Longitudinal migration and inducible displacement of the Mobility Total Ankle System

Guideline for RSA and CT-RSA implant migration measurements: an update of standardizations and recommendations

Opening remarks: These guidelines are the result of discussions within a diverse group of RSA researchers. They were approved in December 2023 by the board and selected members of the International Radiostereometry Society to update the guidelines by Valstar et al. [1]. By adhering to these guidelines, RSA studies will become more transparent and consistent in execution, presentation, reporting, and interpretation. Both authors and reviewers of scientific papers using RSA may use these guidelines, summarized in the Checklist, as a reference. Deviations from these guidelines should have the underlying rationale stated.

In Vivo Total Ankle Arthroplasty Kinematic Evaluation: A Prospective Radiostereometric Analysis

Ankle osteoarthritis (OA) represents a significant social burden and is one of the main causes of chronic disability in a rapidly growing part of the world's population. Total ankle arthroplasty (TAA) has become increasingly popular despite the poor results obtained with the first dedicated designs. The purpose of this paper was to evaluate the ankle kinematics, in vivo and under weight-bearing conditions, of a TAA through a dynamic model-based radiostereometric analysis (MB-RSA). The clinical evaluation was performed by administering the American Orthopaedic Foot and Ankle Society ankle-hindfoot score and Short Form-36 questionnaires. The kinematic evaluation was conducted through MB-RSA during the execution of an open kinetic chain and a closed kinetic chain motor task. Double radiographic images of the ankle joint were processed using dedicated software to obtain a 3D reconstruction of the ankle prosthetic components' motion. Eighteen patients (five females) completed the clinical and instrumental preoperative and postoperative evaluations (age 59.1 ± 10.3). All clinical scores showed a marked improvement (p < 0.005). During the closed kinetic chain motor tasks, the ankle showed a total range of motion (ROM) in dorsi-plantarflexion of 19.84°. The parameters in varus-valgus were recorded. Physiological motion can be achieved in TAA, characterized by a wide range of motion and coupling of movements on the three planes. The results of the present work may help to understand the real movement of a widespread TAA model and possibly to improve future designs and instrumentation.

Lack of Consensus on the Definition of Aseptic Loosening in Total Ankle Replacement: A Narrative Systematic Review

Background: Aseptic loosening is one of the most common modes of failure of total ankle replacement (TAR). However, a precise definition of aseptic loosening is still lacking. This systematic review aimed to identify the variations of applied definitions and offer insights into the lack of consensus. Methods: Human studies reporting aseptic loosening of TAR published in peer-reviewed journals within the last decade were considered. The search strategy involved specific terms in Embase, MEDLINE ALL, and the Cochrane Library. Variations in aseptic loosening definitions were analysed. Results: Of 767 studies, 88 were included in this study. Only nine studies precisely defined aseptic loosening with significant variations. Twenty-two studies referenced the term and fifty-seven reported it as a complication but neither defined nor referenced it. Conclusions: Significant uncertainty exists regarding the universal definition of aseptic loosening of TAR, and many variations occur in terms of the assessment approach and criteria.

Obesity and Ankle Prosthesis Revision: A Systematic Review and Meta-analysis

BACKGROUND

The increasing number of total ankle arthroplasties (TAAs) has led to growing evidence on the risk factors for complications after surgery. However, the role of obesity in this patient group has been the subject of much debate. Therefore, this systematic review aimed to investigate the evidence for untoward effects of obesity following TAA.

METHODS

We conducted a comprehensive search on April 28, 2023, in MEDLINE (via PubMed), Embase, and CENTRAL. Eligible observational studies reported on the short- and long-term outcomes of primary TAA, comparing patients with and without obesity (defined as body mass index > 30). Using a random effects model, we calculated pooled odds ratios (ORs) with 95% confidence intervals (CIs) from 2 by 2 tables (event and nonevent in the obese and nonobese primary TAA groups).

RESULTS

Nine studies with 10 388 patients were eligible for inclusion in the meta-analysis. We found significantly higher odds of revision in the obese group compared to the nonobese group (OR = 1.68, CI: 1.44-1.95). However, the odds of overall perioperative complications (OR = 1.55, CI: 0.50-4.80) and wound complications (OR = 1.34, CI: 0.29-6.20) were nonsignificantly higher in the obese group.

CONCLUSION

Based on our results, obesity may have affected long-term outcomes following TAA and may have negatively affected the prosthesis's survival.

Updates of Total Ankle Replacement Revision Options: New Generation Total Ankle Replacement Revision Options, Stemmed Implants, Peri-Articular Osteotomies

Ankle arthritis is a disabling disease pattern resulting in pain and dysfunction ultimately leading to a reduction in quality of life. Unlike more common arthritides of the knee and hip, ankle arthritis is unique in its presentation with an earlier onset of end-stage disease and an etiology, which is most-commonly posttraumatic in nature. Through continued research and design, improvements have continued to be made as newer generation implants are developed. This article discusses the considerations for revision total ankle replacement based on the current revision options and a treatment algorithm developed by the lead author.

