Fixed-bearing Total Ankle Replacement Research Articles

Early outcomes of the Exactech Vantage fixed-bearing total ankle replacement.

The Vantage Total Ankle System is a fourth-generation low-profile fixed-bearing implant that has been available since 2016. We aimed to describe our early experience with this implant. This is a single-centre retrospective review of patients who underwent primary total ankle arthroplasty (TAA) with a Vantage implant between November 2017 and February 2020, with a minimum of two years' follow-up. Four surgeons contributed patients. The primary outcome was reoperation and revision rate of the Vantage implant at two years. Secondary outcomes included radiological alignment, peri-implant complications, and pre- and postoperative patient-reported outcomes. There were 168 patients (171 ankles) included with a mean follow-up of 2.81 years (2 to 4.6) and mean age of 63.0 years (SD 9.4). Of the ten ankles with implant failure (5.8%), six had loosening of the tibial component. In the remaining four failed implants, one was due to periprosthetic joint infection (PJI), one was due to loosening of the talar component, and two were due to loosening of both the tibial and talar components. Seven patients underwent reoperation: irrigation and debridement for superficial infection (n = 4); bone grafting for cysts (n = 2); and open reduction internal fixation (n = 1). Asymptomatic peri-implant lucency/subsidence occurred in 20.1% of ankles, with the majority involving the tibial component (n = 25). There were statistically significant improvements in PROMs in all domains. Short-term results of this implant demonstrate early survival comparable to the reported survivorship of similar low-profile, non-stemmed implants. Radiological lucency occurred more commonly at the tibial component, and revisions occurred primarily due to loosening of the tibial component. Further research is needed to evaluate longer-term survivorship.

Analysis of Polyethylene-Related Revisions After Total Ankle Replacements Reported in US Food and Drug Administration Medical Device Adverse Event Database.

There are 2 general types of total ankle replacement (TAR) designs with respect to the polyethylene insert, mobile-bearing (MB) and fixed-bearing (FB) TARs. The aim of this study is to compare polyethylene-related adverse events (AEs), particularly revisions, reported for MB TARs and FB TARs using the US Food and Drug Administration's (FDA's) Manufacturer and User Facility Device Experience (MAUDE) database. A text mining method was applied to the medical device reporting (MDR) in the MAUDE database from 1991 to 2020, followed by manual reviews to identify, characterize, and describe all polyethylene-related AEs, including revisions, reported for MB and FB TARs. We found 1841 MDRs for MB (STAR Ankle only) and 1273 MDRs for 40+ FB TARs approved/cleared by the FDA. For the MB design, 33% (606/1841) of the AEs reported related to the polyethylene component, compared to 24% (291/1273) of the AEs reported for FB designs. Polyethylene fractures were reported in 11.3% (208/1841) for the MB designs compared to 0.2% (2/1273) for the FB designs. Half of the polyethylene-related revisions occurred within an average of 4.1 years after implantation for the MB design compared within an average of 5.2 years for FB designs. Analysis of this database revealed a higher proportion of reported polyethylene fractures and greater need for earlier revisions for polyethylene-related issues with use of the primary MB design in the database as compared with FB TAR designs. Further study of device-related complications with more recent designs for both MB and FB ankle replacement components are needed to improve the outcomes of total ankle replacement. Level III, retrospective comparative study.

Changes in ankle and foot kinematic after fixed-bearing total ankle replacement

Ankle osteoarthritis is a chronic debilitating disease marked by cartilage breakdown, pain and significant biomechanical impairment of the entire lower limb. Total ankle replacement (TAR) has been encouraged during the last decade as it has the potential to maintain the existing pre-operative ankle range of motion and to protect the more distally located joints of the foot. Three-dimensional gait analysis using a multi-segment foot model can provide an objective analysis of TAR for the treatment of end-stage ankle osteoarthritis. Thirty-six patients suffering from post-traumatic end-stage ankle osteoarthritis were evaluated before and after TAR. A four-segment kinematic foot model was used to calculate intrinsic foot joint kinematics during gait. Spatio-temporal parameters were also assessed. Kinematic results were compared to a control group of asymptomatic subjects.Differences in waveform patterns were mainly limited to dorsi-/plantarflexion inter-segment angles. At loading response, the Shank-Calcaneus plantarflexion angles as well as the Calcaneus-Midfoot dorsiflexion angle increased slightly in post-operative condition. During propulsion, an increase in Hallux-Metatarsus dorsiflexion angle was observed. Pain improved after surgery as supported by increased spatio-temporal parameters. While multi-segment foot and ankle kinematics were improved, they remained impaired compared to control values. This study confirms that TAR maintains the residual pre-operative range of motion after surgery from midstance to propulsion. Furthermore, the results suggest that the kinematic behavior of the foot joints distal to the affected ankle joint also improves post-operatively. The outcome of this study further emphasizes the clinical relevance of multi-segment foot modeling when assessing the outcome of TAR.

