Introduction

Medical history and clinical examinations are considered to be sufficient in establishing the diagnosis of an acute Achilles tendon rupture [34, 42]. However, occasionally treatment is delayed due to late presentation or misdiagnosis [8, 42]. A delay of treatment leads to larger tendon-end diastasis with interposed scar tissue [9]. Achilles tendon ruptures that have had a delay in treatment by more than 4 weeks, are termed chronic and surgical intervention is required to recover lower leg function [1, 7, 14, 28, 30]. The traditional surgical intervention for chronic Achilles tendon ruptures involves considerably larger incisions than acute repairs leading to an increased risk of complications, such as infections and inadequate wound-healing [41].

Patients with chronic Achilles tendon ruptures report different symptoms compared with those of acute ruptures. Long-term pain and recurrent swelling are more frequent in patients with chronic ruptures [28]. In addition, altered gait with a weakness at push-off, a poor balance, and a reduced capability of performing heel-rises are commonly reported [17, 42].

The literature includes various surgical techniques for the management of chronic Achilles tendon ruptures: V–Y plasty, tendon transfers, gastrocnemius aponeurosis/fascia flaps, direct repair and synthetic grafts, [1, 8, 14, 27, 28, 30, 35, 47, 66, 68]. In recent years endoscopically assisted techniques have been advocated by the literature, including endoscopic transfers of the FHL-tendon [16], peroneus brevis tendon [39] and semitendinosus tendon [46] due to the lower risk of skin complications and wound infections. The choice of surgical procedure depends on the location of the rupture, the size of tendon-end diastasis, individual factors such as patient activity level and age, together with the preference and experience of the surgeon [51].

Even though many surgical techniques are described in the literature, no single technique has been shown to be superior to another. The aim of this systematic review was to analyse the current clinical evidence of two established techniques to treat chronic Achilles tendon ruptures: gastrocnemius aponeurosis flaps and semitendinosus tendon grafts as both FHL-grafts [2] and local tendon transfers [43] have been discussed in recent reviews. However, due to a high heterogenicity between the included studies, it was not deemed possible to do any statistical comparing between the two techniques.

Method and materials

Search query

The systematic search was performed on 2021–07-02, with an updated search a year later, on 2022–09-22, in three established databases: PubMed, Scopus and Cochrane Library using the search queries outlined in Table 1. The initial search query included all studies presenting the outcome of chronic Achilles tendon ruptures treated surgically. In the final stage, studies presenting outcomes of gastrocnemius aponeurosis flaps or semitendinosus tendon grafts were isolated and analysed. The inclusion criteria were all studies, descriptive and comparative, presenting results on the management of chronic Achilles tendon ruptures in adults (> 18 years) using gastrocnemius aponeurosis flap or semitendinosus tendon graft. Numerous studies also included patients surgically treated for a re-rupture using the same technique. The data on re-ruptures was excluded when presented separately. In those studies where it was not possible to separate the results, the study was still included if a majority of the included patients were treated for a chronic Achilles tendon rupture. Other exclusion criteria were (1) case-reports and case series with less than 10 patients, (2) reviews, (3) studies written in non-English languages and (4) expert opinions. The systematic review was registered in PROSPERO (CRD42022294130).

Table 1 Search query, Boolean operators and search results in the databases PubMed, Scopus, and Cochrane
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Study selection

The search was conducted by the authors and the initial search resulted in 1,340 studies, after removing duplicates, 818 studies remained. All studies were uploaded to the website Rayyan® for abstract review. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) was used to structure the filtering of studies [54]. Two authors (NN and IS) independently reviewed the abstracts of the included studies. Disagreement between the authors were settled through discussion. A total of 182 studies remained after the initial abstract review. These were all later successfully imported as full-text versions. For the full-text review, the studies were divided equally between the six authors and checked by a minimum of two authors.

After the full-text filtering, 86 studies remained. Out of these, 36 individual studies used gastrocnemius aponeurosis flaps or semitendinosus tendon grafts to treat chronic Achilles tendon ruptures and were included in the review. The inclusion and exclusion process are illustrated in Fig. 1.

