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The spring ligament complex is an important stabilizer of the medial ankle, together with the posterior tibial tendon (PTT) and the deltoid ligament complex. Lesions in these stabilizers result in acquired adult flatfoot deformity. The spring ligament complex includes three ligaments: the superomedial calcaneonavicular ligament, the medioplantar oblique calcaneonavicular ligament, and the inferoplantar longitudinal calcaneonavicular ligament. Normal MR imaging anatomy of the spring ligament complex and the PTT are described and illustrated in detail. Isolated lesions of the spring ligament complex are rare. In most cases, spring ligament complex lesions are secondary to PTT dysfunction. The best criteria for an injury of the clinically relevant superomedial calcaneonavicular ligament are increased signal on proton-density or T2-weighted sequences with thickening (> 5 mm), thinning (< 2 mm), or partial or complete discontinuity. A thickened ligament can be simulated by the gliding layer between the PTT and the superomedial calcaneonavicular ligament (thickness: 1-3 mm). The most common location of injury is the superior and distal portion of the superomedial calcaneonavicular ligament. A lesion seen by the orthopedic foot surgeon at the junction between the tibiospring ligament and the superomedial portion of the calcaneonavicular ligament is commonly classified as a spring ligament injury. In addition, an overview of MR imaging findings in different stages of the acquired adult flatfoot deformity is provided.