Preoperative PROMIS Physical Function Scores Predict Postoperative Outcomes Following Total Ankle Replacement.

Background:Despite good evidence that supports significant improvements in pain and physical function following a total ankle replacement (TAR) for end-stage ankle arthritis, there is a subset of patients who do not significantly benefit from surgery. The purpose of this study was to perform a preliminary analysis to determine if preoperative Patient-Reported Outcome Measurement Information System (PROMIS) scores could be used to predict which patients were at risk of not meaningfully improving following a TAR.Methods:Prospectively collected preoperative and ≥2-year postoperative PROMIS physical function, pain interference, pain intensity, and depression scores for 111 feet in 105 patients were included in the study. Significant postoperative improvement was defined using minimal clinically important differences (MCIDs). Logistic regression models and area under the curve (AUC) analyses were used to determine whether preoperative PROMIS scores were predictive of postoperative outcomes.Results:Receiver operating characteristic curves found statistically significant AUCs for the PROMIS physical function (AUC = 0.728, P = .004), pain intensity (AUC = 0.720, P = .018), and depression (AUC = 0.761, P < .001) domains. The preoperative PROMIS pain interference domain did not achieve a statistically significant AUC.Conclusion:Preoperative PROMIS physical function and pain intensity t scores may be used to predict postoperative improvement in patients following a fixed-bearing TAR; however, preoperative PROMIS pain interference scores were not good predictors. The results of this study may be used to guide research regarding patient-reported outcomes following TAR.Level of Evidence:Level III, retrospective comparative series.

Sagittal Tibiotalar Alignment May Not Affect Functional Outcomes in Fixed-Bearing Total Ankle Replacement: A Retrospective Cohort Study.

In total ankle replacement (TAR), correct positioning of the implant is crucial. Malposition of the components may increase contact pressures and diminish prosthesis survival. The effect of sagittal tibiotalar alignment on functional outcomes after fixed-bearing TAR remains unclear, however, and nostudies havecompared fixed-bearing implants with respect to the anteroposterior (AP) position of the talar component. The purposes of this study were (1) to evaluate the effect of sagittal tibiotalar alignment on functional outcomes in fixed-bearing TAR and (2) to compare post-operative sagittal tibiotalar alignment in two types of fixed-bearing implants. In a retrospective analysis of 71 primary TARs performed at a single center, we studied the INBONE™ II Total Ankle System and the Salto Talaris® Ankle. Radiographic measurements of the tibial axis-talus (T-T) ratio and the AP offset ratio were performed before and after surgery, respectively, and we evaluated Foot and Ankle Outcome Scores (FAOSs) and the 12-item Short Form Health Survey (SF-12) mental component summary (MCS) and physical component summary (PCS) scales pre-operatively and at 2 years after surgery. The Pearson correlation and independent-samples t test were used to evaluate differences in FAOSs, SF-12 MCS scores, and SF-12 PCS scores regarding post-operative sagittal alignment. Post-operative sagittal tibiotalar alignment was neutral in 39 ankles and anterior in 32 ankles. We observed no significant between-group differences in clinical outcome scores. Patients with a Salto Talaris Ankle prosthesis had a greater AP offset ratio (0.12) than patients with an INBONE II implant (0.05). However, the greater translation did not correlate with outcome scores. At the 2-year follow-up, no correlation between the post-operative AP offset ratio and functional outcome scores was observed between the two fixed-bearing-implant groups. Further studies with longer follow-up are needed to determine whether the difference in sagittal alignment has an effect on functional outcomes in the long term.

TL 18052 - Sagittal tibiotalar alignment in fixed-bearing total ankle replacement

Introduction: Implant positioning is critical in total ankle replacement (TAR). However, the effect of sagittal tibiotalar alignment on functional outcomes in fixed-bearing TAR remains unclear. Furthermore, no studies comparing different fixed-bearing implants with respect to the anteroposterior position of the talar component have been performed to date. Methods: A retrospective analysis of 71 primary TARs in a single center was performed. Prostheses included were the INBONE II® (Wright Medical, Memphis, TN) and the Salto Talaris (Integra LifeSciences, Plainsboro, NJ). Radiographic measurements of the tibial-axis-to-talus ratio (T-T ratio) and the anteroposterior offset ratio (AP offset ratio) were performed preoperatively and postoperatively, respectively. Foot and Ankle Outcome Scores (FAOS) and SF-12 MCS and PCS scales were evaluated preoperatively and 2 years postoperatively. Results: Postoperative sagittal tibiotalar alignment was neutral in 39 ankles and anterior in 32 ankles. No significant differences were observed between groups with respect to clinical outcome scores. Patients with a Salto Talaris prosthesis had a greater AP offset ratio (0.12 ± 0.05) than patients with an INBONE II® implant (0.05 ± 0.04) (P &lt; .01); however, this increased translation did not correlate with the outcome scores. Conclusion: At the 2-year follow-up, the INBONE II® TAA showed a more neutral sagittal alignment compared with the Salto Talaris prosthesis. However, no correlation between the postoperative AP offset ratio and functional outcome scores was observed with the use of the two fixed-bearing TAR. Further studies with longer follow-ups are needed to determine if the difference in sagittal alignment may have an effect on functional outcomes in the long-term.

