Abstract
Background
Atypical triplane fractures (ATFs) defined as a triplane fracture that did not involve the weight-bearing articulating surface or as an extra-articular triplane fracture. ATFs are scarcely reported and the incidence may be underestimated. Moreover, there is no consensus on treatment. This study aimed to evaluate ATFs incidence, fracture pattern, and treatment outcome, and propose treatment recommendations.
Methods
Twenty-five ATFs of 46 triplane fractures were retrospectively reviewed between 2011 and 2017. ATFs were classified according to the modified ATF classification. Treatment methods were analyzed. Radiologic outcomes were measured based on fracture displacement. Clinical outcomes included the American Orthopedic Foot and Ankle Society score, visual analogue scale, ankle range of motion, and complications at final follow-up period.
Results
A total of 11 type IV, 11 type III, and three type II ATFs were identified. All type II ATFs (intra-articular fracture) were treated with operative treatment. Nine patients were treated with operative treatment and 18 patients were treated with non-operative treatment in type III or IV ATFs (extra-articular fracture). Good radiologic and clinical outcomes were observed in all patients. The residual displacement after initial trial of closed reduction was between 4 and 5 mm in ten cases of type III or IV ATFs; however, no complications were observed, and all cases had good clinical results after non-operative treatment.
Conclusions
ATFs may be under-recognized. Operative treatment and non-operative treatment showed good outcome. Non-operative closed reduction and cast immobilization can be recommended for extra-articular ATF with displacement < 4 mm.
Level of Evidence
Level IV, case series.
Keywords: Atypical triplane fracture, Extra-articular triplane, Triplane fracture
Introduction
Triplane fractures, defined as fractures in the sagittal, coronal, and axial planes [1, 2], represent approximately 10–15% of pediatric ankle fractures [3]. The triplane fractures occur between 12 and 15 years of age due to physeal closure [4, 5]. Classically, triplane fracture looks like Salter–Harris types II/IV in the sagittal plane and type III in the coronal plane, although it is a Salter–Harris types IV fracture [2]. The epiphyseal fracture line passes through the weight-bearing portion of the tibial plafond [6]. Nonetheless, a previous study confirmed the existence of variations in triplane fracture pattern and fracture lines [7]. Von Laer et al. described an extra-articular triplane fracture as a biplane fracture through the metaphysis that ends through the growth plate without epiphyseal fracture line. This study also reported a fracture pattern with an epiphyseal fracture line involving the non-weight-bearing portion at the junction of the medial malleolus and tibial plafond [8]. Yung et al. described these fractures as atypical triplane fractures (ATFs). ATFs can be categorized into either intra-articular triplane fractures, which affect the non-weight-bearing area of the tibial plafond, or extra-articular triplane fractures, in which the epiphyseal fracture line exits outside the articulating cortex of the medial malleolus [9]. Ertl reported that a similar fracture pattern accounted for 17% of all triplane fractures [6]. Brown evaluated computed tomography (CT) images of 51 triplane fractures and determined that 24% had a fracture line extending to only the medial malleolus [10]. Shin et al. described five cases of ATFs that were treated using non-operative methods, which led to good outcomes [11]. Yung et al. reported 10 ATFs out of 13 triplane fractures, and recommended operative closed reduction and percutaneous screw fixation for displaced fractures [9]. Despite being described in case reports and small series, ATFs incidence may be underestimated, and there is no consensus on the optimal treatment or surgical indication of ATFs. The present study aimed to evaluate ATF incidence, fracture pattern, injury mechanism, treatment outcome, and proposed treatment recommendations.
Methods
This retrospective study was conducted in accordance with the relevant guidelines and regulations outlined in the Declaration of Helsinki and was approved by the institutional review board (IRB) of our hospital (IRB approval no.: 2021-01-009). The requirement for informed consent was waived by the IRB of our hospital owing to the retrospective nature of this study.