Fig. 1
figure 1

PRISMA-flowchart for the inclusion of studies, The PRISMA 2020 statement [54]

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Quality assessment

To assess the methodological quality and risk of bias for the included studies the validated Methodological Index for Non-Randomized Studies (MINORS). MINORS is a quality assessment tool for systematic reviews first described by Slim et. al [62]. It is widely used and has a strong external validity. The studies included in this systematic review were all non-randomized and non-comparative studies. MINORS consists of twelve questions, where the last four questions are additional criteria in case of comparative studies. Each question can be scored from 0–2. A score of 0 meaning it is not reported in the study, a score of 1 meaning it is reported but inadequate, and a score of 2 meaning it is reported and adequate [62].

Result extraction

Three reviewers extracted the data using a structured extraction protocol. The extracted data was surgical technique, number of patients, mean age, duration of follow-up, outcome measures, presented results. The results analysed were patient-reported outcomes, functional outcome measures and complication rates. Any disagreement was settled through discussion. Moreover, if any author were among the authors of the original study analysed, they did not perform any result extraction or quality assessment of that study.

Results

Study selection

All the included studies were case series (Level IV) that either used a gastrocnemius aponeurosis flap or semitendinosus tendon graft to treat chronic Achilles tendon ruptures. A semitendinosus tendon graft was used in 13 studies and a gastrocnemius aponeurosis flap in 21 studies. There were two studies that used both surgical techniques. In the study by Bai et al. [4] 11 patients were treated with a gastrocnemius aponeurosis flap and 15 were treated with a semitendinosus tendon graft. The study by Gedam et al. [15] used both augmentation techniques in all patients and was therefore not part of the analysis. The extracted data from the studies is presented in Table 3. The grand total number of patients included were 763. The study by Bąkowski et al. [5] included eight additional cadavers which were excluded from this systematic review.

Quality assessment

The included studies MINORS-scores are shown in Table 2. The maximum points are 16 for non-randomized studies. The included studies generally had low quality according to MINORS, with a median of 8 out of 16 (range 2–13) for all studies.

Table 2 The points of each study according to the MINORS-score. The maximum score is 16
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Result extraction

A summary of the results of each individual study is shown in Table 3. The patients treated with gastrocnemius aponeurosis flap had a mean age of 44.5 years and were followed-up for a mean time period of 40 months. The patients treated with semitendinosus tendon grafts had a mean age and follow-up time of 44 years and 28 months, respectively. The outcome measures used in the studies were patient-reported outcome measures (ATRS [48], VAS [21], VISA-A [58], FADI [61], Tegner scale [63], and SF-36 [26]) mixed scores (AOFAS [64], Leppilahti [29, 64], Hooker [52], Arner-Lindholm [3], Rupp-score [24] and Holz-scale [12]) and clinical tests (calf circumference [64], range of motion (ROM), muscle strength/isokinetic testing/heel-rise tests, ultrasonography and Manual Muscle Testing (MMT) [10]). The most used outcome measure was AOFAS with a total of 19 unique studies. Some outcome measures were only used once: including the Holz scale, Tegner scale, FADI, Hooker, MMT, Arner-Lindholm, Rupp-score and SF-36.

Table 3 The included studies, number of patients, age, follow-up time, outcome measures, results and complications
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The mean (SD; n) postoperative ATRS was 83 (14; 6 studies) and the mean (SD; n) AOFAS was 96 (1.7; 12 studies) for patients treated with a gastrocnemius aponeurosis flap. In comparison, the mean (SD; n) ATRS and AOFAS for semitendinosus tendon grafts were similar with scores of ATRS 88 (6.9; 7 studies) and AOFAS 92 (5.6; 9 studies). However, patients treated with semitendinosus tendon grafts had lower mean (SD; n) preoperative values with ATRS 38 (11.3; 6 studies) vs. 50 (11.1; 3 studies) and AOFAS 51 (13.3; 7 studies) vs. 62 (9.0; 10 studies).

A comparison of the complications between gastrocnemius aponeurosis flaps and semitendinosus tendon grafts can be found in Table 4. The most common complication found was superficial wound infection with a total of 27 patients (3.4%), 22 (4.6%) of which were treated with gastrocnemius aponeurosis flaps and 5 (1.5%) with semitendinosus tendon grafts. In general, patients treated with gastrocnemius aponeurosis flap had more complications than patients treated with semitendinosus tendon grafts, mainly due to wound healing problems. However, patients treated with semitendinosus graft were more prone to sural nerve injury due to a smaller surgical incision. Only one re-rupture occurred in the total group of 763 patients. That patient was treated with a gastrocnemius flap.