The ceramic coated implant (CCI). Evolution total ankle replacements: a retrospective analysis of 40 ankles with 8 years follow-up

Diminutive data is available on the outcome of several previously used total ankle replacement implants. The purpose of this study was to investigate the medium-term functional and radiological outcome and implant survival of the CCI Evolution implant. Consecutive series of 40 ankles operated in our hospital with primary TAR using the CCI Evolution implant in 2010-2013 were available for follow-up. The prospective clinical and radiographic data including the Kofoed score, subjective satisfaction and standard radiographs were collected preoperatively and at fixed time-points postoperatively. A CT was obtained in cases where osteolysis or loosening were suspected. The improvement of the Kofoed score and subjective satisfaction were statistically significant (p<0.0001). The implant survival was 97% (95% confidence interval (CI) 81%-100 %) at 5 years, and 81 % (95% confidence interval (CI) 60 %-92%) at 8 years. There were altogether 25 (64%) complications. Overall revision rate was 28% and failure rate 13%. The CCI implant outcome was not acceptable. The malposition of prosthetic components, subsidence, and peri-implant osteolysis were recorded often. Although the patient reported outcome measures improved, mostly due to positive changes in pain severity, overall revision and failure rates were high and comparable with previous findings of the CCI implant.

The role of the depth of resection of the distal tibia on biomechanical performance of the tibial component for TAR: A finite element analysis with three implant designs

The depth of resection of the tibia bone in total ankle replacement (TAR) may influence implant-bone micromotion and stress shielding. High implant-bone micromotion and stress-shielding lead to aseptic loosening of the tibial component for TAR. The aim was to improve the outcomes of the different designs of TAR (STAR, Mobility, and Salto) with the variation of the depth of resection of the distal tibia bone. Finite element (FE) models of the implanted tibia with the depth of resection varying from 6 mm to 16 mm and of the intact tibia was prepared. The value of micromotion increased as the depth of resection increased. The micromotion increased in the proximal anterior-posterior portion of the pegs for STAR, the posterior part of the stem for Mobility, and the proximal lateral portion of the keel for Salto with the increase in the depth of resection. Whereas, the stresses (von Mises) decreased in some regions and increased in some regions depending upon the implant design. But overall stresses decreased in the tibia bone. Furthermore, the mean stress shielding increased in all the designs as the depth of resection increased. This in silico study indicated that the depth of resection should be given more importance during TAR surgery. The ideal depth of resection should be minimum i.e., 6 mm based on this FE study.

Body Mass Index (BMI) Cutoffs and Racial, Ethnic, Sex, or Age Disparities in Patients Treated With Total Ankle Arthroplasty

Background

The rising prevalence of obesity among American adults has disproportionately affected Black adults and women. Furthermore, body mass index (BMI) has historically been used as a relative contraindication to many total joint arthroplasty (TJA) procedures, including total ankle arthroplasty. The purpose of this study was to investigate potential disparities in patient eligibility for total ankle arthroplasty based on race, ethnicity, sex, and age by applying commonly used BMI cutoffs to the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database.

Methods

Patients in the ACS-NSQIP database who underwent TAA from 2011 to 2020 were retrospectively reviewed in a cross-sectional analysis. BMI cutoffs of <50, <45, <40, and <35 were then applied. The eligibility rate for TAA was examined for each BMI cutoff, and findings were stratified by race, ethnicity, sex, and age. Independent t tests, chi-squared tests, and Fisher exact tests were performed to compare differences at an α = 0.05.

Results

A total of 1215 of 1865 TAA patients (65.1%) were included after applying the exclusion criteria. Black patients had disproportionately lower rates of eligibility at the most stringent BMI cutoff of <35 (P = .004). Hispanic patients had generally lower rates of eligibility across all BMI cutoffs. In contrast, Asian American and Pacific Islander patients had higher rates of eligibility at the BMI cutoffs of <35 (P = .033) and <40 (P = .039), and White non-Hispanic patients had higher rates of eligibility across all BMI cutoffs. Females had lower eligibility rates across all BMI cutoffs. Ineligible patients were also younger compared to eligible patients across all BMI cutoffs.

Conclusion

Stringent BMI cutoffs may disproportionately disqualify Black, female, and younger patients from receiving total ankle arthroplasty.

Level of Evidence

Level III, retrospective cross-sectional study.

Total Ankle Arthroplasty: Does Obesity Matter?

BACKGROUND

There is limited data evaluating the effect of obesity on outcomes following total ankle arthroplasty (TAA), especially in adequate sample sizes to detect impacts on patient-reported outcomes (PROs). The purpose of this study was to assess the effect of obesity on complication rates and PROs.

METHODS

This was a single-institution, retrospective study of 1093 primary TAA performed between 2001 and 2020. Minimum follow-up was 2 years. Patients were stratified by body mass index (BMI) into control (BMI = 18.5-29.9; n = 615), obesity class I (BMI = 30.0-34.9; n = 285), and obesity class II (BMI > 35.0; n = 193) groups. Patient information, intraoperative variables, postoperative complications, and PRO measures were compared between groups using univariable statistics. Multivariable Cox regression was performed to assess risk for implant failure. Mean follow-up was 5.6 years (SD: 3.1).

RESULTS

Compared to control and class I, class II patients had the lowest mean age (P = .001), highest mean ASA score (P < .001), and greatest proportion of female sex (P < .001) and Black/African American race (P = .005). There were no statistically significant differences in postoperative complications (infection, implant failure, or impingement) across the BMI classes (P > .05).Preoperatively, class II had lower (worse) mean scores for Foot and Ankle Outcome Score pain and ADL subscales than controls (post hoc pairwise P < .001 for both). At final follow-up, both class II and class I had lower (worse) mean Short Musculoskeletal Function Assessment (post hoc pairwise P < .001 and P = .030, respectively) and 36-Item Short Form Health Survey scores (post hoc pairwise P < .001 and P = .005, respectively) than controls.

CONCLUSION

At midterm follow-up, obesity was not associated with increased rates of complications after TAA. Patients with obesity reported worse musculoskeletal function and overall quality of life after TAA but there was no differential improvement in PROs across BMI classes. To our knowledge, this is the largest single-institution study to date examining the effect of obesity on outcomes after primary TAA.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Republication of "Perspectives in Treatments of End-Stage Ankle Arthritis Among Orthopaedic Surgeons: Analysis of an American Orthopaedic Foot & Ankle Society (AOFAS) Member Survey"

Background

This study aimed to assess the preferred operative treatment for patients over the age of 60 with end-stage ankle arthritis and perspectives on total ankle replacement (TAR) among American Orthopaedic Foot & Ankle Society (AOFAS) members. Associated factors were analyzed for potential contraindications among members with different levels of experience.

Method

A questionnaire containing 6 questions was designed and sent to 2056 members of the AOFAS. Responses were received from 467 orthopaedic surgeons practicing in the United States (76%), Canada (5%), and 26 other countries (20%). Participants were grouped for response comparisons according to country as well as experience level. Differences in contraindications were compared using χ2 tests or exact tests.

Results

Respondents practicing in the United States and surgeons who perform 11 or more TARs per year tended to recommend operative treatments favoring TAR and displayed recognition of its increasing role (P < .05). Overall, respondents felt that 41% of typical patients over 60 years old with end-stage arthritis would be best treated with TAR. Talus avascular necrosis, morbid obesity (body mass index >40 kg/m2), and poorly controlled diabetes with neuropathy were most recognized as the absolute contraindications to TAR. Surgeon's experience affected the consideration of these clinical factors as contraindications.

Conclusions

Total ankle replacement has a substantial and increasing role in the treatment of end-stage ankle arthritis in patients over the age of 60. Absolute and potential contraindications of the procedures were indicated from a cross-sectional survey of AOFAS members. Surgeons more experienced with total ankle replacement felt more comfortable employing it in a wider range of clinical settings.

Level of Evidence

Level III, therapeutic.

Development and validation of a clinical tool to semi-automatic measure three-dimensional TAR alignment on two-dimensional radiographs

BACKGROUND

Malalignment is often postulated as an important reason for the high failure rate of total ankle replacements (TARs). The correlation between TAR malalignment and clinical outcome, however, is not fully understood. Improving and expanding radiographic TAR alignment measurements in the clinic might lead to a better insight into the correlation between malalignment and the clinical outcome. This study aims to develop and validate a tool to semi-automatic measure TAR alignment, and to improve alignment measurements on radiographs in the clinic.

METHODS

A tool to semi-automatically measure TAR alignment on anteroposterior and lateral radiographs was developed in MATLAB. Using the principle of edge contouring and the perpendicular relationship between the anteroposterior and lateral radiographs, the exact configuration of the TAR components can be found. Two observers validated the tool by measuring TAR alignment of ten patients using the tool. The Intraclass Coefficient (ICC) was calculated to assess the reliability of the developed method. The results obtained by the tool were compared to clinical results during radiographic follow-up in the past, and the accuracy of both methods was calculated using three-dimensional CT data.

RESULTS

The tool showed an accuracy of 76% compared to 71% for the method used during follow-up. ICC values were 0.94 (p < 0.01) and higher for both inter-and intra-observer reliability.

CONCLUSIONS

The tool presents a reproducible method to measure TAR alignment parameters. Three-dimensional alignment parameters are obtained from two-dimensional radiographs, and as the tool can be applied to most TAR designs, it offers a valuable addition in the clinic and for research purposes.

