A previously unreported type of extra-articular triplane fracture: A revised classification system

Abstract

Background:

Atypical triplane fractures are defined as triplane fractures that are intra-articular but affect the non-weight-bearing area of the tibia plafond or extra-articular triplane fractures where the epiphyseal fracture line exits outside the articulating cortex of the medial malleolus. These fractures are scarcely reported in the literature. Here, we study the fracture pattern, mechanisms, and recommendations for management.

Methods:

This is a retrospective study of all triplane fractures identified from 2012 to 2016 in a tertiary referral center. There were 10 atypical triplane fracture patterns identified in this cohort. All patients were followed up with an average of 19 months. A modified atypical triplane fracture classification was devised and compared with previously reported classification systems. Clinical outcomes measured included treatment complications, ankle range of motion, and time needed to return to sports.

Results:

We identified a new extra-articular triplane fracture variant with an anteromedial epiphyseal sleeve fragment (fracture variant). There were no long-term complications from operative closed reduction and percutaneous screw fixation. Operative cases had earlier ankle mobilization and regained full range of motion (12.8 weeks vs 13.3 weeks) earlier. The average time to return to sports was 5.2 months.

Conclusions:

We propose a modified classification for atypical triplane fractures and recommend closed reduction and percutaneous screw fixation for displaced atypical triplane fractures.

Level of Evidence:

IV (Case Series).

Introduction

Triplane fractures are rare injuries that occur at the distal tibial epiphysis. Around 4% of all pediatric fractures occur at the ankle and only 6% are triplane fractures. ^1,2 They represent about 10–15% of all intra-articular pediatric ankle fractures. ³ Triplane fractures were first described in 1970 and named after their unique geometry. ^4,5 Classically, the epiphyseal fracture line is through the weight-bearing portion of the tibial plafond. However, variations in the fracture pattern and number of fragments in this geometrical configuration exist. ^{6 –8} The mechanism of injury in classic triplane fractures tends to err on moderate energy injuries including sports-related injuries and fall from height. ^6,9 A lesser majority is from low energy trauma and rarely from motor vehicle accidents. ^9,10

However, in comparison, there is a paucity of literature on the entity of atypical or extra-articular triplane fractures, which have only been described in case reports and case series alone. ^{11 –14} Extra-articular triplane fractures were first described by von Laer, who noted a biplane fracture through the metaphysis and ended through the growth plate with no concomitant epiphyseal fracture line. ¹⁵ He also noted a fracture pattern with the epiphyseal fracture line extending to the non-weight-bearing surface at the junction of the medial malleolus and the tibial plafond. We describe these fractures as atypical triplane fractures. These are either intra-articular but affect the non-weight-bearing area of the tibia plafond or extra-articular triplane fractures where the epiphyseal fracture line exits outside the articulating cortex of the medial malleolus. Ertl saw a similar fracture pattern with 17% of their cases having the epiphyseal fracture exit outside the primary weight-bearing surface of the ankle or were completely extra-articular. ⁶

The largest series to date is by Shin et al., who evaluated a case series of five triplane fractures that did not involve the weight-bearing plafond and labeled them broadly as intramalleolar fractures. ¹³ They developed a classification system based upon the exit site of the epiphyseal fracture line. Three distinct patterns were noted including intra-articular at the junction of the plafond and medial malleolus, intra-articular at the medial malleolus, and finally completely extra-articular through the medial malleolus (Figure 1). In Shin’s series, all but one case were competitive varsity-level athletes with sports-related injuries. Treatment was by closed reduction and cast immobilization with good results.

Figure 1.

Classification of atypical triplane fractures. Types 1–3 as described by Shin et al. for intra-malleolar fractures of the ankle. Type 4: anteromedial epiphyseal sleeve (AMES) fracture pattern.

Despite only being reported in case reports and small series, atypical triplane fractures may in fact be underreported. Brown evaluated CT scans of triplane fractures of 51 patients and noted 24% had fractures involving only the medial malleolus and an additional 16 were described as involving both the plafond and medial malleolus. ¹⁶ We speculate the prevalence of atypical triplane fractures are under-recognized. In our study, we hoped to further evaluate atypical triplane fractures occurrence, mechanism of injury, and fracture patterns in our population group. Reported herein are a series of atypical triplane fractures and proposed treatment recommendations.

