Fractures of the Lateral Process of the Talus: A New Classication Based on CT

Background: The common classications of the fractures of the lateral process of the talus (cid:0) LTPFs (cid:0) are based on radiographs and may underestimate the complexity of LTPF, therefore, requiring a comprehensive classication based on CT(Computed tomography) scan. The aim of this study is to propose a such classication system, and to evaluate its reliability and reproducibility. Methods: On the basis of the most widely recognized classications of Hawkins as well as McCrory-Bladin, we proposed a new and comprehensive classication based on CT scan for the LTPF. We retrospectively reviewed 42 patients involving LTPF. All fractures were classied according to Hawkins, McCrory-Bladin and new proposed classication system by three surgeons. The analysis of interobserver and intraobserver agreements was done using kappa statistics. Results: This new classication included two types based on presence of concomitant injuries or not, with type I consisting of three subtypes and type II of ve subtypes. Interobserver and intraobserver reliability of the new classication system were almost perfect (κ=0.846 and 0.823, respectively) (cid:0) showing a higher interobserver and intraobserver reliability compared to the Hawkins classication (κ=0.737 and 0.689, respectively) as well as McCrory-Bladin classication (κ=0.748 and 0.714, respectively). Conclusion: This new classication system for the LTPF based on CT is a comprehensive classication considering concomitant injuries. It is more reliable and reproducible and can potentially become a useful instrument for decision making of treatment options for LTPFs. Further studies on the evaluation of their clinical relevance (especially the long-term outcome) are warranted.


Introduction
Fracture of the lateral process of the talus (LTPF) occurs infrequently, accounting for 20% of talar fractures and 0.02-0.17% of all fractures in human body [1][2][3][4]. Due to the progressive expansion in recreational sport activities, mainly snowboard, their incidence has markedly increased [5,6]. For this reason, the LTPF has been termed a 'snowboarder's fracture' [7]. Despite its increasing incidence, the LTPF is di cult to diagnose and commonly overlooked on initial plain radiographs, as it may be subtle and di cult to visualize, with a misdiagnosis rate of 15% and up to 21% by radiographs alone [8]. Therefore, CT scan can be used to verify the LTPF and should be considered when more accurately diagnosing the LTPF [9,10].
In 1965, Hawkins initially classi ed LTPF into three types, simple fractures (Type I), comminuted fractures (Type II) and chip fractures (Type III) [11]. Based on Hawkins' classi cation, McCrory and Bladin reorganized and proposed a similar fracture classi cation system, but just in a different order [12]. After then, Tinner and Sommer subdivided type III of McCrory-Bladin classi cation into three subtypes, but didn't consider the concomitant injuries of LTPF [13]. All of the above classi cation systems are based on radiographs and possibly that they might underestimate the complexity of LTPF. It was estimated that, LTPF were associated with 19.6% of talar neck fractures and 24% of all talar body fractures [14,15]. LTPF may also be combined with fractures of talar head and posterior process [3]. However, by far as we know, these concomitant injuries have not been considered in any classi cation system regarding LTPF. Prompt and accurate diagnosis and classi cation of LTPF are crucial for optimized perioperative management [16]; moreover, detailed and extensive knowledge of concomitant injuries are conductive in surgical scheme making and contributed to obtaining of a better surgical outcomes. Sadly, up to date we are missing a comprehensive classi cation for the LTPF, which should include evaluation of LTPF and their concomitant injuries based on CT scan [17].
The objective of this study was to propose a comprehensive classi cation system for the LTPF based on CT and to verify its reliability and repeatability.

Classi cation
The new classi cation includes two types according to whether the LTPF is an isolated fracture or not.
Type I is an isolated fracture. This type is further divided into three subtypes ( Fig. 1), the same as the
Ib: simple fracture with involvement of the talo bular joint.
Ic: multiple fragment fracture with joint involvement.
Type II is a lateral process fracture in combination with other fractures of the ipsilateral talus, regardless of whether the fractures involve the articular surface or not. This type is divided into ve subtypes ( Fig. 2): IIa: lateral process fracture combined with talar head fracture.
IIb: lateral process fracture combined with talar neck fracture.
IIc: lateral process fracture with extension into the remainder of the talar body.
IId: lateral process fracture combined with talar posterior process fracture.
IIe: lateral process fracture combined with any two or more other fractures of the ipsilateral talus.
In order to estimate the reliability and reproducibility of the new classi cation we retrospectively reviewed the records of 370 cases of talus fractures, treated in our hospital from January 2010 to May 2020. The following diagnostic criteria for fractures were used:(1)older than 18 years; 2 fractures involving the lateral process of the talus 3 preoperative and postoperative ankle plain radiographs available and 4 a preoperative CT scan available for review. At last 42 patients (43 LTPFs, with one patient having bilateral fractures) were included in the study.
All fractures were classi ed by three evaluators accordingly to the Hawkins classi cation, the McCrory-Bladin classi cation and the new classi cation proposed. After fully understanding the classi cation system, three independent evaluators experienced in orthopaedics trauma surgery classi ed the 43 LTPFs based on the CT scan. A second round of classifying was performed 2 week later, and the case order was scrambled using a random number generator.

