Open AccessDEFINING TROCHLEAR DYSPLASIA VIA THE LATERAL TROCHLEAR INCLINATION ANGLE
Author(s) -
Christopher Cheng,
Jon Hedgecock,
Matthew J. Solomito,
Sheeba Joseph,
J. Lee Pace
Publication year - 2020
Publication title -
orthopaedic journal of sports medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.329
H-Index - 35
ISSN - 2325-9671
DOI - 10.1177/2325967120s00179
Subject(s) - medicine , receiver operating characteristic , cutoff , magnetic resonance imaging , nuclear medicine , patella , orthodontics , radiology , physics , quantum mechanics
Background: Trochlear dysplasia (TD) is the principle anatomic risk factor for patellar instability (PI). The lateral trochlear inclination (LTI) is a quantitative measure of trochlear morphology on axial magnetic resonance imaging (MRI). Threshold values for patients at risk for PI via LTI measurement have ranged from 11 o to 17 o . Our group recently described a new technique for characterizing LTI by referencing the fully-formed posterior femoral condyles. This novel measurement technique revealed that the historically-used method was comparable in reliability but significantly underestimated TD.Purpose: The purpose of this study was to define, with high specificity, a LTI value cutoff value consistent with patellar instability using the new LTI measurement technique.Methods: MRI scans of 95 patients aged 9 to 18 years treated for PI at our tertiary referral center were compared with a control cohort of 98 age- and gender- matched patients with knee imaging but no clinical evidence of PI. LTI was measured as the angle formed between a line subtended from the cartilaginous surface of the lateral trochlea at its most proximal extent and a line parallel to the fully-formed posterior condyles. Receiver operator characteristic (ROC) curve analysis was conducted to establish a cutoff value with optimal specificity and sensitivity.Results: Average LTI was significantly lower in the study group (5.9±10.4 o ) than control (18.9±5.8 o ) (p<0.001). Area under the ROC curve was 0.86. A proposed 8.9 o LTI threshold angle achieves good discrimination between the two groups, with specificity of 0.904 and sensitivity of 0.684.Conclusion: Re-examination of previously described threshold values using ROC curve analysis of LTI measured in reference to the posterior condyles found 8.9 o as the optimal threshold value to achieve good discrimination between patients with and without PI. The novel technique has previously been established to have excellent intra- and inter-observer reliability and produced significantly lower LTI values than the historically-used technique. Taken in concert, this new cutoff is valuable to improve future clinical decision making in regards to risk stratification, treatment algorithms and research purposes.