***TASK*** the task is to summarize an input biomedical literature in six sentences 
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    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    Input: Background : Mobile-bearing ankle replacements have become popular outside of the United States over the past two decades . The goal of the present study was to perform a prospect i ve evaluation of the safety and efficacy of a mobile-bearing prosthesis to treat end stage ankle arthritis . We report the results of three separate cohorts of patients : a group of Sc and anavian Total Ankle Replacement ( STAR ) patients and a control group of ankle fusion patients ( the Pivotal Study Groups ) and another group of STAR total ankle patients ( Continued Access Group ) whose surgery was performed following the completion of enrollment in the Pivotal Study . Material s and Methods : The Pivotal Study design was a non-inferiority study using ankle fusion as the control . A non-r and omized multi-centered design with concurrent fusion controls was used . We report the initial perioperative findings up to 24 months following surgery . For an individual patient to be considered an overall success , all of the following criteria needed to be met : a ) a 40-point improvement in total Buechel-Pappas ankle score , b ) no device failures , revisions , or removals , c ) radiographic success , and d ) no major complications . In the Pivotal Study ( 9/00 to 12/01 ) , 158 ankle replacement and 66 arthrodesis procedures were performed ; in the Continued Access Study ( 4/02 to 10/06 ) , 448 ankle replacements were performed , of which 416 were at minimum 24 months post-surgery at time of the data base closure . Results : Major complications and need for secondary surgical intervention were more common in the Pivotal Study arthroplasty group than the Pivotal Study ankle fusion group . In the Continued Access Group , secondary procedures performed on these arthroplasty patients decreased by half when compared with the Pivotal Arthroplasty Group . When the Pivotal Groups were compared , treatment efficacy was higher for the ankle replacement group due to improvement in functional scores . Pain relief was equivalent between fusion and replacement patients . The hypothesis of non-inferiority of ankle replacement was met for overall patient success . Conclusion : By 24 months , ankles treated with STAR ankle replacement ( in both the Pivotal and Continued Access Groups ) had better function and equivalent pain relief as ankles treated with fusion . Level of Evidence : II , Prospect i ve Controlled Comparative Surgical We describe the medium-term results of a prospect i ve study of 200 total ankle replacements at a single-centre using the Sc and inavian Total Ankle Replacement . A total of 24 ankles ( 12 % ) have been revised , 20 by fusion and four by further replacement and 27 patients ( 33 ankles ) have died . All the surviving patients were seen at a minimum of five years after operation . The five-year survival was 93.3 % ( 95 % confidence interval ( CI ) 89.8 to 96.8 ) and the ten-year survival 80.3 % ( 95 % CI 71.0 to 89.6 ) . Anterior subluxation of the talus , often seen on the lateral radiograph in osteoarthritic ankles , was corrected and , in most instances , the anatomical alignment was restored by total ankle replacement . The orientation of the tibial component , as seen on the lateral radiograph , also affects the position of the talus and if not correct can hold the talus in an abnormal anterior position . Subtalar arthritis may continue to progress after total ankle replacement . Our results are similar to those published previously We describe the results of a r and omised , prospect i ve 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 Sc and inavian 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 design s 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 The purpose of the current prospect i ve study was to determine the midterm results of 68 total ankle replacements with the Sc and inavian Total Ankle Replacement ( S.T.A.R. ) prosthesis . The 65 patients ( 34 women and 31 men ; mean age at surgery , 56.1 years [ range , 22 - 85 years ] ) were assessed clinical ly and radiologically after 3.7 years ( range , 2.4 - 6.2 years ) . Thirty-five patients ( 54 % ) were totally pain-free . The overall clinical score was grade d as excellent or good in 67 ankles . The American Orthopaedic Foot and Ankle Society hindfoot score improved from 24.7 points ( range , 3 - 44 points ) preoperatively to 84.3 points ( range , 44 - 100 points ) at followup . Three patients ( three ankles , 4.4 % ) had a ballooning bone lysis on the tibial side . Despite prophylaxis , periarticular hypertrophic bone formation was seen in 43 ankles ( 63 % ; 42 patients ) , associated with a decrease of dorsiflexion and plantar flexion . Nine ankles ( 13 % ; nine patients ) had revision surgery because of problems with the components and 14 ankles ( 21 % ; 14 patients ) had secondary or additional operations . All revision or secondary surgeries were successful , and no ankle had to be converted to an ankle arthrodesis . The early experience with the S.T.A.R. ankle implant is encouraging , although we have encountered more complications and potential problems than previously reported Early design s of Total Ankle Replacement ( TAR ) had a high failure rate . More recent experience with the 3-piece , meniscal bearing , total ankle replacement has been more promising . We report a review of the early results of our first 22 prostheses in 20 patients undergoing Sc and inavian Total Ankle Replacement ( STAR ) in Northern Irel and . There was a mean follow-up time of 26 months . Seventeen patients are pain-free at the ankle joint during normal daily activities . Two of the early cases have required revision surgery due to technical errors . Other complications have included malleolar fractures , poor wound healing and postoperative stiffness . These early results show high levels of patient satisfaction , and we are encouraged to continue with total ankle arthroplasty . There is a steep initial learning curve and use of TAR should be restricted to foot and ankle surgeons . ImagesFig 1Figs 2a and bFigs 2 c and Fifty-eight patients with either rheumatoid arthritis or osteoarthritis were treated with meniscal-bearing ankle prostheses .  