A total of 46 patients aged < 16 years were treated for a triplane fracture between January 2011 and January 2017. The classical triplane fractures were excluded from the study. Finally, 25 ATFs were evaluated with a follow-up period from at least 2 years to skeletal maturity (male 16 years old, female 15 years old). ATFs were classified according to the modified classification described by Yung et al., as well as the number of fractured parts (Fig. 1).
Fig. 1.
Classification of atypical triplane fractures described by Yung et al. Type I is an intramalleolar, intra-articular fracture at the junction of the plafond and medial malleolus. Type II is an intramalleolar, intra-articular fracture outside plafond. Type III is an intramalleolar, extra-articular fracture. Type IV is an anteromedial epiphyseal sleeve fragment fracture
All fractures were initially treated with closed reduction under sedation or pain control. Reduction status was confirmed by plain radiography and CT after initial trial of closed reduction. Satisfactory reduction was defined as a displacement of less than 2 mm for intra-articular fracture (type I and II ATFs) and less than 3 mm for extra-articular fracture (type III and IV ATFs). When satisfactory reduction was confirmed, short leg cast immobilization was applied for 4 weeks. When satisfactory reduction was not achieved by closed means, the displaced fracture was treated with closed reduction or open reduction with internal screw fixation under general anesthesia. Patients were placed on a same rehabilitation protocol with non-weight-bearing for 4 weeks followed by partial weight-bearing for 4 weeks.
All radiographs were obtained using similar protocols. Anteroposterior, mortise, and lateral plain radiographs were obtained initially and during follow-up periods. CT scans were performed after initial trial of closed reduction in all patients for accurate diagnosis and delineation of fracture pattern because of the reported discrepancy between plain radiography and CT [12]. Fracture configuration and greatest displacement were evaluated using plain radiography and CT. Displacement of the coronal plane was measured at the epiphysis below the growth plate on anteroposterior, mortise radiographs, and the coronal plane of the CT scan. Sagittal plane displacement was measured at the metaphysis above the growth plate on lateral radiographs and the sagittal plane of the CT scan. All authors independently measured the displacement value of the radiographs and CT scan, and the measurements were repeated three times. Interobserver and intraobserver reliabilities were assessed using intraclass correlation coefficients with 95% confidence intervals. Bone union, leg-length discrepancy, and angular deformity were evaluated on radiographs at the last follow-up visit.
To evaluate the clinical outcome, the American Orthopedic Foot and Ankle Society (AOFAS) score for the ankle–hindfoot was used. This score is widely used by surgeons for ankle and hindfoot problems, and consists of nine criteria grouped into three categories: pain (1 criterion, 40 points), function (7 criteria, 50 points), and alignment (1 criterion, 10 points), with a maximum score of 100 points. Clinical evaluations were performed at the last follow-up visit. Ankle pain was evaluated using the visual analogue scale (VAS) for pain. The time when the patient regained full ankle range of motion (ROM) after injury was evaluated.
The Mann–Whitney U test was used to determine significant differences in AOFAS score, VAS, and radiographic parameters between the operative and non-operative treatment groups. Data were analyzed using SPSS version 19.1 (IBM Corp., Chicago, IL, USA), with P ≤ 0.05 being considered as statistically significant.
Results
Of 46 triplane fractures, 25 (54.3%) were atypical (male, n = 16; female, n = 9). The average age was 12.4 ± 1.3 (range 11.4–15.1) years old at the time of presentation. The mean follow-up period was 3.4 ± 0.8 (range 2.0–4.7) years. According to the modified classification of ATFs by Yung et al., there were no type I ATFs, and three patient had a type II triplane fracture. Type III and IV ATFs were observed in 11 patients each (Fig. 2). All ATFs were two-part fractures. There were no competitive athletes, and only four injuries were sports-related. Most injury mechanisms were low energy: inversion injury (n = 9), fall on level ground (n = 8), and slip down (n = 8) (Table 1). Each radiologic measurement showed good-to-excellent interobserver and intraobserver agreement.
Fig. 2.
Computed tomography scan of atypical triplane fracture (ATF) classification A Coronal image of Case 1, type II ATF. B Coronal image of Case 4, type III ATF. C Coronal image of Case 16, type IV ATF. D Sagittal image of Case 16, type IV ATF
Table 1.