Table 4 Overview of the complications for semitendinosus tendon grafts (ST-grafts) and gastrocnemius flaps (G-flaps)
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Discussion

The most important finding of this systematic review was that both gastrocnemius aponeurosis flap and semitendinosus graft reconstructions were found to be effective in treating chronic Achilles tendon ruptures with similar favourable patient-reported outcome scores and performances in functional tests. Only one re-rupture was reported (0.12%) in the patient group treated with a gastrocnemius aponeurosis flap and no patient in the group treated with a semitendinosus graft. However, studies of higher quality are needed to fully determine the optimal way of treating chronic Achilles tendon ruptures. All the included studies were case series without matched control groups. Additionally, the articles used a variety of different outcome measures, which limited the comparisons between studies. Lastly, even though the gastrocnemius aponeurosis flaps, and semitendinosus tendon grafts are presented as distinctive groups, both groups were heterogenic with different interpretations of the techniques.

In prior systematic reviews by Apinun et al. [2] and Hadi et al. [20], similar results have been shown with good functional patient-reported outcomes, and low re-rupture rates. The review performed by Hadi et al. identified 35 individual studies in 2013 whereas this systematic review identified a total of 86 individual publications on the same subject in 2022. The heterogenicity of outcome measures and surgical techniques, and the retrospective nature of limited cohort sizes remain. This meant that quantitative meta-analysis was deemed inappropriate. Studies including fewer than 10 patients were excluded from this systematic review. Most of these studies were case reports with one to two patients using no outcomes measures. Therefore, the exclusion of case reports did not result in any substantial data loss.

The result of the included studies indicate that patients treated with a gastrocnemius flap are more prone to complications than patients treated with semitendinosus tendon graft. Due to the heterogenicity, no significant difference could be determined, however. Depending on the surgical technique a different pattern of complications occurred. Semitendinosus tendon grafts uses an autologous transplantation with risk of complications related to the hamstring donor site or sural nerve injury due to the location and the smaller size of the surgical incisions. Gastrocnemius flaps uses a turn-down flap or a free-flap from the aponeurosis with larger surgical wounds leading to an increased risk of infections and wound healing problems [42].

The MINORS assessment generally resulted in a low-quality with scores with a median of 8 out of 16. Moreover, the studies included in this review frequently used AOFAS as their main patient-reported outcome. It is known that this outcome measure is not validated for Achilles tendon ruptures. Instead, a patient-reported outcome such as ATRS could be used. This patient-reported outcome measure is also not validated for chronic Achilles tendon ruptures, but it is validated for acute Achilles tendon ruptures. In the future, research of chronic Achilles tendon ruptures would benefit from a patient-reported outcome measure that is validated for chronic ruptures, as that would allow for a clearer comparison between operating methods and outcome.

The exclusions based on the number of patients and the language of the studies might have affected the results of this review. This review excluded all non-English studies and all studies with less than 10 patients. The exclusion criteria removed 108 studies due to language and 47 studies due to a small cohort size. The exclusion of studies in non-English language facilitated data extraction by avoiding outcome heterogeneity between studies, thus improving quality. The number of articles excluded based on sample size were large in number but were usually singular case reports without any outcome measures. Similarly, varying outcomes measures may have made comparisons between studies even harder.

Following this systematic review, the authors recommendation is to individualise the treatment of chronic Achilles tendon ruptures depending on factors such as functional demands, comorbidities, tendon gap size, and the general experience of the orthopaedic surgeon treating the patient. The use of a gastrocnemius aponeurosis flap in tendon ruptures with a gap that is less than 5 cm is regarded as efficient [12, 47]. In tendon ruptures with larger defects (> 5 cm) a semitendinosus tendon graft will bridge the defect [37, 60]. Other alternatives include flexor hallucis longus graft [53, 56] and peroneus tendon graft [40].

Conclusion

In conclusion, surgical reconstruction with both semitendinosus tendon grafts, and gastrocnemius aponeurosis flaps are considered effective in treating chronic Achilles tendon ruptures with good patient-reported outcomes and few re-ruptures. The complication profiles are different between the two techniques with more postoperative infections and wound healing complications in patients treated with a gastrocnemius aponeurosis flap and more sural nerve injuries and donor site weakness in patients treated with a semitendinosus graft. There is a continued need for more prospective randomized controlled trials and a need for an established outcome measure for chronic Achilles tendon ruptures to fully evaluate the effectiveness of different reconstructive techniques in the treatment of chronic Achilles tendon ruptures.