Risk Factors and Time to Recurrent Ipsilateral and Contralateral Patellar Dislocations

Area of Science:

• Orthopedics
• Sports Medicine
• Biomechanics

Background:

• Previous studies on recurrent lateral patellar instability have limited cohort sizes, leading to variable recurrence rate estimations.
• Limited data exists regarding the incidence and risk factors for contralateral patellar instability following an initial lateral dislocation.

Purpose of the Study:

• To determine the cumulative incidence of recurrent ipsilateral and new contralateral patellar dislocations after a first-time lateral patellar dislocation.
• To identify risk factors associated with recurrent dislocations (ipsilateral or contralateral) and analyze the time to recurrence.

Main Methods:

• A population-based cohort study including 584 patients with a first-time lateral patellar dislocation (1990-2010).
• Retrospective review of injury details, subsequent dislocations, and structural characteristics (trochlear dysplasia, patella alta, TT-TG distance).
• Assessment of risk factors for recurrence and time to recurrence.

Main Results:

• At 20 years, cumulative incidence was 36.0% for ipsilateral recurrence and 5.4% for contralateral dislocations.
• Risk factors for ipsilateral recurrence included trochlear dysplasia (OR 18.1), patella alta (OR 10.4), age <18 (OR 2.4), elevated TT-TG (OR 2.1), and female sex (OR 1.5).
• Trochlear dysplasia, elevated TT-TG, patella alta, and age <18 significantly decreased time to recurrence.

Conclusions:

• The 20-year cumulative incidence of recurrent ipsilateral patellar dislocations is 36.0%, with 5.4% for contralateral dislocations.
• Specific anatomical factors (trochlear dysplasia, patella alta, elevated TT-TG) and patient demographics (age <18, female sex) are significant predictors of ipsilateral recurrence.
• These identified risk factors are crucial for predicting recurrence risk and time to recurrence in patients with initial lateral patellar dislocations.