Materials and method

We included all patients of <18 years of age with atypical triplane fractures admitted to our hospital during a 5-year period from 2012 to 2016. All patients had CT scans performed for diagnosis and delineation of fracture pattern. Atypical triplane fractures are defined as triplane fractures that did not involve the weight-bearing articulating surface. Classical triplane fractures were excluded in this study. Atypical triplane fractures were classified according to a modification of the intramalleolar classification described by Shin et al. as well as the number of fracture parts.

Management of displaced fractures consisted of closed reduction or open reduction when failed to achieve adequate reduction by close means. Displaced fractures were fixed with percutaneous internal screw fixation with two lag screws in two directions (anterior to posterior and medial to lateral) under image intensifier (Figure 2) after reduction was achieved. Nondisplaced fractures were treated with cast immobilization. Patients were placed on similar rehabilitation protocols with non-weight-bearing for 6 weeks followed by partial weight-bearing for 6 weeks. Outcome measurements included treatment complications, ankle range of motion at 3, 6, 9, and 12 weeks as well as return to sports. All data collection and analyses were performed by an independent assessor.

Figure 2.

Postoperative radiograph after percutaneous screw fixation.

Results

We identified 10 atypical triplane fractures out of 13 triplane fractures. No open fractures were noted. From the atypical triplane fractures, there were four males and nine females with an average age of 11.8 years old and 12.5 years old, respectively, at the time of presentation. All patients were followed up with an average follow up of 19 months (range 4–48 months). All but two cases had a follow-up of 1 year or more.

There were no competitive athletes in our patient group with only three injuries being sports-related. The majority of atypical triplane fractures derived from a low energy mechanism including five patients with twisting injuries to the ankle on level ground and four after sustaining a fall on level ground (Table 1). The average body weight was 49.9 kg and the weight percentile for gender- and age-specific local growth charts was on average at the 80th percentile.

Table 1.

The distribution of fracture patterns with their associated demographics, mechanism of injuries, and management.

No.	Fracture pattern	Fracture parts	Age	Gender	Mechanism of injury	Energy level	Sports- related	Fracture displacement	Treatment
1.	Atypical triplane type 2	2	14	F	Fall from Trampoline	Moderate	No	Yes	CR + PP
2.	Atypical triplane type 3	2	12	M	Twisting injury	Low	No	No	Short-leg cast
3.	Atypical triplane type 3	2	12	F	Inversion injury	Low	No	No	Short-leg cast
4.	Atypical triplane type 3	2	13	F	Inversion injury	Low	Yes	No	Short-leg cast
5.	Anteromedial epiphyseal fragment	2	9	F	Fall from level ground	Low	No	Yes	CR + PP
6.	Anteromedial epiphyseal fragment	2	11	F	Fall from level ground	Low	No	Yes	ORIF + PP
7.	Anteromedial epiphyseal fragment	2	12	F	Fall from level ground	Low	No	Yes	CR + PP
8.	Anteromedial epiphyseal fragment	2	12	M	Fall from level ground	Low	No	Yes	CR + PP
9.	Anteromedial epiphyseal fragment	2	12	M	Eversion Injury	Low	Yes	No	Short leg cast
10.	Anterior epiphyseal fragment	2	14	M	Eversion injury	Low	Yes	Yes	CR + PP

CR: closed reduction; PP: percutaneous pinning; ORIF: open reduction internal fixation.

Three fractures were intramalleolar triplane type 3 and one was type 2 as previously described by Shin (Figure 3). There were no type 1 fractures noted. However, the most common fracture pattern we noted was an anteromedial epiphyseal sleeve (AMES) fragment not previously described in literature. This fracture pattern accounted for 5 out of 10 of the atypical triplane fractures we saw (Figure 4). It consists of a posterior metaphyseal fragment and fracture through the growth plate in the transverse plane as in a typical triplane fracture. However, there is an anteromedial cortical sleeve fracture of the epiphysis, which is completely extra-articular.

