A Computational Model of Force within the Ligaments and Tendons in Progressive Collapsing Foot Deformity

Progressive collapsing foot deformity results from degeneration of the ligaments and the posterior tibial tendon (PTT). Our understanding of the relationship between the failures of them remains incomplete. We sought to improve this understanding through computational modeling of force in these soft tissues. The impact of PTT and ligament tears on force changes in the remaining ligaments was investigated using a previously validated finite element model of the foot. The ability of the PTT to restore foot alignment in a collapsed foot was evaluated by increasing the PTT force in a foot with attenuated ligaments and comparing the alignment angles to the intact foot. Rupture of any one of the ligaments led to overloading the remaining ligaments, except for the plantar naviculocuneiform, first plantar tarsometatarsal, and spring ligaments, where removing one led to unloading the other two. The attenuation of the plantar fascia, long plantar, short plantar, and spring ligaments significantly overloaded the deltoid and talocalcaneal ligaments. Isolated PTT rupture had no effect on foot alignment, but did increase the force in the deltoid and spring ligaments. Increasing the force within the PTT to 30% of body weight was effective at restoring foot alignment during quiet stance, primarily through reducing hindfoot valgus and forefoot abduction as opposed to improving arch height. The attenuation of any one ligament often leads to overload of the remaining ligaments which may lead to progressive degeneration. The PTT can maintain alignment in the collapsing foot, but at an increased load which could lead to its injury. Early intervention, in the form of ligament repair or reconstruction, might be used to prevent the progression of deformity. Moreover, strengthening the PTT through therapeutic exercise might improve its ability to restore foot alignment.