Tommasini, Steven M.

Background: Trochlear dysplasia is important in recurrent patellofemoral instability (PFI); reliable metrics are essential to understand this condition and help define optimal treatment. One such measurement is the entry point to transition point (EP-TP) angle, which describes 2 components of patellar tracking from full knee extension to flexion: (1) mediodistal movement and (2) pure distal movement. Currently, measurement of this metric relies on 3-dimensional (3D) models. Purpose: To further develop the EP-TP angle metric to allow its digital measurement, to establish cohort and interrater reliability values, and to evaluate its appropriateness for clinical use. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: A data set composed of 30 recurrent PFI patient knees and 30 control knees was acquired. Each knee came with anterior views of the distal femur and curvature maps, which highlighted relevant structures such as the trochlear groove and the medial and proximal ridge. Three raters measured EP-TP angles utilizing a digital tool with and without the curvature maps. Significance of differences in means, presence of a TP, and interrater reliability with intraclass correlation coefficients were tested and evaluated according to an established guideline (<0.5, poor reliability; >0.5-0.75, moderate; >0.75-0.9, good; >0.9 excellent reliability). A significance level of .05 corrected with the Bonferroni method was assumed. Results: PFI knees had a significantly higher EP-TP angle than the control cohort (48.9° ± 10.8° vs 11.8° ± 14.6°; P < .001). Patients had a greater TP prevalence than controls (96.7% vs 10.0%). Interrater reliability for the EP-TP angle with curvature maps was significantly better than without (0.84 [95% CI, 0.76-0.89] vs 0.67 [95% CI, 0.55-0.78]; P < .001). Conclusion: The EP-TP angle is significantly different between PFI patients and controls. This study presents a digital approach for measuring the EP-TP angle, in contrast with the initially described method, which required 3D prints. This digital approach, when aided with curvature mapping, yields better reliability.

Purpose To create a metric for evaluating the degree of laterality of the patella’s entry into the trochlea, the entry point–trochlear groove (EP‐TG) angle, and to evaluate if this laterality is associated with recurrent patella instability. Methods The time frame of the study was January 2020 to February 2023. The inclusion criteria were patients treated by the senior author (J.P.F.) (with the exception of 2 patients who were treated by another provider at the institution who was aware of the study) who have been diagnosed with recurrent atraumatic patellar dislocations. Controls without knee pathology were selected from the New Mexico Decedent Imaging Database (NMDID). Simpleware ScanIP was used to create 3‐dimensional (3D) models of the distal femurs from computed tomography scans. Anteroposterior images of these 3D models were uploaded to a custom EP‐TG angle measuring tool. Three measurers used the tool to measure the EP‐TG angle of the distal femurs. Results Twenty‐eight patients were included for the recurrent dislocator group. Twenty‐four decedents from the NMDID were selected for the control group, each with a left or right knee chosen randomly for measurement. A 1‐sided Mann‐Whitney U test, used to evaluate whether the recurrent dislocators had higher EP‐TG angle values, yielded a P value <.001, demonstrating a high level of significance. A Bayesian mixed‐effect model, used to determine how different the EP‐TG angles are between the 2 groups, gave a posterior predictive interval of [11.93°, 19.12°] for the EP‐TG angle shift of dislocators. The intraclass correlation coefficient was 0.648. Conclusions The morphologic entry point of the patella into the proximal trochlea is more lateral in recurrent patella dislocators than in controls. This increased laterality can be measured by the EP‐TG angle, which may be useful information for optimizing treatment of recurrent patella instability. Level of Evidence Level III, case control study.