Mobile-bearing Total Ankle Replacement Research Articles

Ratio of Range of Motion of the Ankle and Surrounding Joints After Total Ankle Replacement: A Radiographic Cohort Study.

This study attempted to identify where motion occurs after total ankle replacement, the difference in range-of-motion contributions between fixed-bearing and mobile-bearing total ankle replacements, and the contribution of abnormal peritalar motion. We hypothesized that sagittal plane radiographic assessment would demonstrate that actual ankle motion through the prosthesis is less than the total arc of ankle motion that may be observed clinically secondary to contributions from adjacent joints. Patients underwent routine standardized weight-bearing maximum dorsiflexion and plantar flexion sagittal radiographs. Sagittal plane ankle and foot measurements were performed on each dorsiflexion and plantar flexion radiograph to determine the total arc of ankle motion, actual ankle motion through the prosthesis, motion through the subtalar and talonavicular joints, and midfoot motion. Motion radiographs were routinely made at 1 year postoperatively and at the time of the most recent follow-up. A minimum follow-up of 2 years was required of all patients. There were 197 patients who met the inclusion criteria (75 INBONE, 52 Salto Talaris, and 70 STAR prostheses). The mean time to the latest radiographs (and standard deviation) was 42.9 ± 18.8 months. The mean actual ankle motion through the prosthesis was 25.9° ± 12.2°, which was significantly less (p < 0.001) than the mean total motion arc of 37.6° ± 12.0°. The motion of the ankle accounted for 68% of total range of motion, and motion of the peritalar joints accounted for 32%. There was no significant difference (p > 0.05) among the 3 prostheses or when comparing fixed and mobile-bearing designs for both ranges of motion. This study demonstrates that actual ankle motion after total ankle replacement is approximately 12° less than the total arc of motion that might be observed clinically because of increased midfoot and subtalar motion. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Age-Related Outcome of Mobile-Bearing Total Ankle Replacement.

The aim of this study was to investigate clinical and radiographic outcomes in patients 50 years and younger vs patients older than 50 years undergoing total ankle replacement. Seventy consecutive patients who underwent primary total ankle replacement were included in this retrospective study. Patients were assessed clinically and radiographically. There was a statistically significant difference between the 2 groups for the American Orthopaedic Foot & Ankle Society score at final follow-up. The younger group had significantly greater improvement compared with the older group. Total ankle arthroplasty is an effective treatment for young, active patients with symptomatic end-stage ankle arthritis. [Orthopedics. 2017; 40(3):e567-e573.].

Change in Talar Translation in the Coronal Plane After Mobile-Bearing Total Ankle Replacement and Its Association with Lower-Limb and Hindfoot Alignment.

Mobile-bearing total ankle replacement (TAR) enables motion at the tibial implant-polyethylene insert interface. This motion could lead to coronal translation of the talus relative to the tibia and may affect radiographic outcome. We aimed to assess the translation of the talus before and after mobile-bearing TAR to determine whether translation of the talus after TAR is associated with coronal plane alignment of the lower limb and hindfoot as well as to investigate the complications associated with talar translation. In this retrospective cohort study, we enrolled 153 patients (159 ankles) with a minimum follow-up of 3 years who underwent mobile-bearing TAR. The location of the talus in the coronal plane was quantified with use of talar center migration (TCM) on anteroposterior radiographs both preoperatively and at postoperative intervals, and the relationship between them was investigated. Radiographic parameters in the coronal plane-including mechanical axis deviation (MAD), lateral distal tibial angle (LDTA), hindfoot alignment angle, and hindfoot moment arm-were measured. The relationship between TCM and radiographic parameters in the coronal plane was assessed in each group. The complications associated with talar translation were examined during the same period. During the 36-month follow-up period, the postoperative TCM showed a strong relationship with the preoperative TCM. Moreover, MAD, LDTA, and hindfoot alignment were significantly related to talar translation (p < 0.01). Complications included medial malleolar impingement in 5 cases (including delayed medial malleolar fracture due to medial impingement in 2 cases), insert dislocation in 1 case, and edge-loading in 2 cases; all of the cases with complications demonstrated implant overhang with talar translation. Talar translation in the coronal plane after mobile-bearing TAR correlates with the preoperative talar translation. Talar translation arises from deformities of MAD, LDTA, and hindfoot alignment, and it may be accompanied by various complications, as observed on coronal radiography. Therefore, additional realignment procedures for coronal malalignment should be considered to prevent talar translation after mobile-bearing TAR. Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Current and future designs for total ankle replacement

