1 Introduction

Tarsal coalition is an aberrant connection between two or more tarsal bones that result from failure of segmentation of the primitive mesenchyme during the development of the foot.¹ The coalition may be fibrous (syndesmosis), cartilaginous (synchondrosis), or bony (synostosis). Tarsal coalitions are shown to be inherited in an autosomal dominant pattern.² The true incidence of tarsal coalition is unknown due to lack of symptomatology, though a recent cadaveric study showed the incidence of tarsal coalitions could be as high as 13%.³ Approximately, only 25% of individuals with tarsal coalitions become symptomatic.² Although coalitions can occur between any tarsal bones, calcaneonavicular coalitions (CNC) and talocalcaneal coalitions (TCC) account for approximately 90% of all cases.⁴ Bilateral coalitions are seen in 50%–60% of cases.¹

The onset of symptoms usually coincides with the timing of ossification, where fibrous tissue undergoes metaplasia to form a synchondrosis, ultimately forming a synostosis. This occurs between the age of 8 and 12 years in CNC and between 12 and 16 years in TCC.¹ CNC are the most common site of tarsal coalitions.⁴ Patients may present with sinus tarsi pain, activity limitation, or recurrent sprains. Too long anterior process (TLAP) is a rudimentary form of CNC that shares the same embryonic origin. TLAP manifests as an elongated anteromedial process of the calcaneus, which may result in impingement of the navicular or talar head.⁵ TCC are the second most frequent tarsal coalitions. Patients commonly present with medial ankle pain exacerbated by physical activity and a flat foot deformity.⁶

Non-operative interventions such as activity modification, nonsteroidal anti-inflammatories, orthotics, or immobilisation in a walking boot or a short leg cast are the first-line treatment options for symptomatic coalitions.⁷ Corticosteroid injections may provide temporary symptomatic control and help confirm the coalition to be the origin of pain. Surgical options are considered if conservative management fails. Broadly, they include open/arthroscopic resection of the coalition and fusion procedures (subtalar/triple arthrodesis). Surgical resection is indicated in young patients with symptomatic CNC without evidence of further coalitions or arthritic changes in other tarsal joints.⁸ In TCC, surgical resection is preferred over arthrodesis in coalitions that occupy less than 50% of the posterior facet, provided there is no significant valgus deformity of the hindfoot or degenerative changes in the subtalar or adjacent joints.⁹

Resection of symptomatic coalitions has been shown to relieve pain and improve function.^8,10–12 This procedure is conventionally performed using the open approach, with several authors describing different techniques and variable rates of complications and patient-reported outcomes.^8,10–12 The arthroscopic approach in the treatment of various foot and ankle pathologies has gained popularity due to its minimally invasive nature and low complication rates.¹³ Since the first description of the arthroscopic technique by Lui et al., in 2006, many studies have published its successful application in the treatment of symptomatic tarsal coalitions.¹⁴ This systematic review aims to investigate the complication rates and functional outcomes in arthroscopic resection of tarsal coalitions reported in the existing literature.

2 Methods

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The search terms included “tarsal coalition”, “talocalcaneal coalition”, “calcaneonavicular coalition”, “too long anterior process”, “TLAP”, “arthroscopy”, and “endoscopy”. Two reviewers (K.M. and K.W.) conducted independent searches in PubMed, Medline, Embase and Cochrane Library using the same search strategy. Reference lists of the included papers were screened for eligible studies and a further manual search of Google Scholar was also performed. The last search was conducted on May 13, 2020. Studies that reported outcomes of arthroscopic resection of tarsal coalitions (CNC, TLAP, and TCC) with a follow-up period of at least 6 months were deemed eligible for inclusion. No date or language limit was applied to the literature search. Case studies were excluded. Any disagreement regarding the eligibility of a study was resolved by consensus between the two reviewers, and if required, the senior author (B.R.) was consulted.

Outcomes of interest consisted of post-operative complications and patient-reported functional outcomes. Post-operative complications included infection, wound healing problems, neurological or vascular injury, damage to tendons or chondral surface, complex regional pain syndrome (CRPS), and instability. Recurrence of coalition or need for further surgery was considered as a failure of treatment. Extracted data included publication date, number of patients, patients’ age, length of follow-up, type of tarsal coalition, type of arthroscopic approach, complications, rates of recurrence, secondary fusion procedures, and functional outcome scores (Table 1). Individual studies were assigned a level of evidence based on the classification from the Oxford Centre of Evidence-Based Medicine (OCEBM). The National Institutes of Health (NIH) “Quality Assessment Tool for Case Series Studies” was used to evaluate the risk of bias in the included studies.¹⁵

3 Results

3.1

3.1 Study selection

The literature search identified 87 studies. After eliminating 54 duplicate studies, titles and abstracts of the remaining 33 studies were reviewed. Full-text assessment of 21 studies was conducted, of which 8 studies met the inclusion criteria.^16–23 No additional studies were identified during reference screening and citation tracking. A flow chart demonstrating the process of study selection is demonstrated in Fig. 1.

