Interobserver reliability is higher for assessments with 3D software-generated models than with conventional MRI images in the classification of trochlear dysplasia

Purpose Trochlear dysplasia is a significant risk factor for patellofemoral instability. The severity of trochlear dysplasia is commonly evaluated based on the Dejour classification in axial MRI slices. However, this often leads to heterogeneous assessments. A software to generate MRI-based 3D models of the knee was developed to ensure more standardized visualization of knee structures. The purpose of this study was to assess the intra- and interobserver agreements of 2D axial MRI slices and an MRI-based 3D software generated model in classification of trochlear dysplasia as described by Dejour. Methods Four investigators independently assessed 38 axial MRI scans for trochlear dysplasia. Analysis was made according to Dejour’s 4 grade classification as well as differentiating between 2 grades: low-grade (types A + B) and high-grade trochlear dysplasia (types C + D). Assessments were repeated following a one-week interval. The inter- and intraobserver agreement was determined using Cohen’s kappa (κ) and Fleiss kappa statistic (κ). In addition, the proportion of observed agreement (po) was calculated for assessment of intraobserver agreement. Results The assessment of the intraobserver reliability with regard to the Dejour-classification showed moderate agreement values both in the 2D (κ = 0.59 ± 0.08 SD) and in the 3D analysis (κ = 0.57 ± 0.08 SD). Considering the 2-grade classification, the 2D (κ = 0.62 ± 0.12 SD) and 3D analysis (κ = 0.61 ± 0.19 SD) each showed good intraobserver matches. The analysis of the interobserver reliability also showed moderate agreement values with differences in the subgroups (2D vs. 3D). The 2D evaluation showed correspondences of κ = 0.48 (Dejour) and κ = 0.46 (high / low). In the assessment based on the 3D models, correspondence values of κ = 0.53 (Dejour) and κ = 0.59 (high / low) were documented. Conclusion Overall, moderate-to-good agreement values were found in all groups. The analysis of the intraobserver reliability showed no relevant differences between 2 and 3D representation, but better agreement values were found in the 2-degree classification. In the analysis of interobserver reliability, better agreement values were found in the 3D compared to the 2D representation. The clinical relevance of this study lies in the superiority of the 3D representation in the assessment of trochlear dysplasia, which is relevant for future analytical procedures as well as surgical planning. Level of evidence Level II.

Lateral Trochlear Inclination Angle: Measurement via a 2-Image Technique to Reliably Characterize and Quantify Trochlear Dysplasia

Background: Trochlear dysplasia (TD) is a risk factor for patellar instability (PI). The Dejour classification categorizes TD but has suboptimal reliability. Lateral trochlear inclination (LTI) is a quantitative measurement of trochlear dysplasia on a single axial magnetic resonance imaging (MRI) scan. Hypothesis: A modified LTI measurement technique using 2 different axial MRI scans that reference the most proximal aspect of the trochlear cartilage on 1 image and the fully formed posterior condyles on the second image would be as reliable as and significantly different from the single-image measurement technique for LTI. Further, the 2-image LTI would adequately represent overall proximal trochlear morphologic characteristics. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: Patients aged 9 to 18 years treated for PI between 2014 and 2017 were identified. The Dejour classification was radiographically determined. Single-image LTI was measured on a single axial MRI scan at the most proximal aspect of visible trochlear cartilage. A 2-image LTI was measured from 2 separate MRI scans: 1 at the most proximal aspect of trochlear cartilage and the second at the fully formed posterior condyles. This 2-image LTI was repeated at 3 subsequent levels (the first measurement is referred to as LTI-1; repeated measurements are LTI-2, LTI-3, and LTI-4, moving distally). In total, 65 patients met the inclusion criteria, and 30 were randomly selected for reliability analysis. Results: Inter- and intrarater reliability trended toward more variability for single-image LTI (intraclass correlation coefficient [ICC], 0.86 and 0.88, respectively) than for 2-image LTI (ICC, 0.97 and 0.96, respectively). The Dejour classification had lower intra- and interrater reliability (ICC, 0.31 and 0.73, respectively). Average single-image LTI (9.2° ± 12.6°) was greater than average 2-image LTI-1 (4.2° SD ± 11.9°) ( P = .0125). Single-image LTI classified 60% of patients with PI as having TD, whereas the 2-image LTI classified 71% as having TD. The 2-image LTI was able to capture 91% of overall proximal trochlear morphologic characteristics. Conclusion: LTI has higher reliability when performed using a 2-image measurement technique compared with single-image LTI and Dejour classification. The strong correlation between 2-image LTI and average LTI shows that 91% of TD is represented on the most proximal axial image. Because the single-image measurement appears to underestimate dysplasia, previously described thresholds should be reexamined using this 2-image technique to appropriately characterize TD.

