Computer assisted knee surgery: diagnostics and planning of knee surgery.

Cruciate ligament rupture, a common injury among young active adults, disrupts the knee's complex movement and often leads to premature degenerative arthritis of the joint. Prosthetic cruciate ligaments can be used for replacement but often fail owing to incorrect surgical placement. To aid in the planning of cruciate prosthetic substitution, a computerized system has been developed to provide the surgeon with a virtual interface allowing accurate visualization of three-dimensional (3D) bone structure and movement normally hidden beneath layers of soft tissue. Preoperatively, precise in vivo kinematics are quantified with the help of 3D medical images. Three-dimensional imagery techniques based on computed tomography (CT) have been developed to obtain accurate 3D reconstruction of knee geometry preoperatively. The system allows the surgeon to know the real-time spatial position of the patient via magnetic position and orientation sensors attached noninvasively onto the femur and tibia via a new attachment system. An interactive computer program has been developed to allow the user to simulate different prosthetic ligament insertions and compute elongation, bending, and torsion values that will be imposed on the prosthesis. Through comparison with cadaver studies and a perturbation analysis, the system is shown to be sufficiently accurate to predict certain in vivo ligament bending and torsion deformations.