Sabrine Klerx

The aim of this thesis was to investigate the (re)organization of the primary motor cortex in people with low back pain (LBP), as well as to explore whether changes in the primary motor cortex correlate with changes in clinical tests – a motor control test, sensory tests, and pain sensitivity and modulation tests – over time. Additionally, we investigated whether the organization of the primary motor cortex changes in those who recover from LBP, those who do not recover, and those without LBP, and whether these changes differed between groups. Thus, both cross-sectional and longitudinal aspects of the relationship between the organization of the primary motor cortex and clinical tests in LBP and recovery were explored, with the goal of linking fundamental and clinical insights.

In Chapter 2, to ensure that the tests used in Chapters 3, 4, and 5 had adequate clinimetric properties, we modified a movement precision test (a spiral tracking test) to a clinical version. The clinimetric properties of this test and of a proprioceptive test (a repositioning test) were measured, answering Question 1. What are the intra- and interrater reliability and measurement errors of two tests to evaluate lumbar motor control, namely the spiral tracking test (modified for clinical use) and the repositioning test, measured in people with LBP? Participants 18–65 years of age, with current or a history of LBP performed a spiral tracking task (n=33; i.e., tracing a spiral on a computer monitor by making spinal movements) or a repositioning task (n=34; i.e., returning the trunk to a predefined position). Inertial measurement units were used to measure trunk orientations. To explore the potential of these tests, we evaluated a broad range of parameters. To assess intra and interrater reliability, we calculated the intraclass correlation coefficient (ICC(2,1) for absolute agreement), standard error of measurement and smallest detectable change for each parameter. Overall, the interrater reliability of the spiral tracking test was good (ICC>0.75). The reliability of the second and third trial revealed higher ICC values compared to the reliability of the first two trials. The intra- and interrater reliability of the repositioning test was overall poor (ICC<0.5, with the exception of trunk inclination: ICC 0.50 to 0.75). Based on the results of this chapter, the reliability of the spiral tracking test was considered good when one practice trial is performed. Therefore, in the following studies we conducted one practice trial prior to the measurement. Because the reliability of the repositioning test was considered too low, we omitted the repositioning test in the subsequent studies and only included the spiral tracking test as a motor control test in the cross-sectional and longitudinal study, described in Chapter 4 and 5. The reliability and set-up of the spiral tracking test support its feasibility for clinical use. However, prior to implementing the spiral tracking test in the clinic, the outcome measures should be clear for interpretation, and its validity should be well established. In Chapter 3, a protocol for a cross-sectional (Chapter 4) and longitudinal study (Chapter 5) was developed and conducted in 25 people with LBP and 25 people without LBP. This protocol was aimed at studying the relation of the primary motor cortex to motor control and LBP, as well as the changes in these factors during the recovery process. Measures of interest were the organization of trunk muscles in the primary motor cortex, and motor and sensory performance tests. The organization of the primary motor cortex (CoG and area) was assessed using neuronavigated transcranial magnetic stimulation, based on individual MRIs. As clinical tests, a motor control test (spiral tracking test), sensory tests, (vibration threshold, graphaesthesia and two-point discrimination threshold) and pain sensitivity and modulation tests (quantitative sensory testing) were used. Participants with LBP completed the Numeric Pain Rating Scale, Oswestry Disability Index, Pain Anxiety Symptom Scale and Central Sensitization Inventory at baseline and follow-up. In addition, at 5-week follow-up, participants with LBP indicated their overall level of recovery on a Global Perceived Effect scale (GPE-Dutch Version, 7-point Likert scale). Based on the outcome of this scale participants were classified as ‘recovered’ or ‘non-recovered’, which was used for the statistical analysis. In Chapter 4, we addressed research Question 2. Is the organization of the primary motor cortex different in people with LBP compared to people without LBP? We found that people with LBP exhibited a significantly more lateral CoG for the longissimus at L5 and a significantly lower CoG for the obliquus internus, however, only a small portion of our analyses yielded significant results. We also addressed research Question 3. Are the outcomes on the motor control test, sensory tests, and pain sensitivity and modulation tests different in people with LBP compared to people without LBP? Among the clinical tests we administered, only temporal summation of pain showed a significant difference. People with LBP had a significantly higher temporal summation of pain compared to those without LBP. Although most clinical outcomes were not significant, people with LBP generally performed worse on the tests compared to those without LBP. Lastly, in this chapter, we addressed research Question 4. Are the outcomes on the motor control test, sensory tests, and pain sensitivity and modulation tests related to the organization of the primary motor cortex? We found a significant association between the vibration test, the two-point discrimination threshold and the CoG of the longissimus L3, L5 and obliquus internus muscle, such that those participants who scored better on these tests had a more anterior, lateral and lower CoG. This implies that a better vibration or two-point discrimination threshold coincide with a more ‘abnormal’ (i.e., more deviating from the people without LBP) CoG location in medio-lateral and lower direction. In Chapter 5, we answered research Question 5. Does the organization of the primary motor cortex change when people recover from LBP compared to people who do not recover from LBP? Question 6. Do the outcomes on the motor control test, sensory tests, and pain sensitivity and modulation tests change when people recover from LBP compared to people who do not recover from LBP? And Question 7. Are changes over time in the outcomes on the motor control test, sensory tests, and pain sensitivity and modulation tests related to changes over time in the organization of the primary motor cortex? We found that only in non-recovered participants, the CoG of longissimus L5 moved significantly anterior and their temporal summation of pain decreased significantly more than in people without LBP. The spiral tracking path length decreased significantly in participants without LBP, which differed significantly from the increase in participants who recovered. Out of all the association analyses conducted, we found some to be significant. These significant associations over time were demonstrated between the outcomes on several clinical tests and the cortical organization of longissimus L5, with better performance in clinical tests mostly correlating with a medial shift of the longissimus L5 representation. This finding may be due to the fact that the pain is mostly present in the lower regions of the lower back and thus changes in the brain might occur mostly in the areas corresponding to the lower back. Chapter 6 contains a summary of the main findings of the various studies, as well as an in-depth discussion of theoretical and methodological considerations with implications for clinic and further research. In this chapter, I discuss that the findings were limited to that people with LBP had a significantly more lateral location of the CoG for the longissimus muscle at L5 and a significantly lower location of the CoG for the obliquus internus muscle. Furthermore, significant associations were found between changes in the outcomes of several clinical tests with changes in the organization of longissimus L5. This partly supports the idea of reorganization of the primary motor cortex in LBP. However, we did not find a logical result in changes of the organization of the primary motor cortex related to recovery. Therefore, the clinical meaning of these changes remains largely unknown. Given the complexity of the central nervous system and the multiple factors that determine the outcome of the studied tests, it is plausible that a relatively crude measure of brain organization and a simplified outcome measure of a highly complex clinical tests are not sensitive enough to reveal true relations between cortical organization and test performance. Moreover, the work presented in this thesis was based on a relatively small sample size, with participants all experiencing subclinical values of experienced disability, which may have contributed to the limited significant findings. In conclusion, there is currently no clear clinical basis for explaining or intervening in the reorganization of the primary motor cortex as it relates to motor control, including sensory performance, in LBP.