Reliability of the Oswestry-Bristol Classification for trochlear dysplasia

Aims The Oswestry-Bristol Classification (OBC) was recently described as an MRI-based classification tool for the femoral trochlear. The authors demonstrated better inter- and intraobserver agreement compared to the Dejour classification. As the OBC could potentially provide a very useful MRI-based grading system for trochlear dysplasia, it was the aim to determine the inter- and intraobserver reliability of the classification system from the perspective of the non-founder. Methods Two orthopaedic surgeons independently assessed 50 MRI scans for trochlear dysplasia and classified each according to the OBC. Both observers repeated the assessments after six weeks. The inter- and intraobserver agreement was determined using Cohen’s kappa statistic and S-statistic nominal and linear weights. Results The OBC with grading into four different trochlear forms showed excellent inter- and intraobserver agreement with a mean kappa of 0.78. Conclusion The OBC is a simple MRI-based classification system with high inter- and intraobserver reliability. It could present a useful tool for grading the severity of trochlear dysplasia in daily practice. Cite this article: Bone Joint Open 2020;1-7:355–358.

Reliability of the Oswestry-Bristol Classification for trochlear dysplasia

Aims The Oswestry-Bristol Classification (OBC) was recently described as an MRI-based classification tool for the femoral trochlear. The authors demonstrated better inter- and intraobserver agreement compared to the Dejour classification. As the OBC could potentially provide a very useful MRI-based grading system for trochlear dysplasia, it was the aim to determine the inter- and intraobserver reliability of the classification system from the perspective of the non-founder. Methods Two orthopaedic surgeons independently assessed 50 MRI scans for trochlear dysplasia and classified each according to the OBC. Both observers repeated the assessments after six weeks. The inter- and intraobserver agreement was determined using Cohen’s kappa statistic and S-statistic nominal and linear weights. Results The OBC with grading into four different trochlear forms showed excellent inter- and intraobserver agreement with a mean kappa of 0.78. Conclusion The OBC is a simple MRI-based classification system with high inter- and intraobserver reliability. It could present a useful tool for grading the severity of trochlear dysplasia in daily practice. Cite this article: Bone Joint Open 2020;1-7:355–358.

The Oswestry-Bristol Classification

Aims Trochlear dysplasia is a significant risk factor for patellofemoral instability. The Dejour classification is currently considered the standard for classifying trochlear dysplasia, but numerous studies have reported poor reliability on both plain radiography and MRI. The severity of trochlear dysplasia is important to establish in order to guide surgical management. We have developed an MRI-specific classification system to assess the severity of trochlear dysplasia, the Oswestry-Bristol Classification (OBC). This is a four-part classification system comprising normal, mild, moderate, and severe to represent a normal, shallow, flat, and convex trochlear, respectively. The purpose of this study was to assess the inter- and intraobserver reliability of the OBC and compare it with that of the Dejour classification. Methods Four observers (two senior and two junior orthopaedic surgeons) independently assessed 32 CT and axial MRI scans for trochlear dysplasia and classified each according to the OBC and the Dejour classification systems. Assessments were repeated following a four-week interval. The inter- and intraobserver agreement was determined by using Fleiss’ generalization of Cohen’s kappa statistic and S-statistic nominal and linear weights. Results The OBC showed fair-to-good interobserver agreement and good-to-excellent intraobserver agreement (mean kappa 0.68). The Dejour classification showed poor interobserver agreement and fair-to-good intraobserver agreement (mean kappa 0.52) Conclusion The OBC can be used to assess the severity of trochlear dysplasia. It can be applied in clinical practice to simplify and standardize surgical decision-making in patients with recurrent patella instability. Cite this article: Bone Joint J 2020;102-B(1):102–107

Classification of dysplasia of the femoral trochlea in patients with patellar instability depends on the evaluation plane

