Characterizing Sobolev Homeomorphic Extensions via Internal Distances

We give a full characterization of embeddings of the unit circle that admit a Sobolev homeomorphic extension to the unit disk. As a direct corollary, we establish that for quasiconvex target domains $\mathbb{Y}$, any homeomorphism $\phi \text{\hspace{0.17em}⁣}:\mathrm{\partial }\mathbb{D}\to \mathrm{\partial }\mathbb{Y}$ that admits a continuous $W^{1,p}$-extension to the unit disk $\mathbb{D}$ also admits a $W^{1,p}$-homeomorphic extension. These Sobolev variants of the classical Jordan-Schönflies theorem are essential for ensuring the well-posedness of variational problems arising in Nonlinear Elasticity and Geometric Function Theory.