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. All currently utilized components have a long track record of success and have been thoroughly tested and approved by the Food and Drug Administration. Currently the most common material used for components are various metal alloys to include titanium, cobalt-chrome, and stainless steel as well as high grade plastics known as polymers.
There are various implants that may be used to replace any of the three compartments within the knee, depending on which area has been found to cause symptoms for the individual patient. Which component is right for an individual patient must be determined prior to surgery with a conversation between the patient and his or her surgeon. 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 15 years post-operatively.
There are however some studies which demonstrate a lower success rate and survivorship as compared to total knee replacement as well as an increased rate of revision surgery for partial knee replacements when compared to total knee replacement.
Partial Knee Replacement Surgery
Partial knee replacement surgery is the process of surgically replacing the bone and cartilage of only a single are of the joint. 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, 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 diseased 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 24-48hrs after surgery.
Partial (unicompartmental) Knee Osteoarthritis
The knee joint consists of three anatomic compartments. These include the medial (inside), lateral (outside), and anterior (front) compartments. Osteoarthritis (or simply arthritis) is a degenerative condition of the joint which causes progressive loss of articular or joint lining cartilage and is different from auto-immune related arthritis such as Rheumatoid arthritis, which is not the subject of this discussion. Degenerative arthritis of the nee most commonly affects the entire knee for which the treatment is a total knee replacement. With this said, in approximately 5% of patients, arthritis affects only one of the above-mentioned compartments. This is known as partial or uncompartmental osteoarthritis of the knee. It is distinguished from complete or tri-compartmental osteoarthritis as the operative treatment for partial knee arthritis can consist of replacing only a single joint compartment, rather than the entire joint. This procedure is known as partial or unicompartmental knee replacement.
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.