Introduction

The midtarsal or transverse-tarsal joint, is otherwise known eponymously as the Chopart joint, after French surgeon François Chopart described an amputation through the articulation between the hindfoot and the midfoot [1]. The Chopart joint is made up of the TNJ and calcaneocuboid joint CCJ. The TNJ makes up part of the coxa pedis (talocalcaneonavicular joint) which enables pronation and supination of the tarsus [2]. The CCJ provides approximately 25° of rotation for hindfoot eversion and inversion [3]. The Chopart joint enables hindfoot pivot, allowing the forefoot to remain inverted or everted on heel inversion, locking the Chopart joint, stabilizing the midfoot during gait push-off phase [4]. Thus, the Chopart joint is fundamental for normal foot function and requires strong ligamentous support. The TNJ is supported superiorly by the dorsal talonavicular ligament and medial limb of the bifurcate ligament and inferiorly by the spring ligament (calcaenonavicular ligament) comprised of the medioplantar oblique, inferoplantar longitudinal and superomedial components [4]. The CCJ is supported superiorly by the dorsal calcaneocuboid ligament and the lateral limb of the bifurcate ligament and inferiorly by the short plantar ligament (plantar calcaneocuboid ligament) [4].

The cyma line (Fig. 1) represents the Chopart joint and can be observed via dorsoplantar and lateral views [5], where radiological discrepancy indicates pathology. Therefore, Initial imaging should start with radiographs in 3 views dorsoplantar, lateral and oblique [6]. Oblique views are optimal for visualising fractures of the anterior calcaneal process [4].

Fig. 1
figure 1

Dorsoplantar Illustration of the Chopart joint and cyma line dividing the midfoot and hindfoot. This congruent S-shaped line corresponds to the Chopart joint

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Chopart injuries can be allocated into 4 broad groups, ligamentous injury with or without dislocation and fracture with or without dislocation, which must occur at the TNJ and/or CCJ. Chopart dislocations include both pure-dislocations and fracture-dislocations. Pure-dislocations are defined as dislocation of the navicular and/or cuboid without associated fracture. Fracture-dislocations are defined as dislocation of the navicular and/or cuboid with associated fracture of one or more of talus, navicular, calcaneus or cuboid including avulsion fractures. Dislocation of both the TNJ and CCJ simultaneously, may be referred to as a complete Chopart dislocation. Swivel dislocations typically result from medial or lateral deforming forces causing TNJ and/or CCJ dislocation and the calcaneus ‘swivels’ on an intact talocalcaneal ligament [7]. We have provided radiological examples of a Chopart fracture (Fig. 2) and fracture-dislocation (Fig. 3). We have also provided an explanation of Main and Jowett’s landmark classification [8] of Chopart injuries, with a focus on dislocations (Table 1).

Fig. 2
figure 2

Chopart fracture without dislocation example. Anteroposterior radiograph (A) and 3D Surface rendering CT (B, C and D) of a Lateral compression (Anterior process calcaneum) Chopart joint injury and medial distraction injury with tibialis posterior and spring ligament avulsion from the navicular

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Fig. 3
figure 3

Chopart TNJ fracture-dislocation example. Anteroposterior radiograph (A) and axial CT (B) of a talar head dislocation with medial talar head and lateral navicular impaction injury

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Table 1 Explanation of Main and Jowett’s classification [8] of Chopart injuries, according to direction and magnitude of force, with guidance [9, 10]. Talonavicular joint (TNJ), Calcaneocuboid joint (CCJ)
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Aims

We aim to review the literature to provide evidence-based recommendations for the diagnosis and management of Chopart dislocations, to improve outcomes for future patients. We also aim to gain further insight into the incidence and aetiology, prognostic factors and management options for these rare injuries.

Methods

Study selection

The electronic databases PubMed, Medline and Scopus were utilised. A preliminary search with no inclusion or exclusion criteria was carried out to gauge the amount of existing literature. This demonstrated a relatively low quantity of existing papers and as a result the set inclusion and exclusion criteria were broad. We included any papers relating to acute traumatic Chopart dislocations and/or Chopart fracture-dislocations in the adult population (Table 2). We excluded papers that were not accessible from the authors online catalogue and any papers not published in English to mitigate translational errors. A literature search was undertaken to identify all related papers. Two search term strings, one anatomical and one related to the type of injury, were combined to narrow down the search to related papers. Applied search terms included “Chopart joint”, “Midtarsal joint”, “Dislocation” and “Fracture-dislocation”. The search identified 181 papers on PubMed/Medline and 280 on Scopus. The PRISMA flow chart was used to scrutinise the initial search results (Table 3). Duplicates were removed and abstracts from these papers were screened for relevance. Articles were selected based on relevance to the topic area and title of the review. The full text of each study was then assessed, and any further non-suitable papers excluded in accordance with the inclusion and exclusion criteria.

