Management of chronic Achilles ruptures: a scoping review

Purpose This scoping review aims to systematically map and summarise the available evidence on the management of chronic Achilles ruptures, whilst identifying prognostic factors and areas of future research. Methods A scoping review was performed according to the frameworks of Arksey and O’Malley, Levac and Peters. A computer-based search was performed in PubMed, Embase, EmCare, CINAHL, ISI Web of Science and Scopus, for articles reporting treatment of chronic Achilles ruptures. Two reviewers independently performed title/abstract and full text screening according to pre-defined selection criteria. Results A total of 747 unique articles were identified, of which 73 (9.8%) met all inclusion criteria. A variety of methods are described, with flexor hallucis longus tendon transfer being the most common. The most commonly reported outcome is the American Orthopaedic Foot and Ankle Society (AOFAS) score, although 16 other measures were reported in the literatures. All studies comparing pre- and post-operative outcomes reported significant post-treatment improvement. Complications were reported in 50 studies, with an overall pooled complication rate of 168/1065 (15.8%). Conclusion Although beneficial results were reported following a variety of techniques, comparison between these is challenging due to the low-level study designs used and confounding factors such as treatment delay and tendon gap size. Further research comparing the efficacy of different techniques is required in order to facilitate the development of an evidence-based treatment protocol. Such work would allow clinicians to better understand the suitability of the large variety of reported techniques and select the optimal strategy for each individual patient. Supplementary Information The online version contains supplementary material available at 10.1007/s00264-021-05102-5.


Introduction
Rupture of the Achilles tendon is a relatively common injury, with around 4500 Achilles ruptures occurring in the UK every year. Recent epidemiological data demonstrates a significant 39% rise in incidence, from 1.8 per 100,000 person years in the USA in 2012 to 2.5 per 100,000 person years in 2016. A similar trend is also reported in a number of other countries [1][2][3][4]. Given that the majority of Achilles ruptures occur during participation in sports such as basketball, numerous authors suggest that this increasing incidence may be due to an increase in participation in recreation sports, particularly in older adults. Other potential factors include an increased awareness and therefore diagnosis of ruptures by emergency doctors, although there is currently no strong evidence to support either hypothesis.
Treatment of acute ruptures is widely debated with previous research describing both operative and conservative (functional dynamic regime) methods [5][6][7]. Traditionally, open operative repair has been the favoured option with authors showing lower re-rupture rates compared to nonoperative methods [8,9]. More recently, however, a number of authors have reported excellent outcomes and lower re-rupture rates, with the use of nonoperative functional orthotic treatment, such as the Leicester Achilles Management Protocol (LAMP) and Swansea Morriston Achilles Rupture Zaki Arshad and Edward Jun Shing Lau contributed equally to this manuscript and are joint first authors. Treatment (SMART) protocol. Research also suggests that nonoperative management is associated with fewer shortterm complications. The emergence of this new evidence has led to non-operative treatment becoming the mainstay of contemporary treatment protocols. If the initial tendon rupture is not diagnosed promptly, as is the case in up to 20% of patients, the injury may then be termed chronic or neglected [10]. Authors disagree as to the exact definition of a chronic lesion; however, a recent systematic review by Flint et al. suggests that the term chronic should be used to define a rupture presenting at least four weeks after the initial injury [11].
A wide variety of techniques such as flexor hallucis longus tendon transfer and V-Y plasty [12][13][14] have been described in the management of chronic Achilles ruptures. To the best of our knowledge, the only previous scoping/ systematic review investigating the full breadth of treatment options was published in 2013, with 34 studies included. However, since that date, there has been a surge in publications reporting treatment of chronic Achilles ruptures, using various techniques. There is therefore a gap in the current literature for an up-to-date review of management techniques. This scoping review addresses this by systematically mapping and summarising current evidence regarding the management of chronic Achilles ruptures, whilst identifying areas for future research. This aims to improve readers' knowledge of the available treatment strategies and associated outcomes, and aid clinicians in optimising treatment protocols.

Methods
A scoping review methodology was chosen for this article due to the broad aim of systematically mapping and summarising the full breadth of literature regarding the treatment of chronic Achilles ruptures. Methodological guidelines for the conductance of scoping reviews have been developed by Arksey and O'Malley, Levac and The Joanna Briggs Institute [15][16][17]. This review adheres to these guidelines, which all describe five key stages in the conductance of a scoping review, as detailed below.