Atypical triplane fracture type with demographics, injury mechanism, and treatment
| No | Atypical triplane fracture type | Age | Gender | f/u periods (years) | Injury mechanism | Residual displacement after initial CR (mm) | Treatment | Residual displacement at final f/u (mm) |
|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 13.8 | M | 3.5 | Slip down | 2.9 | ORIF | 0.0 |
| 2 | 2 | 11.6 | F | 4.6 | Fall on level ground | 7.2 | ORIF | 0.0 |
| 3 | 2 | 12.5 | F | 3.2 | Slip down | 4.2 | ORIF | 0.0 |
| 4 | 3 | 11.4 | F | 4.2 | Fall on level ground | 2.5 | Cast | 1.0 |
| 5 | 3 | 12.8 | M | 3.7 | Inversion injury | 2.4 | Cast | 0.0 |
| 6 | 3 | 15.1 | M | 2 | Inversion injury | 4.2 | Cast | 0.0 |
| 7 | 3 | 11.9 | F | 4.4 | Inversion injury | 2.3 | Cast | 0.0 |
| 8 | 3 | 14.5 | M | 2.1 | Inversion injury | 4.4 | Cast | 0.0 |
| 9 | 3 | 14.3 | F | 2.0 | Inversion injury | 9 | ORIF | 1.0 |
| 10 | 3 | 13.9 | M | 3.1 | Slip down | 10 | ORIF | 1.5 |
| 11 | 3 | 12.5 | M | 4.1 | Inversion injury | 4.6 | Cast | 1.0 |
| 12 | 3 | 13.3 | M | 3.5 | Inversion injury | 5.5 | ORIF | 0.0 |
| 13 | 3 | 13.6 | F | 2.8 | Slip down | 4.3 | Cast | 0.0 |
| 14 | 3 | 14.2 | M | 2.5 | Inversion injury | 3.8 | ORIF | 0.0 |
| 15 | 4 | 12.2 | F | 3.7 | Slip down | 2.5 | Cast | 0.0 |
| 16 | 4 | 13.1 | M | 3.2 | Fall on level ground | 3 | Cast | 0.0 |
| 17 | 4 | 12.4 | M | 4.3 | Fall on level ground | 4.3 | Cast | 1.5 |
| 18 | 4 | 13.7 | M | 3.3 | Slip down | 2.6 | Cast | 0.0 |
| 19 | 4 | 12.3 | F | 4.2 | Fall on level ground | 1.2 | Cast | 0.0 |
| 20 | 4 | 12.0 | M | 4.5 | Fall on level ground | 5.5 | ORIF | 1.0 |
| 21 | 4 | 13.5 | F | 3.1 | Inversion injury | 5.4 | ORIF | 0.0 |
| 22 | 4 | 12.5 | M | 4.7 | Fall on level ground | 4.2 | Cast | 0.0 |
| 23 | 4 | 13.1 | M | 3.8 | Slip down | 2.7 | Cast | 0.0 |
| 24 | 4 | 14.1 | M | 2.1 | Fall on level ground | 4.7 | Cast | 0.0 |
| 25 | 4 | 13.5 | M | 3.3 | Slip down | 2.9 | Cast | 0.0 |
Operative open reduction and internal fixation were performed in 9 of 25 ATFs: all three type II, four type III, and two type IV. Mean age was 13.2 ± 1.0 (range 11.4–15.1) years. Mean residual displacement after initial trial of closed reduction was 6.7 ± 2.1 (range 5.4–10.0) mm. The mean residual displacement at final follow-up period was 0.6 ± 0.7 (range 0.0–1.5) mm. All patients achieved satisfactory bone union at final follow-up (Fig. 3). Full ankle ROM was achieved at 6.5 ± 0.6 (range 6–7) weeks after operation. At final follow-up, AOFAS score averaged 97.5 ± 5.0 (range 90–100) and VAS score averaged 0.6 ± 0.6 (range 0–1). There was no leg-length discrepancy or angular deformity of the ankle joint (Table 2).
