Introduction

Midportion Achilles tendinopathy is a painful condition of the Achilles tendon located 2–7 cm proximal to the insertion on the calcaneus. Symptoms include pain, swelling and impaired performance. It is an over-use injury, often seen in athletes. The incidence varies from 0.2 % in the general population up to 9 % in recreational runners [12, 17].

Initially, treatment of midportion tendinopathy is nonsurgical. Various noninvasive treatment options have been described, including eccentric exercise, the use of orthoses and rest. Additionally, invasive nonsurgical techniques like extracorporeal shockwave therapy and platelet-rich plasma (PRP) injection are commonly used [39]. In approximately 25 % of the patients nonsurgical treatment fails to alleviate symptoms and surgical treatment is indicated [14].

Historically, surgical treatment was performed using an open procedure [13, 26, 32]. With new insights into the aetiology of tendinopathy, new surgical procedures were developed, resulting in a large variety of surgical techniques [19, 34]. Because of the high complication rates in open procedures, less invasive techniques gained popularity [16, 24, 29, 37].

Due to the variety of surgical techniques and the confusing terminology used to describe pathologies of the Achilles tendon, no study to date has provided a clear overview of the literature regarding the best surgical treatment for midportion Achilles tendinopathy. The aim of this study is to systematically evaluate the available literature on surgical treatment for midportion Achilles tendinopathy and to provide an overview of the different surgical techniques in terms of patient satisfaction and complication rate.

Materials and methods

Search strategy

A systematic review of the literature was performed. In collaboration with a clinical librarian, the databases of MEDLINE, EMBASE and the Cochrane database for controlled trials were searched (Fig. 1).

Fig. 1
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Search strategy

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Inclusion criteria

Studies reporting on the results of surgical treatment for midportion Achilles tendinopathy in humans were included. In this study, the definition of midportion Achilles tendinopathy as described by van Dijk et al. [8] is used. Midportion Achilles tendinopathy is defined as symptoms of pain, swelling and impaired performance in combination with a histopathological diagnosis that includes, but is not limited to, the diagnosis of tendinosis 2–7 cm from the calcaneal insertion. Studies were eligible if they assessed the outcome measures of patient satisfaction or complication rate. Reviews and studies reporting on less than ten patients were excluded. Only studies written in English, French or German were considered eligible. Studies lacking clear distinction between midportion and insertional Achilles tendinopathy were excluded. Two authors (TB & RZ) performed title and abstract screening independently. Subsequently, these two authors individually performed full text selection. Disagreement during study selection was settled by discussion.

Data extraction

Data on patient characteristics, surgical technique and outcome were extracted. Patient satisfaction was the primary outcome measure. Secondary outcome measures consisted of complication rate, functional outcome scores, pain scores and success rate. Complications were divided in minor and major (Table 1). Successful treatment was defined as an excellent or good outcome, or when patients were satisfied with the result.

Table 1 Classification of complications
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Methodological quality

Methodological quality of included studies was assessed using the Downs & Black checklist and the Coleman methodology scale [7, 9]. The Downs & Black checklist was designed to evaluate the methodological quality of randomised and nonrandomised studies. It consists of a 27-item checklist with a highest possible score of 33 points. The Coleman methodology scale was designed to evaluate the methodological quality of studies on Achilles tendinopathies. The checklist consists of two parts and has a maximum possible score of 100 points. Two authors (TB & JW) assessed the included studies independently on methodological quality. Correlations between success rate and both the Coleman scale and Downs & Black checklist were calculated.

Data presentation and statistical analysis

Due to the heterogeneity of the data, results were not pooled. Outcome data were presented per study. Ranges of outcome were reported per type of surgical procedure. To calculate the correlations of nonparametric data, the Spearman’s rho correlation coefficient was used. Correlation with a p value <0.05 was considered significant.

Results

After removal of duplicates, the search yielded 1090 articles. Based on title and abstract screening, 1026 articles were excluded (Fig. 1). The remaining 64 articles were eligible for full text evaluation. Forty-two articles were excluded after full text selection. Finally, after screening references of included articles and the related literature, one article was added [6]. A total of 23 studies were included in this study (Table 2; Appendix 1 in Table 5) [1–4, 6, 10, 11, 13, 15, 18, 20–24, 26–31, 33, 36].

Table 2 Overview of included studies
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Population characteristics

The studies reported on a total of 1177 patients with 1285 affected tendons. 62.7 % of the patients was male. Seven studies did not report on gender distribution [11, 13, 26, 29, 30, 33, 36]. The weighted mean age was 40.2 years. The remaining seven studies did not adequately report on age [1, 10, 21, 26, 29, 33, 36].

