The brain of people with hip osteoarthritis is driving motor control differently and may be contributing to their pain intensity, writes physiotherapist Molly Coventry.
Hip osteoarthritis is a debilitating chronic condition that affects one in 11 Australians.
People with hip osteoarthritis typically experience high levels of pain and impairments to daily function, which both contribute to poorer quality of life. Despite many interventions available to manage hip osteoarthritis, the overall burden continues to grow.
To better understand muscle function in people with the condition, we studied the brain function of people with hip osteoarthritis compared to those without hip osteoarthritis, finding that the mind played a part in this equation.
During the course of our research, we identified changes in both motor cortex processing and maximal muscle activation capacity in people with hip osteoarthritis.
The central nervous system, consisting of the brain and spinal cord, controls and coordinates our body’s movement. The primary motor cortex of the brain sends signals to muscles via the spinal cord and motor neurons.
However, in the presence of pain, particularly chronic pain, these processes can be altered. This can result in a reduced ability to activate muscles, which is problematic as strong muscle activation provides support and stability to joints.
This ability to maximally activate our muscles is quantified using a technique called voluntary activation. It assesses the proportion of muscle fibres activated by the brain to drive strong muscle contractions.
Our research demonstrated voluntary activation of the leg muscles is impaired in individuals with hip osteoarthritis. This finding is comparable to what has been shown in knee osteoarthritis and following anterior cruciate ligament reconstruction.
However, the research also demonstrated higher hip-related pain intensity was associated with a poorer ability to activate the leg muscles.
This finding suggests local pain inhibition is not a factor as we assessed the quadriceps at the knee, not hip, so all testing was pain free.
We suspect that pain may interfere with the ability to perform strong muscle contractions in areas outside of the affected joint. This is clinically important as it suggests individuals with higher levels of pain are more likely to have poor muscle activation irrespective of pain region.
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In the primary motor cortex of the brain, we have facilitatory and inhibitory pathways that work to increase or decrease overall neural drive to muscles. These can be thought of as the accelerator and brake of the brain.
This research demonstrated that greater inhibition was associated with less maximal voluntary activation. Additionally, we found greater levels of facilitation were associated with greater hip-related pain intensity.
Overall, the findings from suggest people with hip osteoarthritis have differences in the intracortical networks within the brain.
These changes within the brain are linked to a poorer ability to activate the leg muscles and produce strong contractions, which means the muscles have a lesser ability to support joint health.
Research investigating interventions which can modulate motor cortex function and improve voluntary activation during rehabilitation is currently being undertaken in an effort to improve outcomes for those with hip osteoarthritis.
ED: Molly Coventry is a PhD candidate in Nutrition and Health Innovation Research Institute at Edith Cowan University
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