ROBOTIC PARTIAL (UNICONDYLAR) KNEE REPLACEMENT

Reha Tandogan, M.D., Asım Kayaalp, M.D.
Ortoklinik & Çankaya Orthopedics, Ankara


Partial (unicondylar, unikompartmental) knee replacement resurfaces only the worn part of the joint, without disturbing the intact ligaments and menisci. Partial knee replacement is usually performed for localized arthritis of the inner (medial) side of the knee, however, the outer (lateral) compartment and undersurface of the kneecap (patello-femoral) knee resurfacing can also be performed (Figure 1). Partial knee replacements are not suitable when there is extensive damage in all three compartments of the knee or for inflammatory arthritis (rheumatoid arthritis, ankylosing spondylitis, systemic lupus). Only the worn part of the knee is replaced, and the ligaments and menisci in the uninvolved compartment are preserved. This results in a faster and easier rehabilitation, better knee motion and a more “normal feeling” knee compared to total knee replacement. Return to activities of daily living and work is faster. Robotic partial knee replacement recreates the dynamics of the joint before it was worn out with great precision and accuracy. Robotic knee replacements initially started with partial knees and FDA approval was first obtained for partial knee replacements. Therefore robotic partial knee replacements have a longer track record than total hips and knees, and outcomes for longer follow-up periods are available.

Figure 1: Only the inner (medial) part of the knee is worn out in this patient, and is a suitable candidate for robotic partial knee replacement.

Figure 1: Only the inner (medial) part of the knee is worn out in this patient, and is a suitable candidate for robotic partial knee replacement.


Before surgery

The pre-operative work-up of robotic partial and total knees are similar. A 3-D computed tomography of the involved limb is obtained and a real time model of your knee is reconstructed with a specialized software. The surgeon plans your surgery on this model in a computer, deciding on the appropriate size, alignment and placement of your implants (Figure 2). This is a preliminary plan and will be modified during surgery to balance the soft tissues. During this time, pre-anesthetic work-up including blood and urine tests, EKG and chest X-rays are performed. You should inform your physician on all your medications and allergies at this time. You will need to modify all blood thinning medication such as Aspirin and Plavix one week before surgery, your surgeon will advise on how to manage your anti-coagulation medication until the day of your surgery. You will be given instructions on antiseptic treatment of your leg one day before surgery. You will be admitted to the hospital on the day of your surgery. Regional (Epidural or spinal) anesthesia is preferred however, you can discuss other options such as general anesthesia with your anesthetist.

Figure 1 : Planning the size and orientation of your robotic partial knee replacement before surgery.

Figure 1: Planning the size and orientation of your robotic partial knee replacement before surgery.


How is robotic partial knee replacement performed

Optical trackers called “arrays” are placed on the femur and tibial bones using 2 pins. These arrays are the “eyes” of the robotic system and will communicate with the robot during surgery to ensure a flawless and accurate surgery (Figure 3).

Figure 3: Placement of the arrays on bone.

Figure 3: Placement of the arrays on bone.


A 7-10 cm incision is made over the involved side of the knee for surgical exposure. This incision is much smaller than the one used for total knee replacement and will cause less damage to the soft tissues and muscles of your leg. The knee is defined to the robotic system by registering 64 points in the femur and tibia. This registration is transferred to the pre-operative model based on the 3D-CT scan. Once this registration process is completed, the robot knows exactly where your knee is located in space (Figure 4). The center of your hip and ankle are also registered to calculate the alignment of the whole leg.

Figure 4 : Registration of the knee to the robotic system.

Figure 4: Registration of the knee to the robotic system.


Soft tissue tension is assessed in at least 5 different knee angles, then the bone cuts, implant size and orientation are then modified to ensure a perfect ligament balance and limb alignment before any cuts are made (Figure 5).

Figure  5: Assessment of soft tissue balance in various degrees of knee flexion. The goal is to create the same soft tissue balance at the end of surgery.

Figure 5: Assessment of soft tissue balance in various degrees of knee flexion. The goal is to create the same soft tissue balance at the end of surgery.


The implant is positioned flush with the surrounding intact cartilage, ensuring a seamless transition from implant to cartilage. The final plan is loaded into the robot and the surgeon is ready to perform the bone cuts under the guidance of the robotic arm (Figure 6).

Figure 6: Precise bone cuts are performed with the robotic arm.

Figure 6: Precise bone cuts are performed with the robotic arm.


The robot does not allow the surgeon to perform any cuts outside the limits set in the final plan and provides audible and visual feedback during the bone preparation on the volume and location of bone cuts (Figure 7).

Figure 7: The surgeon monitors the progress of bone preparation on screen while keeping an eye on the surgical field.

Figure 7: The surgeon monitors the progress of bone preparation on screen while keeping an eye on the surgical field.


The accuracy of the robotic system is 1 mm and 1 degree, this is 3 times more accurate than most experienced surgeons. Once the bone preparation is completed, trial implants are placed and knee motion and soft tissue balance are re-assessed. The next step is the cleaning of bone surfaces with pressurized lavage systems to create a porous surface free of blood and debris to ensure bone cement penetration 3-5 mm into the bone. Bone cement is used to fix the definitive implants onto the bone. This cement polymerizes in 12-14 minutes and creates a strong bond between the bone surfaces and the implant, allowing immediate full weight-bearing after surgery. The final construct is tested with the robotic system before soft tissue closure to check and document that the planned limb alignment and soft tissue balance has been achieved (Figure 8).

