Alignment of CCI total ankle replacements in relation to midterm functional outcome and complication incidence

End-stage arthritis of the ankle joint can substantially disrupt the Quality of Life (QoL) of a patient through functional limitations [1, 2]. Total ankle arthroplasty (TAA) and ankle arthrodesis (AA) are the two primary surgical treatment options for patients who fail conservative measures. Development of the total ankle arthroplasty is challenging because of the small contact area and high forces which can lead to high contact stresses [3‐5].

Ever since TAA surgeries have been undertaken for osteoarthritis, patient satisfaction, pain relief and function have changed for the better [6], however, potential risks of only small improvement of range of motion, persistent pain, and low functional outcome following TAA still remain high [7‐9]. TAA may be more susceptible to complications, failure and subsequent re-operation as compared to other surgical interventions of the ankle, especially compared to ankle arthrodesis [10]. For example, a study conducted by Spirt et al. [11] observed that 28% of the patients that underwent ankle arthroplasty were re-operated due to complications with a follow-up time of 5 years. Watts et al. [12] documented in their systematic review a 2.5 times higher re-operation rate in TAA compared to ankle arthrodesis. Nonetheless, the perioperative major complications in ankle arthrodesis occurred 1.8 times more often but had a 29% lower risk of a minor complication after adjusting for patient and hospital factors, such as gender, age, and health-status [13]. These findings are confirmed by the higher 30-day re-admission rate for ankle arthrodesis, which has an independent risk factor with an odds ratio of 2.51 [14].

Salvage arthrodesis after failed ankle arthroplasty has an overall complication rate of 18.2% whereas the overall non-union rate was 10.6%, and it has also inferior results to primary arthrodesis [15, 16]. Therefore, minimal bone resection is necessary in the surgical procedure of TAA to enhance the union rate [17].

Until January 2023 there were no non-designer studies presenting short-term clinical results of exclusively the CCI ankle prosthesis. The group of Doets et al. reported two designer studies. First report presented both the Buechel-Pappas and the CCI ankle prosthesis showing a survival of 87% in the post fracture group and 79% in the instability group at 6 years of follow-up [18]. The other designer study reported a survival rate of 67.5% at 10-year follow-up, with a complication rate of 54% and 37% patients underwent reoperation [19].

This is the first non-designer study to report the mid-term clinical results of the Ceramic Coated Implant (CCI) ankle replacements. The aim of this study was to report the first clinical results and survival of 65 consecutive CCI ankle replacements with a median follow-up time of 85.2 months. Secondly, to report the complication and failure rate.

Thirdly, to ascertain if associations could be observed between implant migration during follow-up, as measured according to the Rippstein protocol [20], and subsequent failure of the implant.

Sixty-five consecutive CCI total ankle replacements were placed between June 2010 and June 2016 and included in this prospective follow-up study. In January 2021, the last clinical follow-up was performed. The study was approved by the local ethical committee of Maastricht University (METC 2018-0709), and all patients provided written informed consent prior to participation in the study. All TAA’s surgeries were performed by a non-designer single surgeon (JH) in Maastricht University Medical Centre (MUMC +), using the CCI ankle replacement (Wright Medical Technology, Arlington, TN, USA). The importance of single surgeon studies may allow better comparison, because of consistent diagnosis and different experience levels of surgeons.

The following standard surgical protocol and standardized post-op rehabilitation was followed. Postoperative patients had an aftertreatment with a cast for 2-3 weeks, 50%weightbearing till 6 weeks and from 10 weeks onward, the patients were allowed to advance to full weightbearing. Achilles’ tendon lengthening was performed when perioperative an ankle dorsalflexion of 10 degrees couldn’t be reached. Additionally, these patients received a cast as aftertreatment for 6 weeks. Afterwards these patients followed standard aftertreatment protocol. Thromboembolic prophylaxis with low-molecular-weight heparin was given until 6 weeks postoperative. Patients were assessed pre-op and postoperatively at 1 day, 6 weeks, 3-6-12 months and thereafter yearly. The American Orthopedic Foot and Ankle Score (AOFAS) questionnaire and passive range of motion (ROM) were assessed. During every follow-up moment all complications and re-operations were recorded, Radiographic evaluation was performed at follow-up moments of 6 weeks, 3-6-12 months and thereafter yearly according to the Rippstein protocol [20]. Failure of the implant was defined as the need of revision surgery of one of the metal components or (pan)arthrodesis, according Henricson et al. [21]. They define the term revision as removal or exchange of one or more of the prosthetic components except for incidental exchange of the polyethylene insert (e.g., due to infection).

