Finite element analysis of biomechanical effects of total ankle arthroplasty on the foot

An ex vivo sequential ligament transection model of flatfoot

BACKGROUND

The ligaments implicated in the earliest stages of developing a progressive collapsing foot deformity are poorly understood. Commonly employed cadaveric flatfoot models are created from simultaneous transection of multiple ligaments, making it difficult to assess early changes in pressure distribution from ligaments critical for maintaining load distribution. A serial transection of ligaments may provide insight into changes in pressure distribution under the foot to identify a potential combination of ligaments that may be involved in early deformities.

METHODS

Specimens were loaded using a custom designed axial and tendon loading system. Plantar pressure data for the forefoot and hindfoot were recorded before and after six sequential ligament complex transections.

FINDINGS

Sectioning the plantar fascia (first) and short/long plantar ligaments (second) failed to generate appreciable differences in load distribution. Dividing the spring ligament (third) led to changes in hindfoot load distribution with a shift towards the lateral column indicative of hindfoot valgus angulation. All subsequent conditions resulted in similar patterns in hindfoot plantar load distribution. An anterior shift in the center of pressure only occurred after transection of all six ligament complexes.

INTERPRETATION

Loss of the plantar fascia and short/long plantar ligaments are not critical in maintaining plantar load distribution or contact area. However, the additional loss of the spring ligament caused notable changes in hindfoot load distribution, indicating the combination of these three ligament complexes is particularly critical for preventing peritalar subluxation. Minimal changes in load distribution occurred when performing additional transections to reach a complete flatfoot deformity.

Biomechanical role of bone grafting for calcaneal fracture fixation in the presence of bone defect: A finite element analysis

BACKGROUND

The purpose of this study was to compare the biomechanical stress and stability of calcaneal fixations with and without bone defect, before and after bone grafting, through a computational approach.

METHODS

A finite element model of foot-ankle complex was reconstructed, impoverished with a Sanders III calcaneal fracture without bone defect and with moderate and severe bone defects. Plate fixations with and without bone grafting were introduced with walking stance simulated. The stress and fragment displacement of the calcaneus were evaluated.

FINDINGS

Moderate and severe defect increased the calcaneus stress by 16.11% and 32.51%, respectively and subsequently decreased by 10.76% and 20.78% after bone grafting. The total displacement was increased by 3.99% and 24.26%, respectively by moderate and severe defect, while that of posterior joint facet displacement was 86.66% and 104.44%. The former was decreased by 25.73% and 35.96% after grafting, while that of the latter was reduced by 88.09% and 84.78% for moderate and severe defect, respectively.

INTERPRETATION

Our finite element prediction supported that bone grafting for fixation could enhance the stability and reduce the risk of secondary stress fracture in cases of bone defect in calcaneal fracture.

A finite element model of human hindfoot and its application in supramalleolar osteotomy

BACKGROUND

The majority of the ankle osteoarthritis cases are posttraumatic and affect younger patients with a longer projected life span. Hence, joint-preserving surgery, such as supramalleolar osteotomy becomes popular among young patients, especially those with asymmetric arthritis due to alignment deformities. However, there is a lack of biomechanical studies on postoperative evaluation of stress at ankle joints. We aimed to construct a verifiable finite element model of the human hindfoot, and to explore the effect of different osteotomy parameters on the treatment of varus ankle arthritis.

METHODS

The bones of the hindfoot are reconstructed using normal CT tomography data from healthy volunteers, while the cartilages and ligaments are determined from the literature. The finite element calculation results are compared with the weight-bearing CT (WBCT) data to validate the model. By setting different model parameters, such as the osteotomy height (L) and the osteotomy distraction distance (h), the effects of different surgical parameters on the contact stress of the ankle joint surface are compared.

FINDINGS

The alignment and the deformation of hindfoot bones as determined by the finite element analysis aligns closely with the data obtained from WBCT. The maximum contact stress of the ankle joint surface calculated by this model increases with the increase of the varus angle. The maximum contact stresses as a function of the L and h of the ankle joint surface are determined.

INTERPRETATION

The relationship between surgical parameters and stress at the ankle joint in our study could further help guiding the planning of the supramalleolar osteotomy according to the varus/valgus alignment of the patients.

Effect of novel polyethylene insert configurations on bone-implant micromotion and contact stresses in total ankle replacement prostheses: a finite element analysis

Purpose

This study investigates the impact of elastic improvements to the artificial ankle joint insert on prosthesis biomechanics to reduce the risk of prosthesis loosening in TAR patients.

Methods

CT data of the right ankle was collected from one elderly female volunteer. An original TAR model (Model A) was developed from CT images and the INBONE II implant system. The development of the new inserts adopts an elastic improvement design approach, where different geometric configurations of flexible layers are inserted into the traditional insert. The structure can be divided into continuous flexible layers and intermittent flexible layers. The flexible layers aim to improve the elasticity of the component by absorbing and dispersing more kinetic energy. The newly designed inserts are used to replace the original insert in Model A, resulting in the development of Models B-D. A finite element model of gait analysis was based by gait parameters. Discrepancies in micromotion and contact behaviour were analysed during the gait cycle, along with interface fretting and articular surface stress at 50% of the gait cycle.

