Variability of the lower limb symmetry index associated with the gait parameters in the overweight adult population with flatfoot: a case-control study.

Background: Adult acquired flatfoot is characterized by a medial arch collapse during monopodal support in the stance phase, developing eversion of the calcaneus and abduction of the forefoot linked to the hindfoot. The purpose of our research was to analyze the dynamic symmetry index in the lower limbs comparing patients with flatfoot and normal foot. Methods: A case-control study was carried out with a sample of 62 participants divided into two groups consisting of 31 participants were overweight with bilateral flatfoot and 31 participants with healthy feet. A portable plantar pressure platform with piezoresistive sensors was used to measure the load symmetry index in the lower limbs in the foot areas and gait phases. Results: Gait pattern analysis showed statistically significant differences in the symmetry index for lateral load (p = 0.004), the initial contact phase (p = 0.025) and the forefoot phase (p < 0.001). Conclusion: The adults were overweight with bilateral flatfoot evidenced alterations in the symmetry index in the lateral load and in the initial contact and flatfoot contact phases, showing greater instability in overweight adult flatfoot compared to the people with normal feet.

Influence of the center of pressure on baropodometric gait pattern variations in the adult population with flatfoot: A case-control study.

Background: Adult flatfoot is considered an alteration in the foot bone structure characterized by a decrease or collapse of the medial arch during static or dynamic balance in the gait pattern. The aim of our research was to analyze the center of pressure differences between the population with adult flatfoot and the population with normal feet. Methods: A case-control study involving 62 subjects was carried out on 31 adults with bilateral flatfoot and 31 healthy controls. The gait pattern analysis data were collected employing a complete portable baropodometric platform with piezoresistive sensors. Results: Gait pattern analysis showed statistically significant differences in the cases group, revealing lower levels in the left foot loading response of the stance phase in foot contact time (p = 0.016) and contact foot percentage (p = 0.019). Conclusion: The adult population with bilateral flatfoot evidenced higher contact time data in the total stance phase compared to the control group, which seems to be linked to the presence of foot deformity in the adult population.

Influence of insole material density in the stability of patients with prosthetic unilateral transtibial amputation.

People with lower limb amputation present greater displacements of their centre of gravity in a static situation than able-bodied individuals, as they depend on visual information to a greater extent, which implies an altered stability pattern. The efficacy of different hardness of plantar support to help maintain stability has not yet been determined. The aim of the present study is to assess stability in people with unilateral transtibial amputation with prosthesis in a static situation with insoles of different degrees of hardness and visual conditions with respect to the able-bodied population. For this purpose, 25 patients with amputation and 25 able-bodied individuals were included in both groups, postural stability was assessed by stabilometry. This assessment was carried out under normal conditions (on the floor of the dynamometric platform with eyes open), and under altered conditions (with the interposition of different materials such as plantar support: rigid and soft insoles and, eyes shut). Three variables were considered to assess stability: length of movement of the barycenter (mm), lateral velocity (mm/sg) and anterior velocity (mm/sg). All of them were analysed with the patient in static on the dynamometric platform. The results showed statistically significant differences between the two groups, (amputees and controls) with less stability in the amputee group (p < 0.05) when analysing the variables of length of movement of the barycenter, lateral velocity and anterior velocity. Amputee patients with open eyes exhibited greater stability than those with closed eyes. The hard insoles improved the stability data in amputees (length of movement of the barycenter and anterior velocity) with respect to the barefoot condition, and the soft insoles showed less stability than the patients with hard insoles, or than the barefoot patients. From the results obtained in this study, we can conclude that the PP-DWST 4 mm rigid insoles improve static stability in people with amputation. However, soft insoles impair stability and are therefore discouraged.

Peroneus Longus overload caused by soft tissue deficiencies associated with early adult acquired flatfoot: A finite element analysis.

