AJSM - 2026-03-08 - Journal Article
Reevaluating Patellar Height Indices in Pediatric Patellofemoral Instability: Comparative Accuracy of Caton Deschamps Index, Patellotrochlear Index, and Sagittal Patellar Engagement.
Beltrame G, Crippa M, Beber SA, Lu S, Matarangas AI, Jaramillo D, Green DW
Topics
Key Takeaway
CDI outperforms both PTI and SPE in discriminating patellofemoral instability in pediatric patients (AUC 0.534–0.594 for MRI indices vs. CDI sensitivity/specificity >73%), while 40.5% of CDI-defined patella alta cases showed preserved engagement by SPE (>0.45).
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Summary
This study compared CDI, PTI, and SPE in 126 pediatric PFI patients versus 126 age- and sex-matched controls to determine which index best identifies patella alta and predicts instability. CDI was significantly elevated in PFI patients (1.317 vs. 1.094; P<.001) with sensitivity and specificity exceeding 73%, while PTI and SPE showed poor discriminative ability for both patella alta and PFI (AUC 0.461–0.594). Notably, 40.5% of CDI-defined alta cases had SPE >0.45, indicating preserved functional engagement despite radiographic alta.
Key Limitation
Using CDI as the reference standard rather than a validated clinical or biomechanical outcome measure limits conclusions about which index truly reflects instability risk versus radiographic alta.
Original Abstract
BACKGROUND
Patella alta is a key anatomic risk factor for patellofemoral instability (PFI), especially among young athletes performing pivoting sports, as it reduces patellofemoral engagement during early knee flexion. The Caton-Deschamps index (CDI) is a commonly used radiographic measure of patella alta, but it does not provide information on patellofemoral engagement, which is relevant in PFI. Magnetic resonance imaging (MRI)-based indices, such as the patellotrochlear index (PTI) and sagittal patellofemoral engagement (SPE), have been proposed as more appropriate assessments of functional patella alta .
PURPOSE
To (1) compare the performance of PTI and SPE in evaluating functional patella alta in pediatric PFI as determined by CDI; and (2) explore the relationship among indices.
STUDY DESIGN
Case-control study; Level of evidence, 4.
METHODS
We analyzed 252 participants: 126 patients with PFI and 126 age- and sex-matched controls. Radiographic and MRI-based measurements of CDI, PTI, and SPE were compared between groups. Correlations between indices and receiver operating characteristic (ROC) analyses were conducted, using the CDI as a reference standard.
RESULTS
The CDI was significantly higher in patients with PFI than controls (1.317 ± 0.215 vs 1.094 ± 0.171; P < .001), whereas PTI and SPE did not differ significantly. SPE values were lower in patients with patella alta (0.403 ± 0.156 vs 0.476 ± 0.169; P = .013). PTI and SPE were strongly correlated ( r = 0.898; P < .001), both demonstrating weak inverse correlations with CDI. When stratifying by patella alta, 40.5% of alta cases had an SPE of >0.45, and 97.3% had a PTI of >0.125. Univariable logistic regression demonstrated that SPE predicted patella alta (odds ratio = 0.263 [95% CI, 0.024-2.847]; P = .031). ROC analysis demonstrated poor discriminative ability of PTI and SPE for patella alta (area under the ROC curve [AUC], 0.534-0.594) and PFI (AUC, 0.461-0.488), while CDI strongly predicted PFI with sensitivity and specificity exceeding 73%.
CONCLUSION
PTI and SPE demonstrated poorer discriminative ability for patella alta than CDI. However, MRI-based indices frequently indicated preserved patellofemoral engagement despite CDI-defined patella alta, underscoring their complementary role.