Results

In terms of micromotion, the improved elastic models showed reduced micromotion at the tibial-implant interfaces compared to the original model. The peak average micromotion decreased by 12.1%, 13.1%, and 14.5% in Models B, C, and D, respectively. The micromotion distribution also improved in the improved models, especially in Model D. Regarding contact areas, all models showed increased contact areas of articular surfaces with axial load, with Models B, C, and D increasing by 26.8%, 23.9%, and 24.4%, respectively. Contact stress on articular surfaces increased with axial load, reaching peak stress during the late stance phase. Models with continuous flexible layer designs exhibited lower stress levels. The insert and the talar prosthetic articular surfaces showed more uniform stress distribution in the improved models.

Conclusion

Improving the elasticity of the insert can enhance component flexibility, absorb impact forces, reduce micromotion, and improve contact behavior. The design scheme of continuous flexible layers is more advantageous in transmitting and dispersing stress, providing reference value for insert improvement.

The retropharyngeal reduction plate for atlantoaxial dislocation: a finite element analysis

Objective: To investigate the biomechanical properties of the retropharyngeal reduction plate by comparing the traditional posterior pedicle screw-rod fixation by finite element analysis. Methods: Two three-dimensional finite element digital models of the retropharyngeal reduction plate and posterior pedicle screw-rod fixation were constructed and validated based on the DICOM (Digital Imaging and Communications in Medicine) data from C1 to C4. The biomechanical finite element analysis values of two internal fixations were measured and calculated under different conditions, including flexion, extension, bending, and rotation. Results: In addition to the backward extension, there was no significant difference in the maximum von Mises stress between the retropharyngeal reduction plate and posterior pedicle screw fixation under other movement conditions. The retropharyngeal reduction plate has a more uniform distribution under different conditions, such as flexion, extension, bending, and rotation. The stress tolerance of the two internal fixations was basically consistent in flexion, extension, left bending, and right bending. Conclusion: The retropharyngeal reduction plate has a relatively good biomechanical stability without obvious stress concentration under different movement conditions. It shows potential as a fixation option for the treatment of atlantoaxial dislocation.

A numerical investigation of stress, strain, and bone density changes due to bone remodelling in the talus bone following total ankle arthroplasty

Total ankle arthroplasty is the gold standard surgical treatment for severe ankle arthritis and fracture. However, revision surgeries due to the in vivo failure of the ankle implant are a serious concern. Extreme bone density loss due to bone remodelling is one of the main reasons for in situ implant loosening, with aseptic loosening of the talar component being one of the primary reasons for total ankle arthroplasty revisions. This study is aimed at determining the performance and potential causes of failure of the talar component. Herein, we investigated the stress, strain, and bone density changes that take place in the talus bone during the first 6 months of bone remodelling due to the total ankle arthroplasty procedure. Computed tomography scans were used to generate the 3D geometry used in the finite element (FE) model of the Intact and implanted ankle. The Scandinavian Total Ankle Replacement (STAR™) CAD files were generated, and virtual placement within bone models was done following surgical guidelines. The dorsiflexion physiological loading condition was investigated. The cortical region of the talus bone was found to demonstrate the highest values of stress (5.02 MPa). Next, the adaptive bone remodelling theory was used to predict bone density changes over the initial 6-month post-surgery. A significant change in bone density was observed in the talus bone due to bone remodelling. The observed quantitative changes in talus bone density over 6-month period underscore potential implications for implant stability and fracture susceptibility. These findings emphasise the importance of considering such biomechanical factors in ankle implant design and clinical management.

Disease-Specific Finite element Analysis of the Foot and Ankle

Finite-element analysis is a computational modeling technique that can be used to quantify parameters that are difficult or impossible to measure externally in a geometrically complex structure such as the foot and ankle. It has been used to improve our understanding of pathomechanics and to evaluate proposed treatments for several disorders, including progressive collapsing foot deformity, ankle arthritis, syndesmotic injury, ankle fracture, plantar fasciitis, diabetic foot ulceration, hallux valgus, and lesser toe deformities. Parameters calculated from finite-element models have been widely used to make predictions about their biomechanical correlates.

