In addition to searching MedLine and other clinical databases, you can search specific journals directly.
Some of these journals publish 'special issues' dedicated to concussion research.
1. Concussion. Journal of Chiropractic Medicine. December 2013 12(4)
2.Concussion and Mild Traumatic Brain Injury: Current and Future Concepts, PM&R. 2011 3(10) Supplement 2:S387-S395