WHAT IS A PARTIAL KNEE REPLACEMENT?
The knee is divided into 3 compartments – the medial, lateral, and patellofemoral compartments. A partial knee replacement is a surgical procedure used to treat patient with moderate-to-severe osteoarthritis (OA) isolated to only 1 or 2 compartments of the knee. With partial knee replacements, only the damaged compartments of the knee is are replaced, and the healthy compartments are preserved.
A partial knee replacement is designed to resurface the end of the bone and preserve as much bone stock for any future conversions that may be needed. It is expected to last between 10-15 years and would allow an easier conversion to a primary total knee replacement, if needed.
Compared to a total knee replacement, patients who undergo partial knee replacement surgery typically have a quicker and less painful recovery. Additionally, a partial knee replacement removes less bone and preserves all the ligaments of the knee. This gives the knee a more natural feel.
This handout is intended to describe a single compartment replacement (unicompartmental medial or lateral replacement) and 2 compartment replacement (bicompartmental).
WHO IS A CANDIDATE FOR A PARTIAL KNEE REPLACEMENT?
Patients who are candidates for a unicompartmental replacement have moderate-to-severe osteoarthritis of only 1 compartment of the knee, either the medial or lateral weightbearing compartment. Often, the pain is isolated to that single arthritic compartment. Whereas patients who are candidates for a bicompartmental replacement have moderate-to-severe osteoarthritis of 2 compartments of knee – the patellofemoral compartment (kneecap and groove) and either the medial or lateral weightbearing compartment. In these patients, the remaining compartment of their knee is healthy. In addition to radiographic findings of osteoarthritis, these patients have failed conservative/non-operative treatments. Conservative treatments include weight loss, physical therapy, braces, ambulatory aids, anti-inflammatory oral medications, and injection treatments (cortisone, hyaluronic acid, etc.).
Click on “Learn More” at the bottom of this page to see x-rays of patients who underwent a medial unicompartmental replacement (fig. 1), a lateral unicompartmental replacement (fig. 2), and a medial bicompartmental replacement (fig. 3).
To determine if you are a candidate for a partial knee replacement, your surgeon will first obtain plain x-rays to assess areas of bone-on-bone arthritis. Typically, your surgeon will also have you get an MRI of your knee to evaluate all other compartments of your knee and confirm the most suitable type of partial knee replacement. It is critical that the other compartment(s) of your knee that is/are not to be replaced have normal, healthy cartilage. Otherwise, you may not experience significant improvement following surgery and require further surgery.
The goal of a partial knee replacement is to restore your ability to perform everyday activities, such as stair climbing, walking on uneven ground, getting out of a low chair or car, or sitting with the knees bent for a prolonged period of time. These activities are generally difficult to perform when there is osteoarthritis present in the knee.
This procedure will help patients feel very comfortable and pain-free, but it is not intended for return to high-level impact loading, twisting activities. Premature failure of the components by wear is likely in patients who resume running and pivoting sports. The prosthesis is designed to restore quality of life with activities of daily living.
WHAT ARE THE DIFFERENT TYPES OF A PARTIAL KNEE REPLACEMENT SYSTEMS?
Your surgeon has various types of partial knee placement systems readily available. This helps to individualize your surgical needs and give you the best possible outcome. The different types are Zimmer Persona® (Fig. 1), Conformis iUni® (Fig. 2), and Conformis iDuo® (Fig. 3).
The Zimmer Persona® is a component produced by the company Zimmer. Your surgeon will typically use this system for a medial unicompartmental replacement. The components provide accurate reproduction of the anatomic curves and size of the weight bearing surfaces of the knee. Compared to other systems, the Zimmer Persona® allows for the surgeon to make minimal cuts, sparing more bone stock for possible future conversion (if needed) to a total knee arthroplasty. This system provides the patient a normal biomechanical function.
The iUni® is a component produced by the company Conformis. It stands for individualized unicompartmental resurfacing device. It is primarily used for patients needing a lateral unicompartmental replacement. It differs from traditional implants in that traditional implants require the surgeon to choose from a range of standard implants that require the surgeon to cut the bone to fit the implant. iUni offers a more unique approach by creating the implant to specifically fit your knee, mirroring the surface and contours of your anatomic knee. This provides a bone sparing approach to the surgery. It gives the patient a more natural feeling to the knee, preserving bone, cartilage, and ligaments.
The iDuo® is a bicompartmental partial knee replacement system produced by Conformis. It is designed to resurface the either the medial or lateral weight bearing surfaces along with the patellofemoral compartment. This device conforms to your anatomic surfaces and curves with the knee to give the surgeon a way to preserve the bone stock and allow for easy conversion to total knee replacement in the future (if needed).