An investigation into the hammer toe effects on the lower extremity mechanics and plantar fascia tension: A case for a vicious cycle and progressive damage

Hammer toes are one of the common deformities of the forefoot that can lead to compensatory changes during walking in individuals with this condition. Predicting the adverse effects of tissue damage on the performance of other limbs is very important in the prevention of progressive damage. Finite element (FE) and musculoskeletal modeling can be helpful by allowing such effects to be studied in a way where the internal stresses in the tissue could be investigated. Hence, this study aims to investigate the effects of the hammer toe deformity on the lower extremity, especially on the plantar fascia functions. To compare the joint reactions of the hammer toe foot (HTF) and healthy foot (HF), two musculoskeletal models (MSM) of the feet of a healthy individual and that of a participant with hammer toe foot were developed based on gait analysis. A previously validated 3D finite element model which was constructed using Magnetic Resonance Imaging (MRI) of the diabetic participant with the hammer toe deformity was processed at five different events during the stance phase of gait. It was found that the hammer toe deformity makes dorsiflexion of the toes and the windlass mechanism less effective during walking. Specifically, the FE analysis results showed that plantar fascia (PF) in HTF compared to HF played a less dominant role in load bearing with both medial and lateral parts of PF loaded. Also, the results indicated that the stored elastic energy in PF was less in HTF than the HF, which can indicate a higher metabolic cost during walking. Internal stress distribution shows that the majority of ground reaction forces are transmitted through the lateral metatarsals in hammer toe foot, and the probability of fifth metatarsal fracture and also progressive deformity was subsequently increased. The MSM results showed that the joint reaction forces and moments in the hammer toe foot have deviated from normal, where the metatarsophalangeal joint reactions in the hammer toe were less than the values in the healthy foot. This can indicate a vicious cycle of foot deformity, leading to changes in body weight force transmission line, and deviation of joint reactions and plantar fascia function from normal. These in turn lead to increased internal stress concentration, which in turn lead to further foot deformities. This vicious cycle cause progressive damage and can lead to an increase in the risk of ulceration in the diabetic foot.

Biomechanical application of finite elements in the orthopedics of stiff clubfoot

BACKGROUND

The purpose of this study was to evaluate the effect of varying the different correction angles of hindfoot osteotomy orthosis on the biomechanical changes of the adjacent joints after triple arthrodesis in adult patients with stiff clubfoot to determine the optimal hindfoot correction angle and provide a biomechanical basis for the correction of hindfoot deformity in patients with stiff clubfoot.

METHODS

A 26-year-old male patient with a stiff left clubfoot was selected for the study, and his ankle and foot were scanned using dual-source computed tomography. A three-dimensional finite element model of the ankle was established, and after the validity of the model was verified by plantar pressure experiments, triple arthrodesis was simulated to analyze the biomechanical changes of the adjacent joints under the same load with "3°" of posterior varus, "0°" of a neutral position and "3°, 6°, 9°" of valgus as the correction angles.

RESULTS

The peak plantar pressure calculated by the finite element model of the clubfoot was in good agreement with the actual plantar pressure measurements, with an error of less than 1%. In triple arthrodesis, the peak von Mises stress in the adjacent articular cartilage was significantly different and less than the preoperative stress when the corrected angle of the hindfoot was valgus "6°". In comparison, the peak von Mises stress in the adjacent articular cartilage was not significantly different in varus "3°", neutral "0°", valgus "3°" and valgus "9°" compared with the preoperative stress.

CONCLUSION

The results of this study showed that different angles of hindfoot correction in triple arthrodesis did not increase the peak von Mises stress in the adjacent joints, which may not lead to the development of arthritis in the adjacent joint, and a hindfoot correction angle of "6°" of valgus significantly reduced the peak von Mises stress in the adjacent joints after triple arthrodesis.

Modified scarf osteotomy for hallux valgus: From a finite element model to clinical results

PURPOSE

Finite element (FE) analysis and clinical follow-up were used to evaluate the efficacy of modified scarf osteotomy for moderate-to-severe hallux valgus (HV).

METHOD

We retrospectively evaluated 42 patients (44 feet) who underwent modified rotational scarf osteotomy for moderate-to-severe HV at our institution between January 2010 and January 2019. Radiological indicators and subjective scores were recorded at different time points. To compare the results and elemental characteristics, a FE model of the metatarsophalangeal (MTP) joint that included anatomically realistic geometrical and structural characteristics was built. The biomechanical features and correction differences in dynamic loads as well as the incidence of troughing were estimated.

RESULTS

Both the hallux valgus angle (HVA) and intermetatarsal angle (IMA) showed significant improvement 6 weeks postoperatively (p < 0.05); additionally, the HVA increased from 6 weeks postoperatively to the last follow-up, while the IMA showed no significant changes (p > 0.05). The subjective scores significantly improved from the preoperative period to the last follow-up. The percentages of troughing and recurrence were remarkably low in our pilot study because of the innate stability of the modified rotated fixation.

CONCLUSION

Our preliminary findings suggest that modified rotational scarf osteotomy offers sufficient stability, correct HV deformity effectively, and good clinical outcomes for moderate to severe HV.

