Dexterous magnetic manipulation of conductive non-magnetic objects.

Dexterous magnetic manipulation of ferromagnetic objects is well established, with three to six degrees of freedom possible depending on object geometry1. There are objects for which non-contact dexterous manipulation is desirable that do not contain an appreciable amount of ferromagnetic material but do contain electrically conductive material. Time-varying magnetic fields generate eddy currents in conductive materials2-4, with resulting forces and torques due to the interaction of the eddy currents with the magnetic field. This phenomenon has previously been used to induce drag to reduce the motion of objects as they pass through a static field5-8, or to apply force on an object in a single direction using a dynamic field9-11, but has not been used to perform the type of dexterous manipulation of conductive objects that has been demonstrated with ferromagnetic objects. Here we show that manipulation, with six degrees of freedom, of conductive objects is possible by using multiple rotating magnetic dipole fields. Using dimensional analysis12, combined with multiphysics numerical simulations and experimental verification, we characterize the forces and torques generated on a conductive sphere in a rotating magnetic dipole field. With the resulting model, we perform dexterous manipulation in simulations and physical experiments.

A Novel Approach for Assessing and Training the Drilling Skills of Orthopaedic Surgeons.

BACKGROUND: Although experiences in the operating room can help surgeons to learn simple bone-drilling techniques, outside training may be better suited for complex procedures. We adapted a rotary handpiece to evaluate the bone-drilling skills of orthopaedic resident physicians during the 2017 Southwest Orthopaedic Trauma Association (SWOTA) motor skills course. METHODS: Twenty-five postgraduate year (PGY)-1 orthopaedic residents from 7 institutions were asked to perform a bicortical drilling task 3 times both before and after attending a motor skills course. Kinetic and kinematic data were collected using force, acceleration, and visual sensors. RESULTS: Sixteen parameters were measured. The interdependence of these parameters (taken separately for precourse and postcourse performance) is presented. Evidence for motor skill acquisition across a short time scale is elucidated. Noteworthy correlations include overpenetration with force (0.65 mm), palmar-dorsal (P-D) toggle (0.65°), vibration in the P-D direction (0.53 m/s), time (-0.41 sec), and RPM (revolutions per minute; -0.36); time with both RPM (0.38) and P-D toggle (-0.40°); and force with both RPM (-0.41) and P-D toggle (0.32°). Differences in performance before and after the motor skills course include reduction in overpenetration (28.8 to 18.2 mm), reduction in skiving (22% to 6%), and reduction in preparation time (27.3 to 9.65 sec). Additionally, there were several differences in performance by institution that were significant (overpenetration, toggle in the P-D and radial-ulnar [R-U] directions, and both drilling force and drilling time). CONCLUSIONS: Understanding how performance and outcome parameters are correlated provides powerful insight into how surgical procedures can be best performed. In particular, we hope that these findings will inform new training paradigms. Variations in resident training from 1 institution to another are evidenced in surgical performance. Similarly, the methods used here to quantify changes in performance across the 3-day SWOTA training course allow a unique vehicle for optimization of these types of training opportunities outside of the operating room.

Mechanical model of orthopaedic drilling for augmented-haptics-based training.

In this study, augmented-haptic feedback is used to combine a physical object with virtual elements in order to simulate anatomic variability in bone. This requires generating levels of force/torque consistent with clinical bone drilling, which exceed the capabilities of commercially available haptic devices. Accurate total force generation is facilitated by a predictive model of axial force during simulated orthopaedic drilling. This model is informed by kinematic data collected while drilling into synthetic bone samples using an instrumented linkage attached to the orthopaedic drill. Axial force is measured using a force sensor incorporated into the bone fixture. A nonlinear function, relating force to axial position and velocity, was used to fit the data. The normalized root-mean-square error (RMSE) of forces predicted by the model compared to those measured experimentally was 0.11 N across various bones with significant differences in geometry and density. This suggests that a predictive model can be used to capture relevant variations in the thickness and hardness of cortical and cancellous bone. The practical performance of this approach is measured using the Phantom Premium haptic device, with some required customizations.

Objective Evaluation of Motor Skills for Orthopedic Residents Using a Motion Tracking Drill System: Outcomes of an ABOS Approved Surgical Skills Training Program.

BACKGROUND: Orthopedics is a motor skills-demanding surgical specialty requiring surgical skills training outside of the operating room. Unfortunately, limited quantitative techniques exist to determine the effectiveness of these surgical skills training programs. Using a variety of drill, surgeon, and specimen mounted sensors, we evaluated orthopedic surgery residents during a surgical skills training course approved by the American Board of Orthopaedic Surgeons (ABOS). This evaluation consisted of quantitative measures of various kinematic and kinetic parameters with the goal of relating these to clinically-significant outcomes. METHODS: Seven experienced surgeons and 22 surgical residents participated in this study, each performing 5 surgical drilling trials, pre- and post-training. Utilizing arm and tool kinematics, applied force, tool and bone vibration, and drill RPM were measured using a combination of force, acceleration, and optical tracking sensors. Post hoc screw pullout testing and resident survey data were also evaluated. Overall, 25 measured parameters were expressed as scalars and their covariance calculated. RESULTS: Non-trivial direct correlations whose magnitude exceeded 0.5 were: maximum penetration distance with applied force, drill toggle with drill roll angle, and drill RPM with force. Surgeons applying a high drill RPM also yielded a large force which in turn gave an increase in tendency for over-penetration. As a whole, the differences between experienced and novice surgeons measured in these trials were not statistically significant. However, when looking at specific performance criterion individually (maintaining steady force, minimizing over-penetration, minimizing both the major and minor axis diameters, minimizing toggle and drill vibration), experienced surgeons tended to outperform their novice counterparts. CONCLUSIONS: Objective assessment of surgical skills using sensor based technologies may help elucidate differences between novice and experienced surgeons for improved out-of-the-OR training methodologies.