Table 2 Inclusion and exclusion criteria set for the literature search
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Table 3 PRISMA flowchart to scrutinise literature search results
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Results

We identified 58 papers for review, 36 case reports, 4 cohort studies, 4 case series and 14 other papers related to the epidemiology, diagnosis, treatment and outcomes of Chopart dislocations and fracture-dislocations.

Cohort studies and case series

Incidence and aetiology

A retrospective epidemiology cohort study by Ponkilainen et al. of 307 midfoot injuries suggests the incidence of midfoot injury to be 12.1/100,000/year and Chopart injury to be 2.2/100,000/year [16]. Motor vehicle accidents (MVA) are the primary aetiology for Chopart dislocations are more common in males [6, 12]. Richter et al. found 16% of 155 midfoot fractures were Chopart fracture-dislocations [12]. A follow-up study conducted of 110 Chopart-dislocations, 25% were found to be pure-dislocations, 55% fracture-dislocations and 20% combined Chopart-Lisfranc fracture-dislocations [6]. A recent study of 128 Chopart joint injuries found only 5 patients (3.7%) had pure-dislocations and the most frequent fracture-dislocation was transnavicular/transcuboidal in 21% of cases [15]. The average age was 36.8 years (5 studies) (Table 4).

Table 4 Cohort Studies and case series identified by literature review on Chopart dislocation and fracture-dislocation functional outcomes, including: 2 retrospective cohort studies, 1 prospective cohort study and 4 case series
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Diagnosis

5/7 studies did not report method of diagnosis. Of the two studies that did, XR plus CT scanning was used. One reported delayed diagnosis for more than 24 h in 22.1% of the 122-patient cohort [15]. In the second, two injuries were initially missed after inspection of plain films and injury severity was underestimated in three injuries prior to CT scanning (Table 4) [5].

Management

83% of 60 Fracture-dislocations were managed with ORIF ± external fixation [6]. 19 of 28 pure-dislocations were managed initially with closed reduction, although six of these required additional internal fixation and one external fixation [6]. Compartment syndrome requiring fasciotomy was reported in 11.6% of 155 midfoot injuries [12], 9.4% of 128 Chopart injuries [15] and 25.5% of 110 Chopart dislocations [12]. Zero percent of pure-dislocations, 5% of fracture-dislocations and 25% (2 studies, n = 48) of combined Chopart-lisfranc fracture-dislocations required primary amputation [6, 12]. 7/128 Chopart injuries required primary arthrodesis and 4.7% of cases required late fusion at the Chopart joint [15].

Outcomes

Average AOFAS score for each Chopart injury classification across the cohorts and case series reviewed (Table 4). Isolated Chopart fractures: 81.0 (1 study, n = 18). Chopart fracture-dislocations: 70.3 (3 studies, n = 54). Chopart pure-dislocations: 79.0 (1 study, n = 14). Combined Chopart-Lisfranc fracture dislocations: 58.0 (2 studies, n = 26).

Richter et al. reported Isolated Chopart fractures had significantly better AOFAS-Midfoot scores than Chopart fracture-dislocations [12]. The highest scores in all groups were achieved in those fractures treated with early ORIF. No significant differences in the scores were found for age, gender or aetiology. Radiographic comparison of Chopart fracture-dislocation (n = 15) against isolated Chopart fracture (n = 18) at an average follow up of 9 years. Incorrect medial column length 27% vs 6%. Incorrect lateral column length 20% vs 11%. Abnormal longitudinal arch shape 40% vs 22%. Arthritic changes 67% vs 33% [12]. There was a high correlation correct column length and good functional outcomes [12]. Furthermore, Mittlmeier et al. found the loss of foot column length had a substantial influence on gait quality and the severity of post-traumatic arthritis had no significant influence [11].

