A pilot trial comparing the tear-out behavior in screw-sockets and cemented polyethylene acetabular components - a cadaveric study

Wrist at risk? - Considerations derived from a novel experimental setup to assess torques during hip reaming with potential implications on the orthopedic surgeons' health

Orthopedic surgeons endure high physical stresses when performing surgery, as large forces and torques are applied commonly. Occupational risks are consequently higher when compared to other surgical disciplines. One example is the reaming of the acetabula during total hip arthroplasty, using customized instruments. This surgery may predispose the surgeon to overuse-related wrist pathology. In this study, torques acting along the reaming tool were measured, and the resulting forces applied to the orthopedic surgeons' wrists were estimated based on the measured torque data from hip reaming. Different reamer sizes and tool velocities were analyzed to determine how both parameters may influence the torques applied at the surgeon's wrist. Using a highly standardized setup, torques were measured while the reamer was pushed into the acetabula to remove cartilage. Maximum torques and stoppage torques at blocking of the reamer were compared between feed rates and reamer sizes. Peak values of the maximum torques along the reamer axis averaged 1.5-1.8 Nm. No significant difference between maximum torques and reamer sizes was found. A significant difference in maximum torques was noted between feed rates with a large effect (p = 0.010; η² = 0.214) and a large interaction effect (p = 0.017; η² = 0.186). Based on this experimental setup, it can be hypothesized that the impulsive behavior of the torque when the milling tool reaches the subchondral lamella could potentially contribute to wrist pathology. These preliminary data warrant further study. Consequently, torque limiters should be implemented in reamers to minimize the risk of occupation-related pathology to the wrist.

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.