Partial Knee Replacement
Written by: Dr. Frederick Buechel, Jr.
What is a Partial Knee Replacement?
A partial knee replacement is a surgical procedure that places a new artificial surface on the ends of the bones of the knee joint where the original cartilage surface is damaged or worn away. The knee joint has 3 compartments. The medial, lateral and patellofemoral compartments.
It is called a partial knee replacement because we replace the surface of the bone on only one or two of the 3 parts of the knee joint, leaving the healthy compartments and ligaments alone to function normally. A partial knee replacement is made of metal and plastic parts called “implants”. The metal parts are usually cobalt chrome and/or titanium, and the plastic part, called the “insert” or “bearing”, is ultra-high molecular weight polyethylene. The parts are usually attached to the bone using a bone cement, and sometimes they can be attached without cement.
What are the main indications that someone may require partial knee replacement surgery?
The main indication for requiring a partial knee replacement is when a person has weight bearing knee pain because the cartilage surface is worn down in one or two of the 3 compartments of the knee from osteoarthritis, osteonecrosis, or a prior knee injury like a meniscus tear, or fracture.
- The Medial Compartment is the most common partial knee replacement. This is the inner side of the knee joint between the thigh bone (femur) and shin bone (tibia). Medial compartment partial knee candidates have pain with weight bearing in just the medial compartment.
- The Lateral Compartment is next most common partial knee replacement. This is the compartment on the outer side of the knee joint between the thigh bone (femur) and shin bone (tibia). Lateral compartment partial knee candidates have pain with weight bearing in just the lateral compartment.
- The Patellofemoral Compartment is the third most common partial knee replacement. This is the compartment in the front of the knee between the kneecap (patella) and the thigh bone (femur). Patellofemoral partial knee candidates have pain only in the anterior compartment under the kneecap (the front of the knee), but no pain in the medial or lateral joint compartments, and often describe pain with rising and sitting, stair climbing and bending.
The most common diagnosis for patients considering a partial knee replacement are:
- “Osteoarthritis” is the most common diagnosis for partial knee replacement. A degenerative condition of the knee where the cartilage surface wears down.
- “Osteonecrosis” of the medial femoral condyle is another good indication for partial knee replacement if the problem is in the right location and the size of the osteonecrotic area is not too large. Osteonecrosis is a condition where the blood supply to the bone goes bad and the bone cells in a certain area die. This has been postulated to occur for several reasons. “Spontaneous osteonecrosis of the knee (SPONK)” is theorized to be related to microfractures from trauma that creates a cascade of problems for the bone leading to cellular death eventually leading to bone collapse and pain during the process. This is most common in the medial compartment of the knee. Other risk factors for this condition include corticosteroid use (most common cause), alcohol use, deep sea diving (Caisson disease), post-arthroscopy osteonecrosis, Sickle cell disease, Systemic lupus erythematosus.
- “Prior Meniscus Tear” patients that have had surgery or not, and now have arthritis where the cartilage has worn down in the compartment of knee joint where the meniscus was injured, trimmed, repaired or removed are potential partial knee candidates.
- “Post-Traumatic Knee Arthritis” is when the cartilage wears down abnormally early secondary to a traumatic knee injury. This may be from an impact injury long ago that damaged the cartilage, an accident that caused a fracture of the bone or cartilage surface, or a sports injury that caused a meniscus tear or an ACL tear that changed the loading conditions of the knee compartment.
- “Prior ACL reconstruction patients” that now have knee arthritis in the medial or lateral compartment with a functioning ACL, are potentially good candidates for partial knee replacement.
Patients should try non-surgical treatments first to manage their pain. When these options no longer provide pain relief and a persons’ quality of life is reduced, partial knee replacement is a great option. Younger, skeletally mature knee pain patients are potentially good candidates because this procedure maintains all the healthy knee surfaces and ligaments, preserving their functions so the knee acts and feels as normal as possible allowing them to participate in most of life’s activities. It is great for the very old patients because it is much less invasive, causes less physiologic stress to their system during and after surgery, there are fewer potential complications, and the rehabilitation is much less demanding on them than a total knee replacement.
To determine if you are a good candidate for partial knee replacement, you need to see a surgeon who is experienced with partial knee replacement. During this visit you should expect to provide a comprehensive medical and knee history, have a physical examination, have proper x-rays taken and reviewed with you, and if necessary, an MRI of the knee may be ordered if there is further need to confirm the condition of the knee.
A visual guide to partial knee replacement types
MEDIAL PARTIAL KNEE REPLACEMENT
This x-ray represents a medial robotically installed partial knee replacement by Dr. Buechel with precision central tracking and alignment, and an image of the opposite knee showing medial joint space narrowing which is the precursor to this procedure. The Medial side is the inner side of the knee joint made up of the femur and tibia.