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Fig. 1 PRISMA flow diagram summarising study selection.

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4 Discussion

This study represents the first systematic review of the literature that assessed the post-operative complication rates and patient-reported outcome scores in arthroscopic resection of tarsal coalitions. The overall complication rate of all included studies was 13.6%. All studies demonstrated improvement in patient-reported outcome scores. The major complication was an injury to the tibial nerve in 1 patient who required subsequent cable-grafting using the sural nerve.²² Jagodzinski et al. acknowledged that this complication could have been attributed to the use of the lateral arthroscopic approach for resection of middle facet TCC that extended to the posterior facet, which would have been more amenable to the posterior arthroscopic approach.²² Similarly, the only patient who required subsequent subtalar fusions following arthroscopic resections of TCC had bilateral large middle facet coalitions extending to the posterior facets.²² These cases highlighted issues surrounding suboptimal patient selection rather than the technique.

The surgical technique for arthroscopic resection of CNC and TLAP were similar among all included studies.^18–20,23 Patients were positioned in a “saggy” or “lazy” lateral position. The visualisation portal was sited posterior to the anterolateral process of the calcaneus and dorsal to the Angle of Gissane. The instrumentation portal was placed under direct vision at the superolateral aspect of the midfoot, distal to the calcaneus and lateral to the EDL (Fig. 2). This approach provided a direct view of the underlying CNC or TLAP, which could be safely debrided using an arthroscopic burr (Fig. 3). The potential risk of injury to the intermediate dorsal cutaneous nerve (IDCN) during insertion of the instrumentation portal can be reduced by correctly identifying its subcutaneous location by maximally inverting the foot. Additionally, after making a longitudinal incision lateral to the EDL (and medial to the IDCN), blunt dissection down to the bone can also help minimise the risk of iatrogenic injury to the IDCN.

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Fig. 2 Arthroscopic approach for calcaneonavicular coalition resection with portal landmarks and surface anatomy of relevant structures.

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Fig. 3 3-Dimenional illustration of the calcaneonavicular coalition.

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Different variations in the arthroscopic approach for TCC resection were reported by 4 studies.^16,17,21,22 Jagodzinski et al. described the use of two lateral portals in the sinus tarsi for resection of middle facet TCC. With patients positioned in a “lazy” lateral position, debridement of the coalition was performed in a dorsal to plantar, lateral to medial, and distal to proximal direction.²² 2 studies performed posterior arthroscopic resection for TCC (middle and posterior facet) using 2 portals located at either side of the Achilles tendon at the level of the tip of the lateral malleolus (Fig. 4). Patients were positioned prone on the operating table.^17,21 Wu et al. described a slight modification to this technique by utilising a high lateral visualisation portal in combination with a lower medial working portal.¹⁶ In posterior hindfoot arthroscopy, the neurovascular bundle was protected by medial retraction of the flexor hallucis longus (FHL). The coalition was debrided in a medial to lateral direction. This approach allowed resection of both posterior and middle facet TCC. Unlike the posterior arthroscopic approach, the lateral approach does not allow visualisation of the medial neurovascular structures, risking iatrogenic injury during resection of the middle facet coalitions, as witnessed by Jagodzinski et al. (Fig. 5).²¹ Therefore, for arthroscopic resection of TCC, the posterior arthroscopic approach described by Knörr et al. and Aldahshan et al. is preferred by the authors (Fig. 4).^17,21

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Fig. 4 Posterior arthroscopic approach for talocalcaneal coalition resection with portal surface landmarks.

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Fig. 5 Schematic diagram of posterior arthroscopic approach for talocalcaneal coalition resection and demonstration of the location of medial neurovascular bundle.

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In the treatment of symptomatic CNC, the main contraindication for resection is the presence of arthritis in the adjacent joints, particularly in the adult patient. In such cases, triple arthrodesis instead of excision may be indicated.⁸ Conversely, the decision making regarding surgical treatment of TCC is more challenging. The type of surgical intervention is reliant on the accurate pre-operative assessment of the morphology and extent of TCC, as well as the degree of hindfoot valgus. Resection of the TCC alone for patients with significant calcaneovalgus is not recommended, as it is shown to be associated with poor outcomes.⁹ For symptomatic TCC with significant hindfoot valgus, corrective procedures can be performed at the same time as TCC resection, or at a later date. Knörr et al. combined arthroscopic resection of TCC with the calcaneo-stop procedure in 4 patients with pre-operative hindfoot valgus greater than 20°. Improvement in the degree of hindfoot valgus and AOFAS scores were noted in all patients.²¹ The calcaneo-stop procedure, also known as arthroereisis, is a minimally invasive technique originally used to treat paediatric flexible flat foot deformity. It limits eversion of the subtalar joint by inserting an arthroereisis screw into the lateral half of the sinus tarsi, that impinges on the lateral aspect of the talus.²¹ Arthrodesis procedures are recommended for TCC greater than 50% of the size of posterior facet and in cases where subtalar arthritis is identified in pre-operative imaging.⁹

