Purpose

The purpose of this study is to describe the formation of JUPITER and provide preliminary descriptive analysis of patient demographics and clinical features for the initially enrolled patients in this prospective cohort. Patellar instability is common in young patients and can lead to significant morbidity and arthritis. Its management is controversial. JUPITER (Justifying Patellar Instability Treatment by Early Results) is a hypothesis-driven, multi-center, multi-armed, prospective cohort study developed to obtain sufficient subjects to better describe clinical characteristics and predictors of clinical outcomes in the young patellar instability population.

Methods

After training and institutional review board approval, surgeons began enrolling patients between 10-30 years of age who had sustained a patellar dislocation event. Information regarding patient demographics, dislocation history, physical exam characteristics, and baseline validated patient reported outcome scores were collected.

Results

As of December 2020, 21 surgeons from 12 sites had prospectively enrolled a total of 1492 patients (1523 knees) with patellar instability. 62.4% were female and the mean age of the cohort was 17.7 years. 71% knees were enrolled in the operative group and 29% in the non-operative group. 59% of knees reported that they had more than 1 dislocation (operative group 89.7%; non-operative group 10.2%, p<0.001). Operative treatment was indicated in 42.9% of first-time dislocators and 89.7% of recurrent dislocators (p<0.001).
The recurrent and operative group patients were noted to have a higher percent of positive physical exam findings than first-time and non-operative group patients on the affected knee (J-sign [p<0.001], apprehension [p<0.001], crepitus [p=0.041]) and the contralateral knee (except for the crepitus test [p=0.648]). The recurrent group was nearly twice as likely to be ligamentously lax (Beighton score of 5 or greater) compared to first-time patients (p<0.001).

Baseline PROs varied with the recurrent group having lower Pedi-FABS (p=0.001) and KOOS-QoL (0.008) scores and higher Kujala (0.009), KOOS ADL (0.008), KOOS Sports (<0.001), and Pedi-IKDC (0.014) scores than the first-time dislocator group.

Conclusions

The JUPITER Group has been able to accumulate the largest prospectively collected patellar instability database to date. Operative management was indicated in 42.9% of first-time dislocators, 50% of which had sustained an osteochondral fracture, and 89.7% of recurrent dislocators. Recurrent dislocators were more likely to have positive physical exam findings on both knees.

Significance

This epidemiologic study provides demographic information, clinical presentation and baselines PROs of patients with patellar instability. These baseline characteristics would help to identify the at-risk population and compare outcomes over time.