Minimum 2 Year Outcomes of a Fixed Bearing Total Ankle Replacement in the United Kingdom

Category:Ankle, Ankle ArthritisIntroduction/Purpose:The Infinity (Wright medical) total ankle replacement (TAR) has become the most implanted ankle replacement in the UK with a 30.1% share in the most recent 2016 England and Wales NJR 14th report. It is a fixed bearing implant utilising an anterior approach and radiological guidance to aid alignment, and is approved for use in the UK as an uncemented implant.Methods:Since introducing the Infinity TAR in June 2014, all implants from two centres in the UK; The Royal Devon and Exeter Hospital NHS Foundation Trust and Northumbria NHS Healthcare Trust, have been followed up prospectively. 113 implants are included with 2 year minimum follow-up, average follow-up being 33 months (24-52). Pre- and post-operative demographic, radiographic and functional outcomes were collected including Visual Analogue Score (VAS), Manchester Oxford foot questionnaire (MOxFQ, UK validated patient reported outcome score) EQ5D (validated quality of life score). Complexity was assessed using COFAS pre-operative grade.Results:Implant survivorship was 93.8% at 2 years minimum. Median age was 68 (42-92), male: female 72:41. Mean MOxFQ improved by 28, mean EQ5D by 1.4 and mean VAS by 7. 16 cases had planned additional procedures, 5 required intra-operative medial malleolar fixation. There have been 2 revisions for deep infection, 2 for implant subsidence, 1 for instability and 2 for unexplained pain (6.2%). 5 patients have required further surgery to the ankle and hindfoot with implant retention (4.4%). 3 patients have asymptomatic tibial cysts (3.4%) and 1 patient has an asymptomatic talar cyst (0.9%) - there is no evidence of progression or loosening.Conclusion:We report favourable early functional, radiographic and survivorship outcomes of this implant in the UK population.

The Effect of Exchanging a Mobile-Bearing into a Fixed-Bearing Total Ankle Replacement System in Patients with Coronal Plane Instability

Category:Ankle, Ankle ArthritisIntroduction/Purpose:The interface between the polyethylene (PE) inlay and the tibial component in mobile-bearing total ankle replacement (TAR) systems may allow the talus to seek its position according to the individual anatomy. However, chronic overload and/or incompetence of soft tissue may allow medial and/ or lateral translation of the talar component over time. This typically results in medial and/ or lateral gutter pain as well as pain along the syndesmosis. The purpose of this study was to assess the effect of tibial component exchange and conversion from a mobile-bearing into a fixed-bearing TAR system in patients with coronal plane instabilities TAR.Methods:A consecutive series of 30 ankles (29 patients; age 65.6 [48.9 – 86.1]; male, 23; female, 7) with coronal plane instabilities underwent revision TAR with exchange of a mobile-bearing (Hintermann Series, H3) into a fixed-bearing (Hintermann Series, H2) TAR system. Patients presented with a medial (n = 12) or lateral (n = 9) translation of the talar component, or a varus (n = 4) or valgus (n = 5) instability with subsequent tilt of the talar component. After removing the tibial component and PE inlay, a tibial osteotomy was performed and 1 to 2 mm of the distal tibia removed. A tibial component of the H2 total ankle system was inserted. While holding the foot in neutral position, the PE inlay was locked to the tibial component in the appropriate position. Functional outcome and pain were recorded to evaluate clinical outcome, and standard radiographs under fluoroscopy were taken for radiographic assessment.Results:All but one of the remaining 28 patient showed significant improvement of pain (P<0.05). Preoperative gutter pain disappeared completely in 20 ankles (71.4%), and partially in 8 ankles (18.6%). The AOFAS Hindfoot Score improved from 54.3 (range, 21 to 90) preoperatively to 74.0 (range, 48 to 92) at latest follow-up (P<0.05). Radiographic assessment showed firm osteointegration in all patients with the talar component centralized in the ankle mortise, and a free medial and lateral gutter without tilt of talar component (Figure 1). One patient with bilateral revision TAR was affected by a bilateral deep infection of both ankles 9 months after surgery subsequent to a severe pneumonia. Both ankles were removed and replaced by a cement spacer.Conclusion:Converting a mobile-bearing into a fixed-bearing TAR system has shown to be effective in the treatment of patients with coronal plane instabilities following TAR. Allowing the PE inlay to adapt its position according to the talar component before definitive fixation to the tibial component of the H2 series, saved having to replace the talar component. Future long-term studies however are needed to identify significant benefits of this novel total ankle concept in primary and revision TAR.