A combined FE-hybrid MCDM framework for improving the performance of the conical stem tibial design for TAR with the addition of pegs

BACKGROUND AND OBJECTIVES

The conical stemmed design of the tibial component for total ankle replacement (TAR) (example Mobility design) uses a single intramedullary stem for primary fixation. Tibial component loosening is a common mode of failure for TAR. Primary causes of loosening are lack of bone ingrowth due to excessive micromotion at the implant-bone interface and bone resorption due to stress shielding after implantation. The fixation feature of the conical stemmed design can be modified with the addition of small pegs to avoid loosening. The aim of the study is to select the improved design for conical stemmed TAR using a combined Finite Element (FE) hybrid Multi-Criteria Decision-Making (MCDM) framework.

METHODS

The geometry and material properties of the bone for FE modeling were extracted from the CT data. Thirty-two design alternatives with varying pegs in number (one, two, four, eight), location (anterior, posterior, medial, lateral, anterior-posterior, medial-lateral, equally spaced), and height (5 mm, 4 mm, 3 mm, 2 mm) were prepared. All models were analyzed for dorsiflexion, neutral, and plantarflexion loading. The proximal part of the tibia was fixed. The implant-bone interface coefficient of friction was taken as 0.5. The implant-bone micromotion, stress shielding, volume of bone resection, and surgical simplicity were the important criteria considered for evaluating the performance of TAR. The designs were compared using a hybrid MCDM method of WASPAS, TOPSIS, EDAS, and VIKOR. The weight calculations were based on fuzzy AHP and the final ranks on the Degree of Membership method.

RESULTS

The addition of pegs decreased the mean implant-bone micromotions and increased stress shielding. There was a marginal decrease in micromotion and a marginal increase in stress shielding when the peg heights were increased. The results of hybrid MCDM indicated that the most preferable alternative designs were two pegs of 4 mm height in the AP direction to the main stem, two pegs of 4 mm height in the ML direction, and one peg of 3 mm height in the A direction.

CONCLUSIONS

Outcomes of this study suggest that the addition of pegs can reduce the implant-bone micromotions. Modified three designs would be useful by considering implant-bone micromotions, stress shielding, volume of bone resection, and surgical simplicity.

Hybrid-Total Ankle Arthroplasty (H-TAA) for Failed Talar Component in Mobile-Bearing Total Ankle Arthroplasty

INTRODUCTION

Revision Total Ankle Arthroplasty (TAA) surgery due to TAA aseptic loosening is increasing. It is possible to exchange the talar component and inlay to another system for isolated talar component loosening in a primary mobile-bearing TAA: Hybrid-Total Ankle Arthroplasty (H-TAA). The purpose of this study was to analyze the results of the revision surgery of an isolated aseptic talar component loosening in a mobile-bearing three-component TAA with a H-TAA solution.

METHODS

In this prospective case study, nine patients (six women, three men; mean age 59.8 years; range 41-80 years) with symptomatic isolated aseptic loosening of the talar component of a mobile-bearing TAA were treated with an isolated talar component and inlay substitution. In all nine cases, a hybrid TAA revision surgery was performed by implanting a VANTAGE TAA talar and insert component (Flatcut talar component: six cases, standard talar component: three cases). The patients were reviewed with the pain score (VAS Pain Score 0-10), Dorsiflexion/Plantarflexion (DF/PF) Range of Motion (ROM; degrees), the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle/Hindfoot Score (0-100 points), Sports Frequency Score (Level 0-4), and subjective Patients' Satisfaction Score (0-10 points).

RESULTS

The average Pain score improved significantly from preoperative 6.7 points to postoperative 1.1 points (p < 0.001). Average Dorsiflexion/Plantarflexion ROM values increased significantly post-surgery: 21.7° preoperative to 45.6° postoperative (p < 0.001). The postoperative AOFAS scores were significantly greater than the preoperative values: 47.7 points preoperative, 92.3 points postoperative (p < 0.001). The sports activity improved from preoperative to postoperative where, preoperative, none of the patients were able to perform sports. Postoperative, eight patients were able to be sports-active again. The overall average postoperative level of sports activity was 1.4. The postoperative average patient's satisfaction was 9.3 points.

CONCLUSIONS

In painful talar component aseptic loosening of a three-component mobile-bearing TAA, H-TAA is a good surgical solution for reducing pain, restoring ankle function, and improving patients' life quality.

Low Rate of Peri-implant Osteolysis in Trabecular Metal Total Ankle Replacement on Short- to Midterm Follow-up

BACKGROUND

Peri-implant osteolysis is one of the major complications related to total ankle replacement. The aim of this study was to investigate the short- to midterm incidence of peri-implant osteolysis using computed tomography (CT) as imaging method for the Trabecular Metal Total Ankle (TMTA) implant representing a novel total ankle replacement (TAR) implant design regarding material and surgical technique.

METHODS

In total, 104 consecutive patients who had a primary TMTA replacement between March 2013 and October 2017 were included in the study. The radiographic evaluation included weightbearing anteroposterior and lateral views at baseline and after 3, 6, and every 12 months postoperatively. A helical CT was undertaken preoperatively and of the 80 patients available to follow up at least 12 months postoperatively, with average time interval between the TAR operation and the latest CT of 39 (range, 12-85) months.

