Citations

This study evaluated the effects of soft tissue integrity on patellar tracking and patellofemoral joint force after total knee arthroplasty. The results indicate that partial dissection of the soft tissue integrity in the in vitro biomechanical studies of the patellofemoral joint can alter patellar tracking and joint force significantly, leading to improper conclusions.

We defined foot and ankle motion with respect to the neutral position. Thirteen normal fresh-frozen speci mens of the human foot were used. The foot was placed in the extreme positions of pronation, supina tion, dorsiflexion, and plantar flexion, and positions of multiple bones were monitored simultaneously with a magnetic tracking device to determine rotation of the talocrural, subtalar, metatarsal-navicular, and talo navicular joints under the various conditions. In prona tion, the most rotation occurred at the metatarsal-na vicular level, followed by the navicular-talar, talar-tibial, and calcaneal-talar levels. In supination, most rotation occurred at the navicular-talar level, followed by the calcaneal-talar, talar-tibial, and metatarsal-navicular levels. In dorsiflexion, most rotation occurred at the talar-tibial level, followed by the navicular-talar, calca neal-talar, and metatarsal-navicular levels. In plantar flexion, most rotation occurred at the talar-tibial level, but there was considerable motion at the navicular- talar, metatarsal-navicular, and calcaneal-talar levels. Understanding the specific joint motions that occur with various positions of the foot and ankle is important because measurements of joint mobility may assist in establishing diagnoses, monitoring clinical conditions, determining indications for operative treatment, as sessing results of treatment, and following the progress of rehabilitation.

The purpose of this study is to develop an electromechanical system for dynamic simulation of the stance phase of a human gait using cadaveric foot specimens. The system can be used for quantification of foot and ankle pathomechanics and design of foot and ankle reconstructive surgeries. Servo-pneumatic systems were used for application of the tibial weight loading and muscle loadings. A four-bar mechanism was constructed to provide the progressive motion of a tibia during the simulation while the external loadings were simultaneously applied. Muscle loadings were estimated based on the physiological cross-sectional area and normal electromyography (EMG) data with the assumption of the linear EMG–force relationship. Ad hoc tuning of the unknown muscle gains was conducted until a reasonable match with the normal vertical ground reaction force profile, center of pressure advancement, and characteristic foot motion events (heel strike, foot flat, heel rise and toe-off) could be made. Three cadaver feet and an artificial foot were tested with five repeated trials. The simulator reproduced the stance phase of a human gait in the sagittal plane with reasonable accuracy and consistency without compromising either kinematics or kinetics of the foot and ankle complex.

A methodology was developed for determining the compressive properties of the supraspinatus tendon, based on finite element principles. Simplified three-dimensional models were created based on anatomical thickness measurements of unloaded supraspinatus tendons over 15 points. The tendon material was characterized as a composite structure of longitudinally arranged collagen fibers within an extrafibrillar matrix. The matrix was formulated as a hyperelastic material described by the Ogden form of the strain energy potential. The hyperelastic material parameters were parametrically manipulated until the analytical load-displacement results were similar to the results obtained from indentation testing. In the geometrically averaged tendon, the average ratio of experimental to theoretical maximum indentation displacement was 1.00 (SD: 0.01). The average normalization of residuals was 2.1g (SD: 0.9g). Therefore, the compressive material properties of the supraspinatus tendon extrafibrillar matrix were adequately derived with a first-order hyperelastic formulation. The initial compressive elastic modulus ranged from 0.024 to 0.090 MPa over the tendon surface and increased nonlinearly with additional compression. Using these material properties, the stresses induced during acromional impingement can be analyzed.

An optical spin micromotor operated by optical tweezers, described in the present study, converts radiant energy directly to mechanical energy. This conversion is of great practical and fundamental interest. The optical spin micromotor consists of a two-bead linkage. The large bead (2.0 μm in diameter) is trapped by the optical tweezers and rotates around the laser beam axis. The small bead (0.94 μm in diameter) is partially coated with gold/palladium for generating the spin torque through the change of momentum from gradient radiation pressure of the same laser applied on the coated small bead. With a laser power of 29 mW at the sample plane, the spin speed averaged 158.8±155.5 rpm (mean±standard deviation) and the torque was estimated as 101.9±99.8 pN nm. This optical spin micromotor will be useful in (1) providing a fundamental step toward developing optical-operated mechanical devices, (2) twisting macromolecules, and (3) generating vortex and shear force in medium at nanoscale.