Total Ankle Replacement Prosthesis Research Articles

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

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. 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. 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. 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.

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.

STRUCTURAL ANALYSIS OF A NEW TOTAL ANKLE REPLACEMENT PROSTHESIS WITH INTERNAL STRUCTURE

A new prosthesis design for total ankle arthroplasty, with an internal damping structure for the sacrifice component is proposed and analyzed considering experimental data for the material model. Engineering parameters for prosthesis designs are proposed and discussed and physiological load conditions for ankle joint are applied for numerical simulation. Performance of total displacement, strain, safety factors and equivalent stress of structured prosthesis are compared versus a common solid model and literature findings for market-available prosthesis. Results showed that the proposed design can be deformed up to 52.85% compared to the solid model and operated safely on simulated cases. Prosthesis deformation generates a damped load transmission rather than a rigid one, closer to the natural ankle joint behavior. Keywords: ankle joint prosthesis; finite element analysis; computer aided design; orthopedics

Total ankle replacement design and positioning affect implant-bone micromotion and bone strains

Implant loosening – commonly linked with elevated initial micromotion – is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning – previously linked with higher failure rates – remain unexplored. The aim of this study was to estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX®, Mobility® and Salto®) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone micromotion and bone strains, thereby increasing the risk for TAR failure.

Current and future designs for total ankle replacement

Total ankle replacement (TAR) longevity continues to be questioned and poorly understood, especially the effect, if any, specific design characteristics have on prosthesis survival. The commonly held belief that first generation TAR prostheses were far inferior to the second generation prostheses and that these are in turn inferior to available third and fourth generation TAR systems is not universally supported. What is clear is that as the frequency of primary TAR continues to build, revision will become more commonplace. Unfortunately, a large percentage of published literature regarding primary TAR is riddled with bias because of industry sponsorship and inventor-paid consultant involvement. Evaluation of National Joint Registry (NJR) data may provide a better understanding of reasonable outcome expectations for foot and ankle surgeons. When analyzing the data available within NJR specific to primary TAR, four usage trends exist: abandonment, minimal use, initial embracement with diminished use, and initial embracement with sustained growth. Despite 10 fixed-bearing systems and one mobile-bearing TAR system available in the United States, few have any dedicated revision components. This is a problem because currently there are no “standard principles” for revision TAR and the approaches are technically complex, fraught with complications, and no one approach represents the only answer. There is a real need for a NJR that reports on primary TAR in the United States and tracks long-term survivorship after revision TAR. Future efforts should be directed in these areas.

Impact of Ethnicity on Tibial Morphometrics Relevant to Total Ankle Replacement

Category: Ankle Introduction/Purpose: Total ankle replacement (TAR) success has improved since first-generation implants, but patient satisfaction continues to be less than knee and hip replacements. Little is known about variations in distal tibia anatomy between genders and across ethnicities; therefore it is unclear the extent to which current TAR prostheses accommodate variability in patient size and shape. This study quantified distal tibia morphometrics relevant to TAR design, and assessed differences between ethnicities and genders. The hypotheses were: (1) The anterior-posterior (AP) location of the dwell point of the tibia is centralized; (2) The sagittal radius of curvature of the tibial articulation increases with bone size; (3) Differences in dwell point location or sagittal radii between genders and ethnicities can be attributed to size differences between those populations. Methods: Tibial CT scans were obtained from cadavers or individuals of various ethnicities (Table 1). Landmarks were defined on digital models created from the scans, including medial and lateral edges of the distal tibial articulation (Figure 1a), and sagittal contours of the articulation (Figure 1b). The articulation center was defined as the average center point of all contours (Figure 1c). The AP center and AP length at the level of a distal tibial resection for TAR were determined, and the AP offset of the articulation center was calculated (Figure 1c). Differences in metrics for each ethnic and gender group were determined using a one-way Anova (P&lt; .05) with Tukey’s method for differentiating groups. Regression fits of AP offset, average medial radius, and average lateral radius were determined. Utilizing AP length as a covariate, ANCOVA was utilized to assess differences in AP offset and sagittal radii between gender and ethnic groups (P&lt; .05). Results: Descriptive statistics for AP length, AP offset, and medial/lateral radii are shown in Table 1, with Tukey groupings assigned. The relationship between medial and lateral radius was not consistent across all groups. AP length was a significant covariate for medial and lateral radii, but not AP offset. The relationship between lateral radius and AP length was significantly impacted by ethnicity (P&lt; .001), but not by gender (P=.067) (Figure 2a). Medial radius versus AP length was significantly impacted by both ethnicity (P=.01) and gender (P&lt; .03) (Figure 2b). Conclusion: This study illustrates for the first time the complexity of anatomical variation of the distal tibia across ethnic groups and between genders. The location of the articulation center is invariant to tibia size across each ethnicity. Medial and lateral sagittal radii generally increase with bone size, but the relative radii of the medial and lateral compartments are not consistent across ethnicities. These results highlight the need for increased anatomic understanding of the distal tibia, and implications on TAR design and technique.

