Effect of subtalar arthroereisis on the tibiotalar contact characteristics in a cadaveric flatfoot model

Increase in lateral contact force in the tibiotalar joint during walking in flatfoot patients with reduced stiffness of the spring ligament

Foot deformities in patients with flexible flatfeet, such as the flattened medial arch and hindfoot valgus, affect the force distribution around the tibiotalar joint during walking and increase the risk of secondary injuries. In this study, we developed a multi-segment foot model that could calculate the dynamics around the tibiotalar joint and investigated the difference in the kinetics between normal feet and feet with flatfoot. Ten participants with normal feet and ten with flexible flatfoot were enrolled in the study. The body kinematics, ground reaction force, and foot pressure of the participants were recorded during walking. A five-segment foot model was developed to calculate contact forces in the tibiotalar joint. A flatfoot model was developed by modifying the stiffness of the spring ligaments of a normal foot model. Ground reaction force was applied to the plantar surface of the foot models. The foot models were attached to a full-body musculoskeletal model to conduct inverse dynamic simulations of walking. Participants with flatfoot had significantly greater lateral contact force (1.19 BW vs. 0.80 BW) and more posteriorly located center of pressure (33.7 % vs. 46.6 %) in the tibiotalar joint than those with normal feet (p < 0.05). The average and peak posterior tibialis muscle forces were significantly larger in participants with flatfoot than in those with normal feet (3.06 BW vs. 2.22 BW; 4.52 BW vs. 3.33 BW). The altered mechanics may influence the risk of arthritis.

Biomechanical comparison among five mid/hindfoot arthrodeses procedures in treating flatfoot using a musculoskeletal multibody driven finite element model

BACKGROUND AND OBJECTIVE

Mid/hindfoot arthrodesis could modify the misalignment of adult-acquired flatfoot and attenuate pain. However, the long-term biomechanical effects of these surgical procedures remain unclear, and the quantitative evidence is scarce. Therefore, we aimed to investigate and quantify the influences of five mid/hindfoot arthrodeses on the internal foot biomechanics during walking stance.

METHODS

A young participant with flexible flatfoot was recruited for this study. We reconstructed a subject-specific musculoskeletal multibody driven-finite element (FE) foot model based on the foot magnetic resonance imaging. The severe flatfoot model was developed from the flexible flatfoot through the attenuation of ligaments and the unloading of the posterior tibial muscle. The five mid/hindfoot arthrodeses simulations (subtalar, talonavicular, calcaneocuboid, double, and triple arthrodeses) and a control condition (no arthrodesis) were performed simultaneously in the detailed foot multibody dynamics model and FE model. Muscle forces calculated by a detailed multi-segment foot model and ground reaction force were used to drive the foot FE model. The internal foot loadings were compared among control and these arthrodeses conditions at the first and second vertical ground reaction force (VGRF) peak and VGRF valley instants.

RESULTS

The results indicated that the navicular heights in double and triple arthrodeses were higher than other surgical procedures, while the subtalar arthrodesis had the smallest values. Five mid/hindfoot arthrodeses reduced the peak plantar fascia stress compared to control. However, double and triple arthrodeses increased the peak medial cuneo-navicular joint contact pressures and peak foot pressures as well as the metatarsal bones stresses.

CONCLUSION

Although mid/hindfoot arthrodesis generally reduced the collapse of medial longitudinal arch and plantar fascia loading during the stance phase, the increased loading in the adjacent unfused joint and metatarsal bones for double and triple arthrodeses should be noted. These findings could account for some symptoms experienced by flatfoot patients after surgery, which may facilitate the optimization of surgical protocols.

Finite element analysis of subtalar joint arthroereisis on adult-acquired flexible flatfoot deformity using customised sinus tarsi implant

Background

Subtalar arthroereisis may cause sinus tarsi pain complications. In this study, we aimed to introduce a customised implant that facilitated treatment effect and less impingement. The biomechanical outcome between the intact and implant conditions was compared using finite element analysis.

Methods

A female patient with flatfoot (age: 36 years, height: 156 ​cm, body mass: 51 ​kg) was recruited as the model patient. The customised implant was designed from the extracted geometry. Boundary and loading conditions were assumed from the data of a normal participant. Four gait instants, including the ground reaction force first peak (25% stance), valley (45%), initial push-off (60%) and second peak (75%) were analyzed.

