Effects of cognitive- and motor-dual tasks on postural control regularity following anterior cruciate ligament reconstruction.

BACKGROUND: High injury rates following anterior cruciate ligament reconstruction (ACLR) motivate the need to better understand lingering movement deficiencies following return to sport. Athletic competition involves various types of sensory, motor, and cognitive challenges; however, postural control deficiencies during this spectrum of conditions are not well understood following ACLR. RESEARCH QUESTION: To what extent is postural control altered following ACLR in the presence of sensory, motor, and cognitive challenges, and does postural control correlate with patient-reported symptoms? METHODS: Fourteen individuals following ACLR (4 m/10 f, 21.2 ± 2.4 yr, 76.9 ± 19.1 kg, 1.70 ± 0.14 m) and fourteen matched healthy controls (4 m/10 f, 21.2 ± 1.4 yr, 75.4 ± 15.3 kg, 1.70 ± 0.15 m) participated in the study. Participants completed single-leg balance, ACLR limb or matched side for controls, under four conditions: 1) eyes open, 2) eyes closed, 3) visual-cognitive dual task (i.e., reverse digit span), and 4) motor dual task (i.e., catching a ball). Sample entropy (SEn) was calculated for each balance condition to characterize regularity of center of pressure control. Participants also completed patient-reported outcomes to characterize self-reported knee function, symptoms, and fear. A mixed effects model tested for differences in SEn between balance conditions, and Spearman correlations tested for relationships between SEn and patient-reported outcomes. RESULTS: A significant Group-by-Condition interaction was detected (P = 0.043). While the motor dual task and eyes closed balance conditions were associated with the lowest SEn for both groups, only the visual-cognitive dual task condition demonstrated a significant difference between groups, with the ACLR group having lower SEn [95% confidence interval for ΔSEn: (0.03, 0.35)]. Lower KOOS-Sport scores were associated with decreased SEn for the ACLR group (ρ = 0.81, P < 0.001). SIGNIFICANCE: These findings are consistent with ACLR individuals using a less automatic approach to postural control compared to controls, particularly when presented with a visual-cognitive challenge. Altered neuromuscular control persists well after ACLR surgery and can be related to patient-reported outcomes.

Postural stability during visual-based cognitive and motor dual-tasks after ACLR.

OBJECTIVES: Determine the effect of visual-based motor and cognitive dual tasking on postural stability in those with anterior cruciate ligament reconstruction relative to matched controls. DESIGN: Cohort study. METHODS: Fourteen volunteers with history of anterior crucaite ligament reconstruction were matched with fourteen healthy controls. Participants performed single leg balance tasks under 4 conditions: (1) single leg balance with eyes-open, (2) single leg balance while catching a ball (dual-motor), (3) single leg balance while repeating a string of numbers in reverse order after viewing them (dual-cognitive) and (4) single leg balance with eyes-closed. Participants completed several patient-reported outcomes of knee function. Mixed effects models were used to identify group differences on the center of pressure measures of ellipse area and root-mean-squared excursion (medial-lateral and anterior-posterior). The mixed models included subject pair as a random factor and group (control, anterior cruciate liagement reconstruction), balance condition (eyes-open, eyes-closed, dual-cognitive, and dual-motor), and group*condition as fixed effects. Tukey post-hoc pairwise comparisons were performed for significant interaction and main effects with an α=0.05. RESULTS: A significant group by condition interaction was observed for ellipse area and medial-lateral root-mean-squared excursion. The anterior cruciate ligament reconstruction group had higher ellipse area (p=0.002, d=0.44) and medial-lateral root-mean-squared excursion (p<0.001, d=0.49). CONCLUSIONS: Postural stability is greatly impaired under eyes-closed and dual-motor conditions relative to eyes-open. Anterior cruciate ligament reconstructed individuals have greater postural instability during the dual-cognitive condition that may indicate unique neural processing deficits remain following anterior cruciate ligament reconstruction.

Quantitative four-dimensional tracking of cytoplasmic and nuclear HIV-1 complexes.

Emerging real-time techniques for imaging viral infections provide powerful tools for understanding the dynamics of virus-host cell interactions. Here we labeled human immunodeficiency virus-1 (HIV-1) integrase with a small tetracysteine tag, which preserved the virus' infectivity while allowing it to be labeled with the bis-arsenical fluorescein derivative FlAsH. This labeling allowed us to image both intracytoplasmic and intranuclear HIV-1 complexes in three dimensions over time (4D) in human cells and enabled us to analyze HIV-1 kinetics by automated 4D quantitative particle tracking. In the cytoplasm, HIV-1 complexes underwent directed movements toward the nuclear compartment, kinetically characteristic of both microtubule- and actin-dependent transport. The complexes then adopted smaller movements in a very confined volume once associated with the nuclear membrane and more diffuse movements once inside the nucleus. This work contributes new insight into the various movements of HIV-1 complexes within infected cells and provides a useful tool for the study of virus-host cell interactions during infection.