The present study shows that the treatment of acute ATR with a percutaneous suture technique using the Dresden instrument delivers good clinical results combined with very low re-rupture and surgical complication rates. To our knowledge, the present study includes one of the largest ATR patient populations to be treated with the Dresden instrument [
16,
20‐
22]. The clinical scores were very good in the present study. Similar results were noted in the studies of ATR patients treated with the Dresden instrument reported by Amlang et al. and Keller et al. [
16,
20]. Additionally, two other studies have reported low complication rates and good functional results after treatment with the Dresden instrument [
21,
22]. Treatment with the Achillon
® device (Integra, Plainsboro, NJ, USA) also seemed to deliver similar results [
23,
24]. All of the evaluated scores were significantly correlated with patient satisfaction. Analyzing the specific scores for ATR enables further differentiation of the results. In the present population, 11 patients showed inferior Hannover scores, despite the fact that the AOFAS scores were very good in four of those patients and good in six more. This discrepancy in score outcomes reveals a specific issue with clinical studies of Achilles tendon ruptures: Achilles-tendon-specific problems, such as one-leg stand limitations, decreased jumping ability, and muscle atrophy are not taken into consideration in the commonly used AOFAS score, and seem to be better reflected in specific scores such as the ATRS and the Hannover score. Based on our findings, we would recommend the use of such Achilles-tendon-specific scores and not the general AOFAS score to evaluate outcomes after ATR. Indeed, the ATRS and the Hannover score were specifically developed for Achilles tendon ruptures [
18,
19]. Despite this fact, the ATRS and (especially) the Hannover score have not found consistent use in the literature for the long-term follow-up of patients who have undergone percutaneous suture with the Dresden instrument. This means that there are no comparable score data for this percutaneous suture technique. However, the ATRS and Hannover scores noted in our study were comparable to those seen in other studies of different minimally invasive techniques [
10,
25,
26]. Achilles tendon ruptures mainly occur in stop-and-go sports, and one of the major goals of treatment is a return to play at the pre-injury level. In comparable studies by Amlang et al. [
16] and Keller et al. [
20], the proportion of the patients who achieved a return to play at the same level after percutaneous suture with the Dresden instrument ranged from 51 to 80%. Those data were supported by our study, as 66% of the patients in our study achieved the same level in their sporting activity after rehabilitation. In a meta-analysis of 85 studies encompassing over 5500 patients, Zellers et al. noted that 18–100% of patients were able to achieve their pre-injury levels in their favored sporting activities after percutaneous suture with the Dresden instrument [
27]. This wide percentage range should, however, be interpreted with care, as there is neither a standardized definition nor an evaluation protocol for a return to play. Nevertheless, they show that while functional deficits do occur after ATR, some patients seem to overcome these deficits and achieve full rehabilitation. The factors that influence functional rehabilitation are presently unclear. Recent work suggests that functional deficits after ATR are caused by structural impairments of the muscle–tendon unit due to altered tendon properties [
28]. However, to unravel the mystery of functional deficits after ATR, more research must be done in the field of biomechanics to comprehend the process of tendon healing and the factors that influence it. In the present population, the re-rupture rate of the Achilles tendon was 2%, while no sural nerve lesions or infections were observed. Amlang et al. also reported a re-rupture rate of 3.2%, no lesions of the sural nerve, and only one late superficial wound infection after tendon healing [
29]. In the study of Keller et al., a re-rupture rate of 2% was reported, while no nerve lesion or wound infection was described [
20]. These data are comparable to the complication rate of a similar minimally invasive technique: the Achillon device. A meta-analysis of that technique which included 253 patients reported a re-rupture rate of 3.2% and an infection rate of 0.8% [
30]. Pooling these data, minimally invasive techniques such as the Dresden instrument or Achillon device seem to have surmounted the issue with the wound complication rate of open procedures in AT repair, as well as the problem of sural nerve lesions. A meta-analysis by Del Buono and coworkers underlines these findings [
15]. In their study, they presented an overall surgical complication rate (deep infection, wound necrosis, scar tissue adhesion) of 8% (30 of 375 patients) versus 0.25% for minimally invasive techniques (1 of 406 patients). Furthermore, the re-rupture rate after minimally invasive AT repair was 2.2%, as low as the re-rupture rate after an open approach (3.5%) [
15].
While low re-rupture rates and surgical complication rates are prerequisites for a reliable surgical technique, full motor function and a quick return to play at the pre-injury level are the predominant goals for recreational and professional athletes after ATR. However, it remains unclear which therapy—conservative or operative—is superior and the most suitable for the individual patient to achieve these goals. Although good clinical results have been reported for both operative and nonoperative treatments [
9,
15,
31,
32], long-lasting functional deficits are exhibited after ATR regardless of therapy, such as a reduction in plantar flexion strength, a reduced range of motion, or limited plantar flexion moment due to increased tendon stiffness [
10,
33‐
36]. One important aspect seems to be the resulting muscle atrophy, which eventually leads to a loss of strength and inferior functional results [
37‐
39]. A reduction in MCC was observed on the injured side in the present population in comparison to the healthy side. The importance of this finding is reflected in the correlation between MCC and inferior clinical scores in our study. The atrophy of the calf on the injured side seemed to persist even 33 months after the operation in the present study, and it is known that other tendons such as the supraspinatus muscle in the shoulder do not completely recover over time after rupture [
10,
40]. The observed difference in calf circumference was equally distributed across different age groups; no correlation with age was seen. This finding indicates that even younger patients with a potentially higher capacity for muscle growth are failing to achieve a full muscular recovery. However, differences in maximum calf circumference cannot necessarily be equated with muscle atrophy. MRI studies are needed to further differentiate between muscle atrophy and fatty degeneration. Patients with a pathologic Matles test presented larger differences in MCC between sides than those with restored AT length (according to the Matles test) did. However, this finding was not statistical significant.
Limitations
Care should be taken when interpreting the postoperative level of activity and the maximum calf circumference. Due to the retrospective nature of the study, a recall bias in the pre-injury activity level is inevitable, especially after a follow-up period of up to 7 years. There are several potential reasons why ATR patients perform recreational sports to a lower level after surgery. Moreover, assuming that the maximum calf circumference on the contralateral side is equivalent to that on the injured side at the time of AT rupture is a critical but commonly used method in retrospective studies. Prospective data collection would have avoided this aspect. Finally, force measurements and ultrasound to determine AT length were not included in our study. Including those methods would have led to more precise conclusions about the functional and structural impairment of the muscle–tendon unit.
The present study shows that percutaneous suture of an Achilles tendon rupture with the Dresden instrument is a safe and reliable method of treating this injury. Low complication and re-rupture rates, good clinical results, and a high rate of return to play support this fact. Muscle atrophy, measured as muscle circumference, and tendon lengthening resulted in an inferior functional outcome. Future studies on the exact roles of outcome-influencing parameters such as muscle atrophy, tendon properties, and the time point of the operation are needed to elucidate the reasons for functional impairment after this injury.