Surgical techniques

In this review, the techniques were roughly grouped into five types of procedures. Eleven studies reported open techniques as treatment of midportion Achilles tendinopathy [4, 11, 13, 15, 18, 21, 26–29, 31]. Seven studies evaluated minimally invasive procedures [1–3, 6, 20, 24, 36]. Three studies reported on endoscopic techniques [22, 30, 33], one study evaluated gastrocnemius lengthening by an open procedure [10], and one reported on a technique for open resection of the distal Achilles tendon, followed by interposition of FHL graft [23]. Techniques were classified as minimally invasive based on descriptions in the studies. In six of the included studies reporting minimally invasive techniques, incisions were smaller than 2 cm (Appendix 2 in Table 6).

Open surgery

Eleven studies described the outcome of an open surgical approach [4, 11, 13, 15, 18, 21, 26–29, 31]. There is a large variation in techniques; however, each technique consisted of the release of the tendon (adhesiolysis, release or excision of the paratenon), debridement of degenerative tissue, longitudinal tenotomies or a combination of these (Table 2; Appendix 2 in Table 6). Four studies compared the results of release of the tendon with or without tenotomies, with a group of patients that additionally underwent debridement of degenerative tissue [11, 15, 28, 29]. One compared the results between a group of patients that underwent debridement without suturing or augmentation with a group in which the tendon was augmented using fibres of the soleus muscle [4]. In another study, three groups were distinguished: no debridement of the tendon was performed in group A. Group B and C consisted of patients with tendinosis and extensive tendinosis. Both groups were treated by excision of degenerations, followed by side-to-side suture for patients in group B or reconstruction with a turndown flap in group C [26].

None of the studies reported on patient satisfaction (Table 3). Complication rates were adequately reported in eight studies and ranged from 0 up to 85.7 % (Table 3) [4, 11, 13, 18, 21, 27, 29, 31]. Success rates varied from 73.1 up to 100 % (Table 4) [13, 15, 26–28, 31].

Table 3 Patient satisfaction and complication rate
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Table 4 Success rate
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Minimally invasive tendon stripping/tenotomies

Minimally invasive procedures were described in seven included studies [1–3, 6, 20, 24, 36]. Five articles described a technique to perform a release of the Achilles tendon [1–3, 6, 24] with additional excision of the plantaris tendon in one study [6]. The other two minimally invasive techniques described aimed to perform percutaneous longitudinal tenotomies with additional release of adhesions by infiltration performed in one study (Table 2, Appendix 2 in Table 6) [20, 36].

Patient satisfaction was reported in five studies and ranged from 69 up to 100 % (Table 3). [1–3, 6, 24]. Complications rates were adequately reported in four studies, ranging from 2.9 up to 30.6 % (Table 3) [2, 6, 24, 36]. Success rates varied from 69 up to 100 % (Table 4) [1–3, 6, 20, 24, 36].

Endoscopic procedures

Three studies reported on the outcome of endoscopic procedures [22, 30, 33]. In all procedures, debridement of the paratenon was performed, with additional release of the plantaris tendon in two studies [30, 33] and additional longitudinal tenotomies in one study [22] (Table 2, Appendix 2 in Table 6).

Only one study reported on patient satisfaction; in this study 73 % of patients was satisfied (Table 3) [30]. Complications rates varied from 0 to 7.4 % (Table 3) [22, 30, 33]. Success rates varied from 73 up to 100 % (Table 4) [22, 30].

Open surgery: gastrocnemius lengthening

One study evaluated gastrocnemius lengthening through an open procedure (Table 2, Appendix 2 in Table 6) [10]. Using this technique, a satisfaction rate of 92.3 % was achieved in combination with 0 % complications (Table 3). A success rate of 92.3 % was achieved (Table 4).

Open surgery: autologous tendon transfer

One study reported on autologous tendon transfer [23]. The technique consisted of resection of the distal Achilles tendon, followed by interposition of the flexor hallucis longus (FHL) tendon (Table 2, Appendix 2 in Table 6).

The study reported that patient satisfaction was achieved in 86 % of the patients (Table 3). Complications occurred in 11.4 % of the patients (Table 3). A success rate of 86 % was achieved (Table 4).

Methodological quality

The assessment of the methodological quality using the Downs & Black checklist and the Coleman methodological scale resulted in a median score of 12.0 (IQR 10.0–13.25) and 57.5 (IQR 40.0–64.25), respectively (Table 2).

There was no significant correlation between success rate and both Coleman score and Downs & Black score. However, a significant positive correlation was found between year of publication and Coleman score (rho: 0.53, p < 0.01), and year of publication and Downs & Black score (rho 0.66, p < 0.01).

