Femoral version and its clinical relevance in adult hip preservation surgery for developmental dysplasia of the hip.

Femoral version (FV) is more widely adopted with the definition as the angle between the long axis of the femoral neck and the tangent line of the posterior femoral condyles on the axial plane, and the normal range between 5 and 20°. FV can be measured by imaging and functional tests. Cross-sectional CT including both the hip and the knee is the typically used imaging technique, yet variation exists according to the different landmarks used. As MRI investigations are routinely performed preoperatively, and protocols can be easily adopted to include version measurement, they are frequently used as an alternative to CT and offers several advantages. Abnormal FV has adverse effects on the biomechanics and musculoskeletal health of the whole lower limb. It affects the lever arm of muscles and the forces that the hip and patellofemoral joints suffer, and can lead to disorders such as osteoarthritis and impingement. In adult hip preservation surgery for developmental dysplasia of the hip (DDH), abnormal FV is sometimes accompanied by other morphological abnormities of the hip, a more severe DDH, and can help predict postoperative range of motion (ROM), and postoperative impingement. Currently, the most frequently used surgical technique for abnormal FV is femoral derotational osteotomy. Many controversies are left to be solved, including the specific origin of FV, the indication for femoral derotational osteotomy, especially in patients with combined DDH and abnormal FV, and the explicit compensation mechanism of abnormal FV by tibial torsion.

Complete structural characterization of single carbon nanotubes by Rayleigh scattering circular dichroism.

Non-invasive, high-throughput spectroscopic techniques can identify chiral indices (n,m) of carbon nanotubes down to the single-tube level1-6. Yet, for complete characterization and to unlock full functionality, the handedness, the structural property associated with mirror symmetry breaking, also needs to be identified accurately and efficiently7-14. So far, optical methods fail in the handedness characterization of single nanotubes because of the extremely weak chiroptical signals (roughly 10-7) compared with the excitation light15,16. Here we demonstrate the complete structure identification of single nanotubes in terms of both chiral indices and handedness by Rayleigh scattering circular dichroism. Our method is based on the background-free feature of Rayleigh scattering collected at an oblique angle, which enhances the nanotube's chiroptical signal by three to four orders of magnitude compared with conventional absorption circular dichroism. We measured a total of 30 single-walled carbon nanotubes including both semiconducting and metallic nanotubes and found that their absolute chiroptical signals show a distinct structure dependence, which can be qualitatively understood through tight-binding calculations. Our strategy enables the exploration of handedness-related functionality of single nanotubes and provides a facile platform for chiral discrimination and chiral device exploration at the level of individual nanomaterials.

Universal Imaging of Full Strain Tensor in 2D Crystals with Third-Harmonic Generation.

Quantitatively mapping and monitoring the strain distribution in 2D materials is essential for their physical understanding and function engineering. Optical characterization methods are always appealing due to unique noninvasion and high-throughput advantages. However, all currently available optical spectroscopic techniques have application limitation, e.g., photoluminescence spectroscopy is for direct-bandgap semiconducting materials, Raman spectroscopy is for ones with Raman-active and strain-sensitive phonon modes, and second-harmonic generation spectroscopy is only for noncentrosymmetric ones. Here, a universal methodology to measure the full strain tensor in any 2D crystalline material by polarization-dependent third-harmonic generation is reported. This technique utilizes the third-order nonlinear optical response being a universal property in 2D crystals and the nonlinear susceptibility has a one-to-one correspondence to strain tensor via a photoelastic tensor. The photoelastic tensor of both a noncentrosymmetric D3h WS2 monolayer and a centrosymmetric D3d WS2 bilayer is successfully determined, and the strain tensor distribution in homogenously strained and randomly strained monolayer WS2 is further mapped. In addition, an atlas of photoelastic tensors to monitor the strain distribution in 2D materials belonging to all 32 crystallographic point groups is provided. This universal characterization on strain tensor should facilitate new functionality designs and accelerate device applications in 2D-materials-based electronic, optoelectronic, and photovoltaic devices.