There are several potential advantages of arthroscopic treatment of foot and ankle conditions over open surgery. These include quicker post-operative recovery, earlier hospital discharge, reduced levels of post-operative pain, and lower rates of infections and wound complications.¹³ To obtain adequate resection in CNC, a 10 mm clear space must be ensured.²⁴ In the traditional open approach, access to the deeper aspect of the calcaneonavicular bar may be limited, which presents a common site for recurrence.⁸ The arthroscopic approach mitigates this problem by permitting safe debridement of the deep portion of CNC under direct vision.^14,19 Although the open medial approach for TCC resection provides good exposure to the middle facet, it only allows limited access to the posterior facet. This may impede the accurate assessment of the subtalar articular surface and sufficient bony resection.²² On the other hand, resection of both middle and posterior facet TCC, as well as direct inspection the subtalar movement can be achieved through the posterior arthroscopic approach without extensive soft tissue dissection.^16,17,21

The concept of tissue interposition at the site of coalition resection was popularised following reports of high recurrence rates in the earlier studies. In open resection without tissue interposition, recurrence rates were found to be as high as 30%.²⁵ Use of various types of tissues for interposition in open tarsal coalition resection is described in the literature, with varying degree of success. Mubarak et al. showed that interposition of fat graft in the treatment of CNC resulted in a recurrence rate of 13%.⁸ In the comparative open CNC resection study conducted by Masquijo et al. the recurrence rates were 4% with fat graft, 6% with bone wax, and 40% with EDB interposition.¹⁰ Raikin et al. found no cases of recurrence in their series of TCC resection with split FHL tendon interposition.²⁶ This systematic review did not identify any cases of recurrence after arthroscopic resection of tarsal coalitions, despite no tissue interposition in any of the included studies. It is possible that in addition to providing the advantage of improved coalition resection, arthroscopic resection may allow earlier mobilisation and weight-bearing post-operatively, inhibiting re-ossification at the site of debridement. This approach could obviate the need for EDB or FHL autograft harvest for tissue interposition, potentially reducing the risk of donor site morbidity.¹²

Like all other surgical procedure, foot and ankle arthroscopy is not without risk. Even though arthroscopic resection of tarsal coalitions was first described only 14 years ago, the demonstrated complication rate is comparable to the arthroscopic treatment of other foot and ankle pathologies. Zengerink & van Dijk showed that the overall complication rate of ankle arthroscopies in 12 studies published between 1986 and 2012 was 10.3%.²⁷ Although arthroscopic coalition resection is relatively safe, it could be technically more challenging than open procedures. Therefore, inexperienced arthroscopy surgeons need to be aware of the learning curve associated with this technique. Encouragingly, a reduction in complication rates and duration of surgery in ankle arthroscopies has been shown to correlate with increasing experience of the operating surgeon.^27,28

The authors acknowledge the limitations of this study. This systematic review did not identify any randomised controlled trials or comparative studies. There was heterogeneity in the included studies in terms of patients' age, length of follow-up, morphology of the coalition, and surgical technique. Given that tarsal coalitions largely affect a younger population, the period of follow-up in the included studies was relatively short. It is unclear whether late recurrence may occur. Therefore, estimating the true difference in risk of recurrence between open and arthroscopic resection is difficult. Furthermore, we cannot account for surgeons’ experience of arthroscopic surgery or their willingness to suggest arthroscopic treatment based on individual patient factors or expertise.

The strengths of this study are stringent inclusion criteria and rigorous quality assessment of the included studies. This is the first systematic review of the literature that explored outcomes of arthroscopic resection of tarsal coalitions, hence it is unsurprising that only case series were identified. Whilst we accept the limitations of these studies, we also recognise the profoundly positive influence of such studies in describing new techniques in the surgical literature.

This study highlighted areas for further research in the surgical treatment of tarsal coalitions. Given that symptomatic tarsal coalitions are rare and predominately affect the paediatric population, conducting comparative trials could be challenging. Future research efforts should be directed towards designing prospective studies comparing outcomes of open versus arthroscopic resection of tarsal coalitions in matched patient groups. Long term follow-up studies to determine rates of recurrence and conversion to arthrodesis are also prudent.

5 Conclusion

Arthroscopic resection is a feasible and effective treatment method for symptomatic tarsal coalitions. This relatively new technique results in satisfactory clinical and functional outcomes, with no coalition recurrence reported in the literature. Future studies comparing outcomes of arthroscopy with open tarsal coalition resection are warranted.

Authors contributions

KMT: Conceptualisation, methodology, investigation, formal analysis, writing – original draft preparation. KW: Methodology, investigation, formal analysis, writing – original draft preparation. CT, LM: Writing – reviewing and editing. BR: Writing – reviewing and editing, supervision.

Ethics

This study was a systematic review of the literature. Therefore, ethics review by the Research Ethics Committee (REC) was not required.

Funding statement

This study did not receive any funding or grants.