Inter- and intra-observer variation of schatzker classification of tibial plateau fractures and morphological characteristics of each fracture subtype on computed tomography scan
Siddharth Gupta1, Raskesh Malhotra1, Amit Srivastava1, Rajesh Arora1, Aditya N Aggarwal1, Puneet Mishra2
1 Department of Orthopaedics, University College of Medical Sciences and Guru Teg Bahadur Hospital, Delhi, India
2 Department of Orthopaedics, Fortis Hospital, Delhi, India
|Date of Submission||16-Jul-2021|
|Date of Acceptance||01-Dec-2021|
|Date of Web Publication||15-Jun-2022|
Dr. Raskesh Malhotra
Department of Orthopaedics, University College of Medical Sciences and Guru Teg Bahadur Hospital, Delhi – 110 095
Source of Support: None, Conflict of Interest: None
Background: There is little information regarding inter- and intra-observer variation when classifying tibial plateau fractures using Schatzker classification system. There is paucity of literature regarding morphological characteristics of each Schatzker subtype on computerized tomography. Materials and Methods: Fifty-three patients (age 18–70 years) of either sex with fresh (<3 weeks old), closed tibial plateau fracture were included after obtaining their informed consent. Patients with previous surgery around tibia or knee and the ones with pathological fractures were excluded from the study. Standard plain radiographs (anterior, posterior, and lateral views) and an additional noncontrast computed tomography (CT) scan (with three-dimensional reconstruction) of knee and leg of the affected side were done. Five different surgeons classified these fractures as per Schatzker classification on two separate occasions. The intra- and inter-observer variations were calculated using the kappa test of Cohen. Additional morphological characteristics were also evaluated on CT scan. Results: The mean kappa values for five observers (A to E) for inter-observer agreement on Schatzker classification were 0.41 (moderate). The mean kappa value for intra-observer agreement was 0.71 (substantial). Six morphological characteristics were defined on CT scan-lateral condylar impaction (79.2%), tibial tuberosity fracture (3.8%), coronal plane (3.8%), tibial spine avulsion (22.6%), medial condylar impaction (17%), and posteromedial shear fracture (7.5%). Conclusion: There is inter- and intra-observer variation in Schatzker classification of tibial plateau fracture. The intra-observer variation (kappa 0.71) was found to be greater than the inter-observer variation (kappa 0.41). The additional morphological characteristics of tibial plateau fractures are better evaluated on CT scan. The articular depression, splits, and fracture geometry are better delineated on a CT scan than on plain X-rays alone.
Keywords: CT scan, observer variation, schatzker classification, tibial plateau fractures
|How to cite this article:
Gupta S, Malhotra R, Srivastava A, Arora R, Aggarwal AN, Mishra P. Inter- and intra-observer variation of schatzker classification of tibial plateau fractures and morphological characteristics of each fracture subtype on computed tomography scan. J Orthop Traumatol Rehabil 2022;14:18-23
|How to cite this URL:
Gupta S, Malhotra R, Srivastava A, Arora R, Aggarwal AN, Mishra P. Inter- and intra-observer variation of schatzker classification of tibial plateau fractures and morphological characteristics of each fracture subtype on computed tomography scan. J Orthop Traumatol Rehabil [serial online] 2022 [cited 2022 Jun 24];14:18-23. Available from: https://www.jotr.in/text.asp?2022/14/1/18/347372
Tibial plateau fracture constitutes 1% of all fractures and 8% of fractures in the elderly. There is no universally accepted method of classification of tibial plateau fractures as more than six classification schemes have been described; among them, Schatzker and AO/OTA classification are the most commonly used methods for classifying such fractures.,,
Computed tomography (CT scan) is commonly used to assess the proximal tibial fractures.,,,,,,,,,, It helps in better assessment of fracture patterns which is often underestimated with plain radiographs and it also improves surgical planning.,,,,,, An additional CT scan can change the classification in some instances.,,, There are few published reports on inter- and intra-observer variation when classifying tibial plateau features using the Schatzker and AO/OTA classification systems.,,,,,,,,,
The aim of this study was to assess inter- and intra-observer variation of tibial plateau fractures on plain radiographs using Schatzker system of classification and to study the morphological characteristics of each subtype of Schatzker classification system on an additional CT scan.
|Materials and Methods|
This prospective observational study was conducted in the department of orthopedics in a tertiary care hospital after obtaining ethical clearance from the institutional ethical committee. Fifty-three patients (age 18–70 years) of either sex with fresh (<3 weeks), closed tibial plateau fracture were included in our study after obtaining their informed consent [Table 1]. Patients with previous surgery around tibia or knee and the ones with pathological fractures were excluded from the study.
