Dr. Bates describes how a hip implant is fixed to a bone during hip replacement surgery.
There are two methods to fix an implant to the bone. There’s a cemented technique and an uncemented technique. Cemented implies that bone cement, which is called polymethacrylate, it’s a substance that adheres both to the bone and to the implant, and basically it works as a mortar or a glue between the implant and your bone, and it sets up and becomes hard in about five to ten minutes.
So when you are ready to insert the implant you apply the bone cement; you implant the component and then allow it to harden as you remove any excess cement around the implant.
More recently, however, many implants are put in without bone cement. Now the ability to do that is based on the type of surface that is on the implant itself and typically, a coating on the implant, usually it’s a titanium coating that has pores in it, and those pores allow bone to grow into the implant to basically biologically fix the implant to the body.
Those implants are typically press-fit initially, meaning that the bone is contoured such the implant fits in and has a basic macro fit or a fit based on the geometry of the implant initially. Then over a period of time, typically between three and six months, the body incorporates the implant, i.e., it becomes fixed to the implant by virtue of bone growing into the implant.
The patient won’t know that this is occurring as they have no pain initially during this whole process with either cementing or un-cementing, but it’s just a cleaner technique, and it actually is a little bit more desirable nowadays, if you can get away with using an uncemented implant to perform these operations.
About Dr. Bates, M.D.:
Dr. James E. Bates, M.D., is a board-certified orthopedic surgeon specializing in joint replacement surgery and sports medicine at Alvarado Hospital. Dr. Bates places his focus in sports medicine and the reconstruction and replacement of damaged bones, joints, and cartilage resulting from sports injuries, traumatic injuries, and tumors of the extremities. He was trained at the Hospital for Special Surgery/Cornell University Medical Center and Memorial Sloan Kettering Cancer Center in New York. As an orthopedic surgeon, Navy Flight Surgeon, and Navy Diving Medical Officer, he serves as a consultant to the San Diego-based Navy SEAL Teams.