BACKGROUND: Peroneus Longus tendinopathy has been related to overload from cavus and ankle instability. The etiology of isolated Peroneus Longus tendon synovitis has not been elucidated. Loss of foot arch integrity as a cause of isolated Peroneus Longus overload is difficult to establish using cadaver modeling. Our objective was to analyze Peroneus Longus stress changes in pathological scenarios related to flatfoot development. METHODS: A three-dimensional finite element foot model which included the foot bones and main soft tissues that maintain the arch was used. Simulations were performed in midstance of gait. Tendon's maximum principal stress and von Mises were calculated in scenarios where the plantar fascia, spring ligament and the posterior tibial tendon were weakened. FINDINGS: Decreasing plantar fascia stiffness thus weakening arch integrity increases Peroneus Longus stresses by over three times. Additional failure of tissues that support arch, such as the spring ligament and tibialis posterior tendon further overloads this tendon. The absence of Peroneus Longus also affects stresses in tissues that maintain the arch. Stress concentrations increase in the plantar component of the Peroneus Longus. INTERPRETATION: Results offer an explanation into isolated Peroneus Longus overload synovitis. Recognition of failing medial arch structures that occur in early acquired flatfoot as a cause of Peroneus Longus overload could help in its treatment. We caution the practice of transfer of peroneus brevis to longus in surgical treatment of flatfoot as it may further overload an overloaded tendon and focus should be on restoration of arch stability to offload stresses within it.

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.

Biomechanical stress analysis of the main soft tissues associated with the development of adult acquired flatfoot deformity.

BACKGROUND: Adult acquired flatfoot deformity (AAFD) is traditionally related to a tibialis posterior tendon deficiency. In the intermediate stages, treatments are commonly focused on reinforcing this tissue, but sometimes the deformation appears again over time, necessitating the use of more aggressive options. Tissue stress cannot be consistently evaluated through traditional experimental trials. Computational foot modeling extends knowledge of the disease and could help guide the clinical decisions. This study analyzes the biomechanical stress of the main tissues related to AAFD and their capacity to support the plantar arch. METHODS: A FE foot model was reconstructed. All the bones, cartilages and tissues related to AAFD were included, respecting their biomechanical characteristics. The biomechanical tissue stress was quantified. The capacity of each soft tissue to support the plantar arch was measured, following clinical criteria. FINDINGS: Biomechanical stress of the tibialis posterior tendon is considerably superior to both the plantar fascia and spring ligament stress. However, it cannot maintain the plantar arch by itself. Both the tibialis posterior tendon and spring ligament act in reducing the hindfoot pronation, while the plantar fascia is the main tissue that prevents arch elongation. The Achilles tendon action increases the plantar tissue stress. INTERPRETATION: The tibialis posterior tendon stress increases when the spring ligament or the fascia plantar fails. These findings are consistent with the theory that regards the tibialis posterior tendon as a secondary actor because it cannot support the plantar arch and claudicates when the hindfoot has rotated around the talonavicular joint.

Foot internal stress distribution during impact in barefoot running as function of the strike pattern.

The aim of the present study is to examine the impact absorption mechanism of the foot for different strike patterns (rearfoot, midfoot and forefoot) using a continuum mechanics approach. A three-dimensional finite element model of the foot was employed to estimate the stress distribution in the foot at the moment of impact during barefoot running. The effects of stress attenuating factors such as the landing angle and the surface stiffness were also analyzed. We characterized rear and forefoot plantar sole behavior in an experimental test, which allowed for refined modeling of plantar pressures for the different strike patterns. Modeling results on the internal stress distributions allow predictions of the susceptibility to injury for particular anatomical structures in the foot.

Non-linear finite element model to assess the effect of tendon forces on the foot-ankle complex.

