Objectives: Identifying anatomic risk factors for recurrent patella dislocations would help guide clinical decision-making and counseling for first-time dislocators. Many risk factors have been identified that increase the likelihood of patella instability, but little is known about risk stratification for recurrence of dislocation in individuals after a sentinel event. The purpose of this study is to determine if there are statistically significant differences in magnetic resonance imaging (MRI) measurements of patella instability (PI) in patients with a confirmed single dislocation versus those with multiple dislocations.
Methods
We conducted a retrospective cohort study of patients between ages 9 and 25 at a tertiary care center (2012-2023). Patients with prior surgery in the affected knee were excluded. Our recurrent cohort included patients with multiple prior dislocations and the non-recurrent cohort included patients with only one dislocation (without recurrence). All patients with a single dislocation were contacted by phone at final follow-up to confirm their status. Demographics and several (MRI) measurements, including tibial tubercle to proximal trochlear groove (pTT-TG), Caton-Deschamps (CD), relative tibial external rotation (rTER), and patella tilt (PT) were collected. We also recorded the following measurements on proximal, cartilaginous surfaces to assess trochlear dysplasia: two-image lateral trochlea inclination angle (LTI), sulcus angle (SA), trochlear depth (TD). Statistical analyses included Mann-Whitney U test and independent t-test with significance set as 0.05. We conducted receiver operating characteristic curves to assess the clinical utility of these anatomical risk factors.
Results
In total, 181 patients (105 females) were included in analyses. 111 belonged to the recurrent cohort and 70 were in the non-recurrent cohort. Overall recurrence rate was 60.32% and was significantly associated with greater patella alta (CD 1.3 vs 1.4, p=0,03), PT ( 17.7 vs 22.6, p<0.01), SA (156.6 vs 166.6, p<0.01) , and lower TD (1.7 vs 1.2, p<0.01). LTI (8.3 vs 9.5, p=0.65), pTT-TG (16.5 vs 17.6, p=0.12), and rTER (5.8 vs 5.5, p=0.72) were not significantly different in recurrent and non-recurrent dislocators. ROC curve shows that the combination of increased SA and patella alta (CD) is associated with a 72% likelihood of recurrence.
Conclusion
Patella alta (CD), PT, SA and TD, at proximal axial cuts, may be the most important anatomical risk factors for recurrent patella dislocation. pTT-TG, rTER and LTI were not predictive for recurrence. The combination of increased sulcus angle and patella alta (Caton-Deschamps) is associated with a 72% (95% confidence interval, 0.64 - 0.80) likelihood of recurrence. There is a lack of consistent literature reporting on anatomical risk factor differences between patients who experience recurrent versus single patella dislocations. Subsequent analyses should be directed towards establishing a predictive model for recurrent patella dislocation.