Spinal position sense and trunk muscle activity during sitting and standing in non-specific chronic low back pain: classification analysis

Study Design. A cross-sectional study between subgroups of nonspecific chronic low back pain (NSCLBP) and asymptomatic controls. Objective. To investigate NSCLBP subgroup differences in spinal position sense and trunk muscle activity when repositioning thoracic and lumbar spine into neutral (midrange) spinal position during sitting and standing. Summary of Background Data. Patients with NSCLBP report aggravation of symptoms during sitting and standing. Impaired motor control in NSCLBP, associated with sitting and standing postures nearer the end range of spinal motion, may be a contributing factor. Rehabilitation improving neutral (midrange) spinal position control is advocated. Postural and motor control alterations vary in different NSCLBP subgroups, potentially requiring specific postural interventions. There is limited evidence on whether subgroup differences exist when performing neutral spine position tasks. Methods. Ninety patients with NSCLBP and 35 asymptomatic controls were recruited. Two blinded practitioners classified NSCLBP into subgroups of active extension pattern and flexion pattern. Participants were assisted into neutral spine position and asked to reproduce this position 4 times. Absolute, variable, and constant errors were calculated. Three-dimensional thoracic and lumbar kinematics quantified the repositioning accuracy and surface electromyography assessed back and abdominal muscles activity bilaterally. Results. Irrespective of subclassification, patients with NSCLBP produced significantly greater error magnitude and variability than the asymptomatic controls, but subgroup differences were detected in the error direction. Subgroup differences in the trunk muscle activity were not consistently identified. Although both subgroups produced significantly higher abdominal activity, subclassification revealed difference in superficial multifidus activity during standing, with flexion pattern producing significantly greater activity than the asymptomatic controls. Conclusion. Subgroups of NSCLBP had similar neutral spinal position deficits regarding error magnitude and variability, but subclassification revealed clear subgroup differences in the direction of the deficit. The trunk muscle activation was shown to be largely nondiscriminatory between subgroups, with the exception of superficial lumbar multifidus