Background: Youth athletes are more vulnerable to concussive injury. Professional and collegiate athletics have begun to place neurologists, neurosurgeons, athletic trainers and team physicians on the sidelines for the assessment of head injuries sustained during play. In stark contrast, the majority of U.S. high schools do not have access to athletic training staff and there is an even greater lack of medical personnel at the youth and amateur sports level. This marked disparity underscores the need for a predictive sideline test that can be performed by laypersons to help objectively determine concussive injury and remove an athlete from play, particularly since athletes often under-report their symptoms. The King-Devick (K-D) Test is comprised of a demonstration card and three test cards that increase in difficulty. The K-D Test of rapid number naming requires vision, eye movements (saccadic, accommodative and vergence), concentration, language function and attention to perform and has been shown to reflect suboptimal brain function. Many recent studies have highlighted the utility of the K-D test on the sideline to detect both concussive as well as sub-concussive injury in high school, collegiate, and professional level athletes and been has demonstrated high sensitivity, specificity, and test-retest reliability. The purpose of this study is to further examine pre and post-season as well as test-retest reliability of K-D Test performance in youth athletes.

Methods: In this prospective study, youth tackle football athletes (n=178, 100% male, age 12.06 ± 0.93 years [range 10-14 years]) completed pre-season and post-season K-D Test as part of a larger study. Standard published K-D baseline procedures were used for both testing time points. Total K-D Test time was recorded. Athletes with concussion during the season were excluded.

Results: Mean K-D Test time at pre-season was 50.12 ±10.34 sec (range 31.65-81.07 sec). K-D Test scores between the pre- and post-season tests demonstrated high test-retest reliability (ICC 0.94, 95% CI [0.80, 0.98]). Inter-individual change from pre-season to post-season demonstrated an improvement in K-D Test time by 4.87 sec ±0.49. Pre-season K-D Test score improved 3.8 sec with every year increase in age (95% CI [2.3-5.4] p<0.001, R2 = 0.12, linear regression). Mean K-D Test time at post-season was 44.01 sec ± 0.92 (range 25.31-76.84 sec).

Conclusions: In this cohort of non-concussed, youth football athletes, K-D Test demonstrated high test-retest reliability. Similar to previously published literature, pre-season K-D Test times improved with age, however there was a wide range of baseline performance in this age group. This data highlights the necessity for (1) establishing individual baselines for comparison rather than relying on normative data and (2) performing yearly baseline testing due to improvement of K-D Test performance with advancing age during childhood and adolescence. Continued prospective studies of the K-D Test as a sideline tool for concussion detection and management in youth athletes and the clinical utility of the test as a surrogate objective marker for recovery are on-going.

Summary Points:

  • The K-D Test has high test-retest reliability in youth athletes.
  • Pre-season K-D Test times improved 3.8 s with every year increase in age.
  • It is necessary to establish individual baseline for comparison rather than relying on normative data due to the wide range of baseline score among younger ages.
  • It is important to perform annual baseline testing due to the improvement of K-D Test performance with advancing age in young athletes.