Dynamic finite element analyses to compare the influences of customised total talar replacement and total ankle arthroplasty on foot biomechanics during gait

Objective, Total talar replacement (TTR) using a customised talus prosthesis is an emerging surgical alternative to conventional total ankle arthroplasty (TAA) for treating ankle problems. Upon satisfying clinical reports in the literature, this study explored the advantages of TTR in restoring foot biomechanics during walking compared with TAA through computational simulations.Methods, A dynamic finite element foot model was built from the MRIs of a healthy participant and modified into two implanted counterparts (TTR and TAA) by incorporating the corresponding prosthetic components into the ankle joint. Twenty bony parts, thirty-nine ligament/tendon units, nine muscle contractors, and bulk soft tissue were included in the intact foot model. The TTR prosthesis was reconstructed from the mirror image data of the participant's contralateral talus and the TAA prosthesis was modelled by reproducing the Scandinavian ankle replacement procedure in the model assembly. The model was meshed with explicit deformable elements and validated against existing experimental studies that have assessed specific walking scenarios. Simulations were performed using the boundary conditions (time-variant matrix of muscle forces, segment orientation, and ground reaction forces) derived from motion capture analyses and musculoskeletal modelling of the participant's walking gait. Outcome variables, including foot kinematics, joint loading, and plantar pressure were reported and compared among the three model conditions.

RESULTS

Linear regression indicated a better agreement between the TTR model and intact foot model in plots of joint motions and foot segment movements during walking (R² ​= ​0.721-0.993) than between the TAA and intact foot (R² ​= ​0.623-0.990). TAA reduced talocrural excursion by 21.36%-31.92% and increased (MTP) dorsiflexion by 3.03%. Compared with the intact foot, TTR and TAA increased the midtarsal joint contact force by 17.92% and 10.73% respectively. The proximal-to-distal force transmission within the midfoot was shifted to the lateral column in TTR (94.52% or 210.54 ​N higher) while concentrated on the medial column in TAA (41.58% or 27.55 ​N higher). The TTR produced a plantar pressure map similar to that of the intact foot. TAA caused the plantar pressure centre to drift medially and increased the peak forefoot pressure by 7.36% in the late stance.

CONCLUSION

The TTR better reproduced the foot joint motions, segment movements, and plantar pressure map of an intact foot during walking. TAA reduced ankle mobility while increasing movement of the adjacent joints and forefoot plantar pressure. Both implant methods changed force transmission within the midfoot during gait progression.The translational potential of this article Our work is one of the few to report foot segment movements and the internal loading status of implanted ankles during a dynamic locomotion task. These outcomes partially support the conjecture that TTR is a prospective surgical alternative for pathological ankles from a biomechanical perspective. This study paves the way for further clinical investigations and systematic statistics to confirm the effects of TTR on functional joint recovery.

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

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.

Effects of badminton insole design on stress distribution, displacement and bone rotation of ankle joint during single-leg landing: a finite element analysis

Previous research has reported that up to 92% of injuries amongst badminton players consist of lower limb, whereby 35% of foot fractures occurred at the metatarsal bone. In sports, insoles are widely used to increase athletes' performance and prevent many injuries. However, there is still a lack of badminton insole analysis and improvements. Therefore, this study aimed to biomechanically analyse three different insole designs. A validated and converged three-dimensional (3D) finite element model of ankle-foot complex was developed, which consisted of the skin, talus, calcaneus, navicular, three cuneiform, cuboid, five metatarsals and five phalanges. Three existing insoles from the market, (1) Yonex Active Pro Truactive, (2) Victor VT-XD 8 and (3) Li-Ning L6200LA, were scanned using a 3D scanner. For the analysis, single-leg landing was simulated. On the superior surface of the skin, 2.57 times of the bodyweight was axially applied, and the inferior surface of the outsole was fixed. The results showed that Insole 3 was the most optimum design to reduce peak stress on the metatarsals (3.807 MPa). In conclusion, the optimum design of Insole 3, based on the finite element analysis, could be a justification of athletes' choices to prevent injury and other complications.

Workflow assessing the effect of Achilles tendon rupture on gait function and metatarsal stress: Combined musculoskeletal modeling and finite element analysis

Achilles tendon rupture (ATR) incidence has increased among badminton players in recent years. The foot internal stress was hard to obtain through experimental testing. The purpose of the current research is to develop a methodology that could improve the finite element model derived foot internal stress prediction for ATR clinical and rehabilitation applications. A subject-specific musculoskeletal model was combined with a 3D finite element model to predict the metatarsal stress. The 80% point during the push-off phase of walking was selected for the comparing between injured and uninjured sides. The surgical repaired Achilles tendon (AT) after 12 months was elongated by 5.5% than the uninjured tendon. At 80% point of stance phase, the ankle plantarflexion angle and AT force decreased by 39.6% and 21.9% on the injured side, respectively. The foot inversion degree increased by 22.9% and was accompanied by the redistribution of metatarsals von Mises stress. The stresses on the fourth and fifth metatarsals were increased by 59.5% and 85.9% on the injured side. The workflow is available to assess musculoskeletal disorders and obtain foot internal stress after ATR. The decreased ankle plantar flexor force may be affected by triceps surae muscle atrophy and weakened force transmission ability of elongated AT. The increased von Mises stress on fourth and fifth metatarsals accompanied by higher foot inversion may increase the ankle lateral sprain injury risk.