Identifying the research question
The following research questions were developed to guide this review: • What management options are currently reported for the management of chronic Achilles ruptures and what are their outcomes? • If possible to compare outcomes, which techniques have the greatest efficacy?
• What prognostic factors may influence treatment outcome?

Study selection
Following article retrieval, all studies were imported into Rayyan systematic reviews web application to aid the screening process [18]. Two authors performed two-stage screening, initially involving title/abstract screening and then full text screening, guided by the selection criteria below: Two reviewers independently used this form to extract data from the first ten relevant studies. Discussion then took place as to the suitability of the form [19], at which point the decision was taken to add two further headings, 'minimum treatment delay for inclusion' and 'prognostic factors'. Once these headings were added, the final sheet was used to extract relevant data from all studies.

Collating, summarising and reporting the results
Study results are reported in a qualitative thematic manner, with distinct sections focussing on key themes such as the outcome measures used, treatment results and complications. Basic study characteristics including year of publication, number of patients, mean age, male:female ratio and follow-up period are displayed in Table 1. The number of studies retrieved using the search strategy and excluded at both the title/abstract and full text screening stage is detailed in a PRISMA flow diagram [20]. Outcome scores were pooled across studies reporting the same treatment technique if there were at least five studies reporting a particular technique and if at least three of these studies reported both pre-and post-operative outcome scores. Pooling was performed in R 4.0.0 software (R foundation for statistical computing, Vienna, Austria), using DerSimonian and Laird random effects weighting. Missing standard deviation values were imputed according to the method of Walter and Yao [21]. The pooled pre-operative outcome score was subtracted from the equivalent pooled post-operative score to calculate an unstandardised mean difference. Studies which did not record both a pre-and post-operative score were not included in this analysis.

Results
A total of 747 unique articles were identified, of which 73 (10.3%) were included in the final review (Fig. 1). Summary statistics of all included studies are presented in Table 1.

Treatment techniques
A wide variety of treatment methods were reported in the included literature, as detailed in Fig. 2. The most common technique is flexor hallucis longus (FHL) tendon transfer, reported in a total of 22 studies. Of these, two studies used both a single and a double incision approach in different patients, seven exclusively used a single incision, nine a double incision, two an endoscopic approach and two did not specify the exact approach. Other tendon transfer methods, such as semitendinosus tendon transfer (ST transfer), peroneus brevis tendon transfer (PB transfer) and hamstring tendon transfer, were reported in seven, six and two studies, respectively. Percutaneous techniques, including a figure of eight stitch repair or modified Bunnell repair, were reported in two studies [30,52]. A total of ten studies used gastrocnemius flaps with no augmentation, whilst six studies describe additional FHL augmentation (Fig. 2). Techniques such as V-Y and Z plasty were reported both as stand-alone techniques or combined with a synthetic acellular human dermal tissue matrix graft jacket (Wright Medical Technology, Inc., Arlington, TN) or FHL transfer [53]. Other less commonly reported techniques include use of the Ligament Advanced Reinforcement System (LARS) graft (JK Orthomedic, Dollard-des-Ormeaux, Quebec, Canada), polyester tape, scar tissue interposition and Duthie's biological repair [10,43,45,91]. Only one study described nonoperative treatment, using an orthosis as part of the SMART protocol [89].

