An Eleven-Year Follow-up of a Custom Talar Prosthesis After Open Talar Extrusion in an Adolescent Patient

Applications and Effectiveness of 3D Printing in Various Ankle Surgeries: A Narrative Review

BACKGROUND

Technological advancements have made three-dimensional printing prevalent in orthopedic surgery. It facilitates the production of customized implants and tailored patient instruments, enhancing surgical planning and results. This review focuses on the uses and effectiveness of patient-specific products manufactured using three-dimensional printing in ankle surgery.

METHODS

A search of databases-PubMed, Embase, Cochrane Library, and Google Scholar-yielded 41 articles for review.

RESULTS

Total talus replacement offers a viable alternative to standard treatments like arthrodesis and total ankle arthroplasty. Custom implants and patient-specific instrumentation in total ankle arthroplasty procedures guarantee a tailored fit and accurate alignment. For arthrodesis, three-dimensional printing enables the production of cages, effectively solving issues associated with conventional bone grafts, such as poor bone quality, significant defects, and nonunion. Additionally, patient-specific instrumentation facilitates the swift and accurate placement of Kirschner wires at the correct sites. When performing supramalleolar osteotomy, patient-specific instrumentation leads to shorter operation times, reduced blood loss, and less radiation exposure.

CONCLUSIONS

Three-dimensional printing is increasingly employed in ankle surgeries, and as technology advances, it is anticipated to become critical for addressing complex ankle issues.

Total Talus Allograft Transplantation With Subtalar Arthrodesis for Missing Talus: A Report of a Rare Case

Post-traumatic missing talus is a rare and severe injury that often results in poor functional outcomes, with no consensus on the optimal treatment approach as strategies vary based on injury severity. We present the case of a 44-year-old male who sustained a missing talus following a high-energy motorcycle accident. After initial wound management and application of an external fixator, the patient underwent size-matched, fresh-frozen talus allograft transplantation combined with subtalar fusion. Postoperative radiography and CT confirmed successful transplantation with solid subtalar fusion, although progressive osteonecrosis was noted in the medial shoulder region of the talus. At the two-year follow-up, the patient exhibited limited ankle and hindfoot motion but was able to bear weight and walk without assistance, reporting no pain in his feet and achieving a final American Orthopaedic Foot & Ankle Society hindfoot score of 72. This case underscores the potential of total talar allograft transplantation with subtalar arthrodesis in treating severe talar bone loss or missing talus, although long-term follow-up is necessary to assess the clinical implications of medial talar collapse and the possible need for revision surgery.

Ankle and Foot Arthroplasty and Prosthesis: A Review on the Current and Upcoming State of Designs and Manufacturing

The foot and ankle serve vital roles in weight bearing, balance, and flexibility but are susceptible to many diverse ailments, making treatment difficult. More commonly, Total Ankle Arthroplasty (TAA) and Total Talus Replacement (TTR) are used for patients with ankle degeneration and avascular necrosis of the talus, respectively. Ankle prosthesis and orthosis are also indicated for use with lower limb extremity amputations or locomotor disability, leading to the development of powered exoskeletons. However, patient outcomes remain suboptimal, commonly due to the misfitting of implants to the patient-specific anatomy. Additive manufacturing (AM) is being used to create customized, patient-specific implants and porous implant cages that provide structural support while allowing for increased bony ingrowth and to develop customized, lightweight exoskeletons with multifunctional actuators. AM implants and devices have shown success in preserving stability and mobility of the joint and achieving fast recovery, as well as significant improvements in gait rehabilitation, gait assistance, and strength for patients. This review of the literature highlights various devices and technologies currently used for foot and ankle prosthesis and orthosis with deep insight into improvements from historical technologies, manufacturing methods, and future developments in the biomedical space.

