Knee airbags have a nominal effect on reducing injuries and may even increase injury risk in some cases, according to a new study from the Insurance Institute for Highway Safety.

The institute evaluated injury measures from 400 frontal crash tests to determine if injuries were less likely when vehicles were equipped with knee airbags. The institute also examined outcomes from real-world crash reports across 14 states, comparing injury risk in vehicles with and without knee airbags.

The findings linked to real-world crashes showed that knee airbags reduced overall injury risk by just half a percentage point, dropping from 7.9% to 7.4%.

As for the crash test data, the institute's thorough evaluation showed that knee airbags had only a small effect on injury measures recorded by dummies in driver-side small overlap front and moderate overlap front crash tests.

Iin the small overlap test, knee airbags were associated with increased injury risk for lower leg injuries and right femur injuries. However, head injury risk was slightly reduced in the small overlap test when knee airbags deployed.

Finally, the airbags had no effect on injury measures in the moderate overlap test.

IIHS notes that when it comes to knee airbags reducing injuries, the evidence is not statistically significant. However, the study did not look specifically at crashes in which people were not using seat belts, and it is possible that knee airbags would help unbelted occupants in real-world crashes, according to the institute.