Knee ligament injuries in U.S. pedestrian crashes

Objective: Projectile legform tests are used to evaluate pedestrian lower extremity injury risk, including risk of injury to the cruciate and collateral ligaments. However, it has been suggested that cruciate ligament injuries rarely occur without collateral ligament injuries, making a cruciate ligament injury requirement unnecessary in pedestrian test procedures. Therefore, the current study examines cruciate ligament injuries among U.S. pedestrians with and without other injuries that are evaluated in pedestrian test procedures.

Methods: Injury data for pedestrians treated in U.S. trauma centers from 2007 to 2017 were drawn from the National Trauma Data Bank (NTDB) Research Data Set (RDS) and from its successor, the Trauma Quality Program (TQP) Participant User Files (PUF). Crash and demographic details for individual cases with documented knee ligament injuries were obtained from the Pedestrian Crash Data Study (PCDS).

Results: Among pedestrians aged 16 and older with knee ligament injuries, 38% had only collateral injuries, 31% had only cruciate injuries and 31% were documented with injuries to both. Younger pedestrians also sustained cruciate injuries without collateral injuries, with 36% of the 0-15 year-old pedestrians diagnosed with knee ligament injuries having isolated cruciate injuries. Given that injuries to the left and right knee could not be distinguished in NTDB cases, these estimates of isolated ligament injuries are likely conservative, so that at least 31% of pedestrians aged 16 and older and at least 36% of younger pedestrians sustained cruciate ligament injuries without collateral ligament injuries in the same knee. A PCDS case study illustrated how cruciate injury can occur without collateral injury in a lateral bumper impact below the knee.

Conclusions: Cruciate ligament injuries can occur in pedestrian crashes, with or without other injuries that are evaluated in pedestrian test procedures. Isolated cruciate injuries may be more likely in impacts above or below the knee and in impacts with a component of anterior-posterior loading. The frequency of cruciate injury in the absence of collateral injury in lateral and non-lateral impact supports inclusion of injury measures correlating to cruciate injury risk in pedestrian legform test procedures.