The Ankle-Hindfoot Kinematics of Current Generation Total Ankle Replacement: A Cadaveric Gait Simulation

Category:Ankle ArthritisIntroduction/Purpose:Total ankle replacement (TAR) has developed as a standard treatment option for end-stage ankle arthritis with the primary benefit of pain relief and ankle-hindfoot motion preservation. The current generation of TARs features limited bone resection and improved initial fixation of components to restore physiologic constraint and the anatomic articulation of the ankle. However, the ankle-hindfoot kinematics of current TAR designs compared to the baseline native ankle have not yet been extensively studied. Cadaveric gait simulation is a valuable tool for investigating direct effects of surgical procedures on foot and ankle biomechanics. The objective of this study was to assess whether this current generation TAR system could provide normal ankle-hindfoot kinematics as the baseline native ankle using cadaveric gait simulation.Methods:Eleven mid-tibia cadaveric specimens were secured to a static mounting fixture with a six-degree of freedom robotic platform to simulate gait in native-intact and TAR conditions. A force plate was moved relative to the stationary specimen through an inverse tibial kinematic path calculated from in vivo data while extrinsic tendons were actuated using physiologic loads (Figure 1A). Ankle-hindfoot kinematics were measured from reflective markers attached to bones via surgical pins. TAR was performed using a current generation, fixed-bearing system by a fellowship-trained foot-ankle surgeon using the manufacturer described protocol (PROPHECY Patient-specific instrumentation, Infinity, Wright Medical Technology). Ankle-hindfoot joint kinematics were measured using the same tibial kinematic inputs and muscle forces as the intact condition. Non-parametric, bias-corrected bootstrapping was used to calculate 95% confidence intervals to compare motion between intact and total ankle replacement.Results:Analyses demonstrated no significant difference in average ankle-hindfoot joint kinematics between the intact and TAR conditions (Figure 1B). The result was consistent for the ankle, subtalar, and talonavicular joints, in each plane of motion.Conclusion:These findings demonstrate that the current generation of fixed-bearing TAR can recreate normal ankle-hindfoot kinematics patterns seen in normal ankles. Restoring ankle kinematics can be a significant factor in slowing down the progression of adjacent joint arthritis in the foot. However, it is still inconclusive whether ankle-hindfoot kinematics can be restored in patients with long standing ankle arthritis, and this should be addressed in future studies.

Prospective Randomized Trial Comparing Mobile-bearing and Fixed-bearing Total Ankle Replacement

Category: Ankle Arthritis Introduction/Purpose: Outcomes of total ankle replacement for the treatment of end-stage ankle arthritis continue to improve. Debate continues whether a mobile-bearing total ankle replacement (MB-TAR) or a fixed-bearing total ankle replacement (FB-TAR) is superior, with successful outcomes reported longterm for MB-TAR and at intermediate-to-longterm follow-up for newer generation FB-TAR. Although comparisons between the two total ankle designs have been reported, to our knowledge, no investigation has compared the two designs with a high level of evidence. This prospective, randomized controlled trial conducted at a single institution compares patient satisfaction, functional outcomes and radiographic results of the mobile-bearing STAR and the fixed-bearing Salto-Talaris in the treatment of end-stage ankle arthritis. Methods: This investigation was approved by our institution’s IRB committee. Between November 2011 and November 2014, adult patients with end-stage ankle osteoarthritis failing nonoperative treatment were introduced to the study. With informed consent, 100 patients (31 male and 69 female, average age 65, range 35 to 85) were enrolled; demographic comparison between the two cohorts was similar. Exclusion criteria included inflammatory arthropathy, neuropathy, weight exceeding 250 pounds, radiographic coronal plane deformity greater than 15 degrees or extensive talar dome wear pattern (“flat top talus”). Prospective patient-reported outcomes, physical exam and standardized weightbearing ankle radiographs were obtained preoperatively, at 6 and 12 months postoperatively, and then at yearly intervals. Data collection included visual analog pain score (VAS), short form 36 (SF-36), foot and ankle disability index (FADI), short musculoskeletal functional assessment (SMFA) and AOFAS ankle-hindfoot score. Surgeries were performed by non-design team orthopaedic foot and ankle specialists with total ankle replacement expertise. Statistically analysis was performed by a qualified statistician. Results: At average follow-up of 4.5 years (range 2-6 years) complete clinical data and radiographs were available for 84 patients; 7 had incomplete data, one had died, 4 were withdrawn after enrolling but prior to surgery and 4 were lost to follow-up. In all outcome measures, the entire cohort demonstrated statistically significant improvements from preoperative evaluation to most recent follow-up. There was no statistically significant difference in improvement in clinical outcomes between the two groups. Radiographically, tibial lucency/cyst formation was 26.8% and 20.9% for MB-TAR and FB-TAR, respectively. Tibial settling/subsidence occurred in 7.3% of MB-TAR. Talar lucency/cyst formation occurred in 24.3% and 2.0% of MB-TAR and FB-TAR, respectively. Talar subsidence was observed in 21.9% and 2.0% of MB-TAR and FB-TAR, respectively. Re-operations were performed in 8 MB-TAR and 3 FB-TAR, with the majority of procedures being to relieve impingement or treat cysts and not to revise or remove metal implants. Conclusion: For the first time, with a high level of evidence, our study confirms that patient reported and clinical outcomes are favorable for both designs and that there is no significant difference in clinical improvement between the two implants. The incidence of lucency/cyst formation was similar for MB-TAR and FB-TAR for the tibial component, but the MB-TAR had greater talar lucency/cyst formation and tibial and talar subsidence. As has been suggested in previous studies, clinical outcomes do not correlate with radiographic findings. Re-operations were more common for MB-TAR and in the majority of cases were to relieve impingement or treat cysts rather than revise or remove metal implants.

