Mapping the Femoral Trochlea: Development of the Multi-level Axial Patellofemoral Score for Trochlear Dysplasia
Jason D Brenner1, Steven M Henick2, Leila Mehraban Alvandi2
1Albert Einstein College of Medicine, Bronx, New York, USA.
Background:
There is currently no established standard classification system for stratifying trochlear dysplasia (TD) severity. Many magnetic resonance imaging (MRI)-based classification systems focus on only a single axial level, even though the trochlear groove (TG) spans several axial levels. Evaluating multiple axial levels of the TG may allow a complete assessment.
Hypothesis:
A novel MRI-based TD severity classification system based on 4 axial levels will yield a more comprehensive assessment of the TG.
Study Design:
Cross-sectional study; Level of evidence, 3.
Methods:
Pediatric patients were retrospectively categorized into 2 groups: those with recurrent patellar dislocations (RPDs; n = 106; mean age, 15.29 ± 2.45 years) and those with no history of patellar dislocations (controls; n = 98; mean age, 15.56 ± 1.40 years). Cartilaginous sulcus angle (SA) measurements were conducted at 4 consecutive axial levels on MRI starting at the proximal TG (SA1 = most proximal, SA2 = near-proximal, SA3 = near-distal, and SA4 = most distal). Cutoff values were identified using the Youden index. Patients were classified based on the number of elevated SA values: all 4 elevated values indicated grade 4 TD, 3 elevated values indicated grade 3 TD, 2 elevated values indicated grade 2 TD, 1 elevated value indicated grade 1 TD, and all normal values indicated grade 0 TD. Proportions were calculated, and the Fisher exact test was used to compare TD severity between the RPD and control groups.
Results:
Diagnostic cutoff values were as follows: SA1, 160°; SA2, 154°; SA3, 153°; and SA4, 148°. The RPD group was more likely to have grade 4 TD (58% vs 4%, respectively; P < .001) and grade 3 TD (13% vs 4%, respectively; P = .03) compared with the control group. Conversely, the RPD group had less grade 0 TD (8% vs 68%, respectively; P < .001). There was no difference in the proportions with grade 2 TD (13% vs 9%, respectively; P = .39) or grade 1 TD (8% vs 14%, respectively; P = .27) between the RPD and control groups. Intraobserver reliability was excellent for SA1 to SA4, and interobserver reliability was excellent for SA1 and SA4 and good for SA2 and SA3.
Conclusion:
The Multi-level Axial Patellofemoral Score for Trochlear Dysplasia (MAPS-TD) is a novel classification system that stratifies TD severity and has demonstrated accuracy and reliability in distinguishing patients with RPDs from controls. Its primary clinical utility lies in differentiating more extensive TD (especially grade 4) from mild TD (grades 1 and 2). The MAPS-TD may help guide surgical decision-making, possibly even in identifying candidates for surgical procedures (ie, trochleoplasty) among those with grade 4 TD.
