Hip Replacement


The goal of this project is to propose an alternative to “conventional” marked based navigation systems, including those developed within the VRAI group, to improve Total Hip Replacement.
The system is based on a mechanical device and a combination of software. The software processes 2D CT scans into 3D graphical models of the pelvis and femur. These models are then used for pre-operative implant planning. During surgery, software and hardware provide navigational guidance for the surgeon.

Pre-operative planning

The planning software allows the surgeon to visualize implant positioning prior to performing surgery. Pre-operative planning involves the following steps:

3D reconstruction. The surgeon reviews the 3D models that he will use, as well as the CT scan slices from which the models were constructed. Based on the data, the surgeon selects a Position Zero for the patient, which serves as a positioning reference point.

Hip center. The surgeon manipulates (via a simple click) the 3D model to determine the center of rotation of the acetabulum and the femoral head.

Stem and acetabulum implantations. The surgeon selects an implant range and the software automatically computes implant positions by considering the patient anatomy. The surgeon can modify/refine the positions as needed.

Range of motion. Once the surgeon has approved the implant positions the software allows him to visualize the range of motion. The software computes movement range for flexion/extension and adduction/abduction.

Registration. The surgeon designates the points on the pelvis and the femur that will be used for registration during the operation.

/webdav/site/vrai-group/shared/projects/nccr/images/ortho.jpgWe have developed a lightweight (<1 kg), serial-link arm with six degrees of freedom (6dof). The arm has an absolute positioning accuracy of 0.2 mm and has numerous benefits for surgery including, easy installation, allowing rapid tool changes, easy to manipulate, a single cable in the surgical zone, and low cost. During surgery, the arm is attached to the patient and provides highly precise positioning.

The navigation software assists the surgeon to place the implant in the pre-planned location. Combined with the navigation device, the software provides guidance to the surgeon, enabling him to precisely position both the tools and prosthesis.

Specifically, the surgeon receives guidance to:

  1. ream the cotyle
  2. implant the acetabulum into the cotyle
  3. implant the stem into the femoral head
  4. verify implant accuracy


Hôpital Orthopédique de la Suisse Romande (HOSR), the Orthopedic Department of the Centre Hospitalier Universitaire Vaudois (CHUV, Lausanne).