In all patients, standard plain radiographs of knee and leg of the affected side (anterior, posterior, and lateral views) were done. In addition, a noncontrast CT scan with three-dimensional (3D) reconstruction of proximal tibia was also done.
The proximal tibial fractures were classified according to Schatzker classification, by a set of five trained orthopedic surgeons, namely three consultants (named C, D, and E) and two senior residents (named A and B), using plain radiographs on two separate occasions, at “zero” and “8 weeks” (this was deemed long enough time lag to ensure that observer would not recall their initial responses). All the observers were given printed handouts of the Schatzker classification system to make them familiar with the system. They were blinded for the details of patients, and their observations were recorded on a predesigned per forma. The responses made by the observers at “0 week” were not shown to them on the second occasion, at “8th week”.
All responses were entered in a Microsoft Excel sheet, and inter- and intra-observer variation was determined for these responses. For statistical analysis, the kappa test of Cohen was used to determine the level of variation. Kappa is a coefficient of agreement, that varies from + 1 (perfect agreement) to “0” (agreement no better than chance) to-1 (representing absolute disagreement). The results of the first reading were used to determine inter-observer variation. Comparison of first and second readings of a particular observer determined the intra-observer variation.
The morphological characterization of each subtype of Schatzker classification was done by 2D-CT scan with additional 3D reconstruction, which was evaluated by three surgeons. The CT scan was analyzed under the majority consensus response of the subtype of Schatzker classification evaluated on first occasion. The CT scan images of each patient were evaluated for the presence or absence of fracture characteristics (outlined below) that are not included in frequently used classification systems (Schatzker, Hohl and Moore’s, Three column classification and A. O./O. T. A.):
- Posteromedial shear fracture
- Coronal plane fracture
- Lateral condylar impaction
- Medial condylar impaction
- Tibial spine involvement
- Separation of tibial tubercle necessitating fixation
- Any other morphological characteristics.
Fifty-three patients who fulfilled the inclusion criteria were included in the study. The mean kappa values for five observers (A to E) for inter-observer agreement on Schatzker classification was 0.41 (moderate). The mean kappa value for intra-observer agreement was 0.71 (substantial). The kappa values for inter- and intra-observer variation are depicted in [Table 2].
|Table 2: Kappa values for inter- and intra-observer variation for Schatzker classification
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The CT scan of each patient was analyzed for additional morphological fracture characteristics for each subtype of Schatzker classification [Table 3]. Among the six morphological characteristics defined on CT scan:
|Table 3: Morphological characteristics of computed tomography scan on majority consensus in each subtype of Schatzker classification
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- Lateral condylar impaction was found in 79.2% cases (out of these, 50% cases were Schatzker type II on consensus)
- Tibial tuberosity fracture was found in 3.8% of the cases
- Coronal plane fracture was also found in 3.8% of the cases
- Tibial spine avulsion was found in 22.6% of the cases, of which 41.7% each were Schatzker type II and VI on consensus
- Medial condylar impaction was found in 17% of the cases, out of which 55.5% were Schatzker type II on consensus and rest were type VI
- The posteromedial shear fracture was found in 7.5% of the cases, of which 50% were Schatzker type V on consensus.
- Thus, lateral condylar impaction was the most common morphological characteristics, whereas coronal plane fracture and tibial tuberosity fracture were the least common of all.
Some illustrative cases where the CT scan showed other morphological characteristics which were not appreciated on plain radiographs are discussed below.
Posteromedial shear fracture was found in the CT scans of four patients (case numbers 5, 26, 32, and 35). Out of these four patients, one of them (case number 35) showed not only posteromedial shear fracture but also a coronal plane fracture [Figure 1]. The plain radiographs of this patient were classified as Schatzker type VI on consensus. However, the CT scan of the same patient confirmed it as bicondylar fracture (an additional lateral condyle involvement) equivalent to a Schatzker type V fracture.
|Figure 1: (Case 35): Posteromedial shear fracture on sagittal cuts of computed tomography scan, but it also has coronal plane fracture line visualized on axial cuts
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The tibial tuberosity fracture was found in two cases (case number 17 and 38) on CT scan. These were not discernable on plain radiographs. Tibial spine avulsion was found in 12 patients out of a total of 53. It brings out an important lacuna in the Schtazker classification which does not qualify this injury pattern in any of its classification subtypes.