Total Talar Prosthesis, Learning from Experience, Two Reports of Total Talar Prosthesis after Talar Extrusion and Literature Review

Recently, total talar prosthesis has been proposed to substitute the talus during the management of complex talar lesions such as talar extrusion, comminuted talar fractures, or avascular necrosis. Herein, we report two cases of talar extrusion treated with total talar replacement after a high-intensity trauma. Both cases subsequently required revision surgery due to degenerative changes of the tibial plafond (arthrodesis in the first case, conversion to a total ankle prosthesis in the latter). We report and analyze the literature concerning total talar replacement to discuss strategies that could help improve prosthesis survival and reduce the incidence of osteoarthritis.

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.

Polycarbonate-urethane coating can significantly improve talus implant contact characteristics

Talus implants can be utilized in cases of talus avascular necrosis and has been regarded as a promising treatment method. However, existing implants are made of stiff materials that directly oppose natural cartilage. The risk of long-term cartilage wear and bone fracture from the interaction between the cartilage and stiff implant surfaces has been documented in post-hemiarthroplasty of the hip, knee and ankle joints. The aim is to explore the effects of adding a layer of compliant material (polycarbonate-urethane; PCU) over a stiff material (cobalt chromium) in talus implants. To do so, we obtained initial ankle geometry from four cadaveric subjects in neutral standing to create the finite element models. We simulated seven models for each subject: three different types of talus implants, each coated with and without PCU, and a biological model. In total, we constructed 28 finite element models. By comparing the contact characteristics of the implant models with their respective biological model counterparts, our results showed that PCU coated implants have comparable contact area and contact pressure to the biological models, whereas stiff material implants without the PCU coating all have relatively higher contact pressure and smaller contact areas. These results confirmed that adding a layer of compliant material coating reduces the contact pressure and increases the contact area which in turn reduces the risk of cartilage wear and bone fracture. The results also suggest that there can be clinical benefits of adding a layer of compliant material coating on existing stiff material implants, and can provide valuable information towards the design of more biofidelic implants in the future.

Total Talus Replacement: Case Series and Literature Review

Custom 3D printed total talus implants have been used successfully as a functional alternative to arthrodesis or amputation in cases of severe talar destruction or loss. However, the ideal material and construct still remains to be elucidated. Current models have been made from aluminum ceramic, cobalt chrome, stainless steel, titanium, or metal combinations. The implants may be constrained (subtalar arthrodesis) or unconstrained (press fit within mortise). They may also be combined with a tibial prosthesis or used in isolation. The majority of currently published case studies examine unconstrained and isolated implants. This case study presents satisfactory 1-y outcomes in 3 cobalt chrome constrained total talar implants used in combination with a tibial prosthesis, and a literature review of total talus replacements.

Total talar replacement with a novel 3D printed modular prosthesis for tumors

Purpose

Arthrodesis is one of the most widely accepted surgical recommended methods for tumors of the talus, but it may be associated with poor limb functions. The aim of this study was to present a novel reconstruction with ankle function preserved after en bloc talus tumor resection.

Patient and method

A 43-year-old female with mesenchymal sarcoma of the talus was admitted in West China Hospital. Total talar replacement with three-dimensional (3D) printed modular prosthesis was prepared for reconstruction. The 3D printed modular prosthesis was designed exactly as the mirror image of the contralateral talus with complete filling of the sinus tarsi and subtalar joint space. The upper modular component of prosthesis was made of ultra high molecular weight polyethylene, and the lower component, titanium alloy. Pre-drilled holes in three directions were prepared for screw fixation of the subtalar joint.

Results

The patient underwent en bloc talus resection through anterior approach, followed by reconstruction with the 3D printed prosthesis. The whole procedure took 2 hours, and intra-operative blood loss was 50 mL. At the last follow-up, our patient was disease free and she could walk almost normally without any aid or pain. The Musculoskeletal Tumor Society score was 26/30. The American Orthopedic Foot and Ankle Society score was 91/100. The range of motion for dorsiflexion and plantar flexion was 40°. And no abnormalities were observed in the roentgenograph.

Conclusion

Total talar replacement with a 3D printed modular prosthesis may be an effective procedure for patients with tumors of the talus as it could maintain ankle function.