Medio-lateral knee fluency in anterior cruciate ligament-injured athletes during dynamic movement trials

• Anterior cruciate ligament-injured athletes executed dynamic movement trials.
• Knee fluency during landing was calculated for injured and uninjured limbs.
• A stepwise trend in knee fluency between trials was recorded for injured limbs.
• Variable landing strategies were observed in unilateral trials for injured limbs.
• Knee fluency may be a valuable parameter to assess in injury rehabilitation.

BackgroundCorrection of neuromuscular impairments after anterior cruciate ligament injury is vital to successful return to sport. Frontal plane knee control during landing is a common measure of lower-extremity neuromuscular control and asymmetries in neuromuscular control of the knee can predispose injured athletes to additional injury and associated morbidities. Therefore, this study investigated the effects of anterior cruciate ligament injury on knee biomechanics during landing.MethodsTwo-dimensional frontal plane video of single leg drop, cross over drop, and drop vertical jump dynamic movement trials was analyzed for twenty injured and reconstructed athletes. The position of the knee joint center was tracked in ImageJ software for 500 milliseconds after landing to calculate medio-lateral knee motion velocities and determine normal fluency, the number of times per second knee velocity changed direction. The inverse of this calculation, analytical fluency, was used to associate larger numerical values with fluent movement.FindingsAnalytical fluency was decreased in involved limbs for single leg drop trials (P = 0.0018). Importantly, analytical fluency for single leg drop differed compared to cross over drop trials for involved (P < 0.001), but not uninvolved limbs (P = 0.5029). For involved limbs, analytical fluency values exhibited a stepwise trend in relative magnitudes.InterpretationDecreased analytical fluency in involved limbs is consistent with previous studies. Fluency asymmetries observed during single leg drop tasks may be indicative of abhorrent landing strategies in the involved limb. Analytical fluency differences in unilateral tasks for injured limbs may represent neuromuscular impairment as a result of injury.