Multi-segment foot kinematics during gait following ankle arthroplasty

Ankle arthritis is a debilitating disease marked by pain and limited function. Total ankle arthroplasty improves pain while preserving motion and offers an alternative to the traditional treatment of ankle fusion. Gait analysis and functional outcomes tools can provide an objective balanced analysis of ankle replacement for the treatment of ankle arthritis. Twenty-nine patients with end-stage ankle arthritis were evaluated before and after ankle arthroplasty. Multi-segment foot and ankle kinematics were assessed annually following surgery (average 3.5 years, range 1-6 years) using the Milwaukee Foot Model and a Vicon video motion analysis system. Functional outcomes (American Orthopedic Foot and Ankle Society [AOFAS] ankle/hindfoot scale, short form 36 [SF-36] questionnaire) and temporal-spatial parameters were also assessed. Kinematic results were compared to findings from a previously collected group of healthy ambulators. AOFAS and SF-36 mean scores improved postoperatively. Walking speed and stride length increased after surgery. There were significant improvements in tibial sagittal range of motion in terminal stance and hindfoot sagittal range of motion in preswing. Decreased external rotation of the tibia and increased external rotation of the hindfoot were noted throughout the gait cycle. Pain and function improved after ankle replacement as supported by better outcomes scores, increased temporal-spatial parameters, and significant improvement in tibial sagittal range of motion during terminal stance and hindfoot sagittal range of motion during preswing. While multi-segment foot kinematics were improved, they were not restored to control values. Statement of clinical significance: Total ankle arthroplasty does not fully normalize mutli-segment gait kinematics despite improved patient-reported outcomes and gait mechanics.

Finite element stress analysis of the bearing component and bone resected surfaces for total ankle replacement with different implant material combinations

Background

A proper combination of implant materials for Total Ankle Replacement (TAR) may reduce stress at the bearing component and the resected surfaces of the tibia and talus, thus avoiding implant failure of the bearing component or aseptic loosening at the bone-implant interface.

Methods

A comprehensive finite element foot model implanted with the INBONE II implant system was created and the loading at the second peak of ground reaction force was simulated. Twelve material combinations including four materials for tibial and talar components (Ceramic, CoCrMo, Ti6Al4V, CFR-PEEK) and three materials for bearing components (CFR-PEEK, PEEK, and UHMWPE) were analyzed. Von Mises stress at the top and articular surfaces of the bearing component and the resected surfaces of the tibia and talus were recorded.

Results

The stress at both the top and articular surfaces of the bearing component could be greatly reduced with more compliant bearing materials (44.76 to 72.77% difference of peak stress value), and to a lesser extent with more compliant materials for the tibial and talar components (0.94 to 28.09% difference of peak stress value). Peak stresses at both the tibial and talar bone-implant interface could be reduced more strongly by using tibial and talar component materials with smaller material stiffness (7.31 to 66.95% difference of peak stress value) compared with bearing materials with smaller material stiffness (1.11 to 24.77% difference of peak stress value).

Conclusions

Implant components with smaller material stiffness provided a stress reduction at the bearing component and resected surfaces of the tibia and talus. The selection of CFR-PEEK as the material of tibial and talar components and UHMWPE as the material of the bearing component seemed to be a promising material combination for TAR implants. Wear testing and long-term failure analysis of TAR implants with these materials should be included in future studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04982-3.

Polka dot cementless talar component in enhancing total ankle replacement fixation: A parametric study using the finite element analysis approach

The primary stability of a total ankle replacement (TAR) is essential in preventing long-term aseptic loosening failure and could be quantified based on micromotion at the bone-prosthesis interface subjected to physiological loading during the normal walking. A 3D finite element analysis was conducted to investigate the current commercial STAR™ Ankle TAR bone-prosthesis interface relative micromotion (BPIRM) with addition of the talus bone minimum principal bone stresses (MPBS). Comparison was made to the proposed polka dot designs with the hemispheric feature that was demonstrated to enhance BPIRM. Parametric studies were conducted on the hemispheric features with changes in its diameter, length and shape. The FE results indicated high BPIRM at the talar component was primarily contributed by de-bonding (in the normal direction) between the talus bone and talar component. The MPBS were found to be most significant in the superior anterior and superior medial regions of the talus bone. When the pin length was increased from 1.5 to 3 mm, the BPIRM was predicted to fall below 50 μm in favour of bone in-growth. Based on the practicality of the prosthesis implantation during the surgical procedure, the final design that incorporated both the initial polka dot and 3 mm pin length in a crisscross manner was deemed to be a favorable design with reduced BPIRM and MPBS hence lowering the risk of long-term aseptic loosening.

