*2.5. Assessment Methods*

Demographic data, including age, body mass index (BMI), pre-existing conditions (such as those associated with syndrome-x), and nicotine abuse, were obtained for each patient. The Olerud & Molander Ankle Score (OMAS), Foot Function Index in its validated German version (FFI-D), the Short Form-12 Questionnaire (SF-12), and the type and number of revisions were recorded as part of the follow-up (Table 1).

## *2.6. Statistical Analysis*

The primary goal was to compare significant differences in the outcome of TTCA and TTA using a representative number of patients to illustrate the power of the included data with a mean follow-up time of 6.2 years. Due to the retrospective design, there is no case number calculation. So far, monocentric studies with comparable questions have presented significantly smaller populations [7,8]. All statistical analyses were performed using SPSS v. 23 software (IBM Dtl. GmbH, Ehningen, Germany). Furthermore, descriptive and explorative statistical analyses for the queried scores, including within-group means, medians, minima and maxima, and standard deviations, were applied. Student's *t*-test and ANOVA were used. The power of the study was 0.8, and the significance level was set to *p* < 0.05, with a 95% confidence interval.

#### **3. Results**

After an average postoperative follow-up of 74 months (range: 12–154 months), the mean OMAS and FFI-D scores were 50.7 (TTCA: 43.0; TTA: 58.2) and 68.9 points, respectively. The difference was significant, as was the physical component summary of the SF-12 (mean: 39.1; TTCA: 33.5; TTA: 42.5), (*p* < 0.001).

The ability of the patient to return to their job also differed significantly: in the TTCA group, around 15% returned successfully; in the TTA group, 26% (*p* < 0.001). Only the mental component summary of the SF-12 showed no significant difference, with a mean value of 50.6 for all patients (*p* = 0.369). In a free survey, one-third of patients reported that their gait was as expected after the arthrodesis, one-third reported that it was worse, and one-third managed better than expected before surgery. The distribution applied equally to both groups.

#### *Complications*

The overall revision rate was approximately 19%, with a significantly higher proportion in the TTCA group (all *n* = 80; TTCA: *n* = 64 (29.6%), TTA: *n* = 16 (7.41%); *p* < 0.001). Most revisions had to be performed due to non-union and infections. In addition, minor complications, such as delayed wound healing, swelling, discomfort, and cramps, were recorded (Table 2).


**Table 2.** Clinical outcome with subgroups.

SEM, standard error of the mean; MT, metatarsal; SF-12, 12-Item Short Form Health Survey; TTCA, Tibiotalocalcaneal Arthrodesis; TTA, Tibiotalar Arthrodesis.

#### **4. Discussion**

TTCA and TTA for the treatment of end-stage posttraumatic osteoarthritis of the ankle yielded significant differences in our validated scores. If an additional subtalar arthrodesis is necessary, in addition to the pure tibiotalar arthrodesis, this represents a massive impairment of quality of life. These patients will elicit significantly poorer results compared to those undergoing isolated tibiotalar arthrodesis.

The aim of TTCA and TTA is the relief of pain caused by end-stage posttraumatic arthrosis, as well as to straighten possible malpositions and establish stability. Both methods are established in this regard. However, there is still no clear guideline as to which patients benefit from subtalar arthrodesis in the context of ankle fusion. Direct comparisons, especially in studies with a population with only terminal posttraumatic osteoarthritis of the ankle that is comparable in terms of risk profile and demographic data, only show the results of a small number of cases [7]. The results of TTCA and TTA vary from good for bone consolidation, reduced postoperative complications, and improvement of pain and quality of life, to the suggestion that additionally fusing the subtalar joint does not cause greater movement restriction [8–10]. Both these statements are difficult to understand on the basis of our data. Rather, we have confirmed that the subtalar joint plays a decisive

role in mobility, especially in the case of an already fused tibiotalar joint. The additional requirement of a fusion of the subtalar joint leads to a considerable restriction of mobility with a corresponding reduction in quality of life. Regardless of this assessment, the results of the quality of life scores for TTCA and TTA reflect the respective results of the current literature without significant deviations [11–13].

Since no relevant differences could be determined from the subgroup analysis of the respective arthrodesis procedures in the TTA group, a separate presentation of the results was not carried out. This is in accordance with Prissel et al., who also showed no significant difference in clinical and radiological outcomes with similar complication rates after ankle arthrodesis using anterior locking plate fixation or converging screws [14]. Thus, the present data confirm the biomechanical and clinical studies that put the importance of the screw diameter and number into perspective [15]. In our procedures, two, three, or even four converging cannulated screws were inserted in the TTA group. An additional arthrodesis of the distal tibiofibular joint as part of the TTCA or TTA also showed no influence on the results and was carried out in about half of all cases. The clinical impression that simultaneous arthrodesis of the distal tibiofibular joint has no influence on the fusion rate of the tibiotalar joint and the further outcome was confirmed by Schlickewei et al. [16].

The interposition of cancellous bone also showed no influence on the data presented [17,18]. As a rule, there is no need for autologous cancellous bone grafting in the context of ankle arthrodesis, as confirmed by systematic reviews. As in the present case, the underlying studies lack a prospective comparison and, in the case of autologous cancellous bone grafting, an objectifiable representation of the previous bony defect size [18].

We also found that the mental component summary of SF-12 was the only parameter that did not show a significant difference (*p* = 0.369). An obvious explanation for this may be that patients in whom an additional fusion of the subtalar joint was necessary were assumed to have an even worse function. In addition, these patients presumably come from a worse initial function, but this cannot be evaluated on the basis of the available data. Either way, the results of the mental component summary of SF-12 of the present study deviate from those of the current literature in patients after TTCA, TTA, and even after total ankle replacement [10,19–21].

Even though the stated complication rates of 19% for TTCA and TTC remain high, these results differ considerably from those in the literature of up to a frightening 50% [22– 24]. The complication rate for TTCA is approximately four times higher than that for TTA (30% vs. 7%, respectively). TTCA should, therefore, be considered with appropriate restraint. One conceivable explanation would be the higher proportion of smokers in the TTCA group. In addition, the procedure immanent greater soft tissue damage.

This study had some limitations. First, this was a monocentric study with a retrospective design and clinical scores and the extent of posttraumatic damage to the tibiotalar and subtalar joints was not collected preoperatively. This makes it particularly difficult to assess the choice of implant and the need for cancellous bone grafting. Second, the indication for TTCA and TTA was presumably influenced by surgeon experience.
