gms | German Medical Science

Objectives: The aim of this study was to evaluate the reliability of a portable optical scanner for volumetric measurements of the foot and ankle, compared to the water displacement technique. A secondary objective was to compare the acquisition time associated with these two methods. We hypothesized that this optical scanner allows reliable and fast volumetric measurements. Measuring foot and ankle volume remains a technical challenge due to their uneven morphology, especially distal volumes (multiple, low-volume contiguous segments). In clinical practice, perimetric measurements are still widely used, due to their speed and practicability, although their reproducibility may still be improved. The water displacement technique remains the reference method, but its use in clinical practice may raise several issues.

Methods: In this prospective study, foot volume was measured in 29 healthy volunteers (58 feet overall, 24 female/5 male subjects). For each foot, the volume was measured both by using a 3D scanner (UPOD-S 3D Laser Full-Foot Scanner^®) and by water-displacement volumetry. For each subject, measurements were performed on both feet, up to a height of 10 cm above the ground. The acquisition time for each method was timed by an independent rater. The normality of variables was assessed using a Kolmogorov-Smirnov test. Concordance of measurements was evaluated by Lin’s Concordance Correlation Coefficient (CCC). Comparisons were assessed using a Student’'s t-test.

Results and conclusion: Mean foot volume when measured by 3D scanner was 869.7+/-165.1 cm³, versus 867.9+/-155.4 cm³ when using water-displacement volumetry (p <10–5). Concordance of gross measurements was 0.93, which was indicative of a high correlation between the two techniques. Measurement was 47.8 cm³ lower when using the 3D scanner versus water volumetry. After taking into account and statistically correcting this underestimation, the concordance between the two techniques was improved (0.98, residual bias = -0.03 +/- 35.1 cm³). Mean examination time was 4.2 +/-1.7 min when using the 3D optical scanner versus 11.1 +/-2.9 min when using the water volumeter (p<10-4),

Our portable 3D laser scanner showed an excellent correlation with the reference method, and significantly reduces examination time. Its portable use, its speed and the absence of contraindications linked to immersion in water make it an ideal clinical or research tool for measuring and monitoring foot and ankle edema.