Statistical analysis
Interobserver reliability was evaluated to determine the reliability of the opinions of different observers for each case. By contrast, intraobserver reliability was evaluated to determine the reliability of individual observers by comparing the rst and second-round surveys for each case.
To determine the reliability of the classi cation systems we evaluated the interobserver agreement for each classi cation system using the Fleiss Kappa coe cient [18]. In order to evaluate the reproducibility of the classi cation system we calculated the intraobserver agreement using the Cohen Kappa coe cient [19]. Data analysis was conducted with IBM SPSS Statistics 21.0. The coe cients are interpreted using the Landis and Koch grading system, which de nes the reliability or reproducibility of κ values < 0.2 as slight, between 0.2 and 0.4 as fair, between 0.4 and 0.6 as moderate, between 0.6 and 0.8 as substantial, and values > 0.8 as perfect [20].

Results
From January 2010 to May 2020, a total of 370 patients with talus fractures were treated in our hospital, of whom 42 patients with the LTPF were included in the study. There were 37 males and 5 females with a mean age of 34.9 years (range 18-65). Fractures were present bilaterally in 1 patient, left-sided in 20, and right-sided in 21. The mechanisms of injury were a fall from large height (30 patients), a motor vehicle collision (6 patients), a fall from low height (3 patients), a sprain of ankle joint (2 patients) and a crush injury (1 patient). Among all 43 cases of LTPF, there were 9 fractures that were visible on CT but not on radiographs and the overall missed diagnosis rate was 20.9%(9/43). All the fractures were classi ed according Hawkins, McCrory-Bladin and new classi cation system.

Interobserver agreement
The average κ value among the three reviewers was 0.737 when classifying LTPFs using the Hawkins classi cation system, 0.748 when using McCrory-Bladin classi cation and 0.846 when using the new classi cation system ( Table 1). As can be seen, the new classi cation showed the highest interobserver reliability.  (Table 2). Similarly, the new classi cation system has a higher intraobserver agreement than the other two classi cations.

Discussion
In this study, we proposed a new and comprehensive classi cation for LTPF based on CT scan. It was divided into two types according to whether the LTPF was an isolated fracture or not; type I was further divided into three subtypes, the same as the McCrory-Bladin classi cation and type II was divided into ve subtypes. This proposed new classi cation system is simple, comprehensive and easy to remember, which we believe will provide useful information on treatment scheme making.
LTPF is an injury that is often missed because most cases are considered trivial ankle sprains due to nonvisualization of fracture on radiographs, with a resultant overall misdiagnosis rate of 15% and up to 21% by radiographs alone [21,22]. In our study, there were 9 cases of LTPF that were visible on CT but not on radiographs and the overall missed diagnosis rate was 20.9%(9/43), which was in line with previous literature [21]. Missed or untreated LTPFs can potentially lead to permanent pain, healing in malposition, impingement syndrome, pseudoarthrosis development and also, due to joint instability, induced a potential development of severe subtalar arthritis [23].
An ideal fracture classi cation system should be simple, comprehensive, reliable and reproducible [24].
Although various foot classi cation systems, such as the AO/OTA classi cation or Sneppen classi cation [25], do include LTPF, Hawkins as well as McCrory and Bladin are the only two classi cations speci cally focusing on LTPF [11,12,17]. Unfortunately, both classi cations are based on plain radiographs and therefore underestimate the extent of these fractures due to the complexity of the ankle joint [26]. The main objective of the radiology report should be to convey the full range of fracture patterns rather than attempting to t complex LTPF into a limited classi cation scheme. Additional CT scan must be employed in every patient in whom clinical doubts exist, providing additional information on concomitant injuries or associated fractures [27], which is possibly bene cial for operative program making. Therefore, in this study we proposed a new classi cation system based on CT to make a comprehensive classi cation for LTPF. Consistent with our hypothesis, the analysis results showed higher reliability and reproducibility of this new classi cation than previous commonly used Hawkins classi cation and McCrory-Bladin classi cation. This difference may be due to the use of a CT scan as a preoperative imaging modality, which permits a better identi cation of all fragments, their displacements and the areas of comminution.
If an early and accurate diagnosis of the fracture pattern is made and adequate treatment is undertaken, the prognosis of LTPF would be favorable. [28,29]. The lateral process of the talus possesses large articulations for both the distal bula and the posterior facet of the calcaneus. Fixation of LTPF is essential to restore the native architecture of these joint surfaces [30]. An attempt on open reduction and internal xation can potentially improve outcome and delay development of arthritis. For the small avulsion fracture or severe comminuted fracture which cannot be treated by open reduction and internal xation, conservative treatment or resection should be reserved [31]. The new classi cation provides a more comprehensive and practical method for classifying the LTPF, which may improve preoperative planning and subsequently the surgical treatment outcome.
The present study had some limitations, including its retrospective nature and the small sample size. Moreover, due to the lack of clinical data on surgical treatment, particularly the surgical outcome, the study could not con rm the correlation between this classi cation and clinical prognosis. A prospective study including clinical data of relatively large sample is necessitated to evaluate its clinical relevance.

Conclusions
Based on the widespread and established classi cations we present a comprehensive classi cation system for the LTPF based on CT. It has two types, of which type I consists of three subtypes and type II of ve subtypes. The new classi cation system is more reliable and reproducible and can potentially become a useful instrument to adequately correlate the long-term outcomes of these fractures. Further studies on the evaluation of the classi cation are warranted.  lateral process fracture in combination with other fractures of the ipsilateral talus: IIa: lateral process fracture combined with talar head fracture; IIb: lateral process fracture combined with talar neck fracture; IIc: lateral process fracture with extension into the remainder of the talar body; IId: lateral process fracture combined with talar posterior process fracture; IIe: lateral process fracture combined with any two or more other fractures of the ipsilateral talus.