Intraoperative Radiation Exposure During Revision Total Ankle Replacement

Intraoperative C-arm image intensification is required for primary total ankle replacement implantation. Significant radiation exposure has been linked to these procedures; however, the radiation exposure during revision total ankle replacement remains unknown. Therefore, we sought to evaluate the radiation exposure encountered during revision total ankle replacement. The data from 41 patients were retrospectively analyzed from a prospective database: 19 Agility™ to Agility™; 4 Agility™ to Custom Agility™; 9 Agility™ to INBONE® II; 5 Agility™ to Salto Talaris® XT; 2 Scandinavian Total Ankle Replacement Prosthesis to Salto Talaris® XT; and 2 INBONE® I to INBONE® II revision total ankle replacements were performed. Two broad categories were identified: partial revision (Agility™ to Agility™, Agility™ to Custom Agility™, INBONE® I to INBONE® II) and complete conversion (Agility™ to INBONE® II, Agility™ to Salto Talaris® XT, Scandinavian Total Ankle Replacement Prosthesis to Salto Talaris® XT). The mean radiation exposure per case was significant at 3.49 ± 2.21 mGy. Complete conversions, specifically Agility™ to INBONE® II, exhibited the greatest radiation exposure and C-arm time. Revision implant selection and revision type (complete or partial) directly contributed to radiation exposure. Accordingly, revision systems requiring less radiation exposure are preferable. Surgeons should strive to minimize intraoperative complications and limit additional procedures to those necessary, because both lead to additional radiation exposure.

Incidence of Revision After Primary Implantation of the Salto® Mobile Version and Salto Talaris™ Total Ankle Prostheses: A Systematic Review

The incidence of revision of total ankle replacement prostheses remains unclear. We undertook a systematic review to identify the material relating to the incidence of revision after implantation of the Salto® mobile version and Salto Talaris™ total ankle prostheses. Studies were eligible for inclusion only if they had involved primary total ankle replacement with these prostheses and had included the incidence of revision. Eight studies involving 1,209 Salto® mobile version prostheses, with a weighted mean follow-up period of 55.2 months, and 5 studies involving 212 Salto Talaris™ total ankle prostheses, with a weighted mean follow-up period of 34.9 months, were included. Forty-eight patients with Salto® mobile version prostheses (4%) underwent revision, of whom 24 (70.5%) underwent ankle arthrodesis, 9 (26.5%) metallic component replacement, and 1 (3%) below-the-knee amputation. Five (2.4%) Salto Talaris™ total ankle prostheses underwent revision (3 metallic component replacement and 2 ankle arthrodeses). Restricting the data to the inventor, design team, or disclosed consultants, the incidence of revision was 5.2% for the Salto® mobile version and 2.6% for the Salto Talaris™ total ankle prostheses. In contrast, data that excluded these individuals had an incidence of revision of 2.8% for the Salto® mobile version and 2.0% for the Salto Talaris™ total ankle prostheses. We could not identify any obvious difference in the etiology responsible for the incidence of revision between these mobile- and fixed-bearing prostheses. The incidence of revision for the Salto® mobile version and Salto Talaris™ total ankle prostheses was lower than those reported through systematic review for the Agility™ and Scandinavian Total Ankle Replacement™ systems without obvious selection (inventor) or publication (conflict of interest) bias.

Intermediate to Long-Term Outcomes of the STAR Total Ankle Replacement: The Patient Perspective

