Materials and Techniques

Metals

Cobalt Chrome: Cobalt chrome is the standard metal used for the femoral components (end of thigh bone). It is amenable to either cemented or noncemented use. It does contain trace amounts of nickel, so it should not be used in patients who have nickel allergy. The wear properties are excellent. Basically, his metal does not wear out, although it does cause wear against polyethylene.

Dr. Bartlett’s opinion: Cobalt Chrome is the standard femoral component metal. Perfectly acceptable.

Oxinium (oxidized zirconium): Oxinium was introduced in the total joint market in 1997. It is used only for the femoral component (end of thigh bone). This material is proprietary to the Smith & Nephew company so it is used only in implants manufactured by that company. It is amenable only to cemented use. No one is allergic to oxinium so it is the metal of choice in patients allergic to nickel or other metals . The metal itself does not wear out. Laboratory testing has shown 85% less wear used against polyethylene.

Dr. Bartlett’s opinion: Good metal with excellent wear properties, but some benefit is offset by the need to use cement.

Titanium: Titanium is the standard metal used for the tibial component base (top of the shin bone). There is virtually no allergy to titanium (I have seen one only patient in 30 years). Titanium can be used in either a cemented or non-cemented, bone ingrowth mode. Titanium components do not articulate with other metal components in the knee, but titanium does articulate with the smooth undersurface of the tibial polyethylene (plastic). The titanium does not wear, but the polyethylene which rests on it can wear.

Dr. Bartlett’s opinion: Titanium is the standard metal for the tibial base. Perfectly acceptable.

Polyethylene (Plastic)

Polyethylene (ultra-high molecular weight polyethylene or UHMWPE): This is the plastic which forms the articulating surface of the proximal tibia (top of the shin bone). It is used alone (cemented) or is contained on a titanium base which can be cemented or used in a non-cemented, bone in-growth mode. To date, polyethylene is about the best bearing surface that has been created for use on the tibia but it is definitely the weak link of any materials used in knee replacement surgery as it definitely shows signs of wear as years pass. Polyethylene wears at a rate of about 0.2 mm per year. Polyethylene debris can cause pain, swelling and bone dissolution called lysis. Wearing of polyethylene and the effects of polyethylene debris are the most common causes for revision of joint replacement today.

Dr. Bartlett’s opinion: No alternative exists, but definitely the weak link of any joint replacement system.

Fixation to Bone

Cement: The use of bone cement is the standard for fixation today. Benefits include ability to accommodate irregular bone surfaces, less bleeding after surgery and immediate stable fixation. Disadvantages include the possibilities of cement loosening and fragmentation. Particulate debris of cement in the joint hastens wear between the metal femoral component and the tibial polyethylene component.

Dr. Bartlett’s opinion: I have always favored non-cemented, bone ingrowth systems. Fixation provided by bone ingrowth is stronger, and more permanent. The is no cement to loosen. Also, cement debris, whether from the initial cementing or from loosening and cement fracture, will act like sand in a bearing causing component wear, especially the polyethylene.

Bone ingrowth (non-cemented or press fit or porous ingrowth): This technique is used and advocated by many surgeons. The undersurface of metal components is roughened during implant manufacturing in such a way that bone can actually grow into the metal and lock it into place. The benefits include the fact that, by avoiding cement there will be no loosening secondary to cement failure and no increased abrasive wear due to cement fragmentation. The bony ingrowth technique, however, requires a much more precise carpentry as there is no cement to fill gaps and irregularities. Initial fixation must be provided by other means such as press-fit (for the femur or end of the thigh bone), or screws and pegs (for the tibial component or top of the shin bone). There may be more bleeding from bone immediately after surgery since the bone is not “sealed” by the cement.

Dr. Bartlett’s opinion: I have a very strong preference for non-cemented fixation. I believe that these implants last longer (no cement to loosen) and these implants wear longer (no cement debris to act like sand in the joint). Revision is easier as bone stock is preserved when they are removed. I have used this technique since 1983. Only recently have I begun cementing implants because some implants are not manufactured for press fit or non-cemented use (oxinium, Smith & Nephew Accuris, Smith & Nephew Deuce, MAKOplasty).

Alignment

Intramedullary alignment: Placing a thin rod up the shaft of the femur (thigh bone) and down the shaft of the tibia (shin bone) allows the surgeon to identify the proper alignment of the extremity. This technique is the standard and has been used successfully for well over 25 years. The technique is reliable and accurate.

Dr. Bartlett’s opinion: Perfectly satisfactory and my preference for total knee replacement since 1983.

Patient specific: Using an MRI or CT scan, a model of the patient’s knee can be created. This model is then used to guide implant alignment during surgery.

Dr. Bartlett’s opinion: Unnecessary

Computer navigation: This technique has been available since about 2002. A computer with “eyes” observes the surgeon’s instruments and guides him to properly align the knee as he watches a computer screen.

Dr.Bartlett’s opinion: This is my preference for partial knee replacement or resurfacing. Computerized navigation allows the surgeon to achieve very accurate alignment. Navigation can be very useful for total knee replacement too, but it is not currently available for use with the Smith & Nephew Profix implants, the implants I prefer.

Bone Preparation

Traditional bone resection: For years a saw has been used to remove worn out bone and fashion the distal femur (end of the thigh bone) and the proximal tibia (top of the shin bone) to receive the joint components.

Dr. Bartlett’s opinion: The standard since the 1970’s and perfectly acceptable.

Resurfacing: Removing less bone or “just enough” bone to allow for resurfacing can be performed with either a high speed burr or a circular, spinning, planning blade.

Dr. Bartlett’s opinion: Especially for partial knee resurfacing, these systems reduce bone loss during the bone preparation phase of the procedure. This can be beneficial in that it allows a relatively easy conversion to total knee replacement if that should ever be necessary.

Bone Preparation Device Control

Surgeon control: The surgeon is in complete control of the saw, burr, or reamer which is used to remove bone.

Dr. Bartlett’s opinion: Certainly the standard. The skill necessary to use these instruments is what makes an orthopedic surgeon a craftsman.

Robotic assisted: The interactive robotic arm was introduced to the orthopedic market by MAKO Surgical in 2007. A high speed surgical burr is controlled by the surgeon, but the robot assists in determining where bone is to be removed and how much is to be removed. When used in combination with computer navigation, the accuracy of implant position and lower extremity alignment is unequaled.

Dr. Bartlett’s opinion: Superb, cutting edge technology although only available currently for partial knee resurfacing using MAKO implants.