LATERAL PARTIAL KNEE REPLACEMENT
This x-ray represents a lateral robotically installed partial knee replacement by Dr. Buechel with precision central tracking and alignment,and an image of the opposite knee showing a normal joint space. The Lateral side is the outer side of the knee joint made up of the femur and tibia.
PATELLOFEMORAL PARTIAL KNEE REPLACEMENT
This x-ray represents a patellofemoral robotically installed partial knee replacement by Dr. Buechel with normal spaces in the medial and lateral joint compartments. The patellofemoral compartment is the part made up of the knee cap and the front groove of the end of the femur that the knee cap rubs on called the trochlea.
BICOMPARTMENTAL PARTIAL KNEE REPLACEMENT
This x-ray represents a medial robotically installed partial knee replacement by Dr. Buechel with precision central tracking and alignment, along with the patellofemoral compartment replacement and a preserved lateral compartment in the same knee.
LATERAL AND PATELLOFEMORAL REPLACEMENT
This x-ray represents a laterally robotically installed partial knee replacement by Dr. Buechel with precision central tracking and alignment, along with the patellofemoral compartment replacement and a preserved medial compartment in the same knee.
This x-ray view shows the lateral compartment very nicely but is slightly rotated as far as the angle the technician used to see the patellofemoral compartment.
MEDIAL PARTIAL KNEE REPLACEMENT AFTER ACL RECONSTRUCTION
This x-ray shows a front and a side view of a knee that had a medial partial knee replacement preformed precisely with the Mako Robotic System by Dr. Buechel.
It shows precision central alignment of the implants and precision alignment. The opposite compartment is still well preserved with a good joint space of cartilage. You will also see the previous screws that were used to perform the ACL reconstruction that remain in the bone and can be planned around precisely with the computer planning.
What are the main contra-indications to partial knee replacement surgery?
Inflammatory arthritis such as rheumatoid arthritis is not a good indication for partial knee replacement because the entire joint lining is involved in this disease process, not just one or two compartments. Having a prior joint infection is a contraindication to a joint replacement. If the entire knee joint hurts, this is not a good indication for partial knee replacement, this is more of the indication for total knee replacement. If the knee deformity (angle of the knee) is too severe, or if the knee has poor motion, this is not commonly a good indication for partial knee replacement.
What are symptoms of someone who needs total knee replacement surgery?
• Pain that is located all around the knee, not on just one side or under the knee cap alone
• Pain in the knee when walking
• Pain getting up from a seated position
• Pain going up and/or down stairs
• Dull or aching pain
• Stiffness in the knee
• Swelling of the knee joint
• Loss of motion in the knee
• Decreased walk distance
• Reduction in activities of daily living
• Reduction in sports and exercise activities
How do I know I need partial knee replacement surgery instead of a total knee replacement?
The way to differentiate between needing a partial and total knee replacement depends on several factors. These include the location of the pain, the x-ray or advanced imaging findings, and the diagnosis of the knee condition. If the pain is located throughout the entire knee, then these patients most likely require total knee replacement. If the pain is located in just one of the three compartments, then these patients may only require partial knee replacement. If the x-rays show the joint space is decreased or completely lost in just one compartment, this is a possible partial knee patient.
If the x-rays show the joint space is decreased or completely lost in the medial and lateral compartments along with the patellofemoral compartment, this is a total knee patient. Bone spurs are also common findings on x-rays with patients with painful arthritis. These spurs can sometimes have significant meaning and other times may not change the surgeon’s decision. The large variation in clinical presentation is why it is important to have an experienced partial knee surgeon examine your knee and review the x-rays, when making a proper decision between partial and total knee replacement.
Is a partial knee replacement still considered a replacement?
Partial and total knee replacements are both considered knee replacements. They both replace the surfaces of the bone where the cartilage has worn out with metal and plastic parts.
Is there a difference between partial knee replacement and resurfacing?
There are several terms that are used interchangeably to describe partial knee replacement. The synonymous names include knee replacement, knee resurfacing and knee arthroplasty.
Is there a lateral partial knee replacement?
There is a partial knee replacement for the lateral compartment. The lateral compartment is not as common as the medial compartment. You should choose a surgeon who has a significant experience with lateral partial knee replacement if you need this procedure, as it is more complicated than medial and there are several technical requirements to have a successful outcome. Mako Robotic lateral partial knee replacement by an experienced lateral robotic partial knee surgeon is a predictable technique to have positive outcomes with lateral partial knee replacement.
Is this considered a virtual knee surgery?
