Although trigger finger is a relatively common hand disorder, its exact cause remains unknown. Whether the etiology of the abnormality resides in the tendon or in the pulley continues debate. The purpose of this review is to summarize what is known about the clinical and biomechanical presentation of trigger finger. While the A1 pulleys are more accessible for examination than the flexor tendons during surgery and have been more extensively studied, it should not yet be assumed that the tendons are any less responsible for the entrapment symptom. Previous assessments of these tissues include testing of their compliance, friction coefficient, and contact angle. Kinematic and kinetic performance of trigger fingers has been evaluated in vivo. Thickening and changes in gene expression have also been identified in trigger finger tendons. Further investigation into the role of flexor tendons in trigger finger should be performed to facilitate the understanding of the etiology and mechanism of trigger finger development. Future studies could incorporate non-invasive medical imaging in order to understand the appearance and material properties of the involved pulley and tendons, and to combine these characteristics with finger kinematics. Furthermore, understanding the mechanism of biologic adaptations of the A1 pulley and the flexor tendons in response to the mechanical loading might be helpful in providing clues and evidence for effective, novel treatment for trigger finger.
The anterior cruciate ligament (ACL) plays the primary role in resisting anterior tibial translation. ACL rupture inevitably causes alterations in knee kinematics and long-term functional impairment. The purpose of this study was to evaluate a new surgical technique, subosseous screw-suture anchor surgery (SSSAS), for ACL repair of the knee from a biomechanical point of view. Twelve porcine knees were tested with the ACL intact, cut, and repaired (using traditional Pull-Out method or the SSSAS method) on a mechanical testing apparatus. Tibial translation at four knee flexion angles (0°, 30°, 60°, 90°) under three tibial rotation loads (5 N-m, 0, -5 N-m) was measured to determine knee stability. A laxity recovery ratio was defined to account for individual variations and estimate the repair level. Our findings indicate both Pull-Out and SSSAS techniques significantly decreased AP laxity of the knee joint. In addition, the differences between the intact and repaired knees in the Pull-Out group were significant in all three tibial rotation positions. In the SSSAS group, they were significant at 0° and 90° knee flexion for both neutral and internal rotation positions and at 0°, 30°, and 90° knee flexion in the external rotation position. Concerning the laxity recovery ratio, the SSSAS group had higher laxity recovery ratio than the Pull-Out group. In other words, the fixation by directly fixating the ACL on the femoral interchodylar area instead of the fixation through femoral tunnel could give better outcome in terms of knee stability.
Previous studies have shown the high prevalence of cement leakage and its adverse effect in vertebroplasty. Many methods have developed to reduce the risk of leakage; nevertheless, an evaluation of cement flow within the vertebrae and its correspondence to different level of vertebral injury were still less revealed. In this study, twenty human osteoporotic cadaveric vertebrae were used. Two factors, i.e., the injury level and the cement viscosity, were designed in this study. The specimens were compressed to the level of 30% (moderate fracture) and 60% (severe fracture) of original body height. A two-level cement viscosity, powder-liquid ratio with 1.6(g):1(ml) vs. 1.3(g):1(ml), was designed as the higher vs. lower viscosity of cement. During the injection, a cine CT scanning was performed to monitor the cement progression within the vertebra. After the injection, the vertebrae were sliced sagittally to find the cement infiltration within the vertebra. Results show that the injection force dropped dramatically after the cement flowing out, but gradually increased as the cement being injected afterwards. The injection force stood around 100 N when using lower-viscosity cement, and stood around 200 N when using higher-viscosity cement. It was found that fracture severity had less effect on the injection force than cement viscosity. The infiltration volume was larger at a moderate fracture level and lower viscosity. The fracture severity affects the cement leakage more than the viscosity does. The effectiveness of vertebroplasty may be enhanced by preoperative CT scans of the target vertebra.
Articular cartilage is a cushioning material which reduces contact pressure on joint, and protects subchondral bone from direct load. In the recent studies on mechanical behavior of cartilage, detailed cartilage geometries were available by means of in vivo CT and/or MR imaging. The mechanical property on the cross-section of cartilage is inhomogeneous due to its laminar microstructure. However, the studies are limited for detailed stress distribution in cartilage taking the effect of internal microstructure of cartilage even when those have taken the real bone/cartilage shape into account for finite element analysis (FEA). In this study, the FEA of cartilage layer of hip joint extracted from the 3D-CT image was performed in order to obtain knowledge of the stress distribution in detail considering the inhomogeneity of articular cartilage. The real bone surface geometries of femoral heads and acetabular fossae were extracted from 3D-CT image. The geometry of cartilage is defined by referring to the bone surface so that the femoral joint surfaces are reproduced. This study modeled the bilateral hip joints of healthy subjects. The reproduced femurs were discretized into 8-node brick elements for bone and cartilage layers of the hip joint. The mechanical properties used for FEA were those estimated by considering the microstructure in the previous study. High stress was observed mainly on cartilage surface covered with the acetabular fossa. Especially stress concentration was located at proximal surface of femoral head, while the stress at the lower distal region was not significant.
In spinal fusion with instrumentation for the treatment of osteoporotic vertebral fracture, it is common for pedicle screws, which are inserted into vertebrae and strongly immobilized by a rigid rod, to loosen and dissociate. One of their expected causes is failure and reduction of fixity around a screw. An improved rod with a damper structure has thus been proposed to increase the freedom of movement of the rod and allow more flexible fixation of the spine. To evaluate the availability of the proposed structure and establish appropriate improved design of screws and rods with fewer occurrences of loosening and dissociation, effects of the structural change to the improved rod on the distribution of failure risks around the screw need to be investigated. In the present study, we performed nonlinear fracture analysis for spinal instrumentation surgery using an osteoporosis model and evaluated the failure distribution in the vertebrae while changing the apparent stiffness of the damper joint. Our finite element analysis showed that there were few expected failures in the flexible fixation model, indicating the effectiveness of the improved structure of the rod in reducing the loosening and dissociation of screws. It also suggested that the reduction was derived from the allowance of horizontal deformation in the damper joint in the improved rod. The potential of the structural improvement and the mechanism responsible for reducing the risks of loosening and dissociation are discussed.
The range of motion (ROM) resulting from total hip arthroplasty (THA) depends on the relative orientation of the femoral and acetabular components, and malpositioning of components is a possible cause of several complications. The purpose of this study was to validate a 3-dimensional (3D) lower extremity alignment assessment system (3D LAAS) for the measurement of alignment of natural and implanted hip joints and implant position with respect to the target bone with the subject in a standing position. Sawbone femur and pelvis and femoral and acetabular components of a total hip arthroplasty system were used. Three spherical markers were attached to each sawbone and each component to define the local coordinate system. Outlines of the 3D bone models and component computer-aided design models were projected onto extracted contours of the femur, pelvis, and implants in calibrated frontal and oblique X-ray images. The 3D position of each model was recovered by minimizing the differences between projected outlines and contours. Mean absolute errors were less than 1.27 ± 0.79 mm and 0.99 ± 0.52° for femur and pelvis, 1.64 ± 0.66 mm and 1.54 ± 0.39° for femoral and acetabular components, 1.58 ± 0.29 mm and 1.75 ± 0.69° for femur and femoral component, and 1.51 ± 0.49 mm and 1.24 ± 0.14° for pelvis and acetabular component, indicating that the 3D LAAS is applicable to measure the alignment of natural and implanted hip joints and implant position after THA.