Finite element analysis of secondary effect of midfoot fusions on the spring ligament in the management of adult acquired flatfoot.

BACKGROUND: Surgical treatment of adult acquired flatfoot deformity can involve arthrodesis of the midfoot to stabilize the medial column. Few experimental studies have assessed the biomechanical effects of these fusions, because of the difficulty of measuring these parameters in cadavers. Our objective was to quantify the biomechanical stress caused by various types of midfoot arthrodesis on the Spring ligament. To date this is not known. METHODS: An innovative finite element model was used to evaluate flatfoot scenarios treated with various combinations of midfoot arthrodesis. All the bones, cartilages and tissues related to adult acquired flatfoot deformity were included, respecting their biomechanical characteristics. The stress changes on the Spring ligament were quantified. Both foot arch lengthening and falling were measured for each of the midfoot arthrodeses evaluated. FINDINGS: Arthrodesis performed for stabilization of the talonavicular joint leads to a higher decrease in stress on the Spring ligament. Talonavicular fusion generated a Spring ligament stress decrease of about 61% with respect to the reference case (without any fusion). However, fusing the naviculocuneiform joints leads to an increase in the stress on the Spring ligament. INTERPRETATION: This important finding has been unknown to date. We advocate caution regarding fusion of the naviculocuneiform joint as it leads to increased stresses across the Spring ligament and therefore accelerates the development of planovalgus.

Analysis of biomechanical stresses caused by hindfoot joint arthrodesis in the treatment of adult acquired flatfoot deformity: A finite element study.

BACKGROUND: Treatments of adult acquired flatfoot deformity in early stages (I-IIa-IIb) are focused on strengthening tendons, in isolation or combined with osteotomies, but in stage III, rigidity of foot deformity requires more restrictive procedures such as hindfoot joint arthrodesis. Few experimental studies have assessed the biomechanical effects of these treatments, because of the difficulty of measuring these parameters in cadavers. Our objective was to quantify the biomechanical stress caused by both isolated hindfoot arthrodesis and triple arthrodesis on the main tissues that support the plantar arch. METHODS: An innovative finite element model was used to evaluate some flatfoot scenarios treated with isolated hindfoot arthrodesis and triple arthrodesis. RESULTS AND CONCLUSIONS: When arthrodeses are done in situ, talonavicular seems a good option, possible superior to subtalar and at least equivalent to triple. Calcaneocuboid arthrodesis reduces significantly both fascia plantar and spring ligament stresses but concentrates higher stresses around the fused joint.

Analysis of the main passive soft tissues associated with adult acquired flatfoot deformity development: A computational modeling approach.

Adult acquired flatfoot deformity (AAFD) is a pathology with a wide range of treatment options. Physicians decide the best treatment based on their experience, so the process is entirely subjective. A better understanding of soft tissue stress and its contribution in supporting the plantar arch could help to guide the clinical decision. Traditional experimental trials cannot consistently evaluate the contribution of each tissue. Therefore, in this research a 3-Dimensional FE foot model was reconstructed from a normal patient in order to measure the stress of the passive stabilizers of the arch, and its variation in different scenarios related with intermediate stages of AAFD development. All bones, the plantar fascia (PF), cartilages, plantar ligaments and the spring ligament (SL) were included, respecting their anatomical distribution and biomechanical characteristics. An AAFD evaluation scenario was simulated. The relative contribution of each tissue was obtained comparing each result with a normal case. The results show that PF is the main tissue that prevents the arch elongation, while SL mainly reduces the foot pronation. Long and short plantar ligaments play a secondary role in this process. The stress increment on both PF and SL when one of two fails suggests that these tissues complement each other. These findings support the theory that regards the tibialis posterior tendon as a secondary actor in the arch maintenance, compared with the PF and the SL, because this tendon is overstretched by the hindfoot pronation around the talonavicular joint. This approach could help to improve the understanding of AAFD.