Sensorimotor characteristics in chronic neck pain : possible pathophysiological mechanisms and implications for rehabilitation

Sammanfattning: Pain from the musculoskeletal system is very common in the modern society. Chronic musculoskeletal pain syndromes causes not only individual suffering but also dysfunctions of movements and postural control, as large costs for the society. In spite of significant efforts, there is a shortage of knowledge on effective prevention, diagnoses and rehabilitation of different chronic musculoskeletal pain syndromes. The general aims of this thesis was to investigate the predictive value of physical, sociodemographic, and psychosocial-behavioural variables for pain reduction after multimodal rehabilitation in patients with chronic low back or neck pain, and to develop and evaluate tests for objective and quantitative evaluation of characteristic sensorimotor disturbances in chronic neck pain. Logistic regression models revealed that unchanged pain intensity could be predicted with good precision while reduced pain intensity after rehabilitation was poorly predicted by the baseline variables. Altered pain intensity in chronic low back pain was predicted by high pain intensity, low levels of pain severity and high affective distress, while reduced pain intensity for patients with chronic neck pain were predicted by high endurance, low age, high pain intensity, low need of being social along with optimistic attitudes on how the pain will interfere with daily life, and few vegetative symptoms. One of the conclusions was that objective measures of specific sensorimotor disturbances should improve the precision by which treatment-induced effects can be assessed and predicted. A study was designed to objectively and quantitatively evaluate a large numbers of different sensorimotor characteristics in a small group of patients with chronic neck pain of different aetiology (whiplash-related and insidious). Kinematic data was recorded during different motor tasks, involving cervical rotations, arm movements and standing. In comparison to a group of asymptomatic control subjects, patients with chronic neck pain was characterised by slower movements, poor balance, reduced cervical stability during perturbations, altered smoothness of movement (jerk index), and reduced movement precision (variable error and variability in range of motion). The sensorimotor variables velocity of arm movements and cervical stability, could correctly classified nearly 90% of the subjects as having chronic neck pain or being asymptomatic. There was a large diversity of sensorimotor disturbances among the individual patients. This was confirmed in a regression model that failed to separate the groups insidious neck pain (sensitivity 44%) and WAD (sensitivity 67%). By investigating associations between the different sensorimotor variables, close relations was found between the repositioning acuity and variability in range of motion, and between standing balance and cervical stability/ standing balance during perturbation. These two groups of variables were only weakly related to each other and to smoothness of movement and movement velocity. The results indicate that chronic neck pain is characterised by specific sensorimotor deficits, and that there are common pathophysiological mechanisms in chronic neck pain of different aetiology. However, the lack of associations between several sensorimotor disturbances indicates that different mechanisms are involved. The thesis indicates that objective sensorimotor tests should be used to improve the quality of functional assessments in chronic neck pain. Methods that objectively and quantitatively measure e.g. movement precision, balance and cervical stability are also needed in order to evaluate current treatment methods and to develop new rehabilitation programs for specific sensorimotor deficits.