Design of patient-specific hip implants based on the 3D geometry of the human femur

Abstract

Total hip replacement (THR) is a surgical procedure that replaces a diseased hip joint with implants. Due to the various size and shapes of human hip joint of every individual, a chosen commercial hip implant sometimes may not be the best-fit to a patient, or even it cannot be applied because of its discrepancy. To solve the problem of a possible geometric mismatch between a selected implant and the hip joint, we develop a software system that designs a patient-specific hip implant by investigating the anatomical geometry of the patient's hip joints. The major technical challenge of the proposed system is to extract some typical 3D geometry parameters with respect to the patient's 3D bone anatomy and then creates a custom-made hip implant based upon the extracted parameters. This paper describes the overall procedure of creating a patient-specific hip implant based upon the geometry of the patient's femur. The parameters include femoral shaft isthmus, anatomical femoral axis, femoral head center/radius, head offset length, femoral neck, neck shaft angle, anteversion, and canal flare index (CFI). Some of them are semi-automatically recognized and extracted, but others must be determined with the surgeon's intervention. All the parameters are sufficient to construct a primitive 3D geometry model of the specified femur, so that a patient-specific hip implant for individual patients can then be determined from the information of those extracted geometry parameters. The stability of patient-specific implants has been increased by maximizing contact area with the bone. Currently the proposed system is exclusive for the design of a hip implant; however, the concepts are general enough to be applied to any other human joints such as the shoulder, the knee, or the spine. The feasibility and reliability of the method has been tested on some examples.