4D Ultrasound-Based Knee Joint Atlas for Robotic Knee Arthroscopy: A Feasibility Study

In this work, we proved for the first time the feasibility of using high-refresh-rate 3D ultrasound (US) also known as 4D US imaging to create a volumetric atlas of the knee anterior compartment for an autonomous robotic platform for knee arthroscopy. A dataset of 42 4D US sequences (including 94 US volumes) and 25 MRI volumes was collected from seven volunteers, in several leg positions simulating the surgical scenario of knee arthroscopy. MRI-US volume pairs were manually registered, and the knee structures of interest identified on the US volumes. The resulting atlas comprised the femur, tibia and patella surfaces, patellar tendon, femoral cartilage, the anterior parts of the menisci and the ACL, for knee angles between 0 and 90 degrees flexion. The inter-operator reproducibility of the registrations was calculated as the norm of the difference in the translation and the rotation values selected by two experienced orthopaedic surgeons and resulted to be on average of 4.42 mm +/- 1.89 mm SD and 7.77 degrees +/- 2.80 degrees SD, respectively. A new metric was introduced to measure the overlap of the US volume located at the position selected from the first and the second experts and the agreement resulted to be on average of 87% +/- 3 SD. The US scanning protocol adopted could be considered compatible with the arthroscopy procedure, as proved through six cadaver studies. These preliminary results show that 4D US is an excellent candidate for automatic image-based guidance in knee arthroscopy.