Total ankle replacement along with subtalar joint arthrodesis: In-vitro and in-silico biomechanical investigations

Total ankle replacement (TAR) and subtalar joint (STJ) fusion, are popular treatments for ankle osteoarthritis (OA). Short endurance limits the former, and movement disability comes with the latter. It is hypothesized here that fusion of the STJ can improve the longevity of the TAR prosthesis. In this study, a fresh human cadaver's ankle joint underwent TAR surgery, and strain patterns in the vicinity of prosthesis were recorded after the application of axial compressive load on tibia, resembling stance phase of the gait. Then, STJ of the same sample fused (FTAR), and a similar test procedure was pursued. The obtained strains in the FTAR were smaller than those of the TAR (p < .01). Finite element models of the tested samples were also made, and validated by experimental strains. The validated FE models were then employed to find stress distribution on the tibial plateau and prosthesis compartments. FTAR demonstrated more regular stress profiles in bone-prosthesis interface. Also, maximum von Mises stress in the talar component of the FTAR is approximately half of that in the TAR (8 and 15 MPa, respectively). Based on the results of this study, having a more symmetric load distribution on the prosthesis after STJ fusion, longevity of the TAR may likely increase.

Analysis of transient response of the human foot based on the finite element method

BACKGROUND

The foot is an important part of the human body. Its functions are mainly walking and load-bearing. It also keeps the human body stable and absorbs ground vibrations to protect important human organs.

OBJECTIVE

Many researchers use finite element methods to study the biomechanics of the foot. However, current studies on the finite element of the foot are based on the stress and displacement response analysis of the foot under static or quasi-static conditions, ignoring the movement process of the foot and the impact of vibration. Moreover, the joint application of energy method and finite element analysis in foot biomechanics is rarely reported.

METHODS

In this paper, to obtain the foot energy transfer process, the transient response of the foot under neutral position is analyzed based on the energy method.

RESULTS

The results show that: (1) In this model, the energy analysis follows the conservation of energy, which indicates that the transient response analysis has obtained a reasonable response. (2) When the foot touches the ground, the strain energy of the calcaneus, second metatarsal and third metatarsal is relatively large, which is consistent with the main stress concentration area of the plantar. (3) The gravity of the human body is mainly transmitted through the talus to the calcaneus, while the effect of transmittal through the scaphoid to the cuneiform bone and metatarsal is weak.

CONCLUSION

This study can not only more clearly and intuitively reflect the energy transfer and source of various skeletal foreheads in the foot, but also provide a new research idea for the study of foot biomechanics.

Influence of cancellous bone material and dead zone on stress-strain, bone stimulus and bone remodelling around the tibia for total ankle replacement

Extreme bone resorption due to bone remodelling is one of the reasons for ankle component loosening. Finite element (FE) analysis has been effectively used nowadays for pre-clinical analysis of orthopaedic implants. For FE modelling, the selection of bone material and dead zone play a vital role to understand the bone remodelling. This study deals with the effects of different cancellous elastic modulus-density relationships and dead zone on bone remodelling around the tibia owing to total ankle replacement (TAR), using finite element analysis with physiological loading conditions. This study also investigated the bone stimulus distribution in the tibia to identify the initial indication of bone density changes due to bone remodelling. Additionally, the Hoffman failure criterion was used to investigate the chances of implant-bone interface failure due to different cancellous bone material modelling and bone remodelling. The present bone remodelling study consists of three different dead or lazy zones (±0.75, ±0.60 and ±0.35) to examine the influence of the dead zone on bone remodelling. Differences in stress/strain distribution were observed in the tibia bone due to different cancellous bone material modelling. Despite little variations, bone density changes due to bone remodelling were found to be almost similar for two FE models having different cancellous bone material. Similar to these results, the effect of different dead zone on bone density changes due to bone remodelling was found to be minimal. Bone stimulus distribution in the cancellous bone was found to be almost similar for FE models having different cancellous bone material modelling and different dead zones. To understand the stress/strain and interface related failure of the tibial component, cancellous bone material modelling plays a crucial role. However, cancellous bone material modelling and dead zone have minimal influence on bone remodelling around the tibia cancellous bone due to TAR.

Bio-Numerical Analysis of the Human Ankle-Foot Model Corresponding to Neutral Standing Condition

Background:

The foot is the most complex body’s structure; it is highly susceptible to disorders because of its loading pattern. The complexity of the foot structure geometry implies the use of reverse engineering tools to obtain a model that can accurately mimic the biomechanical behavior of the foot.

Objective:

The objective of this study is to establish a state-of-the-art ankle-foot finite element (FE) model with anatomically realistic geometry and structure in order to get the model that will suit all cases for future studies on stress injuries and foot insole designs under different loading conditions.

Material and Methods:

In this analytical study, tomography images were imported in DICOM format, after that, the object was exported in the form of three-dimensional structures in STL file format to define and assemble the structures. After that, the computer simulation on numerical model was done. One-way Analysis of variance (ANOVA) test was performed, and a threshold (p&lt;0.05) was used to indicate the significance of results.