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

The Syndesmotic Insufficiency in Mobile Bearing TAR – A Challenging and Underestimated Problem

Category: Ankle Arthritis Introduction/Purpose: The consequence of a missed syndesmotic insufficiency during mobile bearing total ankle replacement (TAR) surgery is subsequent valgus deformity leading to dissociation of the distal tibiofibular joint and failure of the TAR. The purpose of this study was to retrospectively review the patients who developed a syndesmotic insufficiency, which lead to a revision surgery, after primary TAR in our centre. The primary goal was to identify red-flags for possible syndesmotic insufficiency in preoperative planning of TAR, in order to reduce this type of complication. Methods: We identified twenty patients (12 females and 8 males) with a missed instability of the distal tibio-fibular joint appearing 3.5 years (range 0.8-9.5 years) after primary TAR. Patient’s records, preoperative and postoperative radiographs and intraoperative fluoroscope images were reviewed especially with regard to previous ankle or lower leg fractures. Functional outcome was assessed with the use of the American Orthopaedic Foot&amp;Ankle (AOFAS) hindfoot score. Results: The mean follow-up after last revision surgery was 3.5 years. The median AOFAS Score at last follow-up was 72.5. We could identify 3 risk factors for possible failure: (a) The nature of trauma: Weber-C-Type fractures or Maisonneuve-Type fractures were found in 13 of 20 cases. (b) A defect in the lateral tibial plafond after for example, a pilon fracture or arising due to cyst formation, was found in 3 cases. Here we concluded that the defect lead to a subsequent valgus tilt of the tibial component, acting as a stress riser in the distal tibio-fibular joint. (c) The remaining 4 cases showed a high tibial resection probably leading to an iatrogenic lesion of the anterior and posterior distal tibio-fibular ligaments. Conclusion: Knowing the etiology of posttraumatic osteoarthritis of the ankle joint is mandatory to identify a syndesmotic insufficiency in the preoperative work-up for mobile bearing three-component TAR. Due to these findings, our surgical protocol for TAR was adapted accordingly. If one or more of the risk factors are present during surgery we suggest performing distal tibio- fibular fusion.

Does Post-Traumatic Arthritis Produce Poorer 5 Year Patient Outcomes Following Mobile-Bearing Total Ankle Replacement?

Category: Ankle Arthritis Introduction/Purpose: Little long term data is available on patient-reported outcome measures (PROMs) following total ankle replacement in patients with posttraumatic osteoarthritis (PTOA), osteoarthritis (OA) and rheumatoid arthritis (RA). Patients with post-traumatic osteoarthritis have previously been felt to have poorer short and long term results following total ankle replacement, due to younger age, higher activity levels and greater patient expectations. We report the 3 and 5 year outcomes for patients who underwent total ankle replacement with a mobile bearing prosthesis, comparing prospectively collected PROMs data for PTOA patients with those with OA and RA. Methods: We analysed patient demographic data, American Orthopaedic Foot &amp; Ankle Society (AOFAS) scores, Foot and Ankle Outcome Scores (FAOS), the SF-36 Health Survey, and patient satisfaction scores, collected preoperatively and up to five years postoperatively. Results: The study included 109 consecutive patients with total ankle replacement (58 OA, 21 RA, 30 PTOA). At one and two years postoperatively, the PTOA group reported significantly better scores on the general health domain of the SF-36. At three and five years postoperatively, there was a trend for better scores in the PTOA group for all domains of the SF36, however none of these reached significance (P&gt;0.05). At one year postoperatively, the PTOA group and the RA group had better FAOS results for pain than the OA group. There were no significant differences in FAOS scores between groups at three or five years. There were no significant differences in AOFAS scores or in patient reported satisfaction at any measured time point. Conclusion: Our findings suggest that patients with posttraumatic osteoarthritis of the ankle can expect comparable five year outcomes after total ankle replacement with a mobile bearing prosthesis as patients with osteoarthritis and rheumatoid arthritis.

