Brain gray matter structure
High-resolution MR scanning will be performed on a 3 T Trio Tim magnet (Siemens medical solutions, Erlangen, Germany) with a standard head coil. Using voxel-based morphometry, brain gray matter structure will be investigated in brain areas involved in pain processing and motor control. MRI data will be obtained at baseline, post-treatment, and at 1-year follow-up.
More specifically, a T1 weighted structural MRI will be acquired by using a 3D-FLASH sequence (repetition time 2250 ms, echo time 4.18 ms, flip angle 9°, field of view 256 × 256; 176 slices), acquisition time 05′14″. Regional gray matter density will be assessed with voxel-based morphometry that allows for applying voxelwise statistics to detect regional differences in gray matter volumes. Preprocessing will involve spatial normalization, gray matter segmentation, and 10 mm spatial smoothing with a Gaussian kernel [
52]. The T1-weighted images will be processed and analyzed with FreeSurfer; cortical thickness and surface area will be calculated.
Motor control
Motor control will be assessed by clinical measurements of postural steadiness, habitual standing posture, spinal range of motion, and sensorimotor control. These aspects will be tested at baseline, and at 3-month and 1-year follow-ups.
Postural steadiness will be characterized by postural sway features as measured by an AccuGait portable forceplate (50 cm × 50 cm) (Advanced Medical Technology, Inc. Watertown, MA) during bipedal standing with eyes closed on a firm surface. Centre of pressure (COP) data will be sampled at a frequency of 100 Hz during 3 trials of 90 s. The following COP stability parameters will be computed: mean sway velocity, 95% confidence ellipse area, standard deviation of sway velocity, of medio-lateral COP data and of anterior-posterior COP data. During these posturography measurements, subjects will be barefoot and will be instructed to stand as still as possible with arms by their sides. Test-retest reliability of posturography is well-documented in adult populations [
53]. In addition, each subject will complete a clinical balance test: standing in tandem stance (heel-to-toe) with either the left or right foot in front, with eyes open and eyes closed. Patients’ performance during a 30-second tandem stance will be graded as pass/fail [
54].
For the assessment of
habitual standing posture in the sagittal plane, the orientation of gross body segments with respect to the vertical will be quantified using post-hoc analyses of digitized photographs of participants. Retro-reflective markers will first be placed on the C7 spinous process, greater trochanter, and lateral malleolus by one trained examiner. Lateral photographs will then be taken within a standardized photographic set-up after each patient is asked to stand normally and relaxed, looking straight ahead. Using ImageJ software (National Institutes of Health, Bethesda, MD), the craniovertebral angle will be calculated in patients with dominant neck pain. In patients with dominant pain located in the low back, three angular measures will be determined: trunk lean angle, body lean angle and pelvic displacement angle. For more detailed methods, see previous articles by Dolphens et al. [
55‐
57]. Furthermore, in low back pain patients, lumbar lordosis will be measured using a skin-surface hand-held electromechanical device, the Spinal Mouse (Idiag; Voletswil, Switzerland). The intratester, intertester and day-to-day reliability of this wheeled accelerometer have been published in previous studies [
55,
58‐
60].
Range of motion of the cervical spine (flexion, extension, lateral flexion) will be measured in neck pain patients (seated position) using the Acumar™ digital inclinometer (Model ACU 360, Lafayette Instrument Company, Lafayette, IN) that is placed on the vertex of the head through T1. According to the manufacturer’s specifications, this device is capable of measuring a range up to 180 degrees with an accuracy of ± 1 degree. In low back pain patients, the lumbar range of motion in the sagittal plane (flexion, extension) will be measured using the Spinal Mouse device (see above) with patients in the standing position. Furthermore, lumbar lateral flexion will be measured using the Acumar™ digital inclinometer (see above) placed on T12 through S1. For each movement direction, the mean of three consecutive measurements will be taken.
With regard to sensorimotor control, the following components will be assessed:
Proprioception will be determined by evaluating the position-reposition accuracy of the spine. In neck pain patients, repositioning will be assessed by the cervicocephalic relocation test to the neutral head position with eyes closed [
61]. More specifically, patients will be seated on a stool without backrest with their hands on their thighs, and hips and knees bent 90 degrees. After an active submaximal range cervical flexion-extension and right and left rotation, patients will be instructed to relocate back to the neutral position. Absolute and relative errors will be expressed in degrees [
62]. In low back pain patients, position-reposition accuracy will be assessed both in the sitting and standing position [
63]. First, the tester will place the subject in a neutral lumbar spine position [
63]. Then, after having performed three pelvic rotations (anterior and posterior pelvic rotation), the subject will be asked to reassume the reference position as accurately as possible. Assessment will be based on a clinical rating scale (unpublished results) evaluating the position-reposition accuracy to the neutral lumbar spine and pelvis position, and deviations in adjacent regions (thoracic kyphosis, trunk inclination, antero-posterior translation of the pelvis with respect to the feet (in standing position only), degree of knee flexion (in standing position only)) compared to the initial, neutral position. Each position-reposition cycle will be performed once.
Neuromuscular control will be assessed as the patients’ ability to perform the skill of activation of specific, deep stabilizing muscles for which there is scientific evidence that they play a crucial role in spinal stability. In neck pain patients, the contraction of the deep neck flexors will be evaluated through the craniocervical flexion test [
64], and the lower and middle trapezius muscles will be assessed via the scapular holding test/scapula setting [
65]. More specifically, assessment of contraction of the deep neck flexors will be scored based on the output obtained via an air-filled pressure sensor (Stabilizer, mmHg), substitution of superficial muscles, movement pattern and the holding capacity. Analogously, performance of the neuromuscular control of the scapulothopracic muscles will be based on the quality of contraction, substitution, movement pattern, and ability to maintain contraction as scored on a clinical rating scale (unpublished results). In low back pain patients, multifidus and transverse abdominis contraction will be evaluated in prone and supine (drawing-in action), respectively. Performance will be scored using a clinical rating scale based on the quality of contraction, substitution of superficial muscles, symmetry of contraction and the holding capacity.
Movement control of the lumbar spine will be assessed in low back pain patients. A set of 6 dissociation tests that have shown substantial reliability [k > 0.6] [
66] will be included: 1) waiters bow (flexion of the hips in upright standing position without movement (flexion) of the low back); 2) pelvic tilt (active dorsal tilt of the pelvis in upright standing); 3) one leg stance (from normal standing to one leg stance: measurement of lateral movement of the belly button); 4) sitting knee extension (upright sitting with neutral lumbar lordosis; extension of the knee without movement (flexion) of low back); 5) rocking forward/backward (quadruped position). Starting position 90° hip flexion. Transfer of the pelvis backwards and forwards (“rocking”) keeping low back in neutral; 6) prone knee flexion (prone lying, active knee flexion). The order of the tests will be standardized. A strict protocol to instruct the tests and to rate test performances as “correct” or “incorrect” will be applied as described by Luomajoki et al. [
66], resulting in an overall score between 0 and 6. No movement control test will be performed in neck pain patients.
Low back pain patients will perform a lumbopelvic control test in the sitting and standing position. A clinical rating scale (article submitted for publication) comprising the quality of the lumbopelvic motion, control of the adjacent areas, preference of motion direction, breathing, and repetitions will be used for evaluation, with higher scores indicating better performance.
As the observers’ level of experience is important for good test reliability, all tests will be rated by the same experienced observer [
66‐
69].