There have been cases in our study which have undergone a change in Schatzker classification after a CT scan. Case number 42 which was classified as Schatzker type IV fracture on consensus of plain radiograph, which was found to have fracture line involving the lateral condyle with comminution in the region of tibial spine [Figure 2]. In another case (case number 41), it appears as if it was an unicondylar fracture of Schatzker type II, but on CT scan, it was found to be a bicondylar fracture with metaphysio-diaphyseal discontinuity, equivalent to Schatzker type VI fracture [Figure 3]. There had been similar changes in the perception of the geometry of the fracture in case number 48.
|Figure 2: (Case 42): Plain radiograph showed Schatzker type 4 fracture, but computed tomography scan of same patient showed that fracture line was extending into the lateral condyle with comminution in the region of tibial spine
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|Figure 3: (Case 41): Plain radiograph showing Schatzker type II fracture. computed tomography scan of same patient showing bicondylar fracture (Schatzker type V fracture)
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In case number 15, which was classified as Schatzker type II on consensus, but was found to have a significant finding on CT scan in the geometry of the fracture [Figure 4].
|Figure 4: (Case 15): Plain radiograph showed Schatzker type II fracture but on computed tomography scan (axial cut), there is posteromedial extension of lateral condyle fracture
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The lateral condyle fracture has a posteromedial extension. The management of this patient was changed due to an extension of the intra-articular fragment medially which was not evident on plain radiograph.
The Schatzker classification for tibial plateau fracture has high inter-observer variation which may be due to the fact that tibial plateau fractures are often complex injuries with multiple fracture lines and variable articular line depression, which may be difficult to assess radiologically on plain radiographs alone. Charalambous et al. observed that the intra-observer variation was lower than the inter-observer variation which actually signifies reproducibility independent of agreement. This means the same observer gives a more consistent response even though it may be incorrect. Thus, incorrect responses show less intra-observer variation than inter-observer variation. The level of expertise was not an important factor in their study.
In the current study, observers A and B were registrars and observers C, D, and E were consultants. The intra-observer variation of C (kappa 0.59) and E (0.71) was found higher than that of A (kappa 0.80). Thus, the Schatzker classification has both inter- and intra-observer variations. The variations are more in inter-observer analysis than in intra-observer analysis. [Table 3] gives the comparison of results of various studies, regarding the inter- and intra-observer agreement of tibial plateau fracture using Schatzker classification, with the current study.
From [Table 4], it can be deduced that there has been largely moderate agreement for inter-observer agreement. However, intra-observer agreement has been better than the inter-observer agreement.
|Table 4: Comparison between the current study and previous studies for variations in response for Schatzker classification
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The current study also observed that CT scan adds to the knowledge of the orthopedic surgeon regarding the fracture geometry. Although it has been suggested by some workers that Schatzker type III fractures probably do not exist; however, in the current study, 10 responses out of 318 responses for total 53 radiographs were classified as Schatzker type III fracture. Two of these radiographs got consensus of type III fracture. However, only one of the cases, which was different from the other two (which got consensus of being Schatzker type III fracture) was found to be pure depression type fracture pattern on the CT scan.
There have been studies which have concluded that the inter-observer reliability of tibial plateau fractures improves by the addition of CT scan to plain radiographs.,,, Some studies have also shown that the addition of CT scan to plain radiograph improves the reliability of classification and also modifies the treatment plan of the surgeons for a particular fracture.,,,,,,
Thus, the plain radiographic assessment for the fracture of tibial plateau may not be enough to understand the fracture geometry and decide the treatment strategy. The varying degrees of comminution, articular depression, split, and displacements are better and more meticulously evaluated on a CT scan than on a plain X-ray alone. The lack of morphological characterization of various different fracture patterns which did not find a mention in the Schatzker classification can be filled by a detailed evaluation on CT scan.
The additional morphological characteristics such as tibial spine avulsion, posteromedial shear fracture, and tibial tuberosity fracture find no mention in the conventional Schatzker classification. These injuries may also be found in isolation apart from association with the conventional six types of Schatzker classification. The identification of these additional injury patterns is useful in surgical planning, more so in the ongoing quest for fragment-specific fixation.
The strength of the current study is that it is a prospective cross-sectional study. However, the limitation of the study is that the sample size was relatively small due to the limited duration of the study.
The Schatzker classification of tibial plateau fracture does show inter- and intra-observer variation. The inter-observer variation is greater than the intra-observer variation. The observers show a moderate (kappa 0.41, i.e., <0.5) inter-observer agreement. However, there is a substantial (kappa 0.71, i.e., 0.5–0.75) intra-observer agreement.
The additional morphological characteristics of tibial plateau fractures are better evaluated on CT scan. The articular depression, splits, and fracture geometry are better delineated on a CT scan than on plain X-rays alone.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]