ACL injury is prevalent in athletics. Not only are there immediate injury and changes, but there is substantial evidence that there are long term changes associated with this injury including: osteoarthritis, alterations in gait, changes in body awareness and psychology, and weakness as well as increased risk of further musculoskeletal injury compared to non-injured individuals. Even more studies have reported unresolved neuroplastic changes after injury, reconstruction, and rehabilitation that may limit function and return to sports participation. There has been a large focus in the past decade of creating preventative programs and limiting exposures to potential injuries through conditioning and body awareness. However, decreased body awareness is inevitable with ACL injury. Trauma to the ACL has been shown to modify how the nervous system processes the interactions between vision and sematosensation. The loss of previously recognized reflexes and gama motor neuron drive to prepare the CNS function to engage appropriately may require “up-training” of other systems, such as increased utilization of visual feedback, to maintain the required sensory input for motor control.
Recently in JOPST, Dustin Groomes, MEd, ATC, CSCS, from The Ohio State University recently discussed the importance of understanding the changes in body systems and neuroplasticity after ACL injury. Groomes describes how training the biomechanical factors of the ACL injury may not address all the physiologic consequences. But the capacity for neuroplasticity after injury and during rehabilitation can present an opportunity to close the gap by targeting a broader spectrum of sensorimotor function during neuromuscular training. This can be captured by the non-contact (majority) ACL injury. Generalizing the break down of the typical action is:
- a failure to maintain knee neuromuscular control while attending to an external focus of attention under highly complex visual stimuli, variable surfaces, movement planning, decision making, during classically an open environment.
During this changing environment, the sensory systems 3 main afferent pathways of vestibular, visual, and somatosensory provide complex integrated information. This is rapidly acquired and processed to produce efferent neuromuscular control to maintain adequate stability and control. The interaction between vision and somatosensation is particularly critical for motor control during environmental interaction. This interaction is compromised even after ACL reconstruction. The ACL receives nerve fibers from the posterior articular branches of the tibial nerve. These fibers penetrate the posterior joint capsule and run along with the synovial and periligamentous vessels surrounding the ligament to reach as far anterior to the infrapatellar fat pad. Disruptions in this input yield immediate changes in neuroplasticity and can lead to mechanical changes and compensations that may not be properly or fully rehabilitated during typical training focused solely on biomechanical changes and strength gains.
The loss of ability to relay on the bodies typical reflex afferent inputs may require “up-training” of supplementary mechanisms such as increased utilization of visual feedback to train and maintain required sensory inputs for motor control.
Groomes further states that individuals in his fMRI studies demonstrated increased activity in the posterior inferior temporal gyrus. This area has been linked to many cerebral functions, but may primarily be involved with visual processing of movement. This area must work together with the hippocampus, in order to create an array of understanding of the physical world. The information received in this area is sent to the Primary Visual Cortex (V 1) for processing determining the outputs from the Motor Cortex (M 1). The increased activity in this area post ACL injury may suggest that there is an increased utilization of visual processing and motor planning for movement simultaneous with depression of the somatosensory function of the ACL previously discussed.
Simply put, the body is nothing except adaptable. Even in ways that we don’t even understand, yet. But it seems that if we injure our ACL, the brain automatically changes its preference to more visual based inputs to assist in making decisions for motor control. What about those who aren’t injured yet? On the flip side of that coin, Swanik reported, in 2007, initial findings of decreased visual reaction times and processing speeds as predictive of ACL injury. Perhaps we need more visual based processing and challenges during our preventative strategies as well?
This begs the question. What are we doing for enhancing visual feedback for our ACL or currently healthy clients? How are we up-training them visually in the attempt to prevent overload in the athletic environment? If we know they can’t feel the knee like they used to….literally…how can we impose a greater demand on vision to help adapt more than there body, but also their brain?
Here are a few tips on how you can start addressing this need with your clients:
2) Ensure that we are challenging our clients in an open environment, as soon as it is safely possible, performing dual tasks frequently
3) Consider giving you and the client immediate visual feedback during skill training early in rehabilitation with a device such as the Motion Guidance Clinician Kit
4) Consider taking visual feedback away at times during advanced mechanoreceptor training exercises to continue to challenge the body with different inputs. This might be particularly challenging for the client on altered surfaces or to advance already mastered skills
Hopefully this information has stimulated your own approach to rehabilitation of this challenging population. We need to be aware of utilizing all possible body systems to maximize the ability of our clients to be ready to return to their best potential in their athletic or work environments.
-Eric and Tal