By Jordana Bieze Foster
The sports medicine community is demonstrating increasing interest in the possibility that neurocognitive impairment and musculoskeletal injury may be related, as evidenced most recently by an exchange in the letter to the editor section of the September issue of The American Journal of Sports Medicine (AJSM).
The letter in question, submitted by a team of researchers who have studied concussions in military populations, raised several technical concerns about a 2011 AJSM study from the University of Toronto that compared neurocognitive test scores in 18 concussed athletes, 18 athletes with musculoskeletal injuries, and 36 uninjured athletes.
The Toronto researchers found that although the musculoskeletal injury group fared better on the Automated Neuropsychological Assessment Metrics (ANAM) test than the concussed group did, the musculoskeletal injury group scores in some cases had significantly poorer scores than the uninjured group. In their article, the authors suggested the findings raise the possibility that musculoskeletal injuries may negatively influence performance on neurocognitive tests, and that this negative effect may be related to orthopedic pain and discomfort or to the psychological or emotional stress of being unable to compete.
The letter to the editor cautioned against concluding, based on the Toronto findings, that mild musculoskeletal injury alone causes impaired cognition. Among the study limitations noted in the letter was the observation of baseline differences in ANAM scores among the three study groups. Although the Toronto researchers found the differences were not statistically significant, the musculoskeletal injury group scores were closer at baseline to those of the concussed group than the control group for both throughput and reaction time on the Code Substitution: Learning and Code Substitution: Delayed subtests.
“There is a fairly strong body of knowledge demonstrating that multiple attempts are required on reaction time tests to establish a stable baseline. Other factors that our research demonstrated can affect baseline scores include age, ethnicity, educational level, and sleep deprivation. The biggest concern with such small numbers, though, is still individual variation,” said Rodney Coldren, MD, MPH, assistant professor and director of Tropical Public Health in the Department of Preventive Medicine and Biometrics at Uniformed Services University in Bethesda, MD, and first author of the letter.
But those same baseline differences may be significant in another way. In a 2007 AJSM study, researchers from the University of Delaware found that baseline scores on a different neurocognitive test (ImPACT) were worse in athletes who went on to suffer anterior cruciate ligament injuries than in controls.
“[The University of Toronto] data do add to this idea that neurocognitive impairment may predispose an athlete to injury, although it was not an aim of their study,” said Buz Swanik, PhD, ATC, director of the Biomechanics & Movement Science Program and associate professor in the Department of Kinesiology and Applied Physiology at the University of Dela- ware, and lead author of the 2007 study. “The data also raise a secondary question as to whether people with lower neurocognitive scores predispose themselves to concussions. After all, it is plausible that some athletes may be sustaining concussions because of poor judgment, errors in coordination, or loss of spatial awareness similar to the arguments we raised about ACL injuries.”
Coldren, however, is skeptical. In a study published in the September issue of Military Medicine, he and his colleagues found that baseline ANAM scores did not differentiate uninjured soldiers from those who had suffered mild nonconcussive injuries not related to blast exposures.
“While it makes intuitive sense that cognitive functioning can alter predisposition to injury [faster reaction times might avoid injuries, for example] I do not have any data to support this,” Coldren said. “Our study in Iraq showed no pre-injury differences in ANAM scores between those who suffered injuries and those who did not.”
Coldren RL, Russell M, Kelly MP, et al. Effect of musculoskeletal injury on concussion testing: letter to the editor. Am J Sports Med 2012;40(9):NP18-20.
Hutchison M, Comper P, Mainwaring L, Richards D. The influence of musculoskeletal injury on cognition: implications for concussion research. Am J Sports Med 2011;39(11):2311-2337.
Drestch MN, Coldren RL, Kelly MP, et al. No effect of mild nonconcussive injury on neurocognitive functioning in U.S. Army soldiers deployed to Iraq. Mil Med 2012;177(9):1011-1014.
Swanik CB, Covassin T, Stearne DJ, Schatz P. The relationship between neurocognitive function and noncontact anterior cruciate ligament injuries. Am J Sports Med 2007;35(6):943-948.