Risk for Lower Extremity Injury Following Concussion

Abstract

Concussions may increase the risk for subsequent lower extremity injuries in physically active people. PURPOSE: Examine concussion as a risk factor for lower extremity (LE) injury in soldiers with no history of LE injury. METHODS: Medical encounter data for all active duty US Army soldiers from 2005-2009 were used to identify soldiers who sustained a concussion by way of International Classification of Diseases, Ninth Revision (ICD-9) codes. Soldiers with a history of a LE injury were excluded from the study. LE injuries were defined according to the fractures, dislocations, sprains, and strains ICD-9 codes from the Barell injury diagnosis matrix. Matched controls (age, sex, and military occupational specialty [MOS]) were selected from the population of soldiers in the Army during the same month as each concussion case. Soldiers were followed from the time of incident concussion or matching until: 1) a lower extremity injury, 2) loss to follow-up, or 3) conclusion of a 24-month follow-up period. Using concussion as the primary risk factor, a Cox Proportional Hazard Ratio (HR) was calculated for LE injury, controlling for matched factors, time in military service, and race. Life table methods were used to evaluate LE injury rates for qualitative comparison between the two groups across the 24-month follow-up period. RESULTS: From 2005 to 2009, incident concussions were identified in 7,981 soldiers without a history of LE injuries. Of these cases, 1,892 (~24%) experienced a LE injury within 2 years following concussion. Concussed soldiers were at 53% greater risk of LE injury over the 24-month follow-up period (HR=1.53, 95%CI [1.42, 1.65]) compared to controls. On qualitative examination of unadjusted injury rates, the greatest difference in the rate of LE injuries appeared during the first 6 months post-concussion. CONCLUSION: These results suggest that a concussion puts soldiers at increased risk for sustaining a LE injury. This risk may be greatest during the first several months post-concussion. These findings may have implications for managing people returning to activity after concussion. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.