In the total knee replacement procedure, each prosthesis is made up of four parts. The tibial component has two elements and replaces the top of the shin bone or tibia. This prosthesis is made up of a metal tray attached directly to the bone and a plastic spacer that provides the bearing surface. The femoral component replaces the bottom of the thigh bone or femur. This component also replaces the groove where the patella, or kneecap, sits. The patella component replaces the surface of the patellar bone, which rubs against the femur. The patella protects the joint, and the resurfaced patellar button will slide smoothly on the front of the joint.
In the total hip replacement procedure, the prosthesis is made up of three components. The femoral stem is made out of a metal, such as titanium, and is implanted down the shaft of the thigh bone, or femur. The ball, or femoral head, is attached to the stem and is designed to replace the arthritic femoral head. The third part, the acetabular component, is a metal shell with a plastic inner socket liner. These components are implanted into the pelvis and thigh bone, and are designed to closely approximate the mobility of the natural hip joint.
Before being taken to the operating room, you'll be given medication to help you relax. The anesthesiologist will talk with you about the medication they will be using. Once you are "under", Dr. Martin will begin by making an incision into your leg or hip to allow access to your joint.
Total Knee Arthroplasty Patients
Dr. Martin will then expose the joint and place a cutting jig with the help of the computer on the end of the femur, or thigh bone. This jig allows him to shave the bone precisely so that the prosthesis fits exactly. Once the femur is shaved, the tibia is shaved with the help of a computer using another jig for proper alignment of the knee prosthesis. The undersurface of the patella is shaved. Dr. Martin then cements in the femoral, tibial, and patellar components. This tray will provide the weight-bearing surface. If this component should wear out while the rest of the artificial knee is sound, it can be replaced (This process is known as a "revision"). Finally, the incision is closed and the post-operative bandaging is applied.
For Total Hip Arthroplasty Patients
After the incision is made and exposure is adequate, the ligaments and muscles are separated to allow access to the bones of the hip joint. The femoral head is then dislocated from the hip joint and removed at the level of the femoral neck. After the femoral head is removed, the cartilage of the acetabulum is removed using a special reamer that forms a hemispherical shape. The remaining shape will allow for a proper fit of the metal shell. A trial component is placed in the reamed area to determine the proper size and fit. Once Dr. Martin is satisfied with the size and positioning of the trials, he will implant the metal shell. He then prepares the femoral canal to accept the femoral stem implant. Dr. Martin hallows out the femur to match the shape of the metal stem of the femoral component. Trial components of the femoral stem, femoral head, and acetabular shell are temporarily implanted to ensure the proper size and fit of the final implants.
Computer Assisted Technology
Computer-assisted surgery addresses any issues of alignment of the knee prosthesis. Using infrared cameras and simple tracking devices, alignment comes to within two degrees and two millimeters or total accuracy. While Dr. Martin performs the surgery, the computer helps him determine the precise cuts that need to be made in the bone. Given that every patient's joints and geometry are different, this level of patient-specific, guided accuracy leads to thousands of successful surgeries and satisfied patients within our practice each year.