Figure 3.

(a) Case 1 showing atypical triplane fracture type 2 (far left). (b) Case 2 with atypical triplane fracture type 3, which is also seen in case 3 (c) and case 4 (d) with 3-D reconstruction of the CT scan (far right).

Figure 4.

Anteromedial epiphyseal sleeve fracture: five case examples (cases 5–9) of the extra-articular triplane variant. There is a posterior metaphyseal fracture in sagittal plane, a transverse fracture through the physis and an anteromedial cortical sleeve fragment of the epiphysis. One case (case 10) with an anterior epiphyseal sleeve fracture fragment.

There were two males and three females who had the AMES fracture variant. There was one case of epiphyseal cortical sleeve fracture involving only the anterior cortex. Half of our males with triplanes had the AMES variant with an average age of 12.5 years old. Although the majority of our female patients (three of five) had this variant. They were younger than the mean with an average age of 10.3 years old. All five AMES fracture variants were sustained as a result of low energy trauma in patients with sedentary lifestyles.

Operative management was performed for 6 of 10 cases of extra-articular and atypical triplane fractures. One case with the AMES facture variant failed closed reduction due to interposed periosteum and required open reduction and internal fixation with two lag screws. Two patients were complicated with transient numbness to the first dorsal web space and resolved by postoperative day 2. No implant-related complications were seen.

Nondisplaced fractures were treated conservatively with short-leg plaster immobilization for 6 weeks. Earlier ankle mobilization was achieved in the operative group with cast immobilization for 2–4 weeks only. Full ankle range of motion was achieved in the operative group by 12.8 weeks (standard deviation (SD) ± 6.6), opposed to 13.3 weeks (SD ± 8.8) in the nonoperative group. The average time to return to sports was 5.2 months after initial injury. Operated cases return to sports by 5 months compared to 3 months in the nonoperative group. All patients had good outcome with bony union and no displacement of the fractures.

Discussion

Atypical triplane fractures may be under-reported in today’s literature. ^6,16 The diagnosis may be missed if not clinically suspected. There were more atypical triplane fractures compared to classic triplanes from our experience, with 10 atypical and only three classical triplane fractures during this time period.

From our series, we report a new fracture variant in extra-articular triplanes with the AMES fragment. These fractures are different to the classical type of triplane fractures with the epiphyseal fracture line involving an anteromedial sleeve. They also differ from Tillaux fractures that were classically described as an anterolateral fracture of the distal tibia epiphysis. The AMES fracture variant located differently in addition to a metaphyseal fracture component more akin to a triplane. We postulate that the fracture arises from an external rotation or eversion injury to a plantarflexed foot resulting in a flexed distal fragment, posterolateral widening at the metaphyseal fragment, and an avulsion fracture of the anteromedial cortex. These appear to be low energy injuries in a sedentary patient population group with a larger body build. Possible hormonal influences on fracture pattern could be evaluated in future studies. It is important to be aware of extra-articular triplane fractures and to the AMES facture variant which has a different mechanism of injury compared to the athletic sports-related injuries described by Shin.

We propose a modification of the classification system for intramalleolar fracture patterns proposed by Shin. In the Modified Classification of Atypical Triplane Fractures, the addition of the type 4 AMES variant is included (Figure 1). In our study, the new type 4 AMES variant was the most common fracture pattern followed by types 3 and 2, respectively.

