Dr. Zachary Weidner, M.D.

There are three compartments to the knee joint: the medial, lateral, and patellofemoral compartments.  Partial knee replacement is unique in that only one compartment is replaced at the time of surgery.  This explains why partial knee replacement is also referred to as unicompartmental knee replacement.  Total knee replacement is different in that the entire knee is replaced with implants.  All the ligaments of the knee are maintained in a partial knee replacement whereas in a total knee replacement the anterior cruciate (ACL) and often the posterior cruciate ligaments (PCL) are excised.  Maintaining the cruciate ligments helps the knee to feel more normal because of the proprioception capabilities inherent to these ligaments. 

 

Partial knee replacement can be performed either with or without robotic assistance.  When the robot is used it is called a MAKOplasty ®.  MAKOplasty ® is unique in that a CT scan is performed preoperatively so that the surgical plan for the robot can be prepared using much more information than is obtained from standard knee x-rays.  The robot then guides the surgeon intraoperatively using visual, tactile, and auditory  feedback so that only the bone required to be removed to fit the implants is removed.  It allows for precision down to millimeters and essentially removes any error that can occur during the normal surgical steps of cutting the bone, balancing the joint, and appropriately aligning the implants.  

 

The benefits of partial knee replacement compared to total knee replacement include that it is a smaller surgery with a quicker recovery, it allows for a more normal feeling knee, and there is a greater chance of returning to high level activities such as running.  The main downside of partial knee replacement is that the associated revision rate, or need for a secondary surgery on the knee, is higher compared to total knee replacement.  This is because there is a higher rate of implant loosening over time with partial knee replacements.  Also, because only one part of the knee is replaced, a patient can develop arthritis in the other compartments of the knee which can lead to pain and the need for surgery to convert to a total knee replacement to get rid of all the arthritis.