A three-dimensional foot finite element model with actual geometry and non-linear behavior of tendons is presented. The model is intended for analysis of the lower limb tendon forces effect in the inner foot structure. The geometry of the model was obtained from computational tomographies and magnetic resonance images. Tendon tissue was characterized with the first order Ogden material model based on experimental data from human foot tendons. Kinetic data was employed to set the load conditions. After model validation, a force sensitivity study of the five major foot extrinsic tendons was conducted to evaluate the function of each tendon. A synergic work of the inversion-eversion tendons was predicted. Pulling from a peroneus or tibialis tendon stressed the antagonist tendons while reducing the stress in the agonist. Similar paired action was predicted for the Achilles tendon with the tibialis anterior. This behavior explains the complex control motion performed by the foot. Furthermore, the stress state at the plantar fascia, the talocrural joint cartilage, the plantar soft tissue and the tendons were estimated in the early and late midstance phase of walking. These estimations will help in the understanding of the functional role of the extrinsic muscle-tendon-units in foot pronation-supination.

Structural and material properties of human foot tendons.

BACKGROUNDS: The aim of this study was to assess the mechanical properties of the main balance tendons of the human foot in vitro reporting mechanical structural properties and mechanical material properties separately. Tendon structural properties are relevant for clinical applications, for example in orthopedic surgery to elect suitable replacements. Tendon material properties are important for engineering applications such as the development of refined constitutive models for computational simulation or in the design of synthetic materials. METHODS: One hundred uniaxial tensile tests were performed to obtain the mechanical response of the main intrinsic and extrinsic human foot tendons. The specimens were harvested from five frozen cadaver feet including: Extensor and Flexor tendons of all toes, Tibialis Anterior and Posterior tendons and Peroneus Brevis and Longus tendons. FINDINGS: Cross-sectional area, load and strain failure, Young's modulus and ultimate tensile stress are reported as a reference of foot tendon mechanical properties. Two different behaviors could be differentiated. Tibialis and Peroneus tendons exhibited higher values of strain failure compared to Flexor and Extensor tendons which had higher Young's modulus and ultimate tensile stress. Stress-strain tendon curves exhibited proportionality between regions. The initial strain, the toe region and the yield point corresponded to the 15, 30 and 70% of the strain failure respectively. INTERPRETATION: Mechanical properties of the lesser-studied human foot tendons are presented under the same test protocol for different engineering and clinical applications. The tendons that work at the inversion/eversion plane are more deformable at the same stress and strain rate than those that work at the flexion/extension plane.

Influence of first proximal phalanx geometry on hallux valgus deformity: a finite element analysis.

Hallux abducto valgus (HAV), one of the most common forefoot deformities, occurs primarily in elderly women. HAV is a complex disease without a clearly identifiable cause for its higher prevalence in women compared with men. Several studies have reported various skeletal parameters related to HAV. This study examined the geometry of the proximal phalanx of the hallux (PPH) as a potential etiologic factor in this deformity. A total of 43 cadaver feet (22 males and 21 females) were examined by means of cadaveric dissection. From these data, ten representative PPHs for both genders were selected, corresponding to five percentiles for males (0, 25, 50, 75, and 100%) and five for females. These ten different PPHs were modeled and inserted in ten foot models. Stress distribution patterns within these ten PPH models were qualitatively compared using finite element analysis. In the ten cases analyzed, tensile stresses were larger on the lateral side, whereas compressive stresses were larger on the medial side. The bones of males were larger than female bones for each of the parameters examined; however, the mean difference between lateral and medial sides of the PPH (mean ± SD) was larger in women. Also the shallower the concavity at the base of the PPH, the larger the compressive stresses predicted. Internal forces on the PPH, due to differences in length between its medial and lateral sides, may force the PPH into a less-stressful position. The geometry of the PPH is a significant factor in HAV development influencing the other reported skeletal parameters and, thus, should be considered during preoperative evaluation. Clinical assessment should evaluate the first ray as a whole and not as isolated factors.

Stress at the second metatarsal bone after correction of hammertoe and claw toe deformity: a finite element analysis using an anatomical model.

