A possible cause for a painful total knee prosthesis is flexion gap asymmetry with medial or lateral instability despite adequate axial and rotational alignment of both components and adequate extension gap balancing. To avoid component exchange, ligament advancement techniques can be used. Soft tissue procedures carry the risk of insufficiently stable scarring. Epicondylar sliding osteotomies are accepted as a mode of collateral ligament release in severe varus or valgus knee arthroplasties. We describe a technique of anterior epicondylar advancement for the correction of symptomatic flexion gap instability.