Confidence intervals (95% CI) were calculated where pooling of data was appropriate. The level of statistical significance was 0.05.
We identified 13 studies [1-3, 15, 18, 20, 21, 26, 27, 30-32, 34] published from 2003 to 2008 and reporting on 1105 TAAs (234 Agility™ [DePuy Orthopaedics, Inc, Warsaw, IN], 344 STAR [Waldemar Link, Hamburg, Germany], 153 Buechel-Pappas™ [Endotec, South Orange, NJ], 152 HINTEGRA® [New Deal, Lyon, France], 98 Salto™ [Tornier, Saint Ismier, France], 70 TNK [Kyocera, Kyoto, Japan], and 54 Mobility™ [DePuy International, Leeds, UK]) with a minimum of 2 years followup. There were no randomized trials. All included studies were graded as Level IV evidence . Patients' recruitment rate in 12 of the studies was greater than 90% [1-3, 15, 18, 20, 21, 27, 30-32, 34].
The indications for TAA varied among different studies (Table 3). Trauma was the leading cause (34%) of arthritis in ankles undergoing TAA (Table 3).
With revision, arthrodesis, or amputation as an end point, we identified 108 failures of 1105 TAAs (9.8%; 95% CI, 3.1%-16.5%). The weighted followup for all prostheses was 5.2 years (95% CI, 3.9-6.5 years). Eight studies [1, 3, 15, 18, 20, 27, 31, 34] provided Kaplan-Meier survivorship analysis data  ranging from 67% at 6 years to 95.4% at 12 years (Table 4).
Failures were salvaged with revision of the TAA in the majority of ankles (62%), whereas amputations were rare (Table 5).
Superficial wound healing complications (including superficial infections, delayed healing, and skin necrosis) were documented in 66 of 827 (8%) TAAs, ranging from 0% to 14.7% in the individual studies, and deep infections in seven of 827 (0.8%), ranging from 0% to 4.6% [1-3, 15, 18, 21, 27, 30, 31].
The American Orthopaedic Foot and Ankle Society Ankle (AOFAS)-Hindfoot score  was used most commonly to assess ankle function after TAA (Table 6). Some of the designers of ankle implants have developed their own scores (Kofoed score  and New Jersey ankle score ). Ankle scores improved after TAA in all studies (Table 6).
Ankle range of motion (ROM) as an outcome measure was documented in nine studies [1-3, 18, 21, 27, 30-32] (Table 7). Several methods have been used to measure ROM (radiographic, clinical with the patient sitting or standing). Mean postoperative ROM was equal to preoperatively  or improved by approximately 4° to 14° (Table 7) [2, 3, 30, 31]. Two studies [26, 32] investigated the ability to participate in sports after TAA. In one study , 55 of 152 patients (36%) were active in sports before surgery compared with 85 of 152 after surgery (56%). The most common activities were hiking, swimming, and cycling. In another study , 62.4% of the patients were active in sports preoperatively. This was similar to the 66% who were active after surgery. The patients participated in 3.0 ± 1.8 different sports and recreational activities preoperatively and in 3.0 ± 1.6 activities after surgery. The sports frequency remained unchanged (2.0 ± 1.6 sessions per week before TAA and 2.3 ± 1.7 postoperatively). The most common disciplines after TAA were swimming, cycling, and fitness/weight training.
Residual pain in the hindfoot after a TAA ranged between 23% and 60% in seven studies (Table 8) [2, 18, 21, 27, 31, 32, 34].
Patients' satisfaction after TAA was documented in eight studies [1, 2, 21, 26, 27, 30-32]. Naal et al.  used a visual analog scale to assess satisfaction with surgery. The mean score was 8 (± 2.5) of 10. Other authors did not use rigorously validated scales to evaluate patients' satisfaction. They stated patients were questioned regarding their satisfaction with the outcome (Table 9).
Ten studies [1-3, 18, 21, 26, 27, 30, 34] reported radiographic evaluation of TAAs. Most studies evaluated the presence of radiolucency and prosthesis subsidence or migration (Table 10), with heterogeneity in methods used and in definitions of radiographic loosening. One study evaluated alignment of the TAA . Progression of osteoarthritis in adjacent joints was examined in two studies [18, 34]. Knecht et al.  reported progression at the subtalar joint in 22 of the 117 ankles (19%) and in 17 of 117 (15%) at the talonavicular joint, whereas Wood et al.  reported “deterioration” of subtalar joint arthritis in 15% of 95 ankles without arthritis in this joint before TAA.
Early attempts of TAA with implants have been disappointing [10, 23]; however, implant designs have evolved [5, 7, 10]. What can we learn from the literature regarding the outcome of TAA with implants currently in use?