Finite Element Analysis of Tibial Bone-Implant Load Transfer and Bone Strains with a Modern Fixed-bearing Total Ankle Replacement

Category: Ankle Arthritis Introduction/Purpose: Loosening of the tibial component is the primary failure mode in total ankle arthroplasty (TAA). The mechanics of the tibial component loosening has not been fully elucidated. Clinically observed radiolucency and cyst formation in the periprosthetic bone may be associated with unfavorable load sharing at and adjacent to the tibial bone-implant interface contributory to implant loosening. However, no study has fully investigated the load transfer from the tibial component to the bone under multiaxial loads in the ankle. The objective of this study was to utilize subject-specific finite element (FE) models to investigate the load transfer through tibial bone-implant interface, as well as periprosthetic bone strains under simulated multiaxial loads. Methods: Bone-implant FE models were developed from CT datasets of three cadaveric specimens that underwent TAA using a modern fixed-bearing tibial implant (a cobalt-chrome tray with a polyethylene bearing, Salto Talaris, Integra LifeSciences). Implant placement was estimated from the post-operative CT scans. Bone was modeled as isotropic elastic material with inhomogeneous Young’s modulus (determined from CT Hounsfield units) and a uniform Poisson’s ratio of 0.3. The tibial tray (Young’s modulus: 200,000 MPa, Poisson’s ratio: 0.3) and the polyethylene bearing (Young’s modulus: 600 MPa, Poisson’s ratio: 0.4) were modeled as isotropic elastic. A 100-N compressive force, a 300-N anterior force, and a 3-Nm moment were applied to two literature based loading regions on the surface of the polyethylene bearing. The proximal tibia was fixed in all directions. The bone-implant contact was modeled as frictional with a coefficient of 0.7, whereas the polyethylene bearing was bonded to the tray. Results: Along the long axis of the tibia, load was transferred to the bone primarily through the flat bone-contacting base of the tibial tray and the cylindrical top of the keel, little amount of load was transferred to the bone between those two features (Fig. 1A). Low strain was observed in bone regions medial and lateral to the keel of the tibial tray, where bone cysts were often observed clinically (Fig. 1A). On average, approximated 70% of load was transferred through the anterior aspect of the tibial tray at the flat bone-contacting base, which corresponded to the relatively high bone strain adjacent to the implant edge in the anterior bone-implant interface (Fig. 1B). Conclusion: Our results demonstrated a two-step load transfer pattern along the long axis of the tibia, revealing regions with low bone strain peripheral to the keel indicative to stress shielding. Those regions were consistent with the locations of bone cysts observed clinically, which may be explained by the stress shielding associated remodeling of bone. These findings could also describe the mechanism of implant loosening and failure. Future studies may use our model to simulate more loading scenarios, as well as different implant placement and design, to identify means to optimize load transfer to the bone and prevent stress shielding.