The Modified Classification of Atypical Triplane Fractures developed helps distinguish these fracture patterns that other classification systems more commonly utilized including the Salter-Harris classification and fracture parts classification system described by Marmor ⁴ cannot achieve. We can see that the number of fracture parts cannot help to distinguish these fracture patterns. All of the atypical triplane fractures in our series are two-part fractures as shown in Table 1. From the description by Salter and Harris in 1963, type II injuries are fractures through the epiphyseal plate to a varying degree and exits through the metaphysis creating a triangular-shaped metaphyseal fragment. ¹⁷ Also to note, in the description for Salter–Harris type II injuries is the intact periosteum on the convex side (metaphyseal fragment) and torn periosteum on the concave side. While the classical Salter–Harris type IV injuries are intra-articular and extend into the joint surface. From our series, we note that the fracture patterns cannot be classified to either Salter–Harris type II or type IV injuries. In these atypical triplane fracture patterns, there is an epiphyseal fracture or fragment in the sagittal plane similar to a Salter–Harris type IV, but more akin to a triplane fracture. However, against both descriptions previously mentioned, the fracture does not involve the joint surface. Similarly, this cannot be classified as a Salter–Harris type II with the presence of the epiphyseal fracture. However, the integrity of the periosteum in the AMES fracture variant may hold true to the description of the Salter–Harris type II injury as the epiphyseal sleeve fracture could arise as an avulsion fracture of the periosteal hinge. Further pathophysiological studies would be required to accurately delineate the extent of injury.

Operative management of triplane fractures has reliably shown good clinical outcomes and functional results. ^10,18 Good functional results were maintained in long-term follow-up after closed reduction and percutaneous screw fixation with an articular fracture gap of <2 mm. ^6,19 In a recent study by Choudhry et al. evaluating management of 58 triplane fractures, they noted good clinical outcomes with Foot and Ankle Outcome Scores and Marx Activity Scales with closed reduction alone and closed reduction with percutaneous screw fixation with a fracture gap of <2.4 mm.

Shin et al. recommended that type 1 and type 2 fractures can be managed with closed reduction and cast immobilization because these fractures do not exit the weight-bearing surface of the tibial plafond. However, our experience has been to manage types 1 and 2 fractures with anatomical reduction of the ankle mortise to reduce a widened medial joint space and to reduce an incongruent articular surface due to fracture displacement to prevent secondary osteoarthritis. As there have been demonstrably good results with operative management of displaced triplane fractures with intra-articular involvement, we recommend performing operative closed reduction and percutaneous screw fixation for displaced types 1 and 2 fractures of the modified classification (Figure 5). Percutaneous screw fixation offers a fast and simple procedure with few complications. The average operating time from closed reduction to cast immobilization after screw fixation was 90.5 min in our center. Operative fixation provides more stability and allows patients to have earlier ankle mobilization, which may be an added benefit in our community of overweight and sedentary children. Nonetheless, there are risks to surgical management and possible need for implant removal in the future.

Figure 5.

Treatment algorithm for the modified classification of atypical triplane fractures.

As for the management and comparison of the extra-articular triplane fractures. We noted that all type 3 fracture patterns were nondisplaced while the majority of type 4 fracture patterns (4of 5) were displaced. This was clinically significant as treatment and management was based upon fracture displacement. Majority of cases with the AMES variant, type 4 injuries were subsequently managed with operative closed reduction and percutaneous fixation. This separation of types 3 and 4 fractures was included as they appeared to be two different entities on presentation and could be explained by the mechanism of injury as previously mentioned. Good prognosis would be expected as they were extra-articular. Decision for operative management for types 3 and 4 fractures no longer followed the principle of articular congruity but rather dictated by the presence of fracture displacement. In our series, the outcomes after management have been good overall following these principles.

The limitations to our study include the small sample size from this retrospective analysis. This could account for the differences seen in the age at the time of injury and the type of fracture sustained. The majority of male cases consisted of the AMES fracture variant compared to only two of nine patients in the female group, a phenomenon that we cannot explain from this small series of patients. The mechanism of injury can only be postulated in this small sample series, and further investigations are warranted to determine true pathophysiology in the development of atypical triplane fractures.

In conclusion, atypical and extra-articular triplane fractures are rare but may be under recognized. This is the largest series to date to look specifically at atypical triplane fractures. We report on a new extra-articular triplane fracture variant with an anteromedial epiphyseal sleeve fragment and a Modified Classification of Atypical Triplane Fractures. Operative closed reduction and percutaneous screw fixation is recommended for displaced intra-articular variants of triplane fractures with good clinical outcomes demonstrated.