ObjectiveTrochlear dysplasia is a major predisposing factor of patellar instability (PI). Dysplasia types are generally evaluated using the Dejour classification, but it is unclear whether this classification covers the entire spectrum. The objective of this study was to confirm whether the trochlear types on an axial view categorised according to the classification represent the entire trochlear shape.MethodsNinety knees from 81 patients with PI and 15 knees from 10 healthy volunteers (HVs) were evaluated. Three-dimensional knee models were created by MRIs. The femoral trochlear planes (FTPs) were defined as virtual cross sections including the transepicondylar axis, closer to the perpendicular plane of the articular surface. FTP 0 was defined as the reference plane including the proximal edge of the femoral trochlea and FTP θ as the plane making optional angle θ to FTP 0. Trochlear dysplasia types according to the classification were evaluated at every 10 degrees of FTPs up to 60 degrees (FTP 10, 20, 30, 40, 50 and 60). A trochlea with a sulcus angle <145° was defined as normal. Changes in the trochlear type according to FTPs, and agreement with clinical classification were evaluated.ResultsEighty-six knees (96%) in patients with PI and 12 (80%) in HVs showed changing trochlear types in different FTPs. Patterns of change varied among patients with PI and HVs. This suggests morphological variation of dysplastic trochleae. Agreement of trochlear type on each FTP with the clinically used Dejour classification was 42% on FTP 10, 49% on FTP 20, 33% on FTP 30, 22% on FTP 40, 22% on FTP 50% and 22% on FTP 60 in patients with PI, and 20% at FTP 10, 80% at FTP 20 and 100% on FTP 30 through FTP 60 in HVs. This suggests that the trochlear types in the clinically used plane do not always match the ones on the planes describing the contact surface to the patella.ConclusionThe trochlear types on an axial view provided by the Dejour classification do not represent the entire trochlear geometry. Multiple axial planes should be clinically used to more precisely describe the entire trochlear shape.

LATERAL TROCHLEAR INCLINATION IN CHILDREN AND ADOLESCENTS: MODIFIED MEASUREMENT TECHNIQUE TO CHARACTERIZE PATELLAR INSTABILITY

Background: Patellar instability (PI) is relatively rare but occurs most often in younger patients with underlying pathoanatomy. Trochlear dysplasia (TD) is one of many identified PI risk factors, but consensus is lacking on ideal radiographic measurements. The Dejour classification of TD on lateral radiographs is widely accepted but has suboptimal intra and interrater reliability and does not allow quantification of TD. Lateral trochlear inclination (LTI) measured on the most proximal axial magnetic resonance image (MRI) of the trochlear chondral surface is another described measurement of TD. LTI has historically been described with reference to the posterior aspect of the femur at the same axial level at which the proximal trochlea is measured. However, given the transitional anatomy of the distal femur, the LTI may be better represented by referencing the axis of the fully formed posterior femoral condyles. The posterior condyles represent a true axis of rotation that serves as an internal reference for knee motion and is clearly visible on MRI. We hypothesized that modified LTI measurements (LTI) referencing the posterior condylar axis would differ from the apparent LTI (ALTI) in a pediatric and adolescent population. We also hypothesized that the LTI would have stronger intra and inter reliability than the ALTI measurement and Dejour classification. Lastly, we hypothesized that the most proximal level of the trochlea would adequately represent overall proximal trochlear morphology. This is clinically relevant because dysplasia is most severe on the proximal trochlea and normalizes distally towards the intercondylar notch. Methods: Patients aged 9 to 18 years treated for PI at our tertiary referral center between January 2014 and August 2017 were identified. The Dejour classification was determined on lateral knee radiographs. The ALTI was measured as previously described on axial MRI images (Figure 1A). The LTI (also referred to as LTI #1) was measured on the same MRI image with respect to the angle of the posterior condyles (Figure 1B-C). The LTI was measured again in this fashion at the three subsequent, consecutive axial levels (LTI#2, LTI#3, LTI#4) to capture the first 12 mm of the proximal trochlea. The average of these measurements (LTI-avg) was calculated for each patient. All measurements were performed by two independent observers. A cohort of 30 patients were randomly selected for reliability analysis which was performed twice by three independent observers at least two weeks apart. Inter- and intra-rater correlation coefficients were calculated on this subgroup. Regression analysis was performed on the entire cohort. Results: Sixty-five patients met inclusion criteria for this study, and thirty patients were randomly selected for reliability analysis. Inter- and intra-rater reliability for ALTI showed good agreement but trended towards more variability than the inter- and intra-rater reliability for LTI#1 which had near perfect agreement (Table 1). Inter- and intra-rater reliability for all subsequent LTI measurements and LTI-avg had high or near perfect agreement (Table 2). The Dejour classification had poor to moderate inter-rater and good to near perfect intra-rater reliability. The crossing sign was the most reliable radiographic feature (Table 3). In the entire cohort of 65 patients, the average ALTI (9.2+/-12.6 degrees) was 7.0+/-3.4 degrees greater (less dysplastic) than the average LTI #1 (4.2+/-11.9 degrees) (p = 0.013). Referencing the 11 degrees LTI threshold value for trochlear dysplasia reported in the literature, the ALTI was below 11 degrees in 60% of our PI patients indicating dysplasia, while the LTI was less than 11 degrees in 71% of our PI patients. Regression analysis demonstrated statistically significant positive correlation between LTI#1 and LTI#2 (r=0.88, beta=0.81, p<0.0001), LTI#1 and LTI#3 (r=0.67, beta=0.54, p<0.0001), LTI#1 and LTI#4 (r=0.65, beta=0.43, p<0.001), and LTI#1 and LTI-avg (r=0.91, beta=0.70, p<0.0001). Conclusion: LTI has higher intra and interrater reliability when performed with reference to the posterior condyles compared to the historical measurement (ALTI) and the Dejour classification. The significant and strong correlation between LTI#1 and subsequent LTI measures as well as LTI-avg shows that 90% of TD is represented on the first, most proximal axial image and thus provides an appropriate, reliable and quantifiable measurement of TD in children and adolescents with PI. The significant difference found between LTI and ALTI shows that the historical measurement appears to underestimate dysplasia. Thus, previously described threshold values should be re-examined using this new technique to appropriately characterize trochlear dysplasia in patients with patellar instability as this can have implications for treatment algorithms for these patients. [Table: see text][Table: see text][Table: see text][Figure: see text]

