Introduction <p>Given the inconclusive evidence regarding the effects of foot orthoses in flatfoot management, this study aimed to assess the impact of two distinct types of foot orthoses on three-dimensional bone alignment of the foot using advanced imaging techniques.</p> Materials and methods <p>Sixteen fresh-frozen cadaveric feet showing radiological signs of progressive collapsing foot deformity were collected. Two different types of foot orthoses, type I with medial support and lateral counter-support and type II with an additional metatarsal pad, were custom-made. The feet were loaded using a testing machine and scanned by weight-bearing computed tomography. Semi-automatic 3D models of bone dimensions and axes were generated to compute the foot alignment. This study was designed according to the QUACS scale.</p> Results <p>The sagittal talus-first metatarsal angle was corrected by an average of 2.0±3.0 degrees with type I orthoses (<i>p</i> = 0.019), and 2.6±3.7 degrees with type II orthoses (<i>p</i> = 0.018). The axial talocalcaneal angle was corrected by an average 1.8±2.8 degrees with type I orthoses (<i>p</i> = 0.021), and 2.0±3.1 degrees with type II orthoses (<i>p</i> = 0.02). The axial talus-first metatarsal angle was corrected by an average 1.3±2.0 degrees with type I orthoses (<i>p</i> = 0.024), while type II orthoses caused no significant effect (<i>p</i> = 0.297). No significant differences were found between type I and type II orthoses (all <i>p</i> &gt; 0.05).</p> Conclusions <p>In this cadaveric study, foot orthoses with medial support, with or without a metatarsal pad, improved all angles tested, but the effect appeared to be small. It remains to be determined whether these subtle changes are responsible for the positive clinical effects described in other studies, or whether orthoses have a positive effect even without reaching the intended alignment correction.</p>