Is L5-S1 motion segment different from the rest? A radiographic kinematic assessment of 72 patients with chronic low back pain.

PURPOSE: The relationship between biomechanical instability and degenerative changes in the lumbar spine in chronic low back pain (CLBP) patients remains controversial. The main objective of this retrospective radiographical study was to evaluate changes in kinematics at different lumbar levels (in particular the L5-S1 level) with progressive grades of disc degeneration and facet joint osteoarthritis in CLBP patients. METHODS: Using standing neutral and dynamic flexion/extension (Fx/Ex) radiographs of the lumbar spine, in vivo segmental kinematics at L1-L2 through L5-S1 were evaluated in 72 consecutive CLBP patients. Disc degeneration was quantified using changes in signal intensity and central disc height on mid-sagittal T2-weighted magnetic resonance (MR) scans. Additionally, the presence or absence of facet joint osteoarthritis was noted on T2-weighted axial MR scans. RESULTS: Disc degeneration and facet joint osteoarthritis occurred independent of each other at the L5-S1 level (p = 0.188), but an association was observed between the two at L4-L5 (p < 0.001) and L3-L4 (p < 0.05) levels. In the absence of facet joint osteoarthritis, the L5-S1 segment showed a greater range of motion (ROM) in Ex (3.3° ± 3.6°) and a smaller ROM in Fx (0.6° ± 4.2°) compared with the upper lumbar levels (p < 0.05), but the differences diminished in the presence of it. In the absence of facet joint osteoarthritis, no change in L5-S1 kinematics was observed with progressive disc degeneration, but in its presence, restabilisation of the L5-S1 segment was observed between mild and severe disc degeneration states. CONCLUSION: The L5-S1 motion segment exhibited unique degenerative and kinematic characteristics compared with the upper lumbar motion segments. Disc degeneration and facet joint osteoarthritis occurred independent of each other at the L5-S1 level, but not at the other lumbar levels. Severe disc degeneration in the presence of facet joint osteoarthritis biomechanically restabilised the L5-S1 motion segment

Shear behaviour of pile cap strengthened with carbon fibre reinforced polymers

A pile cap is typically a disturbed region with a very small shear span to depth ratio. Flexural theory for reinforced concrete structures cannot be applied to interpret the behaviour of a pile cap because of the non-uniform stress distribution over the depth. In this research, two series of pile caps were designed with different effective depths using strut-and-tie modelling (STM). Three scaled pile caps were cast for each series and tested under monotonic concentrated load until failure to observe the ultimate shear strength. Two additional series of pile caps strengthened with carbon fibre reinforced polymer (CFRP) with exactly the same geometric and design parameters as the control series were cast to observe the shear strength enhancement in comparison with the control specimens. STM proved to be a reliable solution for predicting the shear strength of the pile caps. The application of CFRP resulted in a 15-17% enhancement in the shear strength of the pile caps. It was also found that different prediction models for the evaluation of shear enhancement in beams can be used in the case of pile caps