Results

The navicular height was elevated by 4.2% at 25% stance, whereas the strain of the spring, plantar cuneonavicular and plantar cuboideonavicular ligaments were reduced. The talonavicular joint force decreased and the calcaneocuboid joint increased by half and 67%, respectively, representing a lateralised load pathway. There was a stress concentration at the sulcus tali reaching 15.29 ​MPa

Conclusion

Subtalar arthroereisis using a customised implant may produce some positive treatment effects in terms of navicular height elevation, ligament strain relief and lateralised joint loading pathway. Although the concentrated stress at the sulcus tali did not exceed the threshold of bone breakdown, we could not rule out the potential of vascular disturbance owing to the remarkable elevation of stress. Future study may enlarge the contact area of the bone–implant interface by considering customisation based on the dynamic change of the sinus tarsi during walking gait.

The translational potential of this article

Geometry mismatch of prefabricated implants could be the reason for complications. With the advancement of 3D printing, customising implant becomes possible and may improve treatment outcome. This study implemented a theoretical model approach to explore its potential under a simulation of walking.

Pediatric Flatfeet-A Disease Entity That Demands Greater Attention and Treatment

Background: Pediatric flatfoot is a common deformity. Unfortunately, the common opinion has been that most children with this faulty foot structure will simply out-grow it, despite no radiographic evidence to support this claim. Every step on a deformed foot leads to excessive tissue strain and further joint damage. Many forms of conservative and surgical treatments have been offered. This study was aimed at investigating the effectiveness of non-surgical and surgical treatment options. Main Text: faulty-foot structure is the leading cause of many secondary orthopedic deformities. A wide range of treatments for pediatric flatfeet have been recommended from the "do-nothing" approach, observation, to irreversible reconstructive surgery. Most forms of conservative care lack evidence of osseous realignment and stability. A conservative surgical option of extra-osseous talotarsal joint stabilization provides patients an effective form of treatment without the complications associated with other irreversible surgical procedures. Conclusion: Pediatric flatfeet should not be ignored or downplayed. The sooner effective treatment is prescribed, the less damage will occur to other parts of the body. When possible, a more conservative corrective procedure should be performed prior to irreversible, joint destructive options.

Comparison of Extraosseous Talotarsal Stabilization Implants in a Stage II Adult-Acquired Flatfoot Model: A Finite Element Analysis

Subtalar arthroereisis has been proved to be an efficient method for correcting flexible adult flatfoot. However, the optimal sinus tarsi implant is still debated and yet to be determined. In the present study, we compared the biomechanical effects of type I and II sinus tarsi implants in stage II adult-acquired flatfoot deformity (AAFD). First, a finite element model of stage II AAFD was established in which virtual surgery of subtalar arthroereisis was simulated. The indexes of plantar stress distribution, peak von Mises of the medial and lateral columns, strain of the medial ligaments and plantar fascia, arch height, talo-first metatarsal angle, calcaneus pitch angle, talonavicular coverage angle, and hindfoot valgus angle were all compared and analyzed. The results of the present study have validated the stage II AAFD finite element model by comparing the simulation results with the same parameters measured from weightbearing radiographs in the midstance phase. All the indexes showed that both types of arthroereisis can lower the plantar pressure and the strain of the medial ligaments that support the medial longitudinal arch and can shift the load of the medial column to the lateral column. They can also help to correct the deformity and restore the arch. However, the type II sinus tarsi implant design exhibited a more obvious effect than that of type I.

Return to sport activities after subtalar arthroereisis for correction of pediatric flexible flatfoot

The aim of this study was to establish whether children treated with subtalar arthroereisis for flexible flatfoot were able to return to sport activities. We reviewed 49 patients with a mean age at the time of surgery of 10.7 years. The type of sport activities, the number of sessions per week, the time dedicated to each session, and the level achieved were assessed preoperatively and at the last follow-up. Overall, 45 patients returned to sports after surgery. Surgery did not alter the duration, frequency, and type of sporting activities, but the participation in physical activities as well as the emotional status and footwear issues improved.

Therapeutic Outcomes of Kalix II in Treating Juvenile Flexible Flatfoot

OBJECTIVES

To evaluate the therapeutic outcomes with Kalix II subtalar arthroereisis in sinus tarsi for juvenile flexible flatfoot.