Discussion

The most important finding of the present study is the large variation in surgical techniques available for the treatment of midportion Achilles tendinopathy. Additionally, it demonstrates that minimally invasive and endoscopic procedures have lower complication rates with comparable patient satisfaction in comparison with open procedures. Due to low methodological quality of included studies in combination with large heterogeneity in population, used techniques and reported outcome measures, we refrained from data pooling.

Hitherto, one review evaluating surgical treatment of Achilles tendinopathy was performed [35]. In this study from 2001 a mean success rate of 77.4 % was reported [35]. Additionally, a negative correlation between success rate and methodological quality in studies on the topic of surgical treatment of tendinopathy was established [35]. In contrast to that review, we found no correlation between effectiveness and methodological quality. However, we found a positive correlation between year of publication and Coleman score, in line with a previous review on insertional tendinopathy [38]. This implicates that in current research on Achilles tendinopathy the methodological quality is improving.

Studies on open surgery reported inconsistent results regarding patient satisfaction and the complication rates varied widely. Particularly high complication rates were observed in studies evaluating the outcome of multiple tenotomies via an open procedure [4, 18, 21].

In general, good results regarding patient satisfaction and complication rates were reported in studies on minimally invasive surgery. Most of these studies reported on minimally invasive release of the Achilles tendon or minimally invasive longitudinal tenotomies of the Achilles tendon. One study evaluated the results of excision of the plantaris tendon [6]. In this study promising results were reported. However, more studies are needed to support these findings.

Minimally invasive procedures are assumed to have lower complication rates. Most studies evaluating minimally invasive techniques reported low complication rates (Table 3). However, a particularly high complication rate was observed in the study evaluating multiple percutaneous tenotomies [36].

Excellent results regarding functional outcome and postoperative pain were reported in three small series on endoscopic surgery. There were significant differences in the evaluated endoscopic procedures. Maquirriain et al. [22] reported the results of multiple endoscopic longitudinal tenotomies where in the other studies endoscopic release of the Achilles tendon in combination with release of the plantaris tendon was evaluated [30, 33]. Compared to the study by Pearce et al. a higher complication rate was observed in this study.

One study evaluating the results of gastrocnemius lengthening was included in this review [10]. Although promising results are reported, the study evaluated a mere 13 patients at final follow-up. A recent study reported less promising results regarding self-reported sport function in patients treated for Achilles tendinopathy with gastrocnemius lengthening [25].

One study on FHL transfer was included [23]. Good results were reported; however, a high complication rate was observed. The included retrospective case series reported on 44 patients with a mean age of 58.2 years. However, patients affected by midportion tendinopathy tend to be younger, and a wish for return to high-level sport is often present.

The most important limitation of this review is the limited level of evidence of included articles resulting in a high risk of bias. In addition, the lack of or incomplete reportage of our primary and secondary outcome measures made for an arduous comparison. In addition, the included studies used a large variety of heterogeneous outcome measures to measure functional outcome and pain. Therefore, caution should be taken when interpreting the results presented in this review. Another limitation is the confusing terminology used to describe the various pathological conditions of the Achilles tendon [8].

Despite the low level of evidence of the included study, this systematic review is of clinical significance [5]. This study is the first systematic review to compare surgical techniques for their effectiveness on patient satisfaction and complication rate. The study provides a comprehensive overview and clearly demonstrates the variation per surgical technique in outcome of patient satisfaction and complication rates.

We strongly encourage future studies to be conducted using validated instruments to assess pain and functional outcome. As often advocated, larger populations, prospective studies and long-term follow-up studies are needed to be conclusive on the best surgical treatment option of midportion Achilles tendinopathy.

In addition, no comparative study of surgical treatment and nonsurgical treatment or placebo intervention has been conducted. Therefore, no additional benefit of surgery over nonsurgical treatment, placebo intervention or wait-and-see policy has been established. Future research should therefore strive to compare surgical treatment with nonsurgical or placebo intervention.

Furthermore, as the exact pathophysiology of midportion tendinopathy is still poorly understood, current surgical techniques address a range of hypothetical abnormalities with varying results (Appendix 1 in Table 5). Future research should aim to determine whether the extent of the pathology influences the required surgical approach.

Conclusion

The study provides a comprehensive overview of the current literature and clearly demonstrates the variation in outcome of patient satisfaction and complication rates. None of the included studies compared surgical treatment with nonsurgical treatment or placebo intervention. However, minimally invasive and endoscopic procedures result in lower complication rates compared to open surgical procedures. Minimally invasive and endoscopic procedures might therefore prove to be the future of surgical treatment of Achilles midportion tendinopathy.