Figure A demonstrates a disrupted calcaneonavicular ligament (Spring ligament). Chronic deficiency of this structure can lead to a flatfoot deformity.
The ability of the medial longitudinal arch to prevent flatfoot deformity depends on the dynamic support of the posterior tibial tendon, the static support of ligaments and capsule (including the Spring ligament), and the manner in which the tarsal bones interlock.
Gadzag retrospectively found that 18 of 22 patients undergoing surgery for flatfoot deformity had varying levels of injury to the spring ligament but their study design prevented them from concluding whether ligament repair was beneficial.
Illustration A contains an MRI of a normal Spring ligament (right) shown with a green arrow compared to a disrupted Spring ligament (left) shown with the red arrow. Illustration B is a cadaveric dissection showing the spring ligament (5) once the posterior tibial tendon (9) has been reflected.
Gazdag AR, Cracchiolo A 3rd. Rupture of the posterior tibial tendon. Evaluation of injury of the spring ligament and clinical assessment of tendon transfer and ligament repair. J Bone Joint Surg Am. 1997 May;79(5):675-81
PMID: 9160939 (Link to Abstract)