Fig. 3.
Operative treatment case. A Initial radiography of case 9 with 9.0-mm residual displacement after closed reduction. B Sagittal image of initial CT after closed reduction. C Coronal image of initial CT after closed reduction. D Postoperative radiography after open reduction and internal fixation. E Final radiography
Table 2.
Treatment outcomes of ATFs
| ORIF | CR & cast | p | |
|---|---|---|---|
| No. of patients | 9 | 17 | |
| Age | 13.2 ± 1.0 | 13.0 ± 1.0 | 0.522 |
| Type of ATFs (Type I:II:III) | 3:4:2 | 0:8:9 | |
| Residual displacement after initial trial of CR | 6.7 ± 2.1 | 3.4 ± 1.0 | < 0.001 |
| Residual displacement at final f/u period | 0.6 ± 0.7 | 0.2 ± 0.4 | 0.673 |
| Time at full ankle ROM (weeks) | 6.5 ± 0.6 | 6.9 ± 0.8 | 0.521 |
| AOFAS score | 97.5 ± 5.0 | 99.0 ± 2 .4 | 0.718 |
| VAS | 0.6 ± 0.6 | 0.6 ± 0.7 | 0.695 |
| Complication | 0 | 0 | – |
ATFs atypical triplane fractures, ORIF open reduction and internal fixation, CR closed reduction, No. number, f/u follow-up, ROM range of motion, AOFAS American Orthopedic Foot and Ankle Society, VAS visual analogue scale
Non-operative closed reduction with cast immobilization was performed in 16 of 25 ATFs: seven type III and nine type IV. Mean age was 13.0 ± 1.0 (range 11.6–14.3) years. Mean residual displacement after initial trial of closed reduction was 3.4 ± 1.0 (range 1.2–4.9) mm. The mean residual displacement at final follow-up period was 0.2 ± 0.4 (range 0.0–1.5) mm. All patients achieved satisfactory bone union at final follow-up. Full ankle ROM was achieved at 6.9 ± 0.8 (range 6–8) weeks after injury. AOFAS score averaged 99.0 ± 2.4 (range 92–100) and VAS score averaged 0.6 ± 0.7 (range 0–2) at final follow-up. There was no leg-length discrepancy or angular deformity of the ankle joint (Table 2). Although the residual displacement after closed reduction was between 4 and 5 mm in seven cases (case number 6, 8, 11, 13, 17, 22, and 24), the patients and parents did not want operative treatment. However, there were no complications with good clinical results after non-operative treatment (Figs. 4, 5, Table 3).
Fig. 4.
Non-operative treatment case 8 with 4.4-mm residual displacement after closed reduction. A Initial X-ray after closed reduction. B Sagittal image of initial CT after closed reduction. C Coronal image of initial CT after closed reduction. D Final radiography
Fig. 5.
Non-operative treatment case 17 with 4.3-mm residual displacement after closed reduction. A Initial X-ray after closed reduction. B Sagittal image of initial CT after closed reduction. C Coronal image of initial CT after closed reduction. D Final radiography
Table 3.
Treatment outcomes of non-operative treatment for ATFs which the residual displacement after initial trial of closed reduction was between 4 and 5 mm
| Treatment outcomes | |
|---|---|
| No. of patients | 7 |
|
Type of ATFs (Type I:II:III) |
0:4:3 |
| Residual displacement after initial trial of CR | 4.3 ± 0.2 |
| Residual displacement at final f/u period | 0.4 ± 0.6 |
| Time at full ankle ROM (weeks) | 6.7 ± 0.6 |
| AOFAS score | 98 ± 3.5 |
| VAS | 0.5 ± 0.4 |
| Complication | 0 |
ATFs atypical triplane fractures, No. number, CR closed reduction, f/u follow-up, ROM range of motion, AOFAS American Orthopedic Foot and Ankle Society, VAS visual analogue scale
Mean residual displacement after initial trial of closed reduction was significantly higher in the operative treatment group (P < 0.05). There were no statistically significant differences in any other parameter. As a result, both the operative treatment and non-operative treatment groups showed good clinical and radiologic outcomes (Table 2).
