Perceived realism of haptic rendering methods for bimanual high force tasks: original and replication study.

Realistic haptic feedback is a key for virtual reality applications in order to transition from solely procedural training to motor-skill training. Currently, haptic feedback is mostly used in low-force medical procedures in dentistry, laparoscopy, arthroscopy and alike. However, joint replacement procedures at hip, knee or shoulder, require the simulation of high-forces in order to enable motor-skill training. In this work a prototype of a haptic device capable of delivering double the force (35 N to 70 N) of state-of-the-art devices is used to examine the four most common haptic rendering methods (penalty-, impulse-, constraint-, rigid body-based haptic rendering) in three bimanual tasks (contact, rotation, uniaxial transition with increasing forces from 30 to 60 N) regarding their capabilities to provide a realistic haptic feedback. In order to provide baseline data, a worst-case scenario of a steel/steel interaction was chosen. The participants needed to compare a real steel/steel interaction with a simulated one. In order to substantiate our results, we replicated the study using the same study protocol and experimental setup at another laboratory. The results of the original study and the replication study deliver almost identical results. We found that certain investigated haptic rendering method are likely able to deliver a realistic sensation for bone-cartilage/steel contact but not for steel/steel contact. Whilst no clear best haptic rendering method emerged, penalty-based haptic rendering performed worst. For simulating high force bimanual tasks, we recommend a mixed implementation approach of using impulse-based haptic rendering for simulating contacts and combine it with constraint or rigid body-based haptic rendering for rotational and translational movements.

A cadaver-based biomechanical model of acetabulum reaming for surgical virtual reality training simulators.

Total hip arthroplasty (THA) is a highly successful surgical procedure, but complications remain, including aseptic loosening, early dislocation and misalignment. These may partly be related to lacking training opportunities for novices or those performing THA less frequently. A standardized training setting with realistic haptic feedback for THA does not exist to date. Virtual Reality (VR) may help establish THA training scenarios under standardized settings, morphology and material properties. This work summarizes the development and acquisition of mechanical properties on hip reaming, resulting in a tissue-based material model of the acetabulum for force feedback VR hip reaming simulators. With the given forces and torques occurring during the reaming, Cubic Hermite Spline interpolation seemed the most suitable approach to represent the nonlinear force-displacement behavior of the acetabular tissues over Cubic Splines. Further, Cubic Hermite Splines allowed for a rapid force feedback computation below the 1 ms hallmark. The Cubic Hermite Spline material model was implemented using a three-dimensional-sphere packing model. The resulting forces were delivered via a human-machine-interaction certified KUKA iiwa robotic arm used as a force feedback device. Consequently, this novel approach presents a concept to obtain mechanical data from high-force surgical interventions as baseline data for material models and biomechanical considerations; this will allow THA surgeons to train with a variety of machining hardness levels of acetabula for haptic VR acetabulum reaming.