Effects of Tensioning the Lumbar Fasciae on Segmental Stiffness During Flexion and Extension

STUDY DESIGN: Biomechanical study of unembalmed human lumbar segments. OBJECTIVE: To investigate the effects of tensioning the lumbar fasciae (transversus abdominis TrA) aponeurosis) on segment stiffness during flexion and extension. SUMMARY OF BACKGROUND DATA: Animal and human studies suggest that TrA may influence intersegmental movement via tension in the middle and posterior layers of lumbar fasciae (MLF, PLF). METHODS: Compressive flexion and extension moments were applied to 17 lumbar segments from 9 unembalmed cadavers with 20 N lateral tension of the TrA aponeurosis during: 1) "static" tests: load was compared when fascial tension was applied during static compressive loads into flexion-extension; 2) "cyclic loading" tests: load, axial displacement, and stiffness were compared during repeated compressive loading cycles into flexion-extension. After testing, the PLF was incised to determine the tension transmitted by each layer. RESULTS: At all segments and loads (<200 N), fascial tension increased resistance to flexion loads by approximately 9.5 N. In 15 of 17, fascial tension decreased resistance to extension by approximately 6.6 N. Fascial tension during cyclic flexion loading decreased axial displacement by 26% at the onset of loading (0-2 N) and 2% at 450 N (13 of 17). During extension loading, fascial tension increased displacement at the onset of loading (10 of 17) by approximately 23% and slightly (1%) decreased displacement at 450 N. Segment stiffness was increased by 6 N/mm in flexion (44% at 25 N) and decreased by 2 N/mm (8% at 25 N) in extension. More than 85% of tension was transmitted through the MLF. CONCLUSIONS: Tension on the lumbar fasciae simulating moderate contraction of TrA affects segmental stiffness, particularly toward the neutral zone.