Discussion
Distal tibial epiphyseal fracture is the second most common fracture in adolescents [13], accounting for 5–10% of pediatric intra-articular ankle fractures [14]. The true incidence of triplane fractures is unknown. Moreover, ATF incidence may be underestimated, and ATFs may be more common than classic triplane fractures. Among 13 triplane fractures, Yung et al. reported that ten were atypical, but only three were classical [9]. In this study, of 46 triplane fractures, 25 (54.3%) were atypical, whereas 21 were classical. Diagnosis of ATFs may be overlooked if not clinically suspected. Because plain radiographs do not consistently demonstrate fracture configuration, CT scanning is necessary to identify and classify the fracture configuration and pattern [15].
There are several classifications for triplane fractures. The Salter–Harris system is most commonly used because of its reliability and reproducibility [16]. Classical triplane fractures are visualized as Salter–Harris types III and IV on anteroposterior and lateral radiographs, respectively. However, triplane fracture of the distal tibia is complex and cannot be categorized using the Salter–Harris system [4].
Two-, three-, and four-part triplane fractures have been reported [1, 17, 18]. Three-part triplane fractures consist of a rectangular fragment of the distal tibial epiphysis in the sagittal plane, an injury to the physis in the axial plane, and a large metaphyseal fragment in the coronal plane [1]. Two-part triplane fractures consist of a sagittal fracture line occurring through the bone of the anterior epiphysis, a coronal fracture line through the posterior metaphysis, and an axial fracture line along the physeal cartilage [17]. Four-part triplane fractures are similar to three-part fractures, except that the fourth fragment consists of the medial malleolus [18]. These fracture-part classifications cannot describe the variations in triplane fracture pattern and fracture lines.
Yung et al. developed a modified classification for ATFs (Fig. 1). Type I is an intramalleolar intra-articular fracture at the junction of the plafond and medial malleolus. Type II is an intramalleolar intra-articular fracture outside the plafond. Type III is an intramalleolar extra-articular fracture. Type IV is an anteromedial epiphyseal sleeve fragment fracture, consisting of a posterior metaphyseal fragment and fracture through the growth plate in the axial plane, similar to a classical triplane fracture. However, there is an anteromedial cortical sleeve fracture of the epiphysis that is completely extra-articular. Yung et al. reported that type IV fractures were the most common fracture pattern among ATFs, followed by type III [9]. In this study, type III and IV ATF was the most common fracture pattern. Therefore, it is important to be aware of extra-articular ATFs (types III and IV) that can be managed with non-operative treatment.
The appropriate treatment for triplane fractures remains controversial. Several treatment methods have been suggested, including non-operative and operative treatments [4]. Most triplane fractures can be managed with non-operative treatment, closed reduction, and cast or splint immobilization. However, anatomical reduction by closed reduction is often difficult because of the interposition of the soft tissue or periosteum [19]. Therefore, some clinicians prefer operative treatment over non-operative treatment.
Operative treatment of triplane fractures has shown good clinical and functional results [20, 21]. Closed reduction and percutaneous screw fixation for an articular fracture displacement of < 2 mm showed good clinical results over long-term follow-up [6, 22]. Choudhry et al. reported good clinical results with closed reduction alone and closed reduction with percutaneous screw fixation for an articular fracture gap < 2.4 mm [21]. Surgical indications for open reduction and internal fixation are initial articular fracture gap > 3 mm or failure to achieve adequate reduction, defined as an articular fracture gap > 2 mm [4]. A recent study by Lurie et al. indicated that operative treatment might have the greatest benefit when the intra-articular gap exceeds 2.5 mm [23].