The concept was to mobilize , align , and stabilize the ankle before resurfacing it . Cement was used for prostheses fixation in 33 patients ( 1986 - 1989 ) and 25 patients had fixation without cement ( 1990 - 1995 ) . All patients in one prospect i ve series were followed up yearly with radiographs and with a clinical scoring system giving a maximum of 100 points . This allowed for a patient-controlled prospect i ve study . No patients were lost to followup . The only detectable difference in the treatment was the fixation mode . For the purpose of comparing patients with cemented and uncemented prostheses , the patients who had surgery between 1986 and 1989 were not followed up after 1997 , and patients who had surgery between 1990 and 1995 were not followed up after 2002 . The mean followup was 9.4 years . Failure was defined as prosthesis revision or change to arthrodesis for any reason . In the cemented group , nine of 33 patients had revision surgery or fusion . In the uncemented group , one of 25 patients had revision surgery . Survivorship analysis for 12 years based on life tables showed a 70 % survival rate ( confidence limit , 60.3 - 78.5 ) for the cemented group and 95.4 % survival rate ( confidence limit , 91.0 - 99.9 ) for the uncemented group . The average clinical scores at the latest followup were 74.2 + /- 19.3 for the cemented group and 91.9 + /- 7.4 points for the uncemented group . Therefore , unconstrained meniscal-bearing ankle prostheses should be uncemented The purpose of this study was to evaluate the function of the ankle joint during walking before and after  Sc and inavian Total Ankle Replacement ( STAR ) . Nine patients ( six males and three females ) with an average age of 65 years , scheduled for unilateral total ankle replacement for osteoarthritis and rheumatoid arthritis , were evaluated both preoperatively and postoperatively in a gait analysis laboratory . Arthroplasty patients showed reduced range of motion at the ankle compared to normal controls . Postoperative arthroplasty subjects had significantly improved external ankle dorsiflexion moment , the moment that affects the plantarflexor muscles , when compared to their preoperative status . The moment in arthroplasty patients was increased , indicating improved function of the ankle joint One hundred consecutive cases treated with ankle arthroplasty for osteoarthritis ( OA ) or rheumatoid arthritis were followed prospect ively and annually for up to 15 years . Survivorship analysis was performed , with the endpoint being prosthesis revision or change to arthrodesis .  Patients who were younger than 50 years at the first implantation constituted one group ( group A , 30 ankles ) . The other group ( group B , 70 ankles ) consisted of patients aged 50 years or older at the first implantation . All patients were assessed clinical ly according to the Kofoed Ankle Score . The distribution of OA/rheumatoid arthritis in group A was 18/12 , and in group B it was 43/27 ( not significant ) . The median age in group A was 46 years ( range , 22–49 years ) , and in group B it was 63 years ( range , 51–83 years ) . In group A , one case was revised , and three cases were converted to  arthrodesis  after a median of 5 years ( range , 5–9 years ) . In group B , four cases were revised , and four cases were converted to  arthrodesis  after a median of 5.5 years ( range , 2–8 years ) . The results of cases with traumatic OA did not differ between groups A and B. It was concluded that the results of ankle arthroplasty were of equal quality in patients younger than 50 years and those who were older An up to 12-year follow-up of 51 single-coated STAR revealed that 15 ankles had undergone fusion . The mean time from primary surgery to the first revision was median 51 months . In a series of 58 double-coated STAR ankles followed up to 5 years only one ankle had to be revised for component loosening . In this series the clinical survival rate was 98 % and the radiographic survival rate 94 % at 5 years . The radiographic survival rate , with component loosening as endpoint , was significantly better for the last 31 cases in the series of the single-coated prostheses . However , the loosening rate did not differ when these latter 31 cases were compared with the cases operated on with a double-coated prosthesis . One may conclude that improvement of the anchoring surfaces has had a limited influence on the radiographic survival of the STAR ankle . However , from the clinical survivorship figures it is obvious that the learning process continues as the difference in revision rate between the 31 last implanted single-coated and the later on implanted double-coated prostheses approached significance 
    Output:
    
Conclusions We found that STAR prosthesis achieved encouraging results in terms of intermediate to long-term outcome .
The major reasons for implant failure were aseptic loosening and malalignment .
Maybe the increase of surgeons ’ experience and patient selection could improve outcomes and decrease failure rate