Partial (unicompartmental) Knee Osteoarthritis
Unicompartmental (partial) Knee Replacement
Partial knee replacement components are designed and manufactured by many different companies in the United States and throughout the world. These implants are unique in that only one area or compartment of the knee is replaced, and are either a fixed bearing ( the plastic is locked into place) polyethylene( “poly” or plastic) or a mobile bearing, meaning that plastic moves with your knee joint movement. All currently utilized partial knee replacement components have a long track record of success and have been thoroughly tested and approved by the US Food and Drug Administration. Currently the most common materials used for components are various metal alloys to include titanium and cobalt-chrome, as well as high grade molecular weight polyethylene or poly.
There are various implants that may be used to replace or resurface any of the three compartments within the knee, the inside part, outside part, or the knee cap joint, depending on which area has been found to have damaged cartilage and become symptomatic for the individual patient. Which component or compartment of the knee that is to be resurfaced for an individual patient must be determined prior to surgery with a conversation between the patient and his or her surgeon, with various xrays or even MRI’s confirming. Unicompartmental knee replacement has been shown to be an effective treatment for patient’s who meet the correct indications for surgery with a greater than 90% success rate and survivorship of implants at 12- 15 years post-operatively.
A discussion on what’s best for you or your loved with your surgeon is important, as not all patients are candidates for partial knee replacement. It should be well understood that overall success for pain relief and increased function are excellent for partial knee replacement, in general survivorship, or how long a partial knee replacement lasts compared to a total knee replacement, is generally less. Therefore, revision surgeries may be necessary earlier or more often with partial knee replacement.
Partial Knee Replacement Surgery
Partial knee replacement surgery is the process of surgically removing a few millimiters of damaged cartilarge and bone from the affected compartment and replacing or resurfacing the that single area with metal and plastic. It can be performed for any of the above mentioned three compartments, although is is most commonly performed to replace the medial or inside region of the knee. The advantages of this procedure are that more of the native knee are retained by the patient which is thought to lead to faster recovery and more anatomic or normal motion within the knee joint.
In order to benefit from partial knee replacement, patient’s must meet certain indications prior to surgery which include pain in only one region of the knee, x-rays demonstrating loss of cartilage in only one are, a stable knee without evidence of ligamentous injury, good range of motion, and a body mass index within an acceptable range. The surgery is performed by making a small incision and the front of the knee and with the use of cutting guides, resecting the regions of damaged bone and cartilage and replacing them with metal and plastic components. Following surgery patients are typically permitted to walk on their new knee the same day and are discharged from the hospital within 24, and more often this operation is performed on an outpatient setting, same day surgery.
The Zimmer-Biomet Oxford TM Partial Knee Replacement System is the most widely used partial knee replacement system in the world. It is designed to replace either the medial (inside) or lateral (outside) compartments of the knee and has a proven track record of success. The components are designed to anatomically replicate the region of the knee that is being replaced. This allows for more anatomic knee motion following replacement.
Additionally, the component is designed to retain the native cruciate ligaments (ACL and PCL) of the knee which again allows for more normal knee motion following surgery. Some studies have shown that this leads to faster recovery and improved patient satisfaction. The components are introduced through standard anterior incisions overlying the compartment being replaced. The tibial component is designed to replace the portion of the joint at the top of the tibia and the femoral component is designed to replace the bone and cartilage removed from the end of the femur.
These components in this system are manufactured from a Cobalt-Chromium alloy. The polymer plastic surface that is placed between these components is made of a highly crossed linked high-molecular weight polyethylene and demonstrates excellent wear characteristic. As with any surgery, the choice of implants used should be at the discretion of the surgeon and his comfort level with various systems. With this said, the Oxford partial knee replacement system is a great option.