Figure 8 : Final check of soft tissue balance after the implants have been placed.

Figure 8: Final check of soft tissue balance after the implants have been placed.


A long acting local anesthetic is injected into the soft tissues to decrease the pain after surgery. The robotic arrays and checkpoints are removed and soft tissues are sutured.No drains are needed after partial knee replacement.

After your surgery

The post-operative course after robotic partial knee replacement is more comfortable than the one after a total joint replacement. Moving your knee is less painful, and rehabilitation goals can be achieved in a shorter time. Once you have recovered from anesthesia and regained muscle control, you can bear weight on the operated leg on the day of your surgery and stand up with help of a walker. There are no restrictions of knee movement or change of position in the bed. Pain control is achieved by intravenous or epidural patient controlled anesthesia (PCA) pumps. These devices let you control the amount of pain killers as needed and built in safety measures prevent overdosing your medication. The PCA pumps are usually discontinued after the first day.

Antibiotics are given for 24 hours to prevent implant infections, no benefit of longer antibiotic treatment has been shown. Anti-coagulants (blood thinning medication) are used for 10-30 days depending on your risk profile to prevent blood clots forming in your legs. These can be in the form of tablets such as Aspirin or Xarelto or self-administered injections under the skin.

Physical therapy under the supervision of a physiotherapist is begun on the day of your surgery. Your surgeon may prescribe the use of a continuous passive motion (CPM) device, which moves your knee in a controlled manner. Stair climbing exercises begin on the second day and you will be free to walk around with a walker or a similar assistive device. An X-ray of your knee is taken on the second day (Figure 9).

Figure 9: X-ray imaging of the patient in Figure 1 following robotic partial knee replacement.

Figure 9: X-ray imaging of the patient in Figure 1 following robotic partial knee replacement.


You will be given an “implant passport” containing information and the barcodes of all the implants placed in your knee. It is essential that you keep this passport in a safe location since it contains essential information regarding the type and properties of your implants should the need for a change of parts rise in later years. You can also document that you have metal implants in your body for airport security and metal detectors.

How long do I have to stay in the hospital after a robotic partial knee replacement ?

You will need to stay in the hospital for 1-2 days after robotic partial knee replacement surgery. Some patients only require an overnight stay. Adequate pain relief, good muscle control, dry surgical wound and the ability to walk independently with an assistive device (walker or crutches) are the main prerequisites for discharge from hospital.

How is the recovery from a robotic partial knee replacement?

You should continue you pain killers, blood thinning medication and stomach protectors as prescribed by your surgeon after discharge from hospital. Although your pain will be manageable with medication, you should expect the need for daily pain killers for 3-4 weeks after surgery. It is essential to continue your pain medication to be able to perform your home exercises adequately. Cold treatment is also beneficial to decrease swelling and pain after exercise. A feeling of stiffness and warmth is normal for up to 4 months after surgery. You will need to protect the surgical incision from getting wet until the wound becomes watertight. This usually takes place in 3 days for self-absorbing sutures. You can shower immediately while keeping the incision site dry, your surgeon will instruct you on how to do this. Depending on your balance and muscle strength you may need a walking support such as a cane for up to 3 weeks. Home exercises are important to regain knee motion and leg control, you should do these diligently even if you have slight pain. Outpatient physiotherapy may be needed if your progress with the home exercise program is not adequate. Your knee will improve gradually and it might take up to six months for the final outcome.

When can I drive after a robotic partial knee replacement?

No specific precautions are needed to drive a car after a robotic partial knee replacement. Once you have recovered your muscle control and brake reflexes you can safely drive a car. This period is 2 weeks for a left knee surgery if the transmission is automatic and 4 weeks if the transmission is manual. For the right knee this period is 4 weeks, however may vary from patient to patient. Remember to ask your surgeon if you are fit to drive before getting into the driver’s seat.

How often should I see my surgeon after a robotic partial knee replacement?

Your follow-visits will be more frequent immediately after surgery, and less so once your recovery is complete. During the first weeks after surgery, your physician will check your wound healing, manage your medication and monitor your progress of knee motion and muscle strength. Once your recovery is complete and you have resumed activities of daily living or work, your follow -up needs to be less frequent. Even if you have no complaints, you should visit your surgeon at regular intervals, typically at 1 and 2 and 5 years thereafter. This is essential for the early diagnosis of potential problems that may occur. Your surgeon will examine you and assess your x-rays to detect situations that might need intervention.

Which sporting activities can I do after robotic partial knee replacement?

Non-impact sports such as swimming, cycling and hiking are allowed after partial knee replacement. If you were a good skier before surgery, you may continue. Doubles tennis may be resumed. However, impact sports such as running, soccer, football, basketball and volleyball are not appropriate and may cause early wear and loosening of your knee replacement. You should consult your surgeon for other sports that you may want to resume. Kneeling for extended periods may harm your knee and should be avoided.