- Anterior cruciate ligament rupture is a common musculoskeletal injury in athletes and active individuals.
- Despite surgical reconstruction and lengthy rehabilitation, injuries can recur.
- Dustin Grooms at Ohio University, USA, believes changes in our brains after such injuries could explain why this happens.
- He studies the relationship between injuries and adaptive brain changes to help improve rehabilitation practices.
The anterior cruciate ligament (ACL) is a supportive knee structure that connects the thigh bone (femur) to the front of the shin bone (tibia) and is important for keeping the joint stable. An ACL rupture is a common orthopaedic injury often seen in athletes and active individuals. Treatment is usually surgical reconstruction followed by lengthy physiotherapy. Unfortunately, people who experience this injury are at increased risk of undergoing another, with athletes returning to activity having a 30 to 40 times higher risk than those never injured.
What is neuroplasticity?
Neuroplasticity is the ability of the nerve circuits in our brain to grow and make new connections. Such rewiring can occur after an ACL injury and is triggered by the need to maintain the joint’s functionality. These events are not yet fully understood but could be key to understanding why recurrent injury occurs and what can be done to prevent it. Professor Dustin Grooms and colleagues at Ohio University, USA, have been conducting comprehensive research on this topic. So far, it has yielded exciting results.
Keeping the eyes peeled
To determine the changes in neural circuitry after ACL reconstruction, the research team used functional magnetic resonance imaging (fMRI) – a radiological method that measures real-time brain activity by detecting changes in the blood flow (neuroimaging). The team’s first experiment included 15 participants who had an ACL injury and underwent surgical reconstruction and 15 healthy participants matched for sex, age, and other characteristics (control group). The participants performed repeated cycles of knee flexion and extension (kicking-like motion) while being scanned by MRI. Analysis revealed that the participants in the ACL group had increased brain activity in areas of the brain responsible for visual control of movements compared to the control group. This suggests that people who had the ACL injury and reconstruction rely more on visual information to adjust their knee movements (visual motor control) rather than on the information provided by the muscles and joints themselves (sensorimotor control).
Grooms studies the relationship between injuries and adaptive brain changes, with a view to improving rehabilitation practices.
A more interactive approach
After the encouraging results of their first experiment, the team designed a new study involving more participants with ACL reconstruction. Participants completed the same movements in the MRI as before but also had to report the perceived overall quality of their knee function. This study revealed that individuals who reported good knee function also demonstrated increased brain activity in areas of the brain that are responsible for movement planning and preparation. The finding could mean that their brain is rewired to be more careful when planning a movement, to protect the knee and preserve its functionality.
Seeing is protecting
In their initial experiment the team showed that ACL injuries were associated with brain changes in regions responsible for visual control of movement, indicating a potential adaptation to preserve motor function after injury. But how does this adaptation preserve motor control function? Building on their very first experiment, the team wanted to answer this question by designing another study. They measured different aspects of neuromuscular control in relation to the visual changes in people that had the surgery and the control group. The team showed that individuals who had undergone ACL surgery were maintaining neuromuscular function in their ability to sense where their knee joint is in space (proprioception), through cognitive processes related to vision (visual memory and visual motor reaction time ability). This finding reinforced the concept that for patients after ACL surgery, vision-related processing was used as an adapting mechanism to compensate for lower levels of sensation.
Is there a correlation between certain motor brain activity patterns and the risk of injury?
Findings to jump at
After their first three studies, the researchers decided to expand their experiment by having participants observe high-energy movements, such as the drop vertical jump. Interestingly, they found that individuals who experienced fear of movement/re-injury after ACL reconstruction demonstrated a higher brain activity in the amygdala and middle temporal gyrus, two areas of the brain associated with fear and anticipating painful events. This finding suggests that the psychological status of the patient influences brain activity for common athletic movements. After injury changes, this could be part of a compensatory strategy when planning to perform a load-bearing movement such as a jump or landing.
What if it’s meant to happen?
It’s clear that there are sensorimotor changes in the brain after an ACL injury but what if some aspects of different brain activity contribute to the original ACL injury? Is there a correlation between certain motor brain-activity patterns and the risk of injury? To shed some light on the matter, the researchers conducted another study where 31 female athletes performed a loaded leg press during fMRI scanning to assay brain activity for leg control. The athletes also had their movements assessed in a 3D motion analysis laboratory to identify their risk of injury. The results suggested that the athletes who demonstrated increased activity in regions of the brain responsible for processing sensory, spatial, and attentional data to generate leg movements had a higher ACL injury movement mechanics during the motion analysis session, potentially meaning that the increased risk might be present before the first injury.
Neuroscience’s approach to rehabilitation
Grooms’ findings provide a variety of new information on the changes the brain goes through after an orthopaedic injury and its surgical reconstruction. This neuroscientific approach provides useful insight and potential new tools that could help clinicians integrate relevant aspects of motor training and attention manipulation in their rehabilitation practices. Such changes could improve the recovery process and the final functional outcome after an ACL reconstruction. By employing strategies that involve visual and proprioceptive exercises, healthcare workers could help improve motor coordination in sport for these patients and reduce their risk of re-injury.
What motivated you to conduct this research?
I started this research journey as a sports medicine clinician working with patients after ACL and other orthopaedic injuries. Despite striving to deliver the best rehabilitative care and doing a host of physical tests of performance to ensure they were ready to return to sport, I had several athletes re-injure. Searching the literature I discovered that there was no obvious answer as to why, when doing seemingly everything right, not every patient had a great outcome. This led me down a path to try and understand what it is about these injuries we were missing. It eventually led me to the neural control of movement, which seemed to be the missing link, and the use of neuroimaging to quantify it.
Which one of your five studies do you believe had the most surprising or exciting findings?
They are all very interesting and build on each other. The findings led by Meredith Chaput are exciting in that she showed how the brain may increase sensory-related (proprioception and vision) processing to allow for visual cognitive abilities (reaction time, processing speed) to compensate for the damaged joints loss of proprioception and stability. However, the findings led by HoWon Kim are the most surprising. Some responses recorded in our patients’ brains showed high levels of emotional and fear-related activity in response to being immersed in a jump landing scenario.
Can you share any specific examples of adaptations/changes to rehabilitation practice that could be made based on your research?
Yes! We have been exploring this a great deal. One up-and-coming tool we’ve worked with is to use virtual reality to modify the visual environment to reverse the sensory reweighting neuroplasticity after injury (Burcal, et al). Another tool is stroboscopic glasses to decrease reliance on visual feedback for movement coordination (Wohl, et al). We also see positive results with simple changes in how therapist cue their patients to move – specifically directing their attention away from the joint and to the environment during exercise (Gokeler, et al).