We note numerous limitations in the literature reviewed. (1) The level of surgeons' experience and variability in patients' selection may have influenced results in the individual studies. (2) Heterogeneity in study design and outcome measures did not allow direct comparisons of much of the data. It therefore is not possible to show superiority of certain implants or directly compare TAA with alternative management options (eg, arthrodesis). A multicenter trial comparing the outcomes of fixed- versus mobile-bearing implants, and a trial comparing TAA with arthrodesis, would be clinically relevant. However, comprehensive cohort studies reporting on the long-term effects of interventions (eg, TAA), although not providing treatment effect estimates, are useful estimates of prognosis, can detect adverse effects and complications, and are indicative of daily clinical practice achievements . (3) The length of followup varied among studies, thus reported outcomes are not directly comparable. (4) Different scales and methodologies of assessment (patient recruitment, questionnaires, independent examiner or not) were used in different studies. (5) Clinical outcome measures frequently were not validated, whereas some TAA implant designers have produced their own outcome scales (Kofoed , New Jersey ). Results reported in the individual studies therefore could be biased. (6) Patient satisfaction was not assessed using rigorous validated methods. (7) Definitions of the radiographic variables used in the assessment were not identical in different studies, and the radiographic examinations were not always standardized.
We evaluated the quality of studies using the CMS [6, 29]. The substantial interobserver and intraobserver agreement is indicative of the reliability of the CMS, although formal validation was not performed. The reader can easily compare the total score, with the maximum possible of 100 points, to get an impression of the study quality. It shares some similarities with the STROBE (Strengthening of Reporting of Observational trials in Epidemiology)  guidelines (study design, type and size, data collection, and recruitment of participants), although these are not a study quality scoring tool. They were developed to provide a checklist and recommendations that could aid authors to conduct and present observational studies .
Rheumatoid arthritis was the primary indication for TAA (reported rates of 39% and 37.5%) in two previous meta-analyses [12, 28]. Our data (Table 3) showed trauma was the leading cause (34%), with a wide range (range, 12%-73%) in reports from different centers. This may reflect extension of the indications by some surgeons.
An overall 9.8% of ankle replacements required revision or conversion to ankle fusion at 5.2 years. The wide CI (CI range, 3.1%-16.5%) shows inconsistency in the presented data from individual studies, and should be interpreted with caution. A meta-analysis comparing TAA with ankle arthrodesis  that included studies published from 1990 to 2005 reported a TAA survival rate of 78% (95% CI, 69.0%-87.6%) at 5 years and 77% (95% CI, 63.3%-90.8%) at 10 years. The data in the current investigation are not directly comparable to those by Guyer and Richardson , as more recent publications have been included and different methods for data analysis were used in the two studies. Another meta-analysis , which reviewed 18 studies on mobile-bearing prostheses published from 1997 to 2002, found the weighted survival rate was 90.6% at 5 years. This is comparable to the survival rate of mobile-bearing implants in our study (Table 4). TAA survivorship data, however, should be interpreted with caution. Results from the prosthesis' inventors can be biased and may reflect the higher familiarity with the implant. Knecht et al.  included the surgeries performed by the designer of the Agility™ prosthesis, evaluated by independent authors, and reported a 95% survival rate at 6 years, whereas others achieved only 67% . Similarly, the designer of the STAR  reported a 95% survivorship rate at 10 years, whereas an independent high-volume surgeon  was reported to have a survivorship rate of 80% at 10 years. Others  reported a better survival rate in their latter 31 TAAs compared with the initial 20. The Swedish Joint Register , possibly representing more closely the average surgeon's outcomes, reported a 77% survival rate. Their data  showed the 5-year survival rate increased from 70% before to 86% after the surgeon had performed 30 TAAs. The designer of the Buechel-Pappas™ prosthesis reported a 92% survivorship rate at 12 years in 75 TAAs with the newer, deep sulcus implant. These results were reproduced by an independent surgeon , however, in patients with rheumatoid arthritis (low demand). Differences therefore may be symptomatic and reflect the surgeon's familiarity with the procedure, or selection of patients, rather than the effect of the intervention and the implant.
Comparing functional outcomes of different implants requires caution because of the different methodologies used, as described earlier. Haddad et al.  reported the mean AOFAS score was 78.2 points, which is comparable to the reported outcomes in our study (Table 6). Two studies [26, 32] suggested participation in certain sports is possible after TAA. It is not known, however, whether this is advisable and how it would affect failure rates in the long term.
The improvement in ankle ROM was relatively small (0°-14°) (Table 7). This is in agreement with the results of others [12, 28]. Our patients therefore should be informed preoperatively, improvement in ankle motion is not one of the expected benefits from TAA.
Furthermore, residual pain after TAA is relatively frequent (23%-60%) (Table 8), whereas the methodologic flaws in assessing patients' satisfaction in the individual studies raise concerns regarding the high satisfaction rates reported (Table 9).
Current TAAs improve ankle function; however, residual pain is common and wound complications can occur. The overall failure rate is approximately 10% at 5 years with a wide range from different centers.
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