Study and design of a cementless femoral stem extractor for the hip revision surgery

The hip revision surgery consists in the removal of a painful artificial hip joint component implanted during a primary hip replacement. This intervention affects 10\% of implanted patients and is mainly performed on elderly, bringing a risk for the patient health. This study focus on the revision of cementless femoral stem. Indeed, the removal of a cementless femoral implant can be a very hard intervention due to the strong link established between the stem and the bone. Sometimes, the removal of such a stem is impossible with the current method, a slap hammer. Thus, a femoral osteotomy has to be performed to remove the stem from the bone before implanting a new one leading to a recovery time of 6 months instead of 6 weeks for the successful method. The purpose of this Master’s thesis is to study and design an extractor helping the surgeon to systematically succeed the extraction of the stem. A structured procedure has been followed to realize the design and manufacture of a prototype for the grasping of the stem and its unsealing. This procedure led to a solution using the propagation of vibrations along the stem in the goal to break the interface bone/implant. The grasping solution is designed to perfectly fit the shape of the stem taper, maximizing the contact surface to allow an optimal transmission of vibrations. Because it has been impossible to test the prototype on an in-vivo implanted femur with a cementless femoral stem, experiments have been performed on an environment trying to mimic the osseointegration of a stem in the bone. However, the mechanical properties and behavior of bones being hard to imitate, the prove of the success of the unsealing component was not achieved. In contrary, the fastening system works successfully. It provides a good transmission of vibrations and never released the hold. Using a hammer drill coupled with this grasping system to perform a hip revision surgery would considerably reduce the operating time, decreasing the risks encountered by the patient. Ultrasounds have proven their efficiency to unseal dental implants, this orthopedic intervention can be seen as an application of this success on a larger scale. The adequate impact frequency and energy allowing the unsealing of the stem over its entire length without damaging the femur or surrounding tissue have to be investigated.