (controls n = 10; bunion n = 19) were examined using a retrospective repeated measures design. Weightbearing magnetic resonance (MR) images were acquired to replicate the position of the foot during the stance phase of gait. The images were reconstructed into virtual bone models using computer processes, whereby measures of hallux and first ray motion were represented by 2D and 3D methods of measurement. An examiner measured 2D motion on the image data sets using a goniometer, and reliability was assessed. The 3D Cardan angle result was derived from a matrix calculation. The 2D-3D comparison of measurements was evaluated with an analysis of variance (ANOVA) model across gait conditions, run separate for groups. Results: The 2D measurement was reliable (ICC ≥ 0.98, SEM ≤ 0.89 degrees). There was no method-by-condition interaction (F ≤ 1.37, P ≥.25) between variables. No significant difference was detected between the 2D-3D measurements in the control group (F ≤ 1.24, P ≥.30), but the measurements were statistically different (F ≥ 4.46, P ≤.049) in the bunion group. Conclusion: This study described a reliable 2D approach for measuring hallux and first ray sagittal motion from weightbearing images. The 2D measurements were comparable to a Cardan angle component motion result in controls, but not in women with bunion. Clinical Relevance: Joint motion measurements may augment clinical decision making. These results suggest that a 2D image-based approach may be adequate to estimate hallux and first ray sagittal motion, although bunion deformity creates out-of-plane motions that may require 3D methods to accurately quantify. Further clinical study is required to assess the differences in clinical outcomes between measurement techniques.