Preoperative virtual reduction method for pelvic fractures based on statistical shape models and partial surface data

Virtual reduction is crucial for successful and accurate reduction of pelvic fractures.Various methods have been proposed in this regard.However,not all of them are applicable to every pelvic fracture.Among these methods,the efficiency and accuracy of the method based on statistical shape models in clinical applications require further improvement.This study proposes a virtual reduction method for pelvic fractures that uses statistical shape models and partial surface data of a broken pelvis.Simulated fracture and clinical case experiments were conducted to validate the accuracy and effectiveness of the proposed method.The simulated fracture experiments yielded an average error of 1.57±0.39 mm and a maximum error of 12.82±3.54 mm.The virtual reduction procedure takes approximately 40 s.Based on three clinical case experiments,the proposed method achieves an acceptable level of accuracy compared with manual reduction by a surgeon.The proposed method offers the advantages of shorter virtual reduction times and satisfactory reduction accuracy.In the future,it will be integrated into the preoperative planning system for pelvic fracture reduction,thereby improving patient outcomes.

Quantified evaluation of particle shape effects from micro-to-macro scales for non-convex grains

Particle shape plays an important role in both the micro and macro scales responses of a granular assem- bly. This paper presents a systematic way to interpret the shape effects of granular material during quasi-static shearing. A more suitable shape descriptor is suggested for the quantitative analysis of the macroscale strength indexes and contact parameters for non-convex grains, with special consid- eration given to the peak state and critical state. Through a series of numerical simulations and related post-processing analysis, particle shape is found to directly influence the strain localisation patterns, microscale fabric distributions, microscale mobilisation indexes, and probability distribution of the nor- malised contact normal force. Additionally, the accuracy of the stress-force-fabric relationship can be influenced by the average normal force and the distribution of contact vectors. Moreover, particle shape plays a more important role than do the confining pressures in determining the friction angle. Strong force chains and the dilation effect are also found to be strongly influenced by the high confinin~ oressure.

Establishing a Customized Guide Plate for Osteotomy in Total Knee Arthroplasty Using Lower-extremity X-ray and Knee Computed Tomography Images

Background： The conventional method cannot guarantee the precise osteotomies required for a perfect realignment and a better prognosis after total knee arthroplasty （TKA）.This study investigated a customized guide plate for osteotomy placement in TKAs with the aid of the statistical shape model technique using weight-bearing lower-extremity X-rays and computed tomography （CT） images of the knee.Methods： From October 2014 to June 2015, 42 patients who underwent a TKA in Guizhou Provincial People＆#39;s Hospital were divided into a guide plate group （GPG, 21 cases） and a traditional surgery group （TSG, 21 cases） using a random number table method.In the GPG group, a guide plate was designed and printed using preoperative three-dimensional measurements to plan and digitally simulate the operation.TSG cases were treated with the conventional method.Outcomes were obtained from the postoperative image examination and short-term follow-up.Results： Operative time was 49.0 ＆#177; 10.5 min for GPG, and 62.0 ＆#177; 9.7 min in TSG.The coronal femoral angle, coronal tibial angle, posterior tibial slope, and the angle between the posterior condylar osteotomy surface and the surgical transepicondylar axis were 89.2 ＆#177; 1.7＆#176;, 89.0 ＆#177; 1.1＆#176;, 6.6 ＆#177; 1.4＆#176;, and 0.9 ＆#177; 0.3＆#176; in GPG, and 86.7 ＆#177; 2.9＆#176;, 87.6 ＆#177; 2.1＆#176;, 8.9 ＆#177; 2.8＆#176;, and 1.7 ＆#177; 0.8＆#176; in TSG, respectively.The Hospital for Special Surgery scores 3 months after surgery were 83.7 ＆#177; 18.4 in GPG and 71.5 ＆#177; 15.2 in TSG.Statistically significant differences were found between GPG and TSG in all measurements.Conclusions： A customized guide plate to create an accurate osteotomy in TKAs may be created using lower-extremity X-ray and knee CT images.This allows for shorter operative times and better postoperative alignment than the traditional surgery.Application of the digital guide plate may also result in better short-term outcomes.

Live facial feature extraction

Precise facial feature extraction is essential to the high-level face recognition and expression analysis. This paper presents a novel method for the real-time geometric facial feature extraction from live video. In this paper, the input image is viewed as a weighted graph. The segmentation of the pixels corresponding to the edges of facial components of the mouth, eyes, brows, and nose is implemented by means of random walks on the weighted graph. The graph has an 8-connected lattice structure and the weight value associated with each edge reflects the likelihood that a random walker will cross that edge. The random walks simulate an anisot- ropic diffusion process that filters out the noise while preserving the facial expression pixels. The seeds for the segmentation are obtained from a color and motion detector. The segmented facial pixels are represented with linked lists in the origi- nal geometric form and grouped into different parts corresponding to facial components. For the convenience of implementing high-level vision, the geometric description of facial component pixels is further decomposed into shape and reg- istration information. Shape is defined as the geometric information that is invariant under the registration transformation, such as translation, rotation, and isotropic scale. Statistical shape analysis is carried out to capture global facial fea- tures where the Procrustes shape distance measure is adopted. A Bayesian ap- proach is used to incorporate high-level prior knowledge of face structure. Experimental results show that the proposed method is capable of real-time extraction of precise geometric facial features from live video. The feature extraction is robust against the illumination changes, scale variation, head rotations, and hand interference.