Association between Patellofemoral Conditions and the Incidence of ACL Injury: Could Patellofemoral Conditions be a Risk Factor for ACL Injury? A 10-year Population-Based Study.

Background: Patellofemoral conditions are common causes of knee symptoms in young and active individuals and have been linked in prior literature to neuromuscular and movement-related deficits that also have been associated with anterior cruciate ligament (ACL) injury risk. However, whether a prior diagnosis of patellofemoral conditions is associated with increased subsequent ACL injury risk remains unclear. Objective: To determine whether prior diagnosis of patellofemoral conditions (PFC) is associated with an increased risk of subsequent anterior cruciate ligament (ACL) injury or other intra-articular knee pathology. Design: Retrospective cohort study. Methods: Electronic medical records from a multi-state health system were reviewed to identify patients aged 14-40 years with patellofemoral conditions (PFC) diagnosed between 2014 and 2016. Exclusion criteria included prior major lower extremity injury or surgery, systemic rheumatologic disease, and incomplete records. Identified patients were followed through 2024 for incident knee injuries or knee-related surgical procedures. The primary outcome tracked was incident ACL injury. Secondary tracked outcomes included meniscal, chondral, medial patellofemoral ligament, and other ligamentous injuries of the knee, as well as knee-related surgical procedures. Cumulative incidence was estimated, and risk factors were compared using Wilcoxon rank-sum, chi-square tests, and multivariable logistic regression adjusting for age, sex, and body mass index (BMI). Results: Of 3,108 screened charts, 1,232 patients met inclusion criteria (median age: 19 years; 69.2% female). During the follow-up time period, 10.9% sustained an intra-articular knee injury or underwent a knee-related surgical procedure. ACL injuries occurred in 2.5% and meniscal injuries in 4.1%; less frequent events included medial collateral ligament injuries (0.7%), osteotomies (0.6%), and patellar tendon injuries (0.2%). The ACL incidence in this cohort was 246 per 100,000 person-years, a 3.6-fold higher rate compared with the general population. Injuries occurred predominantly ipsilateral to the index PFC diagnosis. In adjusted analysis, greater weight and BMI were associated with subsequent knee injury; however, multivariable logistic regression did not identify age, sex, or BMI as independent predictors of ACL injury. Conclusion: Patients with patellofemoral conditions showed a substantially elevated incidence of subsequent ACL injury compared to the general population. A prior diagnosis of PFC may identify a subgroup at greater risk for later intra-articular knee injury and may warrant closer rehabilitation and injury-prevention consideration. Level of Evidence: 3.