Redefining Trochlear Dysplasia: Normal Thresholds Vary by Measurement Technique, Landmarks, and Sex

Abstract

Background: Trochlear dysplasia is a known risk factor for patellar instability. Multiple radiographic measurements exist to assess trochlear morphology, but the optimal measurement technique and threshold for instability are unknown. Purpose: To describe the optimal measurements and thresholds for trochlear dysplasia on magnetic resonance imaging (MRI) that can identify knees with patellar instability in male and female patients. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: Knee MRI scans of patients with patellar instability were compared with those of age- and sex-matched controls. Measurements of the sulcus angle, lateral trochlear inclination (LTI), and trochlear depth were performed on axial images using bony and cartilaginous landmarks. Receiver operating characteristic curve analysis was performed, with the area under the curve (AUC) describing the accuracy of each diagnostic test. Optimal cutoff values were calculated to distinguish between knees with and without patellar instability. AUC and cutoff values were reported for each measurement as well as for male and female subgroups. Results: A total of 238 knee MRI scans were included in this study (138 female, 100 male; age range, 18-39 years). Trochlear depth measurements had the greatest diagnostic value, with AUCs of 0.79 and 0.82 on bone and cartilage, respectively. All measurements (sulcus angle, LTI, trochlear depth) on bone and cartilage had an AUC ≥0.7 (range, 0.70-0.86), with optimal cutoff values of 145° (bone) and 154° (cartilage) for the sulcus angle, 17° (bone) and 13° (cartilage) for LTI, and 4 mm (bone) and 3 mm (cartilage) for trochlear depth. Optimal cutoff values in female patients varied from those in male patients for all measurements except for cartilaginous trochlear depth. Conclusion: Normal thresholds for trochlear dysplasia varied based on the use of bony versus cartilaginous landmarks. Cartilaginous trochlear depth measurements had the greatest ability to identify knees with patellar instability. Furthermore, optimal cutoff values for all measurements except for cartilaginous trochlear depth differed between female and male patients. These findings suggest that sex-specific parameters of normal values may be needed in the assessment of risk factors for patellofemoral instability.

Patients with trochlear dysplasia have dysplastic medial femoral epiphyseal plates

“…Trochlear dysplasia is a known risk factor for patellar instability in adolescents, and studies have demonstrated abnormalities in the trochlear morphology of patients with patellar instability [1,24,31,32,36]. The bony restraint of the patellofemoral joint formed by the femoral trochlea and the patella is one of the main structures that prevents patellar dislocation.…”

Medial condyle hypoplasia in adolescent and young adult patients with trochlear dysplasia: a retrospective study

“…That could be due to the fact that, morphologically, the trochleas of female knees are smaller than are those of male knees. However, in a recent study, that difference was not found to be significant after normalization for patient height ( 26 , 27 ) . Therefore, controversy still exists regarding why females are affected more by trochlear dysplasia; that is, whether it is due to the smaller condyle dimensions or to the wider, shallower trochlear groove.…”

Patellar malalignment: A common disorder associated with knee pain

“…Individuals with bone or muscle anomalies (e.g., trochlear dysplasia or patella alta) have a very unstable patella for which nonsurgical treatment is generally ineffective ( Fig. 1 ) [ 24 , 25 ]. Therefore, surgical intervention is necessary in such cases.…”

“…The function of the reconstructed MPFL gradually decreases [ 68 ]. Thus, a trochleoplasty is indicated in cases of trochlear dysplasia [ 24 , 25 , 69 ].…”