PREPRINT
jkl keys enabled
565 views

Mako Robotic Arm Assisted Total Knee Arthroplasty

  1. Introduction
    1. Pre-Operative Planning
      • The preoperative CT scan provides a virtual bone model that can be used to plan bone cuts as well as implant size, alignment, and position using virtual implant templates on the provided software.
        • Overall limb alignment can be checked with combined femur and tibia component rotation and varus/valgus.
        • Numerous fine-tune adjustments can be made on the software and later edited with more clinical and real-time information including knee kinematics and soft tissue tension intra-operatively.
      • Anatomic landmarks are defined on the CT scan and a pre-op plan is developed based off that by the Mako Product Specialist who presents it to the surgeon for review.
        • Preop plan includes both resection thickness of the distal femur, posterior femur, and proximal tibia and implant size, rotation/alignment, and position.
  2. Patient Positioning
    1. Prep Patient before OR
      • Shave skin around knee using clippers.
    2. Prep Patient in OR
      • Patient is placed in a supine position with a safe belt over their torso and operative side close to the edge of the table.
      • Typically, either a bump under the hip or a post on the lateral side of the hip/proximal thigh is used to prevent natural external rotation of the limb and keep the leg as neutral as possible. I choose to use a lateral post.
      • A non-sterile tourniquet is placed high on the patient’s thigh.
    3. Sterilize
      • The knee is sterilized using the surgical prep solution and technique of the surgeon’s choice. I pre-scrub with a chlorhexidine scrub brush, dry the limb, and then prep the leg with Chloraprep solution.
      • I do not include the foot in the surgical prep, but one can choose to do so.
    4. Drape
      • The patient is draped in the surgeon’s desired manner for a TKA.
      • The drapes at the edge of the operative side of the bed should not be more than a single layer of draping over the side bar in order to place a sterile clamp on the side bar.
      • Too many drapes make it too thick to place a clamp over them onto the side bar.
    5. Set up Leg Positioner
      • There is a leg positioner provided by Mako that is attached to a sterile clamp on the operative side rail. The positioner includes a sterile carbon rail, a base which is adjustable and slides up and down the rail, and a boot to put the foot in. I choose not to use the boot and instead place the foot on the base itself.
    6. Set up Robot
      • The Mako Robot, tower, monitor, and software are set up and positioned by the Mako Product Specialist.
      • The robot comes in from the operative side and the camera is located on the opposite side. The camera needs to have a direct line of sight to the operative knee where the arrays will be placed. The robotic arm is draped and assembled by the sterile scrub technician. The Mako Product Specialist also works with the scrub technician to register the robot and its sterile tools prior to surgery.
    7. Conduct Surgical Timeout in the Standard Site-specific Fashion
      • The Mako Product Specialist confirms the patient name, patient ID, operative side, and implant system with the surgeon.
  3. Surgical Approach
      • Either general or regional anesthesia can be used. As an adjunct, femoral or adductor canal nerve blocks can be used pre or post operatively. Prophylactic antibiotics are given. The leg can be exsanguinated using an Esmarch or gravity by lifting and holding the leg up for 30 seconds or more. I use gravity exsanguination and inflate the tourniquet typically to 275 mmHg.
    1. Midline Skin Incision
      • A midline skin incision is made from the superior edge of the quadriceps tendon to the inferomedial aspect of the tibial tubercle with the knee flexed. Sharp dissection is carried down to the level of the capsule.
    2. Medial Arthrotomy
      • A medial parapatellar arthrotomy is made. The knee is extended and the fat pad released, patella everted, and knee is flexed up again. Our patient was confirmed to have full thickness tricompartmental end-stage degenerative joint disease that was predominant medial and patellofemoral. Osteophytes are left in place to allow for accurate bone registration with the robotic arm.
    3. ACL Resection
      • The ACL is resected off the femoral notch and tibia insertions. I use a Posterior Stabilizing knee, so the PCL is also removed from the notch.
  4. Patellar Bone Preparation
    1. Resurfacing
      • I choose to resurface the patella in every TKA. I do this before femoral and tibial cuts. This patient’s patella measured 24mm thick so I resected 10 mm in order to match the thickness of the patella button.
    2. Implant Placement
      • A size 32 patella button was deemed appropriate and the lugholes are drilled at this point. Pulse irrigation is used to clean the cut surface of the patella and the real implant is cemented in place and clamped tight. The cement is allowed to harden during the remainder of the knee preparation. I cement all patella implants.
  5. Bone Array Placement
    1. Insert Femoral Pins for Mako
      • Two 4.0 mm drill pins are fixed to the distal femoral metaphysis.
    2. Insert Tibial Pins
      • Two 4.0 mm drill pins are fixed to the proximal tibia metaphysis.
    3. Place Tibial Array
      • Adjust the arrays so that they are visible by the camera without any obstructions. The camera can also be adjusted by the Mako Product Specialist so that both arrays are visible throughout the knee arc of motion.
    4. Place Femoral Array
    5. Place Femoral & Tibial Checkpoints
      • They should be placed in hard bone and away from future bone cuts. I place the femur checkpoint at the medial epicondyle and the tibia checkpoint in the anterior proximal diaphysis. The checkpoint locations are registered using the blunt probe.
  6. Patellar Cementing
  7. Robot Landmark Calibration
    1. Hip Center
      • The patient hip is circumducted continuously and in different patterns until the progress bar reaches 100% on the software.
    2. Malleoli
      • The blunt probe is used to identify the center of the medial malleolus and the center of the lateral malleolus. Once the tip of the probe is properly placed on each malleoli, the computer registers the points.
    3. Registration
      • Femur and tibia registration consists of many points for each which are shown on the monitor by the software based on the CT scan. A sharp probe is used to register each point on the femur that corresponds to the virtual picture. The location does not need to exactly match the virtual picture, but should be reasonably close.
        • The sharp probe is used because registration points should be collected on bone, not cartilage, so the sharp probe can penetrate any cartilage to get onto bone surface.
        • It is important not to penetrate the bony surface.
        • If a point is buried under an osteophyte and too difficult to access, pick a location close by on bone.
      • A smaller amount of larger verification points is then shown on the monitor which need to be collected and matched up on both the femur and tibia.
  8. Osteophyte Removal
      • Once the femur and tibia are fully registered, I remove all osteophytes.
  9. Intraoperative Ligament and Gap Balancing
    1. Measured Resection vs Gap Balancing
      • The Mako system allows you to choose between a measured resection workflow and a ligament balancing (or gap balancing) workflow.
        • I use a measured resection technique.
    2. Knee mechanics including knee flexion, varus/valgus, and rotation are shown on the screen and updated in real-time to correspond with the position of the knee.
    3. First, I bring the leg into extension and note any flexion contracture or recurvatum.
      • In this case, the knee had full extension with an 8 degree varus alignment which was lax and could be corrected past neutral to 1 degree of valgus.
      • The knee was a little lax to varus and valgus throughout the arc of motion so I felt that a conservative distal femur resection was indicated.
    4. Software Adjustments
      • Appropriate adjustments were made on the Mako software to balance and gap symmetrically.
      • There are a robust number of adjustments able to be made on the software to account for the patient’s bony and soft tissue anatomