Validation and precision of model-based radiostereometric analysis (MBRSA) for total ankle arthroplasty

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.

Salto Talaris Fixed-Bearing Total Ankle Arthroplasty: Long-Term Results at a Mean of 10.7 Years

Background

Total ankle arthroplasty (TAA) has become increasingly popular in the treatment for end-stage ankle arthritis in recent decades. However, there is limited evidence regarding the long-term clinical outcomes and complication rates of modern TAA implants.

Methods

This study presents a follow-up on a previous cohort involving 78 patients (81 ankles) who underwent Salto Talaris fixed-bearing TAA to treat end-stage arthritis, with a mean postoperative follow-up of 5.2 years. The aim of this follow-up study was to assess the radiographic (33 patients, 35 ankles) and clinical (48 patients, 50 ankles) results from the original cohort at a mean of 10.7 years (range, 7.8-14 years).

Results

At a mean of 10.7 years, the Kaplan-Meier estimated survivorship was 84.2% (95% CI, 71.9%-98.6%). For the patients reviewed, we did not find any change in patient-reported outcomes between an average 5- and 11-year follow-up. Measured total range of motion and plantarflexion did not change between 1 and 11 years, but dorsiflexion was measured as decreasing by an average of 4 degrees (P < .02).

Conclusion

In this longer-term follow-up of a limited cohort, we found that Salto Talaris fixed-bearing TAA demonstrated good long-term survival with relatively low rates of revision or other complications. Patient-reported outcome and range of motion measures revealed good stability.

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.

J-curve design total knee arthroplasty: the posterior stabilized shows wider medial pivot compared to the cruciate retaining during chair raising

PURPOSE

Which total knee arthroplasty (TKA) design represents the better solution to restore a correct knee biomechanics is still debated. The aim of this study was to compare posterior stabilized (PS) and cruciate retaining (CR) version of the same TKA design (femoral component with an anatomic sagittal radius-J-curve design) by the use of dynamic Roentgen stereophotogrammetric analysis (RSA). The hypothesis was that the two models influence differently in vivo knee kinematic.

METHODS

A cohort of 16 randomly selected patients was evaluated 9 months after surgery: Zimmer PERSONA® was implanted, eight with CR design and eight with PS design. The kinematic evaluations were performed using a Dynamic RSA (BI-STAND DRX 2) developed in our Institute, during the execution of the sit-to-stand motor task. The motion parameters were obtained using the Grood and Suntay decomposition and the low-point kinematics methods.

RESULTS

PS TKA lateral femoral compartment had a wider anterior translation (17 ± 2 mm) than the medial one (11 ± 2 mm), while the two compartments of CR TKA showed a similar anterior translation (medial: 9 ± 2 mm/lateral: 11 ± 2 mm). T test for comparison between CR and PS TKA of antero-posterior translation showed a statistically significant difference (p < 0.05) in the flexion range between 15° and 40°. The CR prosthesis did not anteriorly translate during flexion. The PS design translated anteriorly showing a roll-forward mechanism during extension from 80° to 18° of flexion and a posterior translation from 18° to 0°. The same significant differences (p < 0.05) between the PS and CR groups were found comparing the low-point positions of the femoral condyles in the range of flexion between 25° and 40° for the medial compartment and between 15° and 25° for the lateral compartment.

CONCLUSIONS

Dynamic RSA was able to investigate for the first time in vivo the kinematic behaviour of PS and CR version of the same TKA J-curve design. PS type showed a medial pivot during sit-to-stand motion task, while the CR type showed a cylindrical movement. Further studies are needed to evaluate the impact of different TKA designs on clinical results.

LEVEL OF EVIDENCE

IV.

Hindfoot Arthrodesis Screw Position and Trajectory Effect on Talus Subsidence When Performed With Total Ankle Arthroplasty

BACKGROUND:

Total ankle arthroplasty (TAA) is increasingly being recognized as an effective surgical option for end-stage ankle arthritis. Associated hindfoot arthrodesis procedures are at times needed to correct malalignment or to address adjacent joint arthritis. Results following TAA and associated hindfoot arthrodesis have at times been underwhelming and the devascularization of the talar blood supply has been postulated as a potential cause. This study explored the association between hindfoot arthrodesis fixation and talar component subsidence.

METHODS:

The study included 81 consecutive patients who underwent a TAA with either an isolated subtalar arthrodesis or combined subtalar and talonavicular arthrodesis with a minimum of 2 years of follow-up. Radiographic and clinical evaluations including patient-reported outcomes were performed at each postoperative visit. The primary outcome measure was the presence of talar component subsidence while patient-reported outcomes were the secondary outcome measure.

RESULTS:

30.9% of patients had evidence of talar component subsidence. Subsidence was seen in 55.5% of patients with dorsal to plantar subtalar fixation compared to 11.1% of patients with plantar to dorsal screws ( P < .001) and in 44.4% of patients with screws violating the sinus tarsi compared to 3.7% of patients without screws in the sinus tarsi ( P < .001). Screws that were placed from dorsal to plantar were more likely to violate the sinus tarsi ( P < .001). Patients with evidence of talar subsidence reported higher pain scores and lower functional scores. There were 8 TAA failures, and the presence of dorsal to plantar screws was associated with failure ( P < .01).

CONCLUSION:

Screws that are placed across the subtalar joint from a dorsal to plantar approach are more likely to violate the sinus tarsi, contributing to a significantly higher rate of talar component subsidence when associated with TAA.

LEVEL OF EVIDENCE:

Level II, prospective comparative series.

High precision and accuracy of model-based RSA for analysis of wrist arthroplasty

Radiostereometric analysis (RSA) is a method for measuring micromotion in joint arthroplasties. RSA has never been used in total wrist arthroplasties. We evaluated: (i) the precision of model-based RSA in total wrist arthroplasties measured in a phantom model and in patients; (ii) the number of bone markers necessary to ensure the precision; and (iii) the accuracy of model-based RSA in a phantom model. Reverse engineered models of radial and carpal/metacarpal components of two wrist arthroplasties (ReMotion® and Motec®) were obtained by laser scanning. Precision and accuracy of each arthroplasty were analyzed with regards to translation and rotation along the three coordinate axes. Precision was analyzed in 10 phantom and 30 clinical double examinations for each arthroplasty, and was expressed by a repeatability coefficient. The precision of different numbers and configurations of bone markers in the phantom model were compared. Accuracy was tested in a phantom model where the implants were attached to a micrometer, and was defined as the mean difference between measured and true migration. In the phantom model the precision for translations ranged from 0.03 to 0.14 mm and for rotations from 0.18 to 1.52°. In patients the precision for translations ranged from 0.06 to 0.18 mm, and for rotations from 0.32 to 2.18°. Less than four bone markers resulted in inferior precision. Accuracy ranged from -0.06 to 0.04 mm, and from -0.38 to -0.01°. Y-rotations could not be obtained from the Motec® due to rotational symmetry about the longitudinal axis. We conclude that model-based RSA in total wrist arthroplasties is precise, accurate, and feasible to use for clinical evaluation of micromotion in wrist arthroplasties. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3053-3063, 2018.

Additively manufactured implant components for imaging validation studies

Radiographic imaging is the current standard for evaluating postoperative joint replacements. Prior to application, such imaging methods need to be validated to determine the lower limits of performance under ideal conditions, using either a phantom or cadaver setup. Conventionally manufactured orthopedic implants for use in such studies are not always accessible and may be cost-prohibitive to purchase. We propose the use of additively manufactured implants as a cheaper, more accessible alternative for use in radiographic imaging validation studies. Bias and repeatability were compared between conventionally manufactured and additively manufactured reverse total shoulder implant sets under a standard model-based radiostereometric analysis phantom study environment. Measurements were compared using the humeral stem or glenosphere model relative to reference bone beads, and the humeral stem relative to the glenosphere model to measure implant relative displacement. Compared to the conventionally manufactured implants, the additively manufactured implants had less bias along the internal-external rotation axis (p < 0.001), but greater bias along the abduction-adduction and flexion-extension rotation axes (p = 0.005, 0.011). Additively manufactured implants had greater repeatability along the internal-external rotation axis (p < 0.001), but worse repeatability along the medial-lateral translation axis (p = 0.001) and the abduction-adduction rotation axis (p < 0.001). Differences were on the orders of 0.01 mm and 0.5°. For the purpose of validating two-dimensional-three-dimensional radiographic imaging techniques of orthopedic implants, additively manufactured implants can be used in place of conventionally manufactured implants, assuming they are fabricated to the manufacturer's specifications. Observed differences were within the errors of the measurement technique and not clinically meaningful.

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.

Stability and migration across femoral varus derotation osteotomies in children with neuromuscular disorders

Background and purpose - Studies have indicated that one-third of children with cerebral palsy (CP) develop dislocation of the hip that needs surgical intervention. When hip dislocation occurs during childhood surgical treatment consists of tenotomies, femoral varus derotation osteotomy (VDRO), and acetabuloplasty. Relapse is observed in one-fifth of cases during adolescence. In this prospective cohort study, we performed a descriptive evaluation of translation and rotation across VDROs in children with neuromuscular disorders and syndromes by radiostereometric analysis (RSA). We assessed "RSA stability" and migration across the VDROs. Patients and methods - Children with a neuromuscular disorder were set up for skeletal corrective surgery of the hip. RSA follow-ups were performed postoperatively, at 5 weeks, and 3, 6, and 12 months after surgery. Results - 27 femoral VDROs were included; 2 patients were excluded during the study period. RSA data showed stability across the VDRO in the majority of cases within the first 5 weeks. At the 1-year follow-up, the mean translations (SD) of the femoral shaft distal to the VDRO were 0.51 (1.12) mm medial, 0.69 (1.61) mm superior, and 0.21 (1.28) mm posterior. The mean rotations were 0.39° (2.90) anterior tilt, 0.02° (3.07) internal rotation, and 2.17° (2.29) varus angulation. Interpretation - The migration stagnates within the first 5 weeks, indicating stability across the VDRO in most patients.

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.

Salvage of Failed Total Ankle Replacement Using a Custom Titanium Truss

Subsidence of the talar component results in significant morbidity after total ankle replacement. When recognized, prompt revision could be needed to preserve the function of the implant; however, this is not always the case. In situations in which the implant cannot be revised, tibiotalocalcaneal arthrodesis might be necessary to salvage the extremity. The purpose of the present report is to describe the use of a custom titanium alloy truss to fill a bony void created by explantation of the implant components. Total ankle replacement was performed as the initial surgery to address end-stage osteoarthritis. Two years after the index procedure, the patient underwent revision of the polyethylene and talar components with subtalar arthrodesis secondary to progressive subtalar osteoarthritis and talar subsidence. The implant subsequently became infected and was removed. The patient underwent re-implantation after the infection had resolved, but significant talar subsidence required conversion to a tibiotalocalcaneal arthrodesis with a custom titanium alloy truss and retrograde intramedullary nail. At the most recent follow-up appointment, the patient was weightbearing on a stable extremity and pain free. Radiographic examination confirmed appropriate implant alignment and evidence of bone formation throughout the titanium truss. Although our results are restricted to a single case with initial, limited follow-up data, combining sound structural mechanics with an open architecture and unique texture, the custom titanium truss appears to maintain the limb length and promote healing across a large void.

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.

Longitudinal migration and inducible displacement of the Mobility Total Ankle System

BACKGROUND AND PURPOSE

RSA can be used for early detection of unstable implants. We assessed the micromotion of the Mobility Total Ankle System over 2 years, to evaluate the stability of the bone-implant interface using radiostereometric analysis measurements of longitudinal migration and inducible displacement.

PATIENTS AND METHODS

23 patients were implanted with the Mobility system. Median age was 62 (28-75) years and median BMI was 28.8 (26.0-34.5). Supine radiostereometric analysis examinations were done from postoperatively to the 2-year follow-up. Standing examinations were taken from the 3-month to the 2-year follow-up. Migrations and displacements were assessed using model-based RSA software (v. 3.2).

RESULTS

The median maximum total point motion (MTPM) for the implants at 2 years was 1.19 (0.39-1.95) mm for the talar component and 0.90 (0.17-2.28) mm for the spherical tip of the tibial component. The general pattern for all patients was that the slope of the migration curves decreased over time. The main direction of motion for both components was that of subsidence. The median 2-year MTPM inducible displacement for the talar component was 0.49 (0.27-1.15) mm, and it was 0.07 (0.03-0.68) mm for the tibial component tip.

INTERPRETATION

The implants subside into the bone over time and under load. This corresponds to the direction of primary loading during standing or walking. This statistically significant motion may become a clinically significant finding that would correspond with premature implant failure.