In a follow up study by Richter et al. focussed on Chopart dislocations, those who underwent internal fixation following closed reduction had significantly worse outcomes than those who underwent ORIF in the first place [6]. No significant differences in functional outcomes were found between age, gender or methods of internal fixation when comparing screws and/or K-wires [6]. AOFAS scores were significantly lower in MVA than in non-MVA and in open injuries versus closed. Polytrauma, associated fractures and delayed surgery > 1 day from injury were also significant negative prognostic factors. Those with compartment syndrome had significantly better outcomes, however these patients all had expedited surgery within 24 h [6].

Rammelt et al. followed up 75 Chopart injuries for an average of 10.2 years [15]. ORIF led to significantly better results that closed reduction and percutaneous fixation across all Chopart injuries including pure-dislocations and fracture-dislocations [15]. Only 4% of 128, Chopart injuries were pure-dislocations which had significantly inferior Foot Function Index and AOFAS scores than patients with Chopart fractures or fracture–dislocations [15]. Negative prognostic factors included, high injury severity score, work-related accidents, open and multiple fractures, pure-dislocations, staged surgery, delay of treatment > 4 weeks, post-operative infection and primary or secondary fusion [15].

Van Dorp et al. presented 7 patients with Chopart dislocations [5]. The mean AOFAS score was 72 and the mean VAS score for patient satisfaction was 7.1/10 at an average 31.3 month follow-up [5]. 4/7 patients still experienced pain or limitation of daily activities at follow-up [5]. Another case series by Kosters et al. saw 6 patients with Chopart fracture-dislocations report a mean AOFAS of 66, half of patients were found to have post-traumatic arthritis and one patient had pathological medial column length, at a median follow-up of 2.6 years [14]. Eight malunited Chopart fracture-dislocations underwent secondary anatomic reconstruction, on average 10 months following injury [13]. Seven patients had joint sparing reconstruction with ORIF, and one TNJ arthrodesis. The mean AOFAS pre-operatively and at 2-year follow-up were 38.8 and 80.8 respectively, (p < 0.0001). Active inversion/eversion of the foot (total coronal plane motion) averaged 18° preoperatively and 41° at follow-up, excluding the TNJ fusion [13].

Case reports—Chopart pure-dislocation

Twelve case reports of pure-dislocations were identified for review (Appendix Table 5). The average age was 39.1 with a 3:1 male to female ratio. Half of injuries were caused by MVA and One third were precipitated by falls. 5/12 were complete Chopart dislocations. 5/12 reports were isolated swivel dislocations of the navicular (4 medial, 1 lateral), which was most frequently dislocated in isolation (7/12). The CCJ was not found to dislocate in isolation. The plantar ecchymosis sign was not reported in any cases. Imaging most frequently consisted of XR plus CT (7/12). In nine cases, closed reduction was attempted which failed in four. Of the five cases treated with closed reduction, three were managed non-operatively. Seven out of twelve cases underwent open reduction with additional internal fixation of five and arthrodesis of two. Follow up was provided for 10 cases between six and 76 months. Five of these had significant long-term complications, which ranged from pain on prolonged standing, to pes planus and midfoot arthritis.

Case reports—Chopart fracture-dislocation

24 case reports of Chopart fracture-dislocations were identified (Appendix Table 6). The average age was 34.8 with a 2.4:1 male to female ratio. The most common aetiology was MVA in 10 reports. According to dislocation type, 13 were TNJ dislocations, 6 CCJ dislocations and 5 complete Chopart dislocations. The calcaneus was most commonly fractured (13/24), followed by the navicular (10/24), cuboid (7/24) and talus (4/24). Eleven reports used XR alone for diagnosis, 13 used additional CT. Two Chopart fracture-dislocations were initially missed on XR. The plantar ecchymosis sign was reported in two cases. Where closed reduction was attempted, 7/18 failed. 11 cases were successfully reduced, although 8 required surgical fixation. Thirteen cases had open reduction, definitive management was ORIF for 11 and arthrodesis for 2. Follow up ranged from 3.5 months to 5 years with 2 cases lost to follow-up. 13/22 cases had sequalae, ranging from pain to pes planus and malunion. 3/22 of cases required further surgery. Eight cases had definitive treatment more than 48 h after injury, six of these had complications at follow-up. Seven out of twenty-four cases provided AOFAS scores between 3.5 and 24 months, with a mean score of 87.7.