METHODS

A retrospective analysis of the data of 20 juveniles with symptomatic flexible flatfoot (27 feet) who underwent the Kalix II implant procedure from January 2008 to September 2012 was performed. The pain during daily activities was assessed and followed up by use of a standard 10-point visual analog scale (VAS), and function was evaluated using the American Orthopaedic Foot and Ankle Society (AOFAS) ankle and hindfoot scoring system, and anteroposterior talar-first metatarsal angle, lateral talar-first metatarsal angle, calcaneal pitch angle, and talar declination angle at X-ray film were measured to assess the therapeutic outcomes. Patients were asked to grade the result of the procedure as excellent, good, fair, or poor at latest follow-up. The data was expressed as mean ± standard deviation (SD). A paired Student's t -test was used for comparisons of the preoperative and postoperative angular measurements for each foot, VAS scores, and AOFAS scores. In all tests, P < 0.05 was considered statistically significant.

RESULTS

The mean age of the patients was 12.1 years (range, 7-16 years), and 16 left feet and 11 right feet were involved. All patients finished the follow-up with a mean period of 28.1 months (range, 23-60 months). Eleven feet were treated with subtalar arthroereisis combined with reconstruction of the end point of the posterior tibialis tendon after dissection of the accessory scaphoid. The subtalar arthroereisis device displaced in 1 foot due to a fall from the inversion position 3 months after surgery, and was replaced by a new device after the failure of conservative treatment. The mean VAS score decreased from 5.6 ± 0.5 preoperatively to 1.2 ± 0.2 (P < 0.001), and the mean AOFAS hindfoot and ankle score improved from 71.1 ± 6.1 preoperatively to 88.1 ± 6.3 (P < 0.001). Differences between preoperative and postoperative measurements for each radiographic variable were statistically significant (P < 0.001). Comparison of radiographic measurements showed that the anteroposterior talar-first metatarsal (Meary) angle decreased by a mean of 12.8° ± 1.5°, the lateral talar-first metatarsal (Meary) angle decreased by a mean of 15.4° ± 1.3°, the calcaneal pitch angle increased by a mean of -2.1° ± 0.7°, and the talar declination angle decreased by a mean of 17.9° ± 2.8°. Overall, 12 patients rated the result as excellent, 6 as good, and 2 as fair.

CONCLUSION

The application of Kalix II in subtalar arthroereisis combined with dissection of accessory scaphoid and reconstruction of posterior tibialis tendon is an effective therapy for flexible juvenile flatfoot.

Metatarsal Shape and Foot Type: A Geometric Morphometric Analysis

Planus and cavus foot types have been associated with an increased risk of pain and disability. Improving our understanding of the geometric differences between bones in different foot types may provide insights into injury risk profiles and have implications for the design of musculoskeletal and finite-element models. In this study, we performed a geometric morphometric analysis on the geometry of metatarsal bones from 65 feet, segmented from computed tomography (CT) scans. These were categorized into four foot types: pes cavus, neutrally aligned, asymptomatic pes planus, and symptomatic pes planus. Generalized procrustes analysis (GPA) followed by permutation tests was used to determine significant shape differences associated with foot type and sex, and principal component analysis was used to find the modes of variation for each metatarsal. Significant shape differences were found between foot types for all the metatarsals (p < 0.01), most notably in the case of the second metatarsal which showed significant pairwise differences across all the foot types. Analysis of the principal components of variation showed pes cavus bones to have reduced cross-sectional areas in the sagittal and frontal planes. The first (p = 0.02) and fourth metatarsals (p = 0.003) were found to have significant sex-based differences, with first metatarsals from females shown to have reduced width, and fourth metatarsals from females shown to have reduced frontal and sagittal plane cross-sectional areas. Overall, these findings suggest that metatarsal bones have distinct morphological characteristics that are associated with foot type and sex, with implications for our understanding of anatomy and numerical modeling of the foot.

