Proprioceptive impairment and the effect of proprioceptive training in individuals with recurrent non-specific low back pain: from muscle spindle to sensorimotor cortex.

Low back pain (LBP) is a well-described health problem. It is the main cause of disability and absenteeism worldwide and leads to an estimated annual cost of € 1.2 billion for Belgian society. Approximately 84% of the world’s population will experience LBP at least once in their life. In 90%, LBP is ‘non-specific’ as the underlying cause cannot be identified. Although clinical guidelines state that the prognosis of acute non-specific LBP is favorable, two-thirds of patients with non-specific LBP still report pain one year after onset. Moreover, current treatment interventions often remain unsuccessful, which might be due to the fact that the underlying mechanisms of non-specific LBP are still not completely unraveled.
 
A key factor in the development of non-specific LBP is an impaired postural control, or the ability to maintain, achieve or restore a state of balance during any posture or activity. Optimal postural control requires the brain to process, weight and integrate proprioceptive signals from different body regions with vestibular input and visual signals. Based on this integration, appropriate muscle responses are generated to maintain balance. Research shows that patients with LBP have a decreased postural robustness. This might be due to the fact that they rely less on proprioceptive signals from the back muscles and as a compensation rely more on ankle muscle proprioception in a stereotypical (vs. flexible) manner. They show a decreased variability in postural control, whilst variability is considered as a prerequisite for the optimal functioning of biological systems. However, further clarification of the underlying mechanisms of this impaired proprioceptive postural control is needed.
 
In the past few years, research on LBP has been focusing increasingly on the brain. Patients with LBP seem to show several sensory and motor brain changes. For instance, patients with chronic LBP have an altered somatotopic organization of the primary somatosensory cortex during tactile stimulation and a greater symmetrical activation of the motor cortex during an anticipatory postural control task when compared to healthy individuals. The proprioceptive deficits found in patients with LBP could be associated with a decreased ability of the brain to process, weight and integrate proprioceptive signals. However, this proprioceptive processing and the link with postural control have not been investigated yet in patients with LBP.
 
Therefore, the aim of this PhD project is to clarify the processing and weighting of proprioceptive signals in the brain. Functional magnetic resonance imaging (fMRI) and local muscle vibration at the ankle muscles and lower back muscles will be used to determine cortical activation during proprioceptive stimulation. This project consists of three phases. Firstly, proprioceptive deficits and their impact on postural control will be determined in patients with recurrent non-specific LBP and healthy individuals. More specifically, non-linear analysis will be used to determine the proprioceptive variability in postural control or the ability to react flexibly on postural perturbations. Secondly, the central processing of ankle muscle and back muscle proprioception will be investigated and the link with performance on several balance tasks will be determined. Finally, we will determine whether a proprioceptive training program promotes postural control and whether this is supported by functional changes in the brain. This may contribute to the development of a more effective treatment modality to reduce pain and disability in patients with LBP.
 
In summary, the main objective of this PhD project is to elucidate underlying mechanisms of proprioceptive deficits in patients with recurrent, non-specific LBP and consequently contribute to a more optimal prevention, diagnosis and rehabilitation of patients with LBP.