Posterior Talar Shifting in Mobile-Bearing and Fix-Bearing Total Ankle Replacement

Category: Ankle Arthritis Introduction/Purpose: 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 of the tibiotalar ratio (T-T ratio) over time in TARs was assessed in an unconstrained, three component implant. A significant increase in the T-T ratio between 2 and 6 months after surgery (from 34.6% to 37.2%) was documented. This variation of the talar position in the sagittal plane may be due to the presence of an inlay between the tibial and the talar components. Aim: The aim of this study was to compare the translation of the talus in TARs performed with an unconstrained, three-component design (Hintegra, Newdeal, Lyon, France; Integra, Plainsboro, NJ), and those performed with a semi-constrained, two- component design (Zimmer Trabecular Total Ankle, Zimmer, Warsaw, IN). Methods: The study included 71 consecutive patients (71 ankles) who underwent TAR with the Hintegra implant and 24 consecutive patients (24 ankles) who received the Zimmer implant between May 2011 and December 2014. The most common indication for TAR was post-traumatic arthritis (80.3% and 75.0% in the Hintegra group and in the Zimmer group, respectively). Patients were assessed clinically and radiologically preoperatively (T0), at 6 months (T2) and 12 months (T3) post-surgery. There was also a radiological assessment 2 months after surgery (T1). Results: The comparison of the T-T ratio between the two groups and over time indicated an interaction between time and group, therefore the changes of the T-T ratio with time were affected by the implant type factor (p &lt; 0.0001). The changes of the post-operative T-T ratio over time were not significant in the Zimmer group (35.7%±6.7% at T1, T2, and T3; p=1.0 for each pairwise comparison). In the Hintegra 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 &lt; 0.0001). The American Orthopaedic Foot &amp; Ankle Society (AOFAS) score significantly increased from pre-op to 6 months post-surgery in both the Hintegra group (53.3±16.0 at 6 mos; p &lt; 0.0001) and the Zimmer group (76.8±7.0 at 6 mos; p &lt; 0.0001). There was no statistical difference in the preoperative scores (Hintegra: 32.7 ± 12.8; Zimmer: 34.6 ± 11.9; p=0.5347). Conclusion: The significant antero-posterior translation of the talus documented only in the cohort receiving the unconstrained, three-component implant may have associated with, and produced by the presence of the mobile bearing interface between the polyethylene insert and the tibial prosthesis.

Motion at the Tibial and Polyethylene Component Interface in a Mobile-Bearing Total Ankle Replacement.

Normal biomechanics of the ankle joint includes sagittal as well as axial rotation. Current understanding of mobile-bearing motion at the tibial-polyethylene interface in total ankle arthroplasty (TAA) is limited to anterior-posterior (AP) motion of the polyethylene component. The purpose of our study was to define the motion of the polyethylene component in relation to the tibial component in a mobile-bearing TAA in both the sagittal and axial planes in postoperative patients. Patients who were a minimum of 12 months postoperative from a third-generation mobile-bearing TAA were identified. AP images were saved at maximum internal and external rotation, and the lateral images were saved in maximum plantarflexion and dorsiflexion. Sagittal range of motion and AP translation of the polyethylene component were measured from the lateral images. Axial rotation was determined by measuring the relative position of the 2 wires within the polyethylene component on AP internal and external rotation imaging. This relationship was compared to a table developed from fluoroscopic images taken at standardized degrees of axial rotation of a nonimplanted polyethylene with the associated length relationship of the 2 imbedded wires. Sixteen patients were included in this investigation, 9 (56%) were male and average age was 68 (range, 49-80) years. Time from surgery averaged 25 (range, 12-38) months. Total sagittal range of motion averaged 23±9 (range, 9-33) degrees. Axial motion for total internal and external rotation of the polyethylene component on the tibial component averaged 6±5 (range, 0-18) degrees. AP translation of the polyethylene component relative to the tibial component averaged 1±1 (range, 0-3) mm. There was no relationship between axial rotation or AP translation of the polyethylene component and ankle joint range of motion (P > .05). To our knowledge, this is the first investigation to measure axial and sagittal motion of the polyethylene component at the tibial implant interface in patients following a mobile-bearing TAA. Based on outcome scores and range-of-motion measurements, we believe the patients in this study are a representative cross section of subjects compared to other TAA research results. The results from this investigation indicate the potential for a mobile-bearing TAA to fall within the parameters of normal polyaxial ankle motion. The multiplanar articulation in a mobile-bearing TAA may reduce excessively high peak pressures during the complex dynamic tibial and talar motion, which may have a positive influence on gait pattern, polyethylene wear, and implant longevity. Level IV, case series.

Radiographic Outcomes of a Mobile-Bearing Total Ankle Replacement.

