Clinical monitoring of torso deformities in scoliosis using structured splines models.

This paper describes the use of structured splines indices for the clinical monitoring of torso deformity in scoliosis. Structured splines indices are computed from the distribution of points of maximal curvature (dominant points) of an object. The suitability and robustness of the indices for this application is assessed by ascertaining their robustness to inevitable torso shape variations due to sway and breathing and the variability in their values relative to existing clinical measures of deformity. To assess the consistency of these indices with other indices in use for this application, they were used to assess the relative information contents of the front and back of the torso. Results show that structured splines indices are more robust than existing clinical measures for monitoring torso deformity in scoliosis. Results also show that the scoliosis information content ratio of the back torso to the front torso is three to one.

Contribution of loading conditions and material properties to stress shielding near the tibial component of total knee replacements.

This communication reports important preliminary results of a parametric analysis into the stress shielding effects of loading conditions and material properties of a total knee replacement (TKR) prosthesis. A previously developed finite element (FE) model of the proximal tibia that incorporated orthotropic and heterogeneous bone properties was used. Tibiofemoral joint compression and soft tissue (ligament and muscle) forces were also included to better represent the loading condition in the tibia. Stress shielding effects were studied for a prosthesis similar to a commercially available model. Results from the model show that the hypothesis of relatively higher Young's modulus of implant compared to bone as the primary cause of stress shielding is not sufficiently descriptive. Loading conditions as a result of altered bone or implant condylar surface geometry, load placement on the condylar surface, and load pattern created by the TKR are at least as important or, in some cases, more important factors in observed stress shielding immediately post-operation. This finding can be used to focus new implant design on altered loading conditions as well as material selection.

Repetitive pointing to remembered proprioceptive targets improves 3D hand positioning accuracy.

Repetitive pointing movements to remembered proprioceptive targets were investigated to determine whether dynamic proprioception could be used to modify the initial sensorimotor conditions associated with an active definition of the target position. Twelve blindfolded subjects used proprioception to reproduce a self-selected target position as accurately as possible. Ten repetitions for each limb were completed using overhead and scapular plane pointing tasks. A 3D optical tracking system determined hand trajectory start and endpoint positions for each repetition. These positions quantified three-dimensional pointing errors relative to the target position and the initial and preceding movement repetitions, as well as changes in movement direction and extent. Target position and cumulative start position errors were significantly greater than the corresponding preceding movement (inter-repetition) errors, and increased as the trial progressed. In contrast, hand trajectory start and endpoint inter-repetition errors decreased significantly with repeated task performance, as did movement extent, although it was consistently underestimated for each repetition. Pointing direction remained constant, except for the angle of elevation for scapular plane pointing, which consistently decreased throughout the trial. The results suggest that the initial conditions prescribed by actively defining a proprioceptive target were subsequently modified by dynamic proprioception, such that movement reproduction capability improved with repeated task performance.