Results:

The results showed no significant differences (P>0.05) between the values of the plantar pressure corresponding to neutral standing condition with other foot models in literature. The stresses transferred to the bone structure show that the relatively higher stress was located in the fifth, fourth and third tarsometatarsal, where the maximum von Mises stress in the bone structure was 2155.4 kPa.

Conclusion:

The state-of-the-art ankle-foot FE model with anatomically realistic geometry and structure will be very helpful for future studies on stress injuries and foot insole designs under different loading conditions.

Finite Element Analysis of Generalized Ligament Laxity on the Deterioration of Hallux Valgus Deformity (Bunion)

Hallux valgus is a common foot problem affecting nearly one in every four adults. Generalized ligament laxity was proposed as the intrinsic cause or risk factor toward the development of the deformity which was difficult to be investigated by cohort clinical trials. Herein, we aimed to evaluate the isolated influence of generalized ligament laxity on the deterioration using computer simulation (finite element analysis). We reconstructed a computational foot model from a mild hallux valgus participant and conducted a gait analysis to drive the simulation of walking. Through parametric analysis, the stiffness of the ligaments was impoverished at different degrees to resemble different levels of generalized ligament laxity. Our simulation study reported that generalized ligament laxity deteriorated hallux valgus by impairing the load-bearing capacity of the first metatarsal, inducing higher deforming force, moment and malalignment at the first metatarsophalangeal joint. Besides, the deforming moment formed a deteriorating vicious cycle between hallux valgus and forefoot abduction and may result in secondary foot problems, such as flatfoot. However, the metatarsocuneiform joint did not show a worsening trend possibly due to the overriding forefoot abduction. Controlling the deforming load shall be prioritized over the correction of angles to mitigate deterioration or recurrence after surgery.

A novel design, analysis and 3D printing of Ti-6Al-4V alloy bio-inspired porous femoral stem

The current study is proposing a design envelope for porous Ti-6Al-4V alloy femoral stems to survive under fatigue loads. Numerical computational analysis of these stems with a body-centered-cube (BCC) structure is conducted in ABAQUS. Femoral stems without shell and with various outer dense shell thicknesses (0.5, 1.0, 1.5, and 2 mm) and inner cores (porosities of 90, 77, 63, 47, 30, and 18%) are analyzed. A design space (envelope) is derived by using stem stiffnesses close to that of the femur bone, maximum fatigue stresses of 0.3σ_ys in the porous part, and endurance limits of the dense part of the stems. The Soderberg approach is successfully employed to compute the factor of safety N_f > 1.1. Fully porous stems without dense shells are concluded to fail under fatigue load. It is thus safe to use the porous stems with a shell thickness of 1.5 and 2 mm for all porosities (18-90%), 1 mm shell with 18 and 30% porosities, and 0.5 mm shell with 18% porosity. The reduction in stress shielding was achieved by 28%. Porous stems incorporated BCC structures with dense shells and beads were successfully printed.

Predicting ground reaction and tibiotalar contact forces after total ankle arthroplasty during walking

The motion capture and force plates data are essential inputs for musculoskeletal multibody dynamics models to predict in vivo tibiotalar contact forces. However, it could be almost impossible to obtain valid force plates data in old patients undergoing total ankle arthroplasty under some circumstances, such as smaller gait strides and inconsistent walking speeds during gait analysis. To remove the dependence of force plates, this study has established a patient-specific musculoskeletal multibody dynamics model with total ankle arthroplasty by combining a foot-ground contact model based on elastic contact elements. And the established model could predict ground reaction forces, ground reaction moments and tibiotalar contact forces simultaneously. Three patients' motion capture and force plates data during their normal walking were used to establish the patient-specific musculoskeletal models and evaluate the predicted ground reaction forces and ground reaction moments. Reasonable accuracies were achieved for the predicted and measured ground reaction forces and ground reaction moments. The predicted tibiotalar contact forces for all patients using the foot-ground contact model had good consistency with those using force plates data. These findings suggested that the foot-ground contact model could take the place of the force plates data for predicting the tibiotalar contact forces in other total ankle arthroplasty patients, thus providing a simplified and valid platform for further study of the patient-specific prosthetic designs and clinical problems of total ankle arthroplasty in the absence of force plates data.

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.

Finite element analysis of bone-prosthesis interface micromotion for cementless talar component fixation through critical loading conditions

The total ankle replacement (TAR) survivability rate is still suboptimal, and this leads to many orthopaedic surgeons opting arthrodesis as a better option for the ankle arthritis patients. One of the fundamental reasons is due to the lack of primary stability of the prosthesis fixation at the bone-prosthesis interface hence leading to long-term aseptic loosening of the talar component. The commercially available Scandinavian Total Ankle Replacement (STAR) Ankle design and several additional design features (including trabecular metal, side fin, double fin, and polka-dot designs) were studied using finite element analysis, and the bone-prosthesis interface relative micromotion (BPIRM) and talar bone minimum principal stresses were examined and analysed. Three loading conditions at a gait cycle of heel strike, midstance, and toe off with different meniscal bearing displacement were also included as part of the study parameters. The results were correlated to in vitro cadaveric measurements and reported clinical studies. Simulated results showed that the de-bonding relative distance between the bone and prosthesis upon loading (COPEN defined by the simulation software) was the main reason constituting to the high interface micromotion between the talar component and talus bone (which could lead to long-term aseptic loosening). The polka-dot design was shown to induce the lowest BPIRM among all the designs studied.