RESULTS

Eight of 80 patients had altogether 11 osteolytic lesions around the components on CT images. Seven lesions were found in tibia, 3 in talus, and 1 in distal fibula. Four of the tibial lesions were situated in the medial malleolus and were not in contact with the prosthesis component. The sizes of the osteolytic lesions ranged between 7 and 20 mm, and the average volume of the lesions was 689 mm³.

CONCLUSION

We conclude that the risk of peri-implant osteolysis with the TMTA implant is minimal in short to midterm. The anatomic configuration, unique material, and surgical technique may all contribute to the TMTA implant having a low rate of peri-implant osteolysis.

LEVEL OF EVIDENCE

Level IV, case series.

Comparison of Preoperative Bone Density in Patients With and Without Periprosthetic Osteolysis Following Total Ankle Arthroplasty

BACKGROUND

Modern total ankle arthroplasty (TAA) prostheses are uncemented press-fit designs whose stability is dependent on bone ingrowth. Preoperative insufficient bone density reduces initial local stability at the bone-implant interface, and we hypothesized that this may play a role in periprosthetic osteolysis. We aimed to investigate the preoperative bone density of the distal tibia and talus and compare these in patients with and without osteolysis.

METHODS

We enrolled 209 patients (218 ankles) who underwent primary TAA using the HINTEGRA prosthesis. The overall mean follow-up duration was 66 (range, 24-161) months. The patients were allocated into 2 groups according to the presence of periprosthetic osteolysis: the osteolysis group (64 patients, 65 ankles) and nonosteolysis group (145 patients, 153 ankles). Between the 2 groups, we investigated and compared the radiographic outcomes, including the Hounsfield unit (HU) value around the ankle joint and the coronal plane alignment.

RESULTS

HU values of the tibia and talus measured at 5 mm from the reference points were higher than those at 10 mm in each group. However, comparing the osteolysis and nonosteolysis groups, we found no significant intergroup difference in HU value at every measured level in the tibia and talus (P > .05). Concerning the coronal plane alignment, there were no significant between-group differences in the tibiotalar and talar tilt angles (P > .05).

CONCLUSION

Patients with osteolysis showed similar preoperative bone density of the distal tibia and talus compared with patients without osteolysis. Our results suggest that low bone density around the ankle joint may not be associated with increased development of osteolysis.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Obesity in Elective Foot and Ankle Surgery

Obesity is a global health problem with significant economic and health consequences. There is very little literature in regards to obesity and its effect on foot and ankle surgery, and to the author's knowledge, there has been no consolidated review on this subject to date. The purpose of this article is to provide a comprehensive review as it pertains to foot and ankle surgery, with hopes of improving surgeon decision making, mitigating risk, and providing better outcomes for patients. A better understanding of the effects of obesity also allows for improved prognostic performance.

Perspectives in Treatments of End-Stage Ankle Arthritis Among Orthopaedic Surgeons

Background:

This study aimed to assess the preferred operative treatment for patients over the age of 60 with end-stage ankle arthritis and perspectives on total ankle replacement (TAR) among American Orthopaedic Foot & Ankle Society (AOFAS) members. Associated factors were analyzed for potential contraindications among members with different levels of experience.

Method:

A questionnaire containing 6 questions was designed and sent to 2056 members of the AOFAS. Responses were received from 467 orthopaedic surgeons practicing in the United States (76%), Canada (5%), and 26 other countries (20%). Participants were grouped for response comparisons according to country as well as experience level. Differences in contraindications were compared using χ2 tests or exact tests.

Results:

Respondents practicing in the United States and surgeons who perform 11 or more TARs per year tended to recommend operative treatments favoring TAR and displayed recognition of its increasing role ( P < .05). Overall, respondents felt that 41% of typical patients over 60 years old with end-stage arthritis would be best treated with TAR. Talus avascular necrosis, morbid obesity (body mass index >40 kg/m2), and poorly controlled diabetes with neuropathy were most recognized as the absolute contraindications to TAR. Surgeon’s experience affected the consideration of these clinical factors as contraindications.

Conclusions:

Total ankle replacement has a substantial and increasing role in the treatment of end-stage ankle arthritis in patients over the age of 60. Absolute and potential contraindications of the procedures were indicated from a cross-sectional survey of AOFAS members. Surgeons more experienced with total ankle replacement felt more comfortable employing it in a wider range of clinical settings.

Level of Evidence:

Level III, therapeutic.

Management of Talar Component Subsidence

Component subsidence has been found to be the top complication that leads to failure of the total ankle arthroplasty (TAA). The cause of subsidence formation is unclear, and is multifactorial. Talar subsidence is more frequently met than tibial subsidence, and the subsequent big bone loss is demanding to handle. As a revision treatment option, neither a revision TAA nor a salvage ankle and/or hindfoot arthrodesis procedure is easy to perform or can obtain a definite outcome. The Salto XT can be used to treat most of the TAA systems available for use in the United States with acceptable short-term outcomes.

