The contribution of the ligaments in progressive collapsing foot deformity: A comprehensive computational study

Abstract

The contribution of each of the ligaments in preventing the arch loss, hindfoot valgus, and forefoot abduction seen in progressive collapsing foot deformity (PCFD) has not been well characterized. An improved understanding of the individual ligament contributions to the deformity would aid in selecting among available treatments, optimizing current surgical techniques, and developing new ones. In this study, we evaluated the contribution of each ligament to the maintenance of foot alignment using a finite element model of the foot reconstructed from computed tomography scan images. The collapsed foot was modeled by simulating the failure of all the ligaments involved in PCFD. The ligaments were removed one at a time to determine the impact of each ligament on foot alignment, and then restored one at a time to simulate isolated reconstruction. Our findings show that the failure of any one ligament did not immediately lead to deformity, but that combined failure of only a few (the plantar fascia, long plantar, short plantar, deltoid, and spring ligaments) could lead to significant deformity. The plantar fascia, deltoid, and spring ligaments were primarily responsible for the prevention of arch collapse, hindfoot valgus, and forefoot abduction, respectively. Moreover, to produce deformity, a considerable amount of attenuation in the spring, tibiocalcaneal, interosseous talocalcaneal, plantar naviculocuneiform, and first plantar tarsometatarsal ligaments, but only a small amount in the plantar fascia, long plantar, and short plantar ligaments was needed.The results of this study suggest that the ability of a ligament to prevent deformity may not correlate with its attenuation in a collapsed foot.adult-acquired flatfoot deformity, biomechanics, finite element modeling, posterior tibial tendon dysfunction, progressive collapsing foot deformity | INTRODUCTIONProgressive collapsing foot deformity (PCFD), previously known as adult-acquired flatfoot deformity (AAFD), is a common degenerative condition affecting up to 10% of the adults over the age of 65 years. 1,2 As the structures supporting the foot degenerate, a complex three-dimensional (3D) deformity develops at multiple locations in the foot, including hindfoot valgus, midfoot planus (arch collapse), and forefoot abduction, leading to foot and ankle pain, swelling, and decreased ambulatory capacity. It was initially thought that posterior tibial tendon dysfunction (PTTD) leads to the PCFD. 1 However, later studies revealed that the degeneration of the arch and hindfoot supporting ligaments also plays a significant role. 2,3 Once the posterior tibial tendon

A computational model of force within the ligaments and tendons in progressive collapsing foot deformity

“…The finite element model of the foot was completed with 28 bones, 72 ligaments, cartilage, and the EST. 5 The reconstructed geometry was meshed with 608,773 tetrahedral elements in ANSYS. Element sizes of 2, 1, and 3 mm for the bones, cartilage, and EST were obtained, respectively, using a mesh convergence study conducted on the outcome parameters with a 10% reduction in element size.…”

“…The stiffness of the ligaments (k = AE/L), which accounts for both the material properties (elastic modulus E) and the geometry (cross-sectional area A and length L), was determined using published data. 5,24,25…”

“…The degeneration of these ligaments and tibialis posterior tendon dysfunction (PTTD) are the primary causes of collapsing foot deformity. 1,3,5 Specifically, ligaments attenuate over time as a result of repeated loading on the arch, causing them to become stretched and thus nonfunctional. 30,31 To simulate torn or elongated ligaments, the ligaments must be either removed or pre-stretched to specific lengths.…”

“…30,31 To simulate torn or elongated ligaments, the ligaments must be either removed or pre-stretched to specific lengths. 5 Thus, we removed all of the involved ligaments (Table 2) and unloaded the PTT to simulate the collapsed foot. Because torn or stretched ligaments are nonfunctional and bear no or little tension under normal working conditions, 30 their absence properly simulates their failure to function as foot stabilizers.…”

“…[13][14][15] The difficulty in measuring forces and deformations within the foot from experimental models, 16 has led to a rise in the use of computational models such as finite element models to study PCFD. 5,17,18 However, only two of the studies in PCFD focused on forces and stresses in the soft tissues. 19,20 Unfortunately, the models used in both of these studies contain simplifications that limit their ability to make physiologically realistic predictions.…”