Conventional Ultra-high Molecular Weight Polyethylene versus Highly Cross-linked Polyethylene from Semi-constrained, Fixed-bearing Total Ankle Arthroplasty Systems

Category: Ankle Arthritis Introduction/Purpose: The aim of this study was to compare the polyethylene wear rate, particle size, and particle shape of primary semi-constrained, fixed-bearing, bone-sparing total ankle arthroplasty using conventional ultra-high molecular weight polyethylene (CPE) versus highly cross-linked polyethylene (HXLPE) by applying a level walking input using a joint simulator. Methods: Two fixed-bearing total ankle replacement systems with different types of polyethylene liners were tested: 1.) CPE sterilized in ethylene oxide, and 2.) HXLPE sterilized with gas plasma after electron beam irradiation. Three implants for each design underwent wear testing using gravimetric analysis over 5 million simulated walking cycles. A fourth implant was used as a load soak control. Equivalent circle diameter (ECD) and equivalent shape ratio (ESR) were computed to determine particle size and particle shape, respectively. Results: The mean wear rate from 1.5-5 million cycles (MC) was 2.0±0.3mg/MC for HXLPE and 16.7±1.3mg/MC for CPE (P &lt; 0.001). The total number of particles per cycle generated for HXLPE and CPE were 0.17x106 particles/cycle and 0.53x106 particles/cycle, respectively (P &lt; 0.001). The mean ECD of HXLPE particles (0.22 ±0.11μm) was significantly smaller than the mean ECD of CPE particles (0.32±0.14μm) (P&lt;0.001). HXLPE particles were significantly more round than CPE particles (P&lt;0.001). Conclusion: HXLPE liners had a significantly lower wear rate and produced significantly fewer and rounder particles than CPE liners. The results of this study suggest that HXLPE has more favorable wear characteristics for total ankle arthroplasty.

Range of Motion Following Total Ankle Replacement and Subtalar Fusion Through Lateral Versus Anterior Approach. Biomechanics Analysis

Category: Ankle Arthritis Introduction/Purpose: A gait analysis of patients who underwent simultaneous total ankle replacement (TAR) and subtalar fusion allows to assess the ankle range of motion (ROM) with precision. In healthy subjects or in patients who underwent isolated TAR this is not possible because it is influenced by the subtalar ROM and it is not possible to analyse the two joints separately. Excluding the role of the subtalar joint, it is possible to analyse the consequences of different prosthetic designs and different surgical approaches on joint kinematics. The aim was to evaluate and compare with a gait analysis the effects of two different TAR designs on the functionality of the tibiotalar joint by exploiting the exclusion of the subtalar effect determined by the subtalar fusion simultaneously performed. Methods: Minimum follow-up was 12 months. 16 patients underwent a fix-bearing TAR through lateral approach (Zimmer Trabecular Metal Total Ankle), 7 patients underwent a mobile-bearing TAR through anterior approach (Hintegra). A six-camera motion capture system was used to measure foot static posture and foot segment kinematics. Rotations in the sagittal, frontal, and transverse planes between shank and the whole foot, shank and calcaneus, calcaneus and midfoot, midfoot and metatarsus, and calcaneus and metatarsus were calculated. Sagittal and transverse plane rotations of the first matatarso-phalangeal joint, medial longitudinal arch deformation, transverse plane angle between first and second metatarsal bone and between second and fifth metatarsal bone, and sagittal plane orientation of the first and second metatarsal bone with respect to the ground were also calculated. The following spatio-temporal parameters were calculated: stance time, swing time, stride length, normalized stride length, cycle time, cadence, walking speed, and normalized walking speed. Results: On average, the lateral approach group walked at a faster speed and with a longer stride length than the anterior approach group. However, spatio-temporal parameters in both groups were generally lower than the control values. No major differences were detected between the two groups in terms of ROM in any foot joint, with the exception of the frontal-plane motion of the midfoot with respect to the calcaneus (midtarsal joint) which was larger in the anterior approach group. Conclusion: patients with TAR through lateral approach seem to walk at a faster speed and with a longer stride length than patients with TAR through anterior approach; the midtarsal joint ROM was larger in the anterior approach group and this could mean that mobile bearing TARs through an anterior approach could lead to an overload of the midtarsal joint with respect to fixed-bearing TARs through a lateral approach. However, further studies with larger samples of patients are needed to confirm these results.

Contact stresses, pressure and area in a fixed-bearing total ankle replacement: a finite element analysis

