Metal debris release is commonly seen from explanted total ankle replacements

Are We Ready for Pseudotumors in Total Ankle Arthroplasty? A Case Report

Background: Pseudotumors are defined as exuberant non-neoplastic inflammatory masses. This condition can be associated with hip and knee arthroplasty but has not been reported in Total Ankle Arthroplasty (TAA). This paper reports a pseudotumor that formed following TAA, highlighting its clinical presentation, management, and histopathology. Methods: A 55-year-old male with end-stage post-traumatic ankle osteoarthritis underwent TAA using a mobile-bearing prosthesis. The procedure was reported to be successful, with no immediate complications. Results: Three years postoperatively, following a period of symptom resolution, the patient presented with progressively worsening ankle pain, swelling, and limited weight-bearing ability. Imaging revealed indirect signs of a periarticular mass and loosening components. Revision surgery involved prosthesis explantation and mass excision for histological and microbiological analysis, followed by concomitant tibio-talo-calcaneal fusion with a retrograde nail. The histopathology identified a pseudotumor characterized by chronic inflammation, fibrous tissue, and necrotic debris, with no evidence of infection. The postoperative recovery was uneventful, with pain resolution and successful fusion confirmed at a one-year follow-up. Conclusions: In patients experiencing unexplained pain or symptoms following TAA, the possibility of a pseudotumor, although rare, should be considered. Prompt and comprehensive clinical and radiographic evaluation is crucial to raise suspicion and prevent this condition from being overlooked.

Approach to patients with metal allergies in foot and ankle surgery

Metal allergies in surgery are often underreported and under diagnosed. Oftentimes, the symptoms of metal allergy closely resemble those of infection and the protocol is removal of the offending implant. Identification of metal allergies in the preoperative workup is imperative to provide the best patient care and outcomes. The purpose of this report is to present considerations to approach to both preoperative and postoperative identification of patients with metal allergies. Utilizing published algorithms for total knee arthroplasty (TKA) and the author's experience, considerations for both preoperative and postoperative metal allergy have been developed to help the foot and ankle surgeon with the complicated task of addressing patients with metal allergies. To date, the authors have utilized this guidelines for total ankle arthroplasty, ankle fracture open reduction internal fixation, and first metatarsophalangeal joint arthrodesis. While literature has been published with metal allergy algorithms for total knee arthroplasty, this is the first of its kind for adaptation to foot and ankle surgery in general to the author's knowledge. To date, the authors have favorable outcomes utilizing these approaches to not only guide patient care but to help prevent future complications or address them if they present. With a thorough patient history, identification of metal allergies, a multidisciplinary approach and pre-operative planning, good outcomes can be achieved.

Assessment of bone ingrowth around beaded coated tibial implant for total ankle replacement using mechanoregulatory algorithm

The long-term performance of porous coated tibial implants for total ankle replacement (TAR) primarily depends on the extent of bone ingrowth at the bone-implant interface. Although attempts were made for primary fixation for immediate post-operative stability, no investigation was conducted on secondary fixation. The aim of this study is to assess bone ingrowth around the porous beaded coated tibial implant for TAR using a mechanoregulatory algorithm. A realistic macroscale finite element (FE) model of the implanted tibia was developed based on computer tomography (CT) data to assess implant-bone micromotions and coupled with microscale FE models of the implant-bone interface to predict bone ingrowth around tibial implant for TAR. The macroscale FE model was subjected to three near physiological loading conditions to evaluate the site-specific implant-bone micromotion, which were then incorporated into the corresponding microscale model to mimic the near physiological loading conditions. Results of the study demonstrated that the implant experienced tangential micromotion ranged from 0 to 71 μm with a mean of 3.871 μm. Tissue differentiation results revealed that bone ingrowth across the implant ranged from 44 to 96 %, with a mean of around 70 %. The average Young's modulus of the inter-bead tissue layer varied from 1444 to 4180 MPa around the different regions of the implant. The analysis postulates that when peak micromotion touches 30 μm around different regions of the implant, it leads to pronounced fibrous tissues on the implant surface. The highest amount of bone ingrowth was observed in the central regions, and poor bone ingrowth was seen in the anterior parts of the implant, which indicate improper osseointegration around this region. This macro-micro mechanical FE framework can be extended to improve the implant design to enhance the bone ingrowth and in future to develop porous lattice-structured implants to predict and enhance osseointegration around the implant.

A macro-micro FE and ANN framework to assess site-specific bone ingrowth around the porous beaded-coated implant: an example with BOX® tibial implant for total ankle replacement

The use of mechanoregulatory schemes based on finite element (FE) analysis for the evaluation of bone ingrowth around porous surfaces is a viable approach but requires significant computational time and effort. The aim of this study is to develop a combined macro-micro FE and artificial neural network (ANN) framework for rapid and accurate prediction of the site-specific bone ingrowth around the porous beaded-coated tibial implant for total ankle replacement (TAR). A macroscale FE model of the implanted tibia was developed based on CT data. Subsequently, a microscale FE model of the implant-bone interface was created for performing bone ingrowth simulations using mechanoregulatory algorithms. An ANN was trained for rapid and accurate prediction of bone ingrowth. The results predicted by ANN are well comparable to FE-predicted results. Predicted site-specific bone ingrowth using ANN around the implant ranges from 43.04 to 98.24%, with a mean bone ingrowth of around 74.24%. Results suggested that the central region exhibited the highest bone ingrowth, which is also well corroborated with the recent explanted study on BOX®. The proposed methodology has the potential to simulate bone ingrowth rapidly and effectively at any given site over any implant surface.

A numerical investigation for the development of functionally graded Ti/HA tibial implant for total ankle replacement: Influence of material gradation law and volume fraction index

Stress shielding is one of the major concerns for total ankle replacement implants nowadays, because it is responsible for implant-induced bone resorption. The bone resorption contributes to the aseptic loosening and failure of ankle implants in later stages. To reduce the stress shielding, improvements can be made in the implant material by decreasing the elastic mismatch between the implant and the tibia bone. This study proposes a new functionally graded material (FGM) based tibial implant for minimizing the problem of stress shielding. Three-dimensional finite element (FE) models of the intact tibia and the implanted tibiae were created to study the influence of material gradation law and volume fraction index on stress shielding and implant-bone micromotion. Different implant materials were considered that is, cobalt-chromium, titanium (Ti), and FGM with Ti at the bottom and hydroxyapatite (HA) at the top. The FE models of FGM implants were generated by using different volume fractions and the rule of mixtures. The rule of mixtures was used to calculate the FGM properties based on the local volume fraction. The volume fraction was defined by using exponential, power, and sigmoid laws. For the power and sigmoid law varying volume fraction indices (0.1, 0.2, 0.5, 1, 2, and 5) were considered. The geometry resembling STAR® ankle system tibial implant was considered for the present study. The results indicate that FGMs lower stress shielding but also marginally increase implant-bone micromotion; however, the values were within the acceptable limit for bone ingrowth. It is observed that the material gradation law and volume fraction index influence the performance of FGM tibial implants. The tibial implant composed of FGM using power law with a volume fraction index of 0.1 was the preferred option because it showed the least stress shielding.