Acquired adult flatfoot is a frequent deformity which implies multiple, complex and combined 3D modifications of the foot skeletal structure. The difficult thorough evaluation of the degree of severity pre-op and the corresponding assessment post-op can now be overcome by cone-beam (CBCT) technology, which can provide access to the 3D skeletal structure in weight-bearing. This study aims to report flatfoot deformities originally in 3D and in weight-bearing, with measurements taken using two different bone segmentation techniques. 21 such patients, with indication for surgical corrections, underwent CBCT (Carestream, US) while standing on one leg. From these scans, 3D models of each bone of the foot were reconstructed by using two different state-of-the-art segmentation tools: a semi-automatic (Mimics Innovation Suite, Materialise, Belgium), and an automatic (Bonelogic Ortho Foot and Ankle, Disior, Finland). From both reconstructed models, Principal Component Analysis was used to define anatomical reference frames, and original foot and ankle angles and other parameters were calculated mostly based on the longitudinal axis of the bones, in anatomical plane projections and in 3D. Both bone model reconstructions revealed a considerable valgus of the calcareous, plantarflexion and internal rotation of the talus, and typical Meary’s angles in the lateral and transverse plane projections. The mean difference from these angles between semi-automatic and automatic segmentations was larger than 3.5 degrees for only 3 of the 32 measurements, and a large number of these differences were not statistically significant. CBCT and the present techniques for bone shape reconstruction finally provide a novel and valuable 3D assessment of complex foot deformities in weight-bearing, eliminating previous limitations associated to unloaded feet and bidimensional measures. Corresponding measurements on the bone models from the two segmentation tools compared well. Other more representative measurements can be defined in the future using CBCT and these techniques.
In six cadaver specimens the mobility of the proximal fibula in relation to the tibia was investigated during plantar/dorsiflexion of the ankle, using Roentgen Stereophotogrammetric Analysis (RSA). The role of the ankle joint, and of the calcaneofibular and talofibular ligaments was also evaluated. The greatest movements were observed along the mediolateral and anterior-posterior axes, resulting in an anterolateral displacement of the fibula head during dorsiflexion and in a postero-medial displacement during plantarflexion. This study demonstrated a limited mobility of the proximal tibiofibular joint. Moreover, the ligament cutting and the presence of constraints in the ankle region did not show any effect on the fibular movement.
The result does not endorse the recommendation of placing the foot in full dorsal flexion during screw implantation. The choice of screw fixation as a treatment for ankle syndesmosis disruption should be carefully evaluated.
Isolated posteromedial ankle dislocation is a rare condition thanks to the highly congruent anatomical configuration of the ankle mortise, in which the medial and lateral malleoli greatly reduce the rotational movement of the talus, and the strength of the ligaments higher than the malleoli affords protection against fractures. However, other factors, like medial malleolus hypoplasia, laxity of the ligaments, peroneal muscle weakness and previous ankle sprains, could predispose to pure dislocation. In the absence of such factors, only a complex high-energy trauma, with a rotational component, can lead to this event. Irreducibility of an ankle dislocation, which is rarely encountered, can be due to soft tissue interposition. Dislocation of the posterior tibial tendon can be the cause of an irreducible talar dislocation; interposition of this tendon, found to have slid posteriorly to the distal tibia and then passed through the tibioperoneal syndesmosis, is reported in just a few cases of ankle fracture-dislocation.
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