DEFINING TROCHLEAR DYSPLASIA VIA THE LATERAL TROCHLEAR INCLINATION ANGLE. Issue 4 (28th April 2020)

• Record Type: Journal Article
• Authors: Cheng, Christopher; Hedgecock, Jon; Solomito, Matthew; Joseph, Sheeba; Pace, J. Lee
• Is Part Of: Orthopaedic journal of sports medicine. Volume 8:Issue 4(2020)Supplement 3
• Publication Date: 2020-04-28
• Subjects: Sports medicine -- Periodicals; Orthopedics -- Periodicals; Arthroscopy -- Periodicals; Arthroplasty -- Periodicals; Knee -- Surgery -- Periodicals; 616.7
• DOI: 10.1177/2325967120S00179
• Languages: English
• ISSNs: 2325-9671

Abstract

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.