Trends and Epidemiology of Knee Extensor Mechanism Injuries Presenting to United States Emergency Departments From 2001 to 2020

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Injuries to the native extensor mechanism (EM) of the knee are potentially disabling and often require surgical treatment. Large-scale, updated epidemiological data on these injuries is lacking. The objective of the current study was to examine recent trends in EM injuries presenting to United States (US) Emergency Departments (EDs) over the last 20 years using a nationally representative sample.


This study retrospectively analyzed the National Electronic Injury Surveillance System (NEISS) database to identify cases of EM injuries (defined as either a quadriceps tendon rupture, a patella fracture, or a patellar tendon rupture) presenting to EDs in the US from 2001 to 2020.


During the study period, an estimated 214,817 EM injuries occurred in an at-risk population of 6,183,899,410 person-years for an overall incidence rate of 3.47 per 100,000 person-years. Patella fractures (PFs) were the most common injury type, representing 77.5% of all EM injuries (overall incidence rate: 2.69), followed by patellar tendon ruptures (PTRs; 13.5%; incidence: 0.48) and quadriceps tendon ruptures (QTRs; 9%; incidence: 0.31). Demographic characteristics and mechanisms of injury differed between injury types. Annual incidence rates increased significantly during the study period for all EM injury types, with PTRs demonstrating the largest relative increase (average annual percent increase: PF, 2.8%; PTR, 7.2%; QTR, 5.3%). Accounting for population growth yielded an increasing incidence of all EM injuries combined from 3.65 in 2001 to 4.9 in 2020. The largest relative increases in incidence rates were observed in older age groups.


Extensor mechanism injuries of the knee are increasing in the US, which likely reflects an aging and more active population. These types of injuries are associated with substantial functional impairment and recent increases in incidence rates highlight the need for injury prevention and management strategies.



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