Contemporary total ankle prostheses embody design changes intended to address weaknesses in first-generation implants. Due to these changes, outcomes of the newer designs are of particular interest. We have previously published self-reported patient outcomes for the STAR (Scandinavian Total Ankle Replacement) prosthesis. The present study documents radiographic outcome measurements for the STAR prosthesis at intermediate to long-term follow-up. Of 89 consecutive ankle replacements performed between July 1998 and April 2007, 79 had a minimum follow-up of 2 years and were followed prospectively. Serial radiographs were measured by 2 of the authors, including varus, valgus, alpha, beta, and gamma angles, as well as point contact ratio. Inter- and intrarater reliability was calculated and reported. A "severe" subgroup of patients with preoperative coronal plane deformity exceeding 10 degrees was assessed separately. Preoperative and immediate postoperative measurements were compared and maintenance of correction evaluated on subsequent radiographs. Heterotopic ossification and pericomponent lucency were documented and followed, and subsequent procedures were recorded to follow survivorship. The mean follow-up was 8.0 years. Of the 79 ankles, 25 underwent a secondary surgery (31.6%). Coronal correction averaged 5.1 degrees (P < .001), and this was maintained to final follow-up. The severe subgroup (n = 21), with a mean preoperative coronal angulation of 16.1 degrees, was corrected to 4.6 degrees at final follow-up (P < .001). The severe subgroup had a higher secondary surgery rate at 33.3%, with metallic component revision or failure occurring in 3 cases (14.3%) compared to 8 (10.1%) in the entire cohort. The heterotopic ossification rate was 100%, slightly higher than prior reports. STAR prosthesis survivorship was similar to that documented in prior studies of second-generation implants in European patient cohorts. Statistically significant correction in coronal alignment was achieved immediately after surgery and maintained until a final mean follow-up of 8 years, even in patients with preoperative deformity greater than 10 degrees. Level III, retrospective cohort study.

Effect of Coronal and Sagittal Alignment on Outcome After Mobile-Bearing Total Ankle Replacement.

Comparably high revision rates are reported after total ankle replacement (TAR). Therefore, further critical analysis of the influence of implant position on clinical outcome is necessary. We analyzed the reliability and predictive value of previously published pre- and postoperative coronal and sagittal parameters in routine ankle radiographs on the clinical outcome of 84 HINTEGRA total ankle replacements (Newdeal, Lyon, France; Integra, Plainsboro, New Jersey). Mean follow-up was 4.0 years, and 15.5% of the TARs had revision surgery. Mean postoperative American Orthopaedic Foot & Ankle Society ankle-hindfoot score was 71.3; mean postoperative verbal rating scale for pain was 3.1; and mean postoperative ankle range of motion was 26.4 degrees. Most tested radiologic parameters showed moderate or high intra- and interobserver reliability. With the numbers available, no significant difference in clinical outcome for all tested radiologic parameters could be detected. Our results indicate that mild malalignment of TAR, as assessed on routine ankle radiographs, did not affect midterm clinical outcome after TAR. Further multicenter studies with longer follow-up are needed to support our findings. Level III, comparative series.

Intermediate-term Results of Mobile-bearing Total Ankle Replacement.

The literature analyzing total ankle replacement (TAR) results should be critically interpreted because studies made by the design surgeons are potentially subject to bias. European nondesigner surgeon studies reviewing the HINTEGRA TAR system are scarce in the literature. The present study is a European nondesigner surgeon study reviewing a consecutive series of 50 HINTEGRA TAR systems with a minimum follow-up of 2 years, focusing on clinical and radiographic outcomes. Fifty primary TAR procedures were performed between February 2008 and January 2012 by a single surgeon. Every patient underwent a standardized clinical and radiographic follow-up at 6 weeks, 3 and 6 months, and 1 year postoperatively and annually thereafter. The mean time to final follow-up was 45 months. The mean American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Scale score significantly increased from 43.5 preoperatively to 83.8 postoperatively. Clinical range of motion of the ankle also improved from 23.3 degrees preoperatively to 28.3 degrees postoperatively. In 70% of the TAR procedures, the talar component was positioned anteriorly with respect to the tibial axis. Radiological evidence of osteolysis was identified in 24 ankles. The failure rate in the present series was 10%, which was defined as having major revision surgery within 4 years. The survival of the first 50 HINTEGRA TAR systems in this series was satisfactory from clinical and radiological points of view. However, the incidence of asymptomatic periprosthetic osteolytic lesions was quite high (24 ankles). Level IV, retrospective case series.

