In this study, we report the first mid-term clinical outcome results of the Ceramic Coated Implant (CCI) ankle replacements after a median follow-up time of 85.2 months. The functional outcome Range of Motion improved after ankle replacement preoperative from 21.8 to 27.6 degrees postoperative. The AOFAS hindfoot score improved significantly from a mean of 40.9 points preoperative to an average of 82.5 over the entire follow up period of 7.1 years. Valderrabano et al. showed that these changes in gait were accompanied by a significant improvement in AOFAS, SF-36 and ROM [22]. The results of the CCI Evolution Total Ankle System, presented in our study, can be compared to the designer study of Doets [17]. In this study, the results of 75 CCI ankle prosthesis and 15 Buechel-Pappas ankle prostheses showed a survival rate of 87% in the postfracture group and 79% in the instability group. In our study the reported Kaplan-Meier survival analysis of the CCI ankle implant at mid-term follow-up showed a survival rate of 87.7% with a median follow-up of 85.2 months. 1,226 prostheses were analyzed in the Swedish Ankle Registry with a mean follow-up of 7 years. An overall survival rate at 5 years was found of 0.85 (95% CI 0.83-0.87), at 10 years 0.74 (CI 0.70-0.77) [23] which is comparable with our presented results.
TAA is an emerging treatment and might be an alternative to ankle arthrodesis in the treatment of end-stage ankle arthroplasty. However, there are also disadvantages to this intervention. TAA may be more sensitive to complications, failure and subsequent re-operations compared to ankle arthrodesis [24]. Simonson et al. showed that 44,2% of 2453 total ankle replacements had a complication [25]. These complications could lead to failure. Usuelli et al. showed that most of the operative variables as well as clinical and radiological outcomes stabilized after a surgeon had performed 28 cases [26]. We have reported all our perioperative complications in our first thirty ankle replacements. The median time to failure was 12.2 months of follow-up (IQR 6.1, 14.9). Kamrad et al. showed that mean time from primary TAR to revision surgery was about two years [27].
Intra-operative complications occurred in 10 ankles (15.4%) and one or more post- operative complications in 23 ankles (35.4%). Excluding the failures, there were 11 postoperative complications in 65 ankles (16.9%). The most postoperative complications were impingement and deep infection. In the 8 impingements a gradual postoperative coronal translation of the talus was seen 7 cases with a mean translation of 3.8 mm. In the group of impingements, the median was (IQR): 3.0 (2.2-5.0) compared to the group without impingement (IQR): 2.2 (0.0 – 3.4). Similar complication and reoperation rates were found in the designer study which presented results of the Buechel-Pappas and CCI prosthesis [17]. Causes for impingement could be component malrotation that will always lead to gutter impingement [28,29]. Nunley et al. noticed that the reoperation rate was higher in mobile-bearing total ankle replacements compared to fixed bearing total ankle replacements, and in most cases to relieve impingement [30].
In this study, it was also assessed if associations could be observed between implant migration during follow-up, as measured according to the Rippstein protocol, and subsequent failure of the implant [19]. According to the Rippstein protocol analysis, progressive radiolucency was seen in 8 ankle replacements (12.5%). The radiolucency zone 3, for the CCI ankle replacement, was associated with a higher risk for failure; HR 6.4 (95% BI:1.4, 29.0; p=0.0152). Therefore, we advocate to specify these values for TAA patients on X-ray evaluation during clinical follow-up.
The association between total ankle component alignment and biomechanical contact stresses and clinical outcome has been extensively studied [6,8-11,31-35]. Pyevich et al. found higher rates of pain in tibial components placed in more than 4 ° of valgus and 19 cases of migration of a component of TAA [36]. We could not find a significant correlation between failure and varus /valgus malpositioning or a gap between the bone and prosthesis.
In some studies, the rate of radiolucent lines and cysts reaches 75%, with large cysts compromising implant stability at a mean 59.8 months [37,38]. Najefi et al reports that in 78% of the patients bone cysts were not removed by implant resection, of which 30% of the cases were larger than 5 mm. The description of osteolysis as the first “mechanical” type of radiolucency is probably incorrect, as this most likely refers to the presence of pre-existing cysts that had not been observed, or progression of pre-existing cysts due to stress shielding [38]. We reported that 40% of our 65 ankle replacements in our cohort had cyst formation while only two failures showed cyst formation.
Our study has a number of limitations that have to be considered. First, it was a relatively small number of patients. Second, the AOFAS score combines a clinician-reported and patient-reported part. Third, the learning curve of the CCI Evolution Total Ankle System was part of this prospective follow-up, as we have reported all our perioperative complications in our first thirty ankle replacements.