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

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A finite element model was developed to calculate micromotion of ankle implants.

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Both optimally-positioned and malpositioned cases were considered.

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Fixation nearer to the joint line relying on plural pegs improved implant stability.

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Gaps between the implant and bone greatly increased 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.

A Prospective Study of Four Total Ankle Arthroplasty Implants by Non-Designer Investigators

BACKGROUND

There are several types of prostheses available to surgeons when performing a total ankle arthroplasty (TAA). The main objective of this study was to summarize the clinical and functional outcomes of 4 TAA prostheses: the Hintegra implant (Integra LifeSciences), the Agility implant (DePuy), the Mobility implant (DePuy), and the Scandinavian Total Ankle Replacement (STAR) implant (Small Bone Innovations [SBi]).

METHODS

Patients were prospectively recruited. A total of 451 TAAs with a mean follow-up (and standard deviation) of 4.5 ± 2.0 years were included. Patients were assessed annually and completed self-reported outcome measures at these visits. Complications and revisions were reported at the time of incident. Mean improvements are reported by prosthesis. Linear mixed-effects models were used to obtain adjusted comparisons of scores across prostheses. Survivorship curves were generated by prosthesis and type of complication.

RESULTS

Mean improvement in the Ankle Osteoarthritis Scale (AOS) total score was less among patients with the Mobility implant (19.5; 95% confidence interval [CI], 15 to 24) than it was among patients with the Agility implant (29.1; 95% CI, 24 to 34), Hintegra implant (29.7; 95% CI, 27 to 33), and STAR implant (28.5; 95% CI, 23 to 34). Patients in the Mobility group also had less mean improvement in the AOS pain score (21.3; 95% CI, 17 to 26) compared with patients in the Hintegra (29.0; 95% CI, 26 to 32), Agility (29.8; 95% CI, 25 to 35), and STAR (29.1; 95% CI, 23 to 35) groups. The Mobility group also had less mean improvement in the AOS disability score (17.3; 95% CI, 12 to 23) compared with the Hintegra (30.4; 95% CI, 27 to 34), Agility (28.8; 95% CI, 23 to 34), and STAR (27.8; 95% CI, 21 to 34) groups. Survival results among the 4 prostheses are reported.

CONCLUSIONS

This study demonstrated acceptable outcomes of 4 modern TAA prostheses. Outcome results from patient-reported scores were comparable between at least 3 of the 4 prostheses (the Hintegra, STAR, and Agility implants). The rates of complications and revisions found in this study are within the limits reported in the literature for similar prostheses and methods of reporting.

LEVEL OF EVIDENCE

Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

The Effect of Obesity on Functional Outcomes and Complications in Total Ankle Arthroplasty

BACKGROUND

The prevalence of obesity in the United States is staggering. Currently, the effect of obesity on third-generation total ankle replacement (TAR) is unknown.

METHODS

We prospectively identified a consecutive series of 455 primary TARs operated between May 2007 and September 2013 who had a minimum follow-up of 2 years. We identified 266 patients with a body mass index (BMI) <30 (control), 116 with a BMI between 30 and 35 (Obese I), and 73 with a BMI >35 (Obese II). Clinical outcomes including wound issues, infection rate, complications, and failure rates were compared. Functional outcomes including American Orthopaedic Foot & Ankle Society hindfoot score, Short Form-36 (SF-36), Short Musculoskeletal Function Assessment (SMFA), Foot and Ankle Disability Index (FADI), and Foot and Ankle Outcome Score (FAOS) were compared. Average patient follow-up in the Obese I group was 44.7 ± 17.3 months, Obese II was 42.7 ± 16.4 months, and 45.2 ± 17.4 months in the control group.

RESULTS

Age, race, and smoking history in the obese group were not significantly higher than the control group; however, sex was significantly related to BMI. There was no difference in complication, infection, or failure rates between the groups. Preoperatively, the Obese II group had significantly lower SF-36 scores and higher SMFA function, FADI, and FAOS Symptoms scores. For each of the Obese I, Obese II, and control groups, all functional outcome scores 1 year postoperatively and at most recent follow-up were significantly improved. However, at most recent follow-up, Obese II patients had lower FAOS Pain and SF-36 scores and higher FADI and SMFA Functional scores.

CONCLUSION

Total ankle arthroplasty in obese patients was a relatively safe procedure. Although obese patients after TAR had lower functional outcome scores compared to their nonobese counterpart, they did experience significant functional and pain improvements at most recent follow-up.

LEVEL OF EVIDENCE

Level III, comparative series.

The impact of obesity on the outcome of total ankle replacement

BACKGROUND

Obese patients have a slightly higher proportion of revision and infection following knee or hip replacement, but functional improvement is equivalent to that of normal-weight patients. We compared outcomes of total ankle replacement for end-stage ankle arthritis in obese and normal-weight patients.