Patient-Reported Outcomes, Function, and Gait Mechanics After Fixed and Mobile-Bearing Total Ankle Replacement.

The popularity of total ankle replacement as a treatment for end-stage arthritis continues to grow. The purpose of this study was to assess changes in ankle kinetics and kinematics from a preoperative time point through two years postoperatively in patients who had received either a fixed-bearing or a mobile-bearing implant. Ninety patients who received a primary total ankle replacement (forty-nine mobile-bearing and forty-one fixed-bearing) were examined. Three-dimensional joint mechanics and ground reaction forces were measured during level walking preoperatively and one and two years postoperatively. Patient-reported and functional outcomes were also collected. Data were analyzed with use of a 3 × 2 repeated-measures analysis of variance (ANOVA) to determine significant differences between implant types and across time (α = 0.05). No significant difference was observed in the ankle motion or step time between implant types or across time. However, there was a greater increase in the peak plantar flexion moment and the Short Form-36 (SF-36) total score across time in the fixed-bearing group than in the mobile-bearing group. Conversely, visual analog scale (VAS) pain scores exhibited greater improvement in the mobile-bearing group than in the fixed-bearing group. Independent of implant type, a significant improvement was observed in walking speed, results of the functional tests, spatiotemporal variables, patient-reported outcomes, and vertical ground reaction forces. Independent of time, the fixed-bearing group demonstrated a significant increase in both the weight-acceptance and the propulsion ground reaction forces compared with the mobile-bearing group. The mobile-bearing group completed the Sit-to-Stand test significantly faster. All of the observed changes suggest improved or maintenance of function following total ankle replacement. In general, the group with a fixed-bearing implant demonstrated improvements in ankle moment and ground reaction forces, while the mobile-bearing-implant group demonstrated improvements in patient-reported pain outcome. There were few significant changes between the two implant types. Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

In vivo kinematics of three-component mobile-bearing total ankle replacement in rheumatoid ankle with talocalcaneal arthrodesis and spontaneous talocalcaneal fusion

Objective. It is often that patients with rheumatoid arthritis (RA) who require ankle surgeries already have the degeneration of talocalcaneal joints. When talocalcaneal joint was fused, whether operatively or spontaneously, ankle kinematics would be affected. The purpose of this paper was to study in vivo kinematics of mobile-bearing total ankle replacement (TAR) in rheumatoid ankle with concomitant talocalcaneal arthrodesis or with preexisting spontaneous talocalcaneal fusion.Methods. Thirteen TARs in ten patients with RA, in whom talocalcaneal joints had already been fused spontaneously or surgically, were studied. Fluoroscopic images were obtained while each patient was walking with full weightbearing on the implanted ankle. Thereafter tibio–talar motion was analyzed by 2D/3D registration technique.Results. Average tibio–talar motion was 4.0 ± 5.3° for plantarflexion and 6.6 ± 0.3° for dorsiflexion. Average range of internal/external rotation, inversion/eversion and AP translation was 3.8 ± 1.3°, 2.7 ± 1.0° and 1.6 ± 0.6 mm, respectively.Conclusions. Mobility of mobile-bearing TAR with talocalcaneal fusion was small during the stance phase of gait, but clinically measured ROM was mostly preserved. The movements of internal/external rotation and AP translation were allowed to a certain degree, but not of inversion/eversion. Even though the movement of inversion/eversion is limited, talocalcaneal arthrodesis could be accompanied with mobile-bearing TAR in rheumatoid ankles.

Long-Term Effectiveness of Cementless Shallow-sulcus and Deep-sulcus Mobile-Bearing Total Ankle Replacements: 2 Case Reports with over 20 years Follow-up

Long-term studies of 20 years or more concerning ankle replacements are rare. Problems of loosening, avascular necrosis of the talus, component subsidence, osteolysis, bearing dislocation, bearing wear, stress fractures and infections have been reported causes of failure

Long-term follow-up of mobile-bearing total ankle replacement in patients with inflammatory joint disease