Reducible valgus flat-foot: assessment of posterior subtalar joint surface displacement by posterior arthroscopy during sinus tarsi expansion screwing

INTRODUCTION

Subtalar arthroereisis corrects childhood and adult reducible valgus flat-foot in certain indications. Inserting an expansion screw in the sinus tarsi simultaneously corrects the calcaneal valgus of the talocalcaneal divergence and first-ray pronation if these are reducible. The displacement induced in the posterior subtalar joint (decoaptation, translation, rotation) is, however, poorly known. The present study involved arthroscopic assessment of posterior subtalar joint surface displacement during insertion of a talocalcaneal arthroereisis screw, with the hypothesis that displacement varies in three dimensions according to screw size.

MATERIAL AND METHOD

Eight specimens were used for the study. All ankles were supple, taken from adult subjects. A 4.5-mm arthroscope was used and measurements were taken with a graduated palpator in the posterior subtalar joint. Three sinus tarsi expansion screws of incremental diameter were assessed. Before and after insertion measurements were made of posterolateral and posteromedial talar exposure on the calcaneus, anteroposterior and lateromedial translation, and talocalcaneal joint-line opening.

RESULTS

Medial rotation, varization and anterior translation of the calcaneus were comparable in all cases. Mean lateral opening of the posterior subtalar joint was 0.88 mm with 8-mm screws and 1.25 mm with 16-mm screws. Significant differences between 8 and 16 mm screws were found for lateral subtalar joint opening (P=0.028) and for lateromedial translation (P=0.004).

CONCLUSION

Sinus tarsi expansion screwing corrects hindfoot valgus and talocalcaneal divergence by inducing medial translation of the calcaneus under the talus and talar medial rotation and varization, proportional to screw size (medial translation and lateral opening of the subtalar joint).

LEVEL OF EVIDENCE

III.

An in vitro and finite element study of load redistribution in the midfoot

A good knowledge of midfoot biomechanics is important in understanding the biomechanics of the entire foot, but it has never been investigated thoroughly in the literature. This study carried out in vitro experiments and finite element analysis to investigate the midfoot biomechanics. A foot-ankle finite element model simulating the mid-stance phase of the normal gait was developed and the model validated in in vitro experimental tests. Experiments used seven in vitro samples of fresh human cadavers. The simulation found that the first principal stress peaks of all midfoot bones occurred at the navicular bone and that the tensile force of the spring ligament was greater than that of any other ligament. The experiments showed that the longitudinal strain acting on the medial cuneiform bone was -26.2±10.8 μ-strain, and the navicular strain was -240.0±169.1 μ-strain along the longitudinal direction and 65.1±25.8 μ-strain along the transverse direction. The anatomical position and the spring ligament both result in higher shear stress in the navicular bone. The load from the ankle joint to five branches of the forefoot is redistributed among the cuneiforms and cuboid bones. Further studies on the mechanism of loading redistribution will be helpful in understanding the biomechanics of the entire foot.

Maintenance of longitudinal foot arch after different mid/hind-foot arthrodesis procedures in a cadaveric model

BACKGROUND

Currently, the optimal treatment of flatfoot remains inconclusive. Our objectives were to understand the effect of different arthrodeses on maintenance of foot arch and provide experimental basis for rational selection in treatment of flatfoot.

METHODS

Sixteen fresh-frozen cadaver feet amputated above the ankle along with a section of leg were studied from ten males and six females. We used standard clinical techniques and hardware for making the arthrodeses. Plantar pressure in the medial and lateral longitudinal arch distribution was measured with a plantar pressure mapping system under different loading conditions.

FINDINGS

Values of plantar pressure reaction, mean and maximum dynamic peak pressure between all group pairs were statistically significant (P<0.05). The plantar pressure reaction appeared at the load of 960 N in the medial arch of the unoperated foot, compared with 1080 N after subtalar arthrodesis, 1200 N after talonavicular arthrodesis, 1080 N after calcaneocuboid arthrodesis, 1320 N after double arthrodesis, and 1560 N after triple arthrodesis. The plantar pressure reaction appeared at the load of 360 N in the lateral arch of the unoperated foot, compared with 600 N after subtalar arthrodesis, 600 N after talonavicular arthrodesis, 840 N after calcaneocuboid arthrodesis, 960 N after double arthrodesis, and 1440 N after triple arthrodesis.

INTERPRETATION

The triple arthrodesis provided the highest support to both arches; the double arthrodesis appeared to be similar to talonavicular arthrodesis in supporting the medial arch and similar to calcaneocuboid arthrodesis in supporting the lateral arch; subtalar arthrodesis was less effective in supporting both arches.