The purpose of the present study was to document the patient self-reported improvements in quality of life, function, and overall impairment scores, as well as the improvement in the clinically derived outcome scores, following a Scandinavian Total Ankle Replacement (STAR) arthroplasty performed for the treatment of end-stage ankle arthritis. All patients who underwent a Scandinavian Total Ankle Replacement arthroplasty from July 1998 through February 2008 were prospectively followed and retrospectively reviewed. All surgical procedures were performed by a single surgeon. Preoperatively and at subsequent follow-up visits, patients were assessed with (1) a visual analog scale (VAS) score for pain, (2) the Short Form-36 (SF-36) quality-of-life scale, (3) the American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot scale and subscales, (4) the Buechel-Pappas pain and function scores, and (5) the ankle range of motion. Additional measures that were recorded included (1) concomitant surgical procedures during the initial ankle replacement, (2) revision surgery during the follow-up period, and (3) any additional surgical procedures. Revision was defined as failure of either the tibial or the talar metallic component that required removal of a metallic implant for any reason. Eighty-two consecutive patients were evaluated. The duration of follow-up ranged from twenty-four to 108 months (mean, sixty-one months; median, sixty months). During the follow-up period, three patients died and six patients moved out of the region. The latter six patients were followed by another surgeon group, and their data were included. Eight patients were lost to follow-up after twelve months. There were significant improvements in all outcome categories between the preoperative and postoperative evaluations. The most compelling finding of the present study involved the marked improvement in terms of the self-reported measures of impairments, quality of life, pain, and function. Total ankle arthroplasty with the Scandinavian Total Ankle Replacement prosthesis was associated with significant improvements in terms of pain, function, and quality of life after intermediate to long-term follow-up.

Ankle arthroplasty

Intraoperative C-arm image intensification is required for primary total ankle replacement implantation. Significant radiation exposure has been linked to these procedures; however, the radiation exposure during revision total ankle replacement remains unknown. Therefore, we sought to evaluate the radiation exposure encountered during revision total ankle replacement. The data from 41 patients were retrospectively analyzed from a prospective database: 19 Agility™ to Agility™; 4 Agility™ to Custom Agility™; 9 Agility™ to INBONE® II; 5 Agility™ to Salto Talaris® XT; 2 Scandinavian Total Ankle Replacement Prosthesis to Salto Talaris® XT; and 2 INBONE® I to INBONE® II revision total ankle replacements were performed. Two broad categories were identified: partial revision (Agility™ to Agility™, Agility™ to Custom Agility™, INBONE® I to INBONE® II) and complete conversion (Agility™ to INBONE® II, Agility™ to Salto Talaris® XT, Scandinavian Total Ankle Replacement Prosthesis to Salto Talaris® XT). The mean radiation exposure per case was significant at 3.49 ± 2.21 mGy. Complete conversions, specifically Agility™ to INBONE® II, exhibited the greatest radiation exposure and C-arm time. Revision implant selection and revision type (complete or partial) directly contributed to radiation exposure. Accordingly, revision systems requiring less radiation exposure are preferable. Surgeons should strive to minimize intraoperative complications and limit additional procedures to those necessary, because both lead to additional radiation exposure.

Misalignment of Total Ankle Components Can Induce High Joint Contact Pressures

A major cause of the limited longevity of total ankle replacements is premature polyethylene component wear, which can be induced by high joint contact pressures. We implemented a computational model to parametrically explore the hypothesis that intercomponent positioning deviating from the manufacturer's recommendations can result in pressure distributions that may predispose to wear of the polyethylene insert. We also investigated the hypothesis that a modern mobile-bearing design may be able to better compensate for imposed misalignments compared with an early two-component design. Two finite element models of total ankle replacement prostheses were built to quantify peak and average contact pressures on the polyethylene insert surfaces. Models were validated by biomechanical testing of the two implant designs with use of pressure-sensitive film. The validated models were configured to replicate three potential misalignments with the most version of the tibial component, version of the talar component, and relative component rotation of the two-component design. The misalignments were simulated with use of the computer model with physiologically relevant boundary loads. With use of the manufacturer's guidelines for positioning of the two-component design, the predicted average joint contact pressures exceeded the yield stress of polyethylene (18 to 20 MPa). Pressure magnitudes increased as implant alignment was systematically deviated from this reference position. The three-component design showed lower-magnitude contact pressures in the standard position (<10 MPa) and was generally less sensitive to misalignment. Both implant systems were sensitive to version misalignment. In the tested implants, a highly congruent mobile-bearing total ankle replacement design yields more evenly distributed and lower-magnitude joint contact pressures than a less congruent design. Although the mobile-bearing implant reduced susceptibility to aberrant joint contact characteristics that were induced by misalignment, predicted average contact stresses reached the yield stress of polyethylene for imposed version misalignments of >5 degrees.

The effect of specimen size and geometry on the mechanical behaviour of trabecular bone specimens

Implant loosening – commonly linked with elevated initial micromotion – is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning – previously linked with higher failure rates – remain unexplored. The aim of this study was to estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX®, Mobility® and Salto®) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone micromotion and bone strains, thereby increasing the risk for TAR failure.