July 2012

Concussion conundrum: Chronic postural deficits elude detection

In the moment: Sports medicine

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By Jordana Bieze Foster

Sophisticated laboratory experiments have documented postural control deficits in athletes with a history of concussion, but research presented in June at the annual meeting of the National Athletic Trainers Association (NATA) suggests clinicians may find it difficult to identify similar deficits in concussed athletes once their other symptoms have resolved.

Because returning to athletic activity too soon after a concussion can exacerbate the initial injury’s effects, return-to-play guidelines require resolution of all symptoms and a return to baseline levels on neurocognitive test scores. But the extent to which postural control deficits linger after other symptoms have resolved remains unclear. A 2011 Journal of Athletic Training study found that approximate entropy measures identified significant postural differences between athletes with a history of concussion and nonconcussed athletes—differences that not were not evident using the more conventional Sensory Organization Test (SOT).

Researchers from the University of North Carolina at Chapel Hill analyzed 27 asymptomatic athletes a mean of 7.5 days postconcussion and found that their SOT scores were no different from those of nonconcussed controls, even though the concussed athletes had significantly lower neurocognitive scores.

“It may be because we used a static balance measure,” said Julianne Schmidt, ATC, who presented the findings at the NATA meeting. “It does seem that with more dynamic tasks we may be able to pick up more prolonged deficits.”

Two other studies presented at the NATA meeting found no postural control deficits in athletes with a self-reported history of concussion. Sway velocity, measured using the Stability Evaluation Test (an instrumented version of the Balance Error Scoring System [BESS]), did not differ significantly between 30 athletes with a concussion history and 175 nonconcussed controls in a study from A.T. Still University in Mesa, AZ. And researchers from Georgia Southern University in Statesboro, GA, found no significant differences between 10 athletes with at least three prior concussions and 10 controls for step length velocity, center of pressure (COP) displacement, or COP–center of mass separation during gait initiation.

A second Georgia Southern study had better luck differentiating acutely concussed athletes from controls using a dual task gait assessment. Investigators analyzed 17 athletes assessed within 24 hours of concussion and 17 controls as they walked at a self-selected speed on an instrumented walkway while performing working memory cognitive challenges (e.g., saying the days of the week backwards). The concussed athletes walked 13% more slowly, had a 7% shorter stride length, and spent 3.5% more time in stance phase.

“Postconcussion participants demonstrate a conservative locomotor performance during a dual task gait test,” said Thomas Buckley EdD, ATC, an associate professor of athletic training at Georgia Southern, who presented the findings at the NATA meeting.

Age and gender may also affect postural stability after concussion, according to a Michigan State University study published in the June issue of the American Journal of Sports Medicine and presented at the NATA meeting. In 222 athletes assessed within three days of concussion, BESS scores for male athletes were worse in high school than in college, but for female athletes that pattern was reversed.

Sosnoff JJ, Broglio SP, Shin S, Ferrara MS. Previous mild traumatic brain injury and postural-control dynamics. J Athl Train 2011;46(1):85-91.

Schmidt JD, Register-Mihalik JK, Mihal­ik JP, Guskiewicz KM. Neurocognition and postural control of asymptomatic concussed athletes compared to healthy controls. Presented at the 63rd annual meeting of the National Athletic Trainers Association, St. Louis, MO, June 2012.

Corvo MA, Williams TA, Lam KC, Valovich McLeod TC. Does concussion history affect postural control as measured by the Stability Evaluation Test? Presented at the 63rd annual meeting of the National Athletic Train­ers Association, St. Louis, MO, June 2012.

Krazeise DA, Munkasy BA, Joyner AB, Buckley TA. Dynamic postural control is not impaired in individuals with multiple concussions. Presented at the 63rd annual meeting of the National Athletic Trainers Association, St. Louis, MO, June 2012.

Buckley TA, Munkasy BA. Acute con­cus­sion impairs dual task gait perfor­mance. Presented at the 63rd annual meeting of the National Athletic Trainers Association, St. Louis, MO, June 2012.

Covassin T, Elbin RJ, Harris W, et al. The role of age and sex in symptoms, neurocognitive performance, and postural stability in athletes after con­cus­sion. Am J Sports Med 2012;40(6): 1303-1312.

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