In computer-assisted orthopedic surgery (CAOS), accurate pre-operative to intra-operative bone registration is an essential and critical requirement for providing navigational guidance. This registration process is challenging since the intra-operative 3D points are sparse, only partially overlapped with the pre-operative model, and disturbed by noise and outliers. The commonly used method in current state-of-the-art orthopedic robotic system is bony landmarks based registration, but it is very time-consuming for the surgeons. To address these issues, we propose a novel partial-to-full registration framework based on gradient-SDF for CAOS. The simulation experiments using bone models from publicly available datasets and the phantom experiments performed under both optical tracking and electromagnetic tracking systems demonstrate that the proposed method can provide more accurate results than standard benchmarks and be robust to 90% outliers. Importantly, our method achieves convergence in less than 1 second in real scenarios and mean target registration error values as low as 2.198 mm for the entire bone model. Finally, it only requires random acquisition of points for registration by moving a surgical probe over the bone surface without the need for correspondences, thus showing significant potential clinical value. The code of the framework is available*.

When performing total hip replacement (THR) surgery, high-quality preparation of acetabulum is critical as it contributes to the patient’s recovery speed and the consistency of bone ingrowth. Conventionally, surgeons prepare the acetabulum manually by reaming it with a handheld electric drill and a reamer. It not only increases the surgeon’s workload but more importantly, it is difficult to control the reaming depth and direction accurately. Utilizing an admittance-controlled (AC) collaborative robot (cobot) to enable physical human-robot collaboration (pHRC) possesses a promising solution. For primitive AC, a compromise must be made between compliance and task accuracy. In this paper, we present a novel variable admittance control (VAC) design that considers the reactive force of bone while ensuring the passivity and stability of the system during pHRC-assisted acetabular preparation. The qualitative results show that VAC was more desirable by users than the conventional manual reaming method. Compared to other pHRC controls, quantitative results on user energy consumption, reaming error, and smoothness showed the proposed VAC can achieve a balance between physical workload and acetabular quality. Compared to manual reaming, VAC reduced the reaming error by 67.47% and improved the final acetabulum surface smoothness by 18.30%.