Little is known about the long-term outcome of mobile-bearing total ankle replacement (TAR) in the treatment of end-stage arthritis of the ankle, and in particular for patients with inflammatory joint disease. The aim of this study was to assess the minimum ten-year outcome of TAR in this group of patients. We prospectively followed 76 patients (93 TARs) who underwent surgery between 1988 and 1999. No patients were lost to follow-up. At latest follow-up at a mean of 14.8 years (10.7 to 22.8), 30 patients (39 TARs) had died and the original TAR remained in situ in 28 patients (31 TARs). The cumulative incidence of failure at 15 years was 20% (95% confidence interval (CI) 11 to 28). The mean American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score of the surviving patients at latest follow-up was 80.4 (95% CI 72 to 88). In total, 21 patients (23 TARs) underwent subsequent surgery: three implant exchanges, three bearing exchanges and 17 arthrodeses. Neither design of TAR described in this study, the LCS and the Buechel-Pappas, remains currently available. However, based both on this study and on other reports, we believe that TAR using current mobile-bearing designs for patients with end-stage arthritis of the ankle due to inflammatory joint disease remains justified.

AB0354 In vivo kinematics of three-component mobile-bearing total ankle replacement for rheumatoid arthritis during gait.

BackgroundThe standard treatment for end-stage arthritis of ankle joint due to rheumatoid arthritis (RA) has been arthrodesis. It is often that patients with RA who require ankle surgery already have...

AB0353 In vivo kinematics of three-component mobile-bearing total ankle replacement for rheumatoid arthritis during non-weightbearing plantarflexion/dorsiflexion.

BackgroundTotal ankle replacement (TAR) that can relieve pain while retaining ankle movement is a useful surgical option for patients with rheumatoid arthritis (RA). However, high complication rates and low survivorship...

Misalignment of Total Ankle Components Can Induce High Joint Contact Pressures

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

Clinical Evaluation and Radiographic Assessment of Bone Lysis of the AES Total Ankle Replacement

AES mobile-bearing total ankle replacement is evolved from the Buechel Pappas model. We report medium-term results of a prospective study with AES. All patients who underwent AES TAR for ankle arthritis, by a single surgeon, from 2003 to 2006 were included, excluding neurologic disease, talar osteonecrosis and malalignment more than 20 degrees. All were reviewed at 6 months, 1 year, and at yearly intervals thereafter. X-rays were analyzed by three observers, using a 10-zone protocol. Fifty consecutive AES implants in 47 patients (mean age, 56 years; range, 21 to 79 year) were included, with at least 2 years' followup (mean 40 months). Preoperative diagnosis was mainly post-traumatic (50%) and osteoarthritis secondary to instability (36%). Associated procedures were performed in 38%. Eighty-two percent had good functional results. The mean AOFAS score rose from 36.9 +/- 1.7 preoperatively to 85.4 +/- 12, dorsiflexion from 3 degrees to 7.3 degrees, and plantarflexion from 30.8 degrees to 37.8 degrees. Two ankles underwent secondary arthrodesis for talar subsidence and mechanical dislocation. Ninety-eight percent of implants were well positioned at 90 degrees +/-4. Mean prosthesis ROM on X-ray was 22.1 degrees. There were tibia/implant interface cysts (greater than 5 mm) in 62% of cases, and talar/implant interface cysts in 43%. Although functional outcomes were comparable to the other mobile TAR in the literature, bone lysis with the AES prosthesis was more frequent with risk of subsidence. We therefore stopped implantation of this prosthesis and recommend preventive grafting for severe lysis.

A randomised, controlled trial of two mobile-bearing total ankle replacements

We describe the results of a randomised, prospective study of 200 ankle replacements carried out between March 2000 and July 2003 at a single centre to compare the Buechel-Pappas (BP) and the Scandinavian Total Ankle Replacement (STAR) implant with a minimum follow-up of 36 months. The two prostheses were similar in design consisting of three components with a meniscal polyethylene bearing which was highly congruent on its planar tibial surface and on its curved talar surface. However, the designs were markedly different with respect to the geometry of the articular surface of the talus and its overall shape. A total of 16 ankles (18%) was revised, of which 12 were from the BP group and four of the STAR group. The six-year survivorship of the BP design was 79% (95% confidence interval (CI) 63.4 to 88.5 and of the STAR 95% (95% CI 87.2 to 98.1). The difference did not reach statistical significance (p = 0.09). However, varus or valgus deformity before surgery did have a significant effect) (p = 0.02) on survivorship in both groups, with the likelihood of revision being directly proportional to the size of the angular deformity. Our findings support previous studies which suggested that total ankle replacement should be undertaken with extreme caution in the presence of marked varus or valgus deformity.