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Findings Starting with the radiographs, there is severe flatfoot deformity with small foci of heterotopic ossification situated in the medial gutter/deltoid ligament and a loss of joint space along the medial aspect of the ankle joint. The MRI demonstrates moderate tendinosis of the posterior tibial tendon (PTT) at the navicular tuberosity but no disruption and relatively well maintained architecture. There is a markedly attenuated/partially disrupted superomedial band of the spring ligament, previously injured and marked ganglion formation of the interosseous ligament in the sinus tarsi, and previously injured and poorly remodeled deltoid ligament especially involving the deep fibers. The MRI also shows areas of full thickness cartilage loss of the ankle joint and suggestion of excessive heel valgus.
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Diagnosis: Ligament insufficiency in AAFD (adult acquired flatfoot deformity) This case is a bit different than many others as the overall diagnosis of AAFD is not difficult but I think this is a nice illustration of many of the other drivers of more advanced levels of AAFD. The PTT is the dynamic support of the arch and the vast majority of the time by this stage the PTT is torn or so abnormal just distal to the ankle extending to the navicular tuberosity that it is easy to ascertain how it is not functioning. In this case though it is the ligamentous structures which have particularly failed helping lead to the higher levels of AAFD. In particular the superomedial band of the spring (plantar calcaneonavicular) ligament is structurally the most important part of the spring ligament (the other two portions being the medial plantar oblique and inferoplantar longitudinal components) to help prevent plantar flexion of the talus. This component in particular should be a stout band of low signal collagen running from the sustentaculum talus to the dorsal medial navicular and not the flimsy structure shown in this case.
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Continued The failure of the interosseous ligament (between the talus and calcaneus) spanning the sinus tarsi contributes to heel valgus. This ligament in normal cases should have well defined fibers with fat of the sinus tarsi insinuating about it and not the amorphous, globular mass shown in this case. Lastly failure of the deltoid ligament leads to greater ankle instability and towards the end stages full thickness cartilage loss/advanced degenerative change of the ankle joint. This staging is very helpful in knowing what to look for on imaging but also in terms of planning surgery as relates to potential ligament reconstruction, osteotomy/fusions, and potentially ankle replacement or arthrodesis. It is clearly not possible to completely/comprehensively cover the topic of AAFD in this one case but hopefully the illustration of the ligamentous contributions to the deformity have been made clear.
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References Approach and treatment of the adult acquired flatfoot deformity. Vulcano E, Deland JT, Ellis SJ. Curr Rev Musculoskelet Med. 2013 Dec;6(4):294-303. doi: 10.1007/s12178-013-9173-z. Spring Ligament Tear. Michael E. Stadnick, M.D. Radsource MRI Web Clinic January 2008
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