Outcome measures
A similarly wide variety was seen in the outcome measures used to assess treatment outcomes. AOFAS is the most commonly used score, followed by ATRS, Leppilahti score and VAS (Table 2).  [57,61,79]. No formal comparison of these mean differences was performed, due to the heterogeneity in outcome measure and low-level case series study design used and inability to control for potential confounding factors such as treatment delay, length of tendon gap, patient age and follow-up period.
There is a large degree of heterogeneity in treatment methods for chronic Achilles ruptures, with studies reporting a variety of tendon transfer, turndown flap, tendon lengthening and synthetic repair techniques. A number of authors also described the use of dual techniques involving a combination of more than one of the above methods. All techniques described appeared to show good post-operative results, with all relevant included studies reporting a statistically significant increase in pre-to post-operative scores such as AOFAS and ATRS (Table 3). However, ascertaining the most efficacious technique is challenging, due to the poor quality of the existing literature. A formal meta-analysis comparing pooled outcomes of different treatment strategies was not possible due to a number of factors including large number of different techniques, large variety in outcome measures reported, low-level case series study design and inability to control for factors which may influence outcomes such as patient age, length of treatment delay and length of tendon gap. Comparison is also currently hampered by the widespread use of non-validated outcome measures. The most commonly used measure was the AOFAS (Table 2), which is not validated for use in Achilles ruptures and its use is no longer recommended by The American Orthopaedic Foot and Ankle Society [93]. Future research should therefore endeavour to use outcome measures specifically validated for Achilles ruptures such as the ATRS.
However, even if such a comparison between treatment techniques was possible, it is likely that there is no a single        optimal operative strategy for all patients. Instead, it may be more important to develop an evidence-based optimal treatment protocol, identifying stratification criteria that takes into account unique patient factors, such as length of treatment delay and tendon gap size, which may determine the suitability of a particular technique. Some authors have described such treatment protocols. For example, Myerson recommends primary repair in cases with < 2 cm gap, V-Y plasty in the case of a 2-5 cm gap and tendon transfer with or without V-Y plasty in cases with gap > 5 cm [94]. Maffulli et al. use peroneus brevis transfer for gaps < 6 cm, semitendinosus graft for gaps > 6 cm and FHL transfer for gaps > 5 cm [61]. Similar gap size-based protocols are also described by Kuwada, Den Hartog and Krahe [95][96][97]. However, these protocols are not based on definitive evidence as there is currently a lack of literature comparing different treatment methods. Although Elias et al., who described FHL transfer, did not find any significant difference in outcomes according to age or length of delay, worse outcomes were seen in those with larger tendon gaps of 7-8 cm [97]. However, firm conclusions cannot be drawn from the findings of these 15-patient case series describing only one technique. It is therefore important that further high-quality research, comparing different treatment techniques in patients of varying age, tendon gap length, treatment delay, injury aetiology and degree of tendon degeneration, is performed. Such works would aid the development of an evidence-based treatment protocol, which would allow clinicians to select the optimal technique for each specific patient, taking into account the above factors. Furthermore, although there is a growing body of evidence supporting the role of conservative treatment in acute Achilles rupture, there is a paucity of literature investigating the same in chronic ruptures [9]. This is likely due to the traditional view that operative treatment yields superior outcomes for chronic ruptures. However, again, this seems to be derived from anectodical evidence rather than high-quality research. Only one included study investigates the role of conservative treatment and, to the best of our knowledge, the only article directly comparing operative versus conservative treatment in chronic ruptures is the 1953 study of Christensen [89,98]. This study does indeed suggest superiority of operative treatment; however, it is not possible to draw conclusions from a single small case series. Further research is therefore required in ascertaining the suitability of conservative treatment and specific factors which may predict response to such treatment. Even if it is the case that operative treatment is superior, there may be certain patients who decline, or are not suitable for operative intervention. Although Achilles tendon rupture most frequently occurs in adults aged between 30 and 40, there are a group of older patients sustaining Achilles tendon rupture who may not be able to tolerate surgery and the mean age at which rupture occurs has increased by at least 0.721 years every five years since 1953 [99]. This suggests that clinicians are likely to come across an increasing number of patients for whom operative intervention is not suitable, further emphasising the importance of research into the development of effective conservative therapies.
Despite the rigorous methodology employed in this review, it must be acknowledged that certain biases do exist. For example, due to the limited linguistic capabilities of the research team, only studies published in the English language were included. Furthermore, as described, there are a number of confounding factors such as treatment delay and tendon gap length, which may differ between individual studies and affect reported outcomes. As outlined in Table 1, the large majority of studies utilise a level IV retrospective case series design. Such studies are particularly prone to selection bias, drawing patients from a relatively narrow sample population. Lastly, it was decided to include studies reporting both validated and non-validated outcome scores, as well as patient reported, and researcher assessed scores. This may cause some bias in outcome scores, with only 21 of 73 included studies using the validated ATRS outcome scale.

Conclusion
The current literature describes a number of different operative strategies for the management of chronic Achilles rupture, all of which demonstrate beneficial outcomes. However, comparison of specific techniques is currently hampered by the low-level evidence and inability to control for potential confounding factors. Future research directly comparing treatment strategies in patients stratified according to specific injury characteristics may aid in the development of an evidence-based optimal treatment protocol. This would allow clinicians to determine which of the multitude of available techniques is most suitable for each unique patient.
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