BackgroundMobile-bearing ankle implants with good clinical results continued to increase the popularity of total ankle arthroplasty to address endstage ankle osteoarthritis preserving joint movement. Alternative solutions used fixed-bearing designs, which increase stability and reduce the risk of bearing dislocation, but with a theoretical increase of contact stresses leading to a higher polyethylene wear. The purpose of this study was to investigate the contact stresses, pressure and area in the polyethylene component of a new total ankle replacement with a fixed-bearing design, using 3D finite element analysis.MethodsA three-dimensional finite element model of the Zimmer Trabecular Metal Total Ankle was developed and assembled based on computed tomography images. Three different sizes of the polyethylene insert were modeled, and a finite element analysis was conducted to investigate the contact pressure, the von Mises stresses and the contact area of the polyethylene component during the stance phase of the gait cycle.ResultsThe peak value of pressure was found in the anterior region of the articulating surface, where it reached 19.8 MPa at 40% of the gait cycle. The average contact pressure during the stance phase was 6.9 MPa. The maximum von Mises stress of 14.1 MPa was reached at 40% of the gait cycle in the anterior section. In the central section, the maximum von Mises stress of 10.8 MPa was reached at 37% of the gait cycle, whereas in the posterior section the maximum stress of 5.4 MPa was reached at the end of the stance phase.DiscussionThe new fixed-bearing total ankle replacement showed a safe mechanical behavior and many clinical advantages. However, advanced models to quantitatively estimate the wear are need.ConclusionTo the light of the clinical advantages, we conclude that the presented prosthesis is a good alternative to the other products present in the market.

Mobile- vs. Fixed-Bearing Total Ankle Prostheses

Category: Ankle, Ankle Arthritis Introduction/Purpose: Total ankle replacement (TAR) is a well-accepted treatment option in patients with end-stage ankle osteoarthritis. In general, TAR designs can be classified based on their number of components: 2-components (fixed-bearing) vs. 3- components (mobile-bearing). In the U.S. the STAR prosthesis is the only one mobile-bearing TAR with FDA approval. It remains unclear whether 3-component TAR designs have superior clinical outcomes including prosthesis survivorship. Therefore we performed a systematic review and meta-analysis of the available TAR designs to determine prosthesis survivorship and whether there is a statistically significant difference between mobile- and fixed-bearing TAR designs. Methods: We reviewed literature using common data bases. All searches were unlimited. For the search we used the subject heading terms: “ankle”, “replacement”, “arthroplasty”, and “prosthesis”. For meta-analysis a checklist was used as described by Meta-analysis Of Observational Studies in Epidemiology (MOOSE) Group. The quality of included studies was assessed using Coleman’s Methodology Score. The following parameters were reviewed: type of study, inventor bias, number of patients/ankles, mean age with range, gender, etiology of underlying ankle osteoarthritis, average and maximum follow-up, number of TAR failures, and total exposure time. For each study, failure rate was estimated as the number of failures/total exposure years. N-year (here, 5 or 10 years) failure rate was calculated as 1-exp(-N*failure rate). The pooled estimate of failure rate was a weighted average across studies using the inverse variance weighting method. The test for heterogeneity was not significant so fixed effects models were used. Results: In total, 32 studies with 3968 ankles were included into the analysis. Nine studies included 844 fixed-bearing TARs and 23 studies included 3124 mobile-bearing TARs. Patient characteristics were comparable in both study groups. For fixed-bearing TAR, the 5-year and 10-year failure rate was 0.077 and 0.149 with an average annual failure rate of 0.016 (95%CI 0.008-0.025). For mobile-bearing TAR, the 5-year and 10-year failure rate was 0.074 and 0.142with an annual failure rate of 0.015 (95%CI 0.011- 0.020). Two studies with fixed-bearing TAR and six studies with mobile-bearing TAR had inventor bias. The average annual failure rate was comparable in both groups (P = 0.88), with and without inventor bias, 0.013 vs. 0.018 (P = 0.87). Conclusion: We have shown that TAR has an overall failure rate of 0.149 and 0.142 at 10 years in patients with fixed-bearing and mobile-bearing TAR design, respectively. No superiority of one implant design over another can be supported by the available data.

Contact stresses in a fixed-bearing total ankle replacement: A finite element analysis

We performed the finite element modeling for the first time to analyze the effect of gradient structures (GS) on the wear fatigue-resistant of rails in the rolling-sliding contacts. We found that GS can enhance the wear fatigue-resistant of rails by reducing the maximum horizontal and vertical displacements on the surface of rails. The thicker GS layers, the better the performance is. For a fixed GS layer thickness, increasing the surface yield strength can effectively reduce surface displacements. The outcome from this study can provide the design guideline for processing the gradient structures in the rail steels to obtain superior mechanical properties.