Mako Robotic Partial knee replacement is not virtual surgery like the DaVinci Robotic Surgery System. Mako Robotic Partial Knee Replacement uses a CAT scan to allow the surgeon to perform extremely accurate preoperative implant planning customized to the individual. Intraoperatively, the surgeon attaches communication arrays (reflectors) to the two bones that allows the surgeon to see the live knee motion, balance and tracking on the computer display, and make fine adjustments to the implants position prior to preparing the bone with the robotic cutting tool. The Mako Robot is then used to remove the bone exactly where it was planned in the software, with reproducible precision of 1mm and 1 degree. The software can then be used to confirm the implants are installed properly in the bone and cement using tracking probes, to confirm the final position.
What is the expected pain with a partial knee replacement?
Partial knee replacement can be significantly less painful than total knee replacement when done properly by an experienced partial knee surgeon. I use a minimally invasive incision that avoids cutting into the muscle of the quadriceps which makes a big difference. Using the Mako Robot has also been shown to significantly reduce the pain associated with partial knee replacement in several published studies. The process by which the surgeon performs the procedure makes a significant difference in pain as well. Performing over 1,500 robotic partial knee replacements has allowed me to refine my process to reduce pain and enhance the recovery process. I have found that using a spinal anesthetic, along with regional blocks, and local anesthesia in the surgical site provides the best pain control in the early post-operative period. For those that chose general anesthesia, similar pain control can be obtained with local blocks and regional blocks. Using a knee cooling sleeve after surgery reduces pain and swelling. A sports compression sleeve postoperatively reduces swelling and pain. Avoiding aggressive physical therapy early in the first week to allow the wound to seal and swelling to reduce improves early function. Minimal pain for the first 2-3 days is expected from the anesthesia blocks. As the blocks wear off the pain is mild sometimes moderate from days 4-6. This pain is easily controlled with over the counter medication, the cold therapy sleeve, and sometimes one or two pain pills for a couple days. Most patients use narcotics very little, if at all, after partial knee replacement of the medial and lateral compartment. The patellofemoral compartment replacement is more painful than the medial and lateral compartment replacements post-operatively.
The incision should not be the main focus of a joint replacement surgery, but it is what the patient sees in the end, and a cosmetic small incision is usually more desirable. My incision is approximately 2.5 inches in length just next to the kneecap. With my technique and the special sutures I use under the skin, the skin adhesive used to seal the incision, and the silicon dressings after the surgery, the resultant scar is usually a fine line about 3-6 months after surgery.
What is partial knee replacement recovery like?
Recovery for a Medial compartment partial knee replacement is significantly less difficult than patients expect. The mild to moderate pain is generally limited to the first 2-3 weeks. Most patients require very little narcotic mediation if at all. Physical therapy for partial knee replacement is not an aggressive painful process like most total knee replacement therapy can be. Swelling control is the main goal in the first 3 weeks. Once the swelling has resolved, the range of motion generally returns to the preop motion. Most patients by 6 weeks have all their preop motion back. By 3-6 months, many patients have increased their motion by 8-10 degrees. Physical therapy is focused on improving the quadriceps strength and proper return of a normal, or near normal gait cycle. My Lateral compartment patients often have a similar recovery to the medial side partial knee patients, but sometimes it takes 4-6 months for the patients to feel as good on the lateral side as the medial compartment patients do at 3 months. Patellofemoral compartment partial knee replacement patients take longer than the Medial and Lateral compartment partial knee replacement patients to recover. Because the incision involves entering into the quadriceps muscle or tendon, there is more post-operative soreness and stiffness than the other partial knee replacements. Therapy is also more aggressive to get the range of motion and strength to return. This is less difficult than a total knee recovery.
How do most patients feel after their partial knee replacement?
The best part about Medial and Lateral partial knee replacement is that patients really do feel either like their knee is normal, or near normal compared to total knee replacement. By maintaining the ACL and PCL ligaments in the middle of the knee with this procedure, the knee motion and kinematics return to, or remain normal. By using the software in the Mako Robotic Partial Knee System to custom balance the knee ligaments, patients have been found in published studies to feel more normal than with manual partial knee replacements or total knee replacement. And in just a few short weeks, patients generally feel better with less pain than before surgery.
What is the follow up care like for a partial knee replacement surgery?
I perform my Mako Robotic Partial Knee Replacements as an outpatient procedure. Patients return to the office the day after surgery to have their dressing changed and to address any issues right away. Patients can return home if they are traveling to New York for their surgery generally in 3-4 days if needed. We have a great team of therapists if you stay in the area. We provide several means by which to stay in contact after your surgery including office visits, text, mobile phone, email, video conferencing. We maintain close contact with you in the early recovery phase to make sure you feel comfortable and all your concerns are addressed. We like to see you back if possible, in 4-6 weeks after surgery, or check in via any of our contact means along with photos of your leg during the healing process. 6 months after surgery is another check-in milestone we like to hear from you. Annually we like to have an x-ray of the operative knee to ensure everything is as desired.