Long-term Effects of ACL Reconstruction Surgery on Neurophysiologic Correlates of Movement Planning During Complex Jump Landing Tasks and the Role of Neuropsychological Performance Measures: An Explorative Cross-sectional Study

Particularly, in the context of ball sports ruptures of the anterior cruciate ligament (ACL) are among the most frequent injuries. However, the ACL tear does not only result in a loss of mechanical stability in the knee joint: the tear of the ligament and the subsequent reconstructive surgery lead to a massive damage of so-called mechanoreceptors (proprioceptors). These small sensors provide the brain with precise information on the tension of the cruciate ligament and the position of the knee joint. Due to this feedback, it is possible for humans to adjust the activity of the stabilizing muscles to various situations in sports and daily life and to protect the knee from injuries. Thus, coordination deficits are common consequences after ACL-rupture and reconstruction due to the poorer sensory feedback.

New findings provide evidence that the injury-induced damage of the mechanoreceptors also causes persistent, neuronal reorganisations in the brain (injury induced neuroplasticity). These relate in particular to the motor cortex by which voluntary movements are controlled. According to the results of imaging (eg. functional magnetic resonance tomography; MRI) and electrophysiological studies (eg. Electroencephalography; EEG), these neurologic adaptation appear to persist far beyond the resumption of daily, sporting or competitive activities. Researchers suggest that these adaptations of the central nervous system might be the underlying cause of the frequently observed, persistent motor control and functional deficits (eg. muscle strength and muscle activation deficits), the relatively high re-injury, low return to sports rates and small proportions returning to their initial performance level after ACL tears and reconstruction. A pure restoration of the neuromuscular function without the elimination of the neuroplastic changes in the brain does therefore not appear sufficient.

In recent studies the effects of ACL trauma on brain activity have been investigated exclusively during unspecific, sport- and injury-unrelated tests (eg. simple flexion and extension movements and angular reproduction tasks of the knee). Often, injuries to the ACL occur under unpredictable conditions, especially in complex, dynamic movements such as changes of direction, jumps and landings. Here, the brain has to process information from the receptors of the ACL as quickly as possible to initiate an adequate motor response to protect the knee.

Against the background of the above described findings, this cross-sectional case-control study will firstly investigate the effects of completely healed ACL tears and reconstruction (side symmetry of neuromuscular performance measures above 85%) on movement planning related cortical activity (via Electroencephalography) measures during complex jump-landing tasks: The study participants perform counter-movement jumps (n=80; CMJ, flight time approximately 500 ms) followed by single leg landings. While under an anticipated condition (n=40), the individuals receive the visual information (presented on a screen) on which leg/ foot (left, right) they are required to land before self-initiated CMJs, the individuals will receive this information under the non-anticipated condition (n=40) only after take-off (approximately 400 ms before ground contact). The measurement of the landing stability is standardized by means of selected biomechanical parameters (capacitive force platform). Injury-relevant, cognitive characteristics (e.g., reaction, information processing speed and working memory) are detected by computer and paper-based clinical cognition tests.

The investigators hypothesize that the injury-related neurological adjustments in the motor cortex lead to a more intensive motor action planning before movement initiation (compensation of sensory deficits). The increased use of neuronal capacities for movement planning could subsequently lead to a slower or to unprecise motor responses to unforeseen/ non-anticipated events and subsequently cause greater landing instability, or increase the knee injury risk, respectively. It is also assumed that a lower cognitive information processing is associated with a more instable landing, or a higher risk of injury or higher injury incidence rate, respectively.