Contact Stresses in a Fixed-Bearing Total Ankle Replacement

Category: Ankle, Ankle Arthritis, Basic Sciences/Biologics Introduction/Purpose: Third-generation ankle implants with good clinical results continued to increase the popularity of total ankle arthroplasty (TAA) to address end-stage ankle osteoarthritis preserving joint movement. Newer TAA used fixed-bearing designs, with a theoretical increase of contact stresses leading to a higher polyethylene wear. The purpose of this study was to investigate the contact stresses in the polyethylene component of a new third-generation TAA, with a fixed-bearing design, using 3D finite element analysis. Methods: A three-dimensional finite element model was developed based on the Zimmer Trabecular Metal Total Ankle (ZTMTA) and a finite element analysis was employed to evaluate the contact pressure, contact area and Von Mises stress in the polyethylene articular surface in the stance phase of the gait cycle. Results: The peak values were found at the anterior regions of the articulating surface, where reached 19.8 MPa at 40% of gait cycle. The average contact pressure during the stance phase of gait was 6.9 MPa. The maximum von Mises stress of 14.1 MPa in the anterior section was reached at 40% of the gait cycle. For the central section the maximum von Mises stress of 10.8 MPa was reached at 37% of the gait cycle, whereas for posterior section the maximum of 5.4 MPa was reached at the end of the stance phase (60% of the gait cycle). Conclusion: Although, the average von Mises stress was less than 10 MPa, high peak pressure values were recorded. Advanced models to quantitatively estimate the wear are needed to assess polyethylene and metal component survivorship.

Sagittal tibiotalar translation and clinical outcomes in mobile and fixed-bearing total ankle replacement.

Sagittal implant malalignment after total ankle replacement (TAR) has been considered to be a possible cause for premature implant failure. In a prior study, the change over time of the tibiotalar ratio (T-T ratio), which is the ratio between the posterior longitudinal talar length and the full longitudinal talar length, was assessed in 66 TARs where an unconstrained, mobile-bearing implant was implanted. The analysis documented an increase in the T-T ratio between 2 and 6 months post-surgery (on average from 34.6% to 37.2%). We hypothesized that this change might have been related to the presence of a mobile-bearing insert. In order to test our hypothesis, we designed a study to compare the translation of the talus in TARs performed with an unconstrained, mobile-bearing implant (designated the "Mobile ankle") and those performed with a semi-constrained, fixed-bearing implant (designated the "Fixed ankle"). The study included 71 consecutive patients (71 ankles) who underwent TAR with the Mobile ankle and 24 consecutive patients (24 ankles) who received the Fixed ankle from May 2011 to December 2014. Patients were assessed clinically and radiologically preoperatively (T0), at 6 months (T2) and 12 months (T3) post-surgery. There was also a radiological assessment at 2 months post-surgery (T1). The comparison of the T-T ratio between the two implant groups and over time indicated an interaction between time and group, therefore the changes of the T-T ratio over time were affected by the implant type factor (P<0.001). The changes of the postoperative T-T ratio over time were not significant in the Fixed ankle group (35.7±6.7% at T1, T2, and T3; P=1.0 for each pairwise comparison). In the Mobile ankle group, the T-T ratio at 2 months (34.4±5.5%) was significantly different to the T-T ratio at 6 months (37.0±5.8%; P<0.001; i.e. there was a significant posterior translation of the talus). The AOFAS score increased from preop to 12 months post-surgery in both the Mobile ankle (72.7±12.8 at 12 months; P<0.001) and the Fixed ankle (85.0±9.7 at 12 months; P<0.001). The significant posterior translation of the talus from 2 to 6 months documented only in the Mobile ankle group may have been associated with the presence of the mobile bearing interface.

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 (R2 = 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.

Modular Stem Fixed-Bearing Total Ankle Replacement: Prospective Results of 23 Consecutive Cases with 3-Year Follow-up

In the present report, the 3-year outcomes of 23 consecutive patients treated with a modular stem fixed-bearing total ankle replacement are described. Pain, functional impairment, and disability were assessed annually using a visual analog scale. Complications and additional procedures also were recorded. Compared with preoperative pain (8.4 ± 1.4), functional impairment (8.7 ± 2.3), and disability (3.0 ± 2.5), there were statistically significant postoperative improvements at 1 year (pain, 2.6 ± 1.6; functional impairment, 3.1 ± 2.1; disability, 0.9 ± 1.2), 2 years (pain, 1.5 ± 1.3; functional impairment, 1.9 ± 1.4; disability, 0.6 ± 1.4), and 3 years (pain, 1.3 ± 1.3; functional impairment, 1.9 ± 1.9; disability, 0.4 ± 0.9; p ≤ .001). Pain, function, and disability significantly improved postoperatively from 1 to 2 years (p ≤ .008) and from 1 to 3 years (p ≤ .008). The reductions in pain, functional impairment, and disability were maintained from 2 to 3 years (p ≥ .08). Nine complications (39.1%) were encountered: 1 deep infection, 2 pulmonary embolisms, 3 wounds, 1 ectopic bone formation, 1 stiff joint, and 1 talar subsidence. In the 3-year follow-up period, 3 patients (13.0%) required additional procedures after the immediate postoperative phase. Our results have demonstrated that modular stem fixed-bearing prostheses can be implanted in a predictable and consistent fashion with resultant improvements in pain, function, and disability. Future studies evaluating the clinical outcomes after modular stem fixed-bearing total ankle replacement are warranted.