Measurement of three-dimensional morphological characteristics of the calcaneus using CT image post-processing

BACKGROUND: Although computed tomography (CT) with three-dimensional (3D) rendering of the calcaneus is used for diagnostic evaluation of disorders, morphological measurements for the calcaneus are mostly based on a two-dimensional plane. The purposes of this study were to design a method for 3D morphological measurements of the normal calcaneus based on CT post-processing techniques, to measure morphological parameters in the male and female groups and describe gender differences of the parameters, and to investigate the reliability of such measurements. METHODS: One hundred and seventy-nine patients (83 men and 96 women) with a mean age of 40.6 (range, 21 to 59) years who underwent CT scans for their feet were reviewed retrospectively. The 3D structure of a normal calcaneus after shaded surface display reconstruction was extracted by interactive and automatic segmentation. Morphological measurements were achieved by means of a 3D measurement method based on CT image post-processing. Lengths and heights of the main parts of the calcaneus, Gissane’s angle, Böhler’s angle and the area of articular facet were worked out in 3D space. Gender-related size differences of parameters were compared using analysis of covariance (ANCOVA), adjusting for body height. Intra-observer and inter-observer reliabilities were assessed using intraclass correlation coefficients (ICCs) and the root mean square standard deviation (RMS-SD) for precision study. RESULTS: A large range of measurement values was found. Only the length of the anterior process was without gender difference (p > 0.05). The other parameters in the male group were greater than those in the female group (p < 0.01 for each, ANCOVA). All parameters had excellent reliability and reproducibility (ICC > 0.8). Precision was acceptable for intra-observer RMS-SD (linear, angular and areal measurements no more than 0.6 mm, 1.2° and 0.25 mm(2), respectively). Inter-observer RMS-SD ranged from 0.4 to 1.6 mm for linear measurements, 1.2 to 2.5° for angles and 0.24 to 0.40 mm(2) for areas. CONCLUSIONS: Three-dimensional morphological measurement based on a CT post-processing technique was highly reliable and repeatable for calcaneal anatomic morphological measurement. The current data will be helpful for anatomic reduction of calcaneal fractures and calcaneal malunion.