Musculoskeletal modeling of total ankle arthroplasty using force-dependent kinematics for predicting in vivo joint mechanics

In vivo load and motion in the ankle joint play a key role in the understanding of the failure mechanism and function outcomes of total ankle arthroplasty. However, a thorough understanding of the biomechanics of the ankle joint in daily activities is lacking. The objective of this study was to develop a novel lower extremity musculoskeletal multibody dynamics model with total ankle arthroplasty considering the 6 degrees of freedom of the ankle joint motions and the deformable contact mechanics of the implant, based on force-dependent kinematics method. A patient who underwent total ankle arthroplasty surgery was considered. The walking gait data of the patient was measured in a gait laboratory and used as the input for the patient-specific musculoskeletal modeling. The predictions from the musculoskeletal model of total ankle arthroplasty included dorsiflexion-plantar flexion, inversion-eversion, internal-external rotation, anterior-posterior translation, inferior-superior translation, and medial-lateral translation of the tibiotalar joint, the ankle contact forces, the muscle activations, and the ligament forces. The magnitudes and tendencies of the predicted results were all within reasonable ranges, as compared with the data available in the literature. The predicted peak total ankle contact force was 6.55 body weight. In addition, the peak contact forces of the lateral and medial compartments were 4.22 body weight and 2.59 body weight, respectively. This study provides a potential new platform for the design of a better ankle prosthesis, the improvement of the operation techniques of the clinicians, and the accelerated postoperative recovery of the patients.

Experimental and finite element investigation of total ankle replacement: A review of literature and recommendations

This paper briefly reviews the different methodology, technology, challenges, and outcomes of various studies related to TAR prosthesis based on numerical and experimental techniques. Very less in-vitro experimental studies on TAR have been found than finite element (FE) studies. Due to the invasive nature of the experimental approach, inadequacy and less clinical information, computational modelling has been widely used by the researchers. This paper critically examines the part related to FE modelling and experimental analysis. Some recommendation related to modelling of bones, cartilages, ligaments, muscles, and implant-bone interface condition were discussed for better understanding the results and better clinical significance.

A COMPUTATIONAL STUDY OF DIFFERENT ADDITIVE MANUFACTURING-BASED TOTAL ANKLE REPLACEMENT DEVICES USING THREE-DIMENSIONAL HUMAN LOWER EXTREMITY MODELS WITH VARIOUS ANKLE POSTURES

Total ankle replacement (TAR) surgery is one of the useful methods to treat ankle arthritis. Selective laser melting that is an additive manufacturing (AM) technique has made it possible to fabricate orthopedic implants. However, there are rare studies to analyze AM implants using finite element method. Thus, the purpose of this study was to investigate the effect of the various porous designs with three types of tibial shapes for five ankle postures using three-dimensional (3D) human lower extremity models. The variable-axis-mobile-bearing (VAMB) TAR models were developed in one solid TAR design and three porous TAR designs on the tibial and talar components. Additionally, three shape designs (curved, flat, and tilted) of the tibial component were also evaluated. Each TAR design was assembled on the human lower extremity model with standing, inversion, eversion, plantar flexion, and dorsiflexion ankle postures. The results showed that there was a minor effect among the solid and porous TAR designs on the implant stability, the bone stress, and the implant stress. However, those performances in the plantar flexion were significantly reduced compared to that in the other ankle postures. Although the porous TAR designs have a higher risk of implant failure and bone breakage, it may have better bone-implant bonding ability. This study could help engineers and surgeons to understand the design rationale and biomechanics of AM-based TAR devices.

A Strain Distribution Sensing System for Bone-Implant Interfaces Based on Digital Speckle Pattern Interferometry

This paper aims to provide an effective measurement method for the distribution of deformations and strains focusing on the response to external loading of bone-implant interfaces. To achieve this target, a novel speckle interference imaging method is proposed by introducing phosphate buffer saline medium, in which the samples were completely placed into a phosphate buffer saline solution medium to stable the water molecules. The stability of interferometry imaging is analyzed by using the concepts of co-occurrence matrix and moment of inertia. A series of experiments to measure load-driven deformation and strain in the bone-implant interface was carried out, and the experiments results were analyzed and discussed. It shows that the proposed method is feasible and effective for the no-contact strain measurements of biomaterials in a physiological condition. The proposed strain distribution sensing system will contribute to evaluating computational simulations and improving selection of implant designs and materials.