Discussion

Clinical signs

The plantar ecchymosis sign (PES) describes a central midfoot plantar ecchymosis that is pathognomic for relevant midfoot injuries indicating rupture of strong plantar ligaments and resulting haematoma [17]. PES has been recorded following calcaneal fractures [18], Lisfranc [19] and Chopart injuries [20]. PES was not reported in the cohort studies or case series reviewed, although 2/36 case reports reported the PES. The PES is a rarely reported but valuable clinical sign indicating underlying midfoot injury, CT is encouraged where PES is positive and radiographs negative. Clinicians should carefully examine and palpate the entire foot alongside confirming the neurovascular status and have a high index of suspicion for compartment syndrome which is common in Chopart injuries [12, 15], especially dislocations [6].

Imaging

The wider literature has shown, up to 41% of Chopart injuries are missed at first presentation [5]. Haapamaki et al. found plain radiographs alone missed 33% of fractures in Chopart injuries [21]. From Van Dorp et al. Case series of 9 Chopart dislocations, 2 were initially missed from XR alone and the severity of injury was underestimated for 3 prior to CT, alongside this 2/24 fracture-dislocations from case reports were initially missed on XR (Appendix Table 6). Furthermore Rammelt et al. found pure-dislocations to be very rare (4%) and encourage CT scanning to rule out associated fracture [15]. This is in concordance with Almeida et al. who found a significant improvement in identifying additional Chopart fractures missed on XR with CT [22]. Furthermore, CT allows reconstructive modelling to determine the degree of dislocation [4]. We recommend CT to be included in the diagnostic workup of all suspected Chopart injuries.

Management and outcomes

For Chopart dislocations including pure-dislocations and fracture-dislocations, initial ORIF provides better outcomes than closed reduction prior to internal fixation [6]. Closed reduction alone was found to have statistically similar outcomes to operative treatment [6], however, 6 of 14 pure-dislocations required internal fixation following closed reduction and therefore should have undergone ORIF initially. Due to the risk of requiring internal fixation following closed reduction, urgent ORIF is advised and closed reduction should be discouraged. Furthermore, closed reduction is challenging, often fails and repeated attempts may cause further damage [23]. For Chopart injuries in general including isolated fractures, fracture-dislocations and pure-dislocations, Rammelt et al. found over a 10-year follow up that ORIF generates significantly better results than closed reduction and percutaneous fixation [15]. It is important to note that according to Rammelt et al. [15] pure-dislocations had the worst prognosis, however, AOFAS scores were not provided and could not be included in the average across studies.

Maintenance of foot column length significantly improves gait quality [11]. We agree with Van Dorp et al. that correct alignment of the foot axes and correct length of medial and lateral columns should be a major goal of therapy [5], these have been regularly incorrect at follow up, thus this should be addressed peri-operatively and corrected where possible. For malunited Chopart fracture-dislocations, secondary reconstruction improves outcomes in suitable patients otherwise joint fusion is required [13]. Arthrodesis is implemented in late presentations [24], in patients with diabetic arthropathy [25], or when other treatment strategies have failed where arthrodesis can prevent midfoot collapse [26]. TNJ Arthrodesis can reduce the Chopart joint range of motion by 50% and is a negative prognostic factor [15], so is considered a last resort [27]. Soft tissue condition can help to dictate treatment methods, where external fixation can maintain reduction during soft tissue healing [15, 28] and maintain column length with unstable ORIF [29]. Patients with Chopart pure-dislocations and fracture-dislocations require long term follow-up to monitor for complications which were common [5, 14].

Limitations

There was marked heterogeneity of the reviewed studies in terms of injury pattern, injury classification, treatment modality and outcome reporting which led to difficulties in performing systematic review, which was our original intention. This was coupled with the paucity of research on this topic due to the rarity of the injury itself.

Conclusion

This review focussed on Chopart dislocations. Pure-dislocations appear to have inferior outcomes due to the high energy required to disrupt the strong ligamentous anatomy at the Chopart joint. There is a general consensus that closed reduction often fails and leads to poorer outcomes, even if followed by ORIF. Besides joint reconstruction, restoring and maintaining the medial and lateral foot columns is essential to obtain reasonable results. CT and compartment syndrome evaluation is highly recommended. Urgent ORIF ± external fixation is the management of choice for pure-dislocations and fracture-dislocations. Negative prognostic markers included, severity of injury, delayed or staged treatment, arthrodesis and MVA.