METHODS

This retrospective cohort study compared thirty-nine obese patients (those with a body mass index of ≥30 kg/m(2)) at a mean follow-up time of 3.76 years and forty-eight non-obese patients (those with a body mass index of <30 kg/m(2)) at a mean follow-up time of 3.92 years after total ankle replacement. Outcome measure scores (Ankle Osteoarthritis Scale [AOS] and Short-Form 36 [SF-36]) were collected preoperatively and at least two years postoperatively. Complication and revision data were collected by manual chart audits. Statistical analyses were performed with use of t tests, Wilcoxon signed-rank tests, and Mann-Whitney U tests. Survival analysis was conducted with use of the Kaplan-Meier method.

RESULTS

The two cohorts had similar demographic characteristics. Ten (26%) of thirty-nine patients in the obese group were morbidly obese (having a body mass index of >40 kg/m(2)). There were thirty-nine patients in the obese group and forty-eight patients in the non-obese group. The mean body mass index (and standard deviation) was 36.28 ± 5.43 kg/m(2) for the obese group and 25.84 ± 3.00 kg/m(2) for the non-obese group. The obese group had significantly worse preoperative SF-36 Physical Component Summary scores (p = 0.01) than the non-obese group. Preoperatively to postoperatively, both obese and non-obese patients demonstrated significant improvements (p < 0.001) in AOS pain, AOS disability, and SF-36 Physical Component Summary scores, and the changes in these scores were similar for both groups. The SF-36 Mental Component Summary scores did not change significantly (p = 0.30) in either group. There was no significant difference (p = 0.48) in the proportion of complications or revisions between the groups.

CONCLUSIONS

Although obese patients had increased disability and worse function preoperatively, total ankle replacement significantly and similarly improved pain and disability scores in both obese and non-obese patients, with no significant difference in the proportion of complications. We therefore maintain that total ankle replacement is a reliable treatment option for patients with end-stage ankle arthritis, including those who are obese.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Etiopathogenesis of osteolytic cysts associated with total ankle arthroplasty, a histological study

BACKGROUND

Osteolytic cyst formation after total ankle arthroplasty has been identified in recent years and is probably an important problem with longer follow-up. The aim of this study is to describe the outcome of a histological analysis of samples from periprosthetic intra-osseous cysts and joint capsules, retrieved during revision surgery after primary total ankle arthroplasty.

METHODS

All samples (n=22) were analyzed and scored using a semi-quantitative grading system. The main items of interest were polyethylene (PE) particles, metal particles, histiocytes, and giant cells.

RESULTS

All cyst samples contained PE particles. A similar number of PE particles were found in talar and tibial cysts. No significant correlation between the number of PE particles and time to reoperation was found. Metal particles were found in 16 cysts.

CONCLUSIONS

We suggest that PE particles are not the primary cause of osteolytic cyst formation but a secondary contributing factor probably accelerating the process of osteolysis. It is likely that implant design, biomechanical factors and local anatomic-physiological factors play an important role.

Evaluating Component Migration: Comparing Two Generations of the INBONE(®) Total Ankle Replacement

Although total ankle replacement (TAR) designs have radically evolved, the compressive forces at the ankle can cause aseptic loosening, talar subsidence, and implant failure. The purpose of the present report was to compare the implant migration associated with the INBONE(®) I, a TAR system with a stemmed talar component, and the newer generation INBONE(®) II, a TAR system without a stemmed talar component (Wright Medical Technology, Inc., Arlington, TN). Because core decompression could weaken the integrity of the talus, we hypothesized that the stemmed component would result in greater implant migration. A total of 35 consecutive patients (age 58.2 ± 12.1 years; 23 men) were included. Of these 35 patients, 20 (57.1%) had been treated with the INBONE(®) I and 15 (42.9%) with the INBONE(®) II. To assess implant migration, using anteroposterior radiographs, the distance from the apex of the tibial component to the most distal aspect of the talar stem or to the mid-saddle of the nonstemmed component was measured. The measurements were recorded from the immediate postoperative radiographs and the 12-month postoperative radiographs. Implant migration was quantified as the difference between the 12-month and the immediate postoperative measurements. Despite our hypothesis, no significant difference was found in implant migration between the INBONE(®) I (0.7 ± 1.2 mm) and INBONE(®) II (0.6 ± 1.3 mm, p = .981). However, previously published data have suggested that implant migration can continue for ≥2 years after surgery. Therefore, additional investigations with larger sample sizes and longer follow-up periods are needed to draw definitive conclusions.

