Consistent differences in lumbar spine alignment between low back pain subgroups and genders during clinical and functional activity sitting tests

Background: Subgroups of people with low back pain display differences in their lumbar alignment during tests from a clinical examination. However, it is unknown if subgroups display the same patterns during a functional activity test and if gender influences subgroup-related differences. Objectives: Test if differences in lumbar alignment between two LBP subgroups are 1) present during a functional activity test of preferred sitting and 2) independent of gender. Design: Cross-sectional. Method: 154 participants with chronic low back pain were classified based on the Movement System Impairment Classification System by a physical therapist. Participants performed a functional activity test of preferred sitting and clinical tests of maximum flexed and extended sitting. 3D marker co-ordinate data were collected. Sagittal plane lumbar alignment, indexed by lumbar curvature angle, was calculated. A three-way mixed effect analysis of variance was used to examine effects of test, subgroup, gender, subgroup × test, gender × test and subgroup × gender. Results/findings: The lumbar rotation with extension subgroup [LCA = −8.0° (−9.5,-6.5)] displayed a more extended lumbar alignment than lumbar rotation [LCA = −5.9° (−7.4,-4.4)]. Women [LCA = −10.7° (−12.3,-9.2)] displayed a more extended lumbar alignment than men [LCA = −3.2° (−4.7,-1.7)]. There was a significant gender × test interaction (p = 0.01). The subgroup × test (p = 0.99) and subgroup × gender (p = 0.76) interactions were not significant. Conclusions: LBP subgroup differences in lumbar alignment are present during preferred sitting. Gender-related differences in lumbar alignment are not driving subgroup differences. These findings highlight the need to use patient-specific clinical characteristics to guide treatment of a functional activity of preferred sitting limited due to low back pain.