Cementless Total Knees
Cementless Total Knees have been available for custom use for Orthopedic surgeons since 2003. Similarly, Cementless Total Hips, have been used for over 20 years. Dr. Baier has been performing Cementless Total Knees since 2004. Most surgeons use a bone cement, called methylmethacrylate, to glue the prosthesis to the patient’s bone. The cement can last an average of 10-15 years before it loosens and a revision surgery is required.
Cementless knee replacements have special pores on the bone surface of the prosthesis, so the patient’s own bone growth into it to hold it in place. Currently, Dr. Baier is using Zimmer-Biomet cementless knee, Persona. (See video link for more information) The special pores are made out of trabecular metal, a new synthetic metal that has the closest porosity to the human bone than any other metal. The components are inserted with a tight pressure fit. This secure fixation allows the patient to fully weight bear right on the day of surgery. In early trials, the cementless models appear to be lasting at least as long as the cemented models. The cementless prosthesis may last longer than the cemented ones. Since our bones are living tissue, this bone ingrowth continues the rest of our lives. Plus, if a revision is ever needed, it is easier to revise a cementless prosthesis, with less bone destruction compared to removing the old cement.
Patient Specific Instrumentation (PSI)
Dr. Baier is one of the few surgeons who use PSI (Patient Specific Instrumentation). The patient must have a special MRI on their extremity about 4 weeks prior to surgery. From this MRI, guides and bone models of the patient’s knee are manufactured specifically for that individual patient. These guides are used during the procedure, which assists the surgeon. The guides are placed directly onto the patient’s bone setting up the jigs to cut the bone. This way less instruments, less drilling and less measuring are required. Dr. Baier has found that these guides speeds up his surgery so less anesthesia time and intraoperative blood loss is noted. These factors assist in helping patients to start rehab sooner, often the very day of surgery. In cases where the patient cannot have a MRI, a CT scan maybe used.
The disadvantage of PSI is the additional expense of preop MRI or CT scan and the cost of making the guides. While some surgeons prefer not to use PSI guides, Dr. Baier feels the benefits of the guides are worth the cost.
Most patients, but not all, are candidates for a cementless knee replacement. Some patients with severe osteoporosis may not be a good candidate. Also, patients with severe deformity or require a revision type model, maybe better served with a cemented model.