AJSM - 2026-09-09 - Journal Article
Patella Alta and Trochlear Dysplasia as a Determinant of Patellar Tendon Lateralization and Inclination: A Cross-sectional MRI Study in Adolescents With Patellofemoral Instability.
Crippa M, Beltrame G, Beber SA, Matarangas AI, Lu S, Lijesen E, Jaramillo D, Green DW
Topics
Key Takeaway
PT-LTR (AUC 0.903, cutoff 4 mm) and the novel PTIA (AUC 0.866, cutoff 16°) discriminate adolescent patellofemoral instability from controls with excellent diagnostic accuracy, including in knees with normal TT-TG distance.
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Summary
This case-control MRI study in adolescents defined and validated PTIA—a novel measure of patellar tendon obliquity relative to the femoral condyles—and compared it against PT-LTR and established morphologic parameters. PFI knees showed significantly higher PT-LTR (9.76 vs control) and PTIA (22.76° vs control), both correlating positively with CDI, sulcus angle, and patellar tilt. ROC analysis yielded AUC 0.903 for PT-LTR (cutoff 4 mm) and AUC 0.866 for PTIA (cutoff 16°), with both measures retaining discriminatory value even when TT-TG distance was normal.
Key Limitation
Controls were not age- and sex-matched with confirmed absence of patellofemoral symptoms, introducing potential selection bias that could inflate diagnostic accuracy metrics.
Original Abstract
BACKGROUND
Patellofemoral instability (PFI) is traditionally assessed using tibial tubercle-trochlear groove (TT-TG) distance, patellar height indices, and trochlear morphology. However, soft tissue-based measures of patellar tendon orientation may provide complementary insight into patellar containment and extensor mechanism malalignment. Patellar tendon-lateral trochlear ridge distance (PT-LTR) has been proposed as a tendon-based marker of lateralization. The authors introduce the patellar tendon inclination angle (PTIA): a magnetic resonance imaging (MRI)-based parameter designed to quantify the obliquity of the patellar tendon relative to the femoral condyles.
PURPOSE
To define and validate PTIA and to compare its performance with PT-LTR. Secondary objectives were to assess correlation of PTIA and PT-LTR with established morphologic risk factors for PFI and to evaluate their diagnostic accuracy for identifying PFI.
STUDY DESIGN
Case-control study; Level of evidence, 3.
METHODS
MRI studies of 284 knees (PFI, n = 142; controls, n = 142) were included in this analysis. PTIA was developed and measured by orthopaedic surgeons, and their agreement was calculated. PT-LTR, sulcus angle, patellar tilt, lateral patellofemoral angle, TT-TG distance, and Caton-Deschamps index (CDI) were measured for all knees as well. Correlations between PT-LTR/PTIA and other classic measurements were assessed to evaluate the relationship of these novel tendon-based parameters. Subgroup analyses examined the effect of abnormal TT-TG distance (>16 mm), patella alta (CDI ≥ 1.3), and trochlear dysplasia (sulcus angle ≥ 145°). Receiver operating characteristic curves were used to determine diagnostic accuracy.
RESULTS
Patients with PFI demonstrated significantly higher PT-LTR (mean ± SD, 9.76 ± 7.66 mm) and PTIA (22.76°± 11.22°) as compared with controls ( P < .001). PT-LTR and PTIA were significantly positively correlated with patellar tilt, CDI, and sulcus angle. Patella alta significantly increased PT-LTR ( P < .001). Receiver operating characteristic analysis demonstrated excellent diagnostic performance for PT-LTR (area under the curve, 0.903; optimal cutoff, 4 mm) and PTIA (area under the curve, 0.866; optimal cutoff, 16°).
CONCLUSION
PT-LTR and PTIA are reliable MRI-based markers of PFI in adolescents. Although both correlate with established risk factors, including TT-TG distance, patella alta, and trochlear dysplasia, they remain informative even in the setting of normal TT-TG values. PTIA, introduced as a novel parameter, complements PT-LTR by quantifying tendon obliquity and providing additional information on patellar tendon alignment.