System Summary

Problem Description

Total Hip Arthroplasty (THA) Surgery as performed in the present involves the reaming of the acetabulum (pelvis), cutting of the femur, drilling into the femur, placing the cup into the acetabulum, and hammering the prosthesis into the femur. One of the most crucial factors in determining a successful surgery is the accuracy of acetabular cup position and orientation placement, as the correct position and orientation would avoid future dislocation of the hip joint and increase patient comfort. Therefore, it is imperative that surgeons know exactly what orientation and depth they are reaming the acetabulum to.

However, most surgeons cannot see the site of surgery well during surgery and do not use the proper tools to obtain accurate results, leading to malpositioned cups. In fact, it is estimated that less than 50% of THA outcomes are within surgical safe zones (Lewinnek Safe Zone). This is a result of “intraoperative pelvic tilt, distorted anatomical landmarks, and limited accuracy and reproducibility of the alignment guides.” Other factors of malpositioned cups are “minimally invasive surgical approaches, low surgeon volume, and obesity” [1]. While there are modern robotic systems that can help mitigate this problem, all increase the time of surgery and lack robustness during surgery.

“More recently, patient-specific safe zones based on preoperative assessments of pelvic kinematics have gathered momentum as a route for improving stability and reducing complications in THA.” With the manual surgery, these plans would be hard to execute with high accuracy. However, autonomous robotic technology can provide a way to execute patient-specific surgical plans to meet these patient-specific safe zones with high accuracy [1].

To meet this need, our team is proposing the ARTHuR (Autonomous Reaming for Total Hip Replacement) Robot, which will maximize the accuracy of acetabular reaming, while remaining robust during surgery.

Use Case

Dr. Hip is an orthopedic surgeon and needs to perform a total hip replacement/arthroplasty on a patient suffering from osteoarthritis in their hip joint. Prior to the beginning of the surgery, Dr. Hip takes a CT scan of the patient’s pelvis in order to reconstruct the 3D geometry of the patient’s pelvis, specifically their acetabulum. With this 3D geometry, Dr. Hip is able to use his intuition to choose an acetabular cup specifically suited for the patient, and plan the exact location and orientation of the acetabular cup, such that the resulting prosthesis will be in the Lewinnek Safe Zone.

Dr. Hip will then begin the surgery by orienting the patient to their side such that the hip which is being operated on is facing upwards. Dr. Hip , using the typical surgical techniques for hip replacement surgeries, will expose the acetabulum and clean the desired amount of soft tissue from the pelvis. With the acetabulum exposed, the surgeon would then drill in a reflective marker array into the pelvis which will be used to locate the pelvis in 3-dimensional space. Using a probe, the surgeon will register the position of 3-5 points of interest on the pelvis and generate a point cloud that represents the anatomy of the patient’s pelvis. This point cloud and the points of interest are then used to localize the hip in 3-dimensional space, fitting the 3D geometry from the CT scan to the patient’s pelvis on the operating table. Given this localization and the desired acetabular cup location, a cutting trajectory is then generated which a robotic arm will follow in order to ream the acetabulum as desired. Dr. Hip then fixes a reamer onto the end-effector of the robotic arm. From here, the doctor manipulates the robotic arm such that the end-effector is close to where the reamer would begin cutting into the acetabulum. Dr. Hip then starts the robotic arm, which begins to autonomously track the trajectory and ream the acetabulum to the surgical plan. During the reaming, the robot arm detects and compensates for movements in the patient’s pelvis that occur as a result of the applied forces, maintaining the surgical plan. Furthermore, Dr. Hip is provided with visual feedback on a monitor, which demonstrates the current progress in reaming the acetabulum, and metrics the surgeon would need, as well as an emergency stop. Once the robot arm has completed the planned trajectory, it stops and allows for Dr. Hip to remove it from the surgical site and analyze the resulting reamed acetabulum.

References

[1] Kayani, B., Konan, S., Ayuob, A., Ayyad, S., & Haddad, F. S. (2019). The current role of robotics in total hip arthroplasty. EFORT open reviews, 4(11), 618–625. https://doi.org/10.1302/2058-5241.4.180088