Biomechanical comparison of lumbar rotational manipulations in two different positions using force measurement and finite element analysis.

purposeTo investigate the biomechanical characteristics of lateral decubitus and sitting lumbar rotational manipulations (LRM) by combining experimental force measurements with finite element analysis (FEA), with a particular focus on regional stress and displacement distributions and areas of stress concentration that may have relevance for future clinical and safety studies.

methodsTwenty healthy volunteers were randomly assigned to receive either lateral decubitus or sitting LRM. Practitioner-generated forces were recorded using instrumented gloves, and preliminary cluster analysis was performed to explore distinct operational patterns. The measured loading parameters were then used to define the loading conditions in a validated lumbar finite element model to compare stress and displacement distributions in the intervertebral discs and facet cartilage across the two techniques and five clusters.

resultsPreliminary cluster analysis identified two clusters for the lateral decubitus technique (shoulder-hip coordinated and hip-dominant) and three for the sitting technique (shoulder-waist coordinated, shoulder-dominant, and gentle-loading). No significant left-right differences in practitioner-generated forces were observed for the lateral decubitus technique (all P > 0.05). For the sitting technique, the force applied at the shoulder was lower on the left than on the right (62.56 ± 15.58 vs. 77.70 ± 7.72 N; t = -10.088, P < 0.001), whereas the force applied at the waist was higher on the left than on the right [32.80 (27.75-38.20) vs. 26.06 (22.66-33.54) N; Z = 2.129, P = 0.042]. FEA showed distinct mechanical patterns between the two techniques. Across the two lateral decubitus clusters, the maximum intervertebral disc stress ranged from 7.87 to 13.40 MPa and the maximum deformation from 7.22 to 12.31 mm, with the main mechanical effects concentrated at L3/4-L4/5. Across the three sitting clusters, the maximum disc stress ranged from 5.87 to 8.09 MPa and the maximum deformation from 11.68 to 16.44 mm, with greater displacement mainly involving L1/2-L2/3. A similar contrast was observed in the facet cartilage, with the lateral decubitus technique generally producing higher peak stress but lower deformation than the sitting technique.

conclusionLateral decubitus and sitting LRM produced distinct regional biomechanical patterns. Lateral decubitus manipulation was characterized by a higher-stress/lower-displacement profile predominantly involving the lower lumbar spine, whereas sitting manipulation showed a lower-stress/higher-displacement profile with greater involvement of the upper lumbar spine. These findings provide a quantitative biomechanical basis for further investigation of technique-specific loading characteristics, tissue safety, and individualized clinical application. CLINICAL TRIAL NUMBER: Not applicable.