Evaluating component migration after modular stem fixed-bearing total ankle replacement

To date, no studies have evaluated implant migration after implantation of a modular stem fixed-bearing total ankle replacement. The purpose of the present report was to determine the inter-rater and intrarater reliability of our proposed measurement technique and to assess implant migration over time. Twenty consecutive patients (aged 59.3 ± 12.2 years) who had undergone implantation with this modern, third-generation prosthetic were included. To assess implant migration, measurements were made from non-weightbearing, postoperative radiographs immediately after surgery and again at 1 year and 2 years. Implant migration was defined as a change in implant location from the immediate postoperative radiograph. The proposed measurement technique appears to be a reliable method of assessing implant migration, evidenced by the high inter-rater reliability and intrarater reliability (intraclass correlation [2,1] 0.993 and intraclass correlation [1,1] 0.997, respectively). The mean implant migration was 0.7 mm at 1 year and 1.0 mm at 2 years. Time (r = 0.42) and gender (r = 0.31) were significant predictors of implant migration (R(2) = 0.27, p = .008). Therefore, we confirmed our hypothesis that implant migration would significantly increase over time and discovered that implant migration was greater in males (1.2 ± 1.1 mm) than females (0.1 ± 0.8 mm). Given the gross stability of the implant and lack of revision within the follow-up period, the measurements obtained could serve as clinical guidelines for acceptable implant migration in the short term. To determine the thresholds correlated with implant failure, future studies with long-term follow-up are warranted.

Risks to the blood supply of the talus with four methods of total ankle arthroplasty: a cadaveric injection study

BACKGROUND

Despite the use of contemporary total ankle arthroplasty implant designs, clinical outcomes of total ankle arthroplasty continue to lag behind those of other joint replacement procedures. Disruption of the extraosseous talar blood supply at the time of ankle replacement may be a factor contributing to talar component subsidence-a common mechanism of early failure following ankle replacement. We evaluated the risk of injury to specific extraosseous arteries supplying the talus associated with specific total ankle arthroplasty implants.

METHODS

Sixteen fresh-frozen through-knee cadaveric specimens were injected with latex and barium sulfate distal to the popliteal trifurcation to visualize the arteries. Four specimens each were prepared for implantation of four contemporary total ankle arthroplasty systems: Scandinavian Total Ankle Replacement (STAR), INBONE II, Salto Talaris, and Trabecular Metal Total Ankle (TMTA). Postoperative computed tomography scans and 6% sodium hypochlorite chemical debridement were used to examine, measure, and document the proximity of the total ankle arthroplasty instrumentation to the extraosseous talar blood supply.

RESULTS

All four implant types subjected the extraosseous talar blood supply to the risk of injury. The INBONE subtalar drill hole directly transected the artery of the tarsal canal in three of four specimens. The lateral approach for the TMTA transected the first perforator of the peroneal artery in two of four specimens. The STAR caused medial injury to the deltoid branches in all four specimens, whereas the other three systems did not directly affect this supply (p < 0.005). The Salto Talaris and STAR implants caused injury to the artery of the tarsal canal in one of four specimens.

CONCLUSIONS

All four total ankle arthroplasty systems tested posed a risk of injury to the extraosseous talar blood supply, but the risks of injury to specific arteries were higher for specific implants.

Bone microarchitecture of the talus changes with aging

BACKGROUND

Fractures of the talus in the elderly are rare and usually result from high-impact injuries, suggesting only minor age-related bone structure changes. However, total ankle replacement failures with age often result from talar subsidence, suggesting age-related bone loss in the talus. Despite a number of histological analyses of talar microarchitecture, the effects of age and sex on talar microarchitecture changes remain poorly defined.

QUESTIONS/PURPOSES

The aim of this study was to analyze changes or differences in the trabecular microarchitecture of the talus with regard to (1) age and (2) sex.

METHODS

Sixty human tali were harvested from 30 patients at autopsy of three different age groups (20-40, 41-60, 61-80 years). The specimens were analyzed by radiography, micro-CT, and histological analysis. Given that there was no difference between the left and right talus, static histomorphometric parameters were assessed in three regions of interest of the right talus only (body, neck, head; n = 30).

RESULTS

The talar body, neck, and head were affected differently by age-related changes. The greatest loss of bone volume with age was seen in the talar body (estimate: -0.239; 95% confidence interval [CI], -0.365 to -0.114; p < 0.001). In the talar neck (estimate: -0.165; 95% CI, -0.307 to -0.023; p = 0.025), bone loss was only moderate and primarily was the result of reduction in trabecular thickness (estimate: -1.288; 95% CI, -2.449 to -0.127; p = 0.031) instead of number (estimate: -0.001; 95% CI, -0.005 to -0.003; p = 0.593). Bone structure changes were independent of sex.

CONCLUSIONS

Age-related bone structure changes predominantly occur in the talar body, which poses a potential risk factor for total ankle replacement loosening. The moderate changes in the talar neck might explain the persistent low incidence of talar neck fractures with age.

CLINICAL RELEVANCE

Our findings suggest that before total ankle replacement implantation, careful patient selection with dual-energy xray absorptiometry evaluation may be necessary to reduce the risk of talar implant subsidence.