Femoral Trochleoplasty for Recurrent Patellar Dislocation: Treating the Underlying Trochlear Dysplasia

The patellofemoral joint presents a complex biomechanical interaction involving soft tissues and bony structures to maintain joint stability. The most relevant factor is trochlear dysplasia which is present in 85% of patients. Femoral trochleoplasty is a surgical procedure to recreate the trochlear groove. This case report describes a young patient who had all clinical factors of patellar instability and trochlear dysplasia. Radiology studies showed trochlear dysplasia type C according to the Dejour classification. The patient underwent a trochleoplasty with an elevated flap of cartilage and subchondral bone as described by Ryzek and Schöttle [J Knee Surg 2015; 28(4): 297–302], associated with the reconstruction of the medial patellofemoral ligament. Femoral trochleoplasty is a surgical procedure to recreate the trochlear groove by removing subchondral bone to create a new trochlear sulcus, while respecting the kinematics and biomechanics of the patellofemoral joint.

Conventional Radiographs and Magnetic Resonance Imaging for the Analysis of Trochlear Dysplasia: The Influence of Selected Levels on Magnetic Resonance Imaging

Background: Trochlear dysplasia is one of the most important risk factors for recurrent patellar instability. It is defined on true lateral conventional radiographs (CR) and axial magnetic resonance imaging (MRI). The type of trochlear dysplasia is decisive for surgical treatment; however, low agreement between CR and MRI has been reported. Purpose: To compare the Dejour classification of trochlear dysplasia on CR and axial MRI using differing levels defined in the literature. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: The 4-type classification of trochlear dysplasia by Dejour was used to analyze 228 knees with recurrent patellar dislocations on true lateral CR and axial MRI. The 2-type modification of the Dejour classification was also similarly analyzed. Measurements on axial MRI were performed at 3 different levels: MR1, the most proximal level where the intercondylar notch forms a “Roman arch”; MR2, 3 cm above the joint line; and MR3, the midpatellar height. Results: MR1 was measured at a mean distance of 29 ± 3.5 mm and MR3 at a mean of 38 ± 5.8 mm above the joint line. MR1 and MR2 were always measured on the cartilaginous trochlea, whereas 52% of MR3 was found more proximally. Overall agreement was fair between CR and MR1/MR2 (31.1%/25.4%, respectively) and highest for MR3 (45.2%; P < .01). The highest agreement (81.8%) was found for MR3 with the 2-type trochlear dysplasia classification (low-grade trochlear dysplasia: type A vs high-grade trochlear dysplasia: types B, C, and D) and lower for MR1 (67.5%) and MR2 (62.0%). Conclusion: Trochlear dysplasia measured on CR and MRI shows only fair agreement, especially when the supratrochlear region of the distal femur is not analyzed on axial MRI. MRI analysis that considers the cartilaginous trochlea only tends to underestimate the severity of dysplasia according to Dejour. For a more precise evaluation of trochlear dysplasia, the entire distal femur should be analyzed on axial MRI.