BACKGROUND: We used finite element analysis to evaluate three techniques for the correction of hammertoe and claw toe deformities: flexor digitorum longus tendon transfer (FDLT), flexor digitorum brevis tendon transfer (FDBT), and proximal interphalangeal joint arthrodesis (PIPJA). METHODS: We performed a finite element analysis of FDLT and FDBT compared with PIPJA of the second toe using multislice computed tomography and 93 tomographic images of the foot obtained in a healthy 36-year-old man. RESULTS: The PIPJA showed a significantly higher increase in traction and compressive stresses and strain at the medial aspect of the shaft of the second metatarsal bone compared with FDLT or FDBT (P < .01). Mean ± SD compressive stresses increased to -4.35 ± 7.05 MPa compared with the nonsurgical foot (-3.10 ± 4.90 MPa). It can, therefore, be hypothesized that if PIPJA is used to correct the hammertoe and claw toe deformities, it could also increase traction and compressive stresses and strain in the metatarsals during running and other vigorous activities. CONCLUSIONS: There is a biomechanical advantage to performing FDLT or FDBT instead of PIPJA to surgically treat a hammertoe or claw toe deformity. In addition, tensile strain at the dorsal aspect of the second metatarsal bone when performing PIPJA increases the risk of metatarsalgia or stress fracture in patients at risk.

Advantages and drawbacks of proximal interphalangeal joint fusion versus flexor tendon transfer in the correction of hammer and claw toe deformity. A finite-element study.

Correction of claw or hammer toe deformity can be achieved using various techniques, including proximal interphalangeal joint arthrodesis (PIPJA), flexor digitorum longus tendon transfer (FDLT), and flexor digitorum brevis transfer. PIPJA is the oldest technique, but is associated with significant complications (infection, fracture, delayed union, and nonunion). FDLT eliminates the deformity, but leads to loss of stability during gait. Flexor digitorum brevis tendon transfer (FDBT) seems to be the best surgical alternative, but it is a recent technique with still limited results. In this work, these three techniques have been analyzed by means of the finite-element method and a comparative analysis was done with the aim of extracting advantages and drawbacks. The results show that the best technique for reducing dorsal displacement of the proximal phalanx is PIPJA (2.28 mm versus 2.73 mm for FDLT, and 3.31 mm for FDBT). However, the best technique for reducing stresses on phalanges is FDLT or FDBT (a reduction of approximately 35% regarding the pathologic case versus the increase of 7% for the PIPJA in tensile stresses, and a reduction of approximately 40% versus 25% for the PIPJA in compression stresses). Moreover, the distribution of stresses in the entire phalanx is different for the PIPJA case. These facts could cause problems for patients, in particular, those with pain in the surgical toe.

Finite-element simulation of flexor digitorum longus or flexor digitorum brevis tendon transfer for the treatment of claw toe deformity.

Claw toe deformity sometimes leads to dorsiflexion of the metatarsophalangeal joint (MPJ) and plantar flexion of the proximal (PIPJ) and distal interphalangeal (DIPJ) joints. Flexor digitorum longus tendon transfer (FDL) is currently the gold standard for the correction of this problem. Transfer of the flexor digitorum brevis (FDB) has been recently proposed as an alternative method to treat such deformity. The aim of this work is to compare the biomechanical outcome of these two methods by means of finite-element simulation. The results show that the reduction in the dorsal displacement of the proximal phalanx (PP) for the second and third toes were very similar (about 4.3 mm for each intervention), both achieving a significant reduction in MPJ dorsiflexion when compared to no intervention (displacements are reduced by approximately 51%). In the fourth and fifth toes, only a small correction in the deformity was achieved with both the techniques (10% and 7%, respectively). FDB and FDL tendon transfer reduced the stress level when compared with the non-operated pathologic foot (the reduction of stresses for the second and third PP ranged between 20% and 40%). FDB transfer resulted in a more uniform distribution of stress along the entire toe, although differences were small in all cases. These results confirm that both the tendon-transfer techniques are effective in the treatment of claw toe deformity. Therefore, the choice of technique is at the discretion of the surgeon.