Radiographic Evaluation assessment consisted of the estimation of prosthesis alignment, migration, translation, and radiolucent lines using the Rippstein protocol (Fig. 1) [20]. These assessments were evaluated by two independent reviewers (JV, PV) who did not perform an operation on any of the patients.

Standing anteroposterior (AP) and lateral (LAT) radiographs of the ankle were made preoperatively and at each follow-up visit. Ankle alignment was determined on the anteroposterior radiograph by measuring the angle between the talar and the tibial component. An angle of 0° is considered ideal, and > 5° was defined as varus or valgus ankle alignment compared to the tibial anatomical axis. The posterior slope of the tibial component was measured on the lateral radiograph. The components were considered to be improperly aligned on the anteroposterior radiograph if the medial or the lateral border of the talar component extended more than 2 mm beyond the border of the tibial component.

Tibial radiolucencies > 1 mm in width were assessed in five zones around the implant on the anteroposterior radiograph and in five zones on the lateral radiograph. Talar radiolucencies were assessed in three zones around the implant on the lateral radiograph. Migration of the tibial component was defined 121 as a change of an angle of > 3°. Migration of the talar component was defined as > 2 mm of subsidence into the talar bone. In addition, we recorded the presence and location of periprosthetic cysts and osteophytes [20].

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 from 21.8 preoperative 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. [24] showed that these changes in gait were accompanied by a significant improvement in AOFAS, SF-36 and ROM [24]. The results of the CCI Evolution Total Ankle System, presented in this study, can be compared to the designer study of Doets [17]. In this study, the 5-year follow-up 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 [18]. Recently the group of Doets reported even a lower survival rate of 67.5% at 10-year follow-up [19].

In this non-designer 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) [25] 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 [26]. Simonson et al. [27] showed that 44,2% of 2453 total ankle replacements had a complication. These complications could lead to failure. Usuelli et al. [28] showed that most of the operative variables as well as clinical and radiological outcomes stabilized after a surgeon had performed 28 cases. 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. [29] showed that mean time from primary TAR to revision surgery was about two years.

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 15 postoperative complications in the remaining 57 ankles (26.3%). 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 271 (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 [18]. The 10-year follow-up study of the same group 45% of the total ankle replacements had developed a complication of which only 16% was treated conservatively [19]. Causes for impingement could be component malrotation that will always lead to gutter impingement [30, 31]. Nunley et al. [32] 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.

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 [20], and subsequent failure of the implant. 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, 33‐37]. Pyevich et al. [38] 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. We could not find a significant correlation between failure and varus /valgus malpositioning or a gap between the bone and prosthesis.

In the prospective cohort study of Dalat et al. [39] 29.8% had symptomatic cysts which required treatment at a mean 59.8 months. Of which 16.7% of their patients were treated by curettage and grafting, 13.9% ended up in an arthrodesis. Najefi et al. [40] reports that in 78% of the patient’s 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. We reported that 40% of our 65 ankle replacements in our cohort had cyst formation while only two failures showed cyst formation.

This study has a number of limitations that have to be considered. First, this study includes a relatively small number of patients. Making generalizations from a small sample size is a cognitive bias. Second, the AOFAS score combines a clinician-reported and patient-reported parts. Forty of the possible 100 points are determined by clinical examination and, therefore, the evaluator can be biased when grading the clinical results [41]. 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. Finally, this study reports on the CCI TAR, a prosthesis that was withdrawn from the market in 2016 by Wright Medical Group (Memphis, USA). However, mid-term outcomes of this 3-component prosthesis remains relevant and will contribute to the limited literature available.

The mid-term results of the CCI Evolution Total Ankle System cohort are comparable to literature of other TAA designs with a survival of 87.7% at 7.1 years of follow-up [18, 25].

Functional recovery is two-fold with most progression in ROM seen in the first 10 months, while the mean AOFAS gradually increased during follow-up postoperative.

Additional studies with larger cohorts and longer follow-up are warranted to determine which patient specific factors, surgical technique and designs are a higher risk for failure to improve the patient satisfaction, clinical outcome and survival rate of ankle replacement.