There are only a few studies on the treatment of ATFs. Shin et al. recommended that type I and II ATFs be treated with closed reduction and cast immobilization, as they do not involve the weight-bearing portion of the tibial plafond [11]; however, Yung et al. recommended operative closed reduction and percutaneous screw fixation. They also reported that operative fixation provided more stability and allowed patients to have earlier ankle mobilization and weight-bearing [9]. In this study, all of the type II ATFs (intra-articular triplane fracture) were treated with operative treatment due to the residual displacement after initial trial of closed reduction > 2 mm. We also agree that displaced type I and type II ATFs need to be reduced anatomically, because the widened medial joint space and incongruent articular surface result in secondary osteoarthritis.
Extra-articular triplane fractures are more commonly treated with non-operative management than with anatomical reduction [4]. O’Connor et al. reported good prognosis with non-operative treatment for intramalleolar extra-articular triplane fractures [24]. In this study, type III and IV ATFs (extra-articular triplane fracture) showed good clinical and radiologic outcome with non-operative treatment. However, the decision regarding operative treatment for type III and IV ATFs no longer followed the principle of articular congruity but was instead made based on the amount of fracture displacement [9]. Fracture displacement > 3 mm cannot be anatomically reduced by closed methods because of soft-tissue interposition and swelling [25], and Ertl et al. reported no successful closed reduction in these fractures [6]. Previous studies on displaced extra-articular triplane fractures reported that premature physeal closure occurred in 60% of fractures with > 3 mm of physeal displacement and 17% of fractures with < 3 mm of physeal displacement after reduction [26, 27]. According to these studies, extra-articular triplane fractures (types III and IV) with displacement > 3 mm should be managed with operative treatment: closed reduction and percutaneous screw fixation with open reduction and internal fixation. However, in our study, the residual displacement after initial trial of closed reduction was between 4 and 5 mm in seven cases; there were no complications, and all cases had good clinical results after non-operative treatment. A more detailed study is needed; however, our results indicate that non-operative closed reduction and cast immobilization are recommended for extra-articular ATF type III and IV with displacement < 4 mm. Moreover, considering postoperative complications, risk of general anesthesia, and second operation for implant removal, broader indications for non-operative treatment might be effective in children and adolescents with extra-articular triplane fractures.
This study has several limitations. One of the limitation of this study is relatively small sample size. It would be difficult to draw the conclusion from this small study and a larger number of samples size would be need to confirm the conclusion of our study. However, the triplane fracture is relatively rare injury and the total of 26 cases in this study is not small compared with previous study. A randomized controlled trial was not performed for treatment of ATFs due to its retrospective nature. Moreover, there was no comparison group for non-operative treatment for extra-articular ATFs with displacement < 4 mm. However, we believe that this study provides important information for determining treatment methods for type III and IV extra-articular ATFs. Future randomized controlled trials with larger sample sizes are needed. A final follow-up CT scan was not performed to limit excessive radiation exposure; hence, the quality of reduction and articular gap at final follow-up period could not be accurately assessed. Finally, the mean follow-up period of this study may have been too short to detect post-traumatic arthritis. However, all patients were evaluated with a follow-up period from at least 2 years to skeletal maturity (male 16 years old, female 15 years old). We believed that this period is enough for evaluation of complications (bone union, leg-length discrepancy, and angular deformity).
In conclusion, ATFs may be under-recognized. Operative treatment and non-operative treatment showed good outcome. Non-operative closed reduction and cast immobilization can be recommended for extra-articular ATF with displacement < 4 mm.
Author Contributions
Study design: CL and HK. Data acquisition: CL and TK. Data analysis: CL and TK. Drafting of manuscript: CL and HK. Review and editing of manuscript: CL, TK, and HK.
Funding
This work was supported by a research grant from of Jeju National University Hospital in 2020 (202000390001).
Declarations
Conflict of Interest
All authors declare that they have no conflict of interest.
Ethical Approval
This retrospective study was conducted in accordance with the relevant guidelines and regulations outlined in the Declaration of Helsinki, and was approved by the institutional review board (IRB) of our hospital (IRB Approval No.: 2020-01-009).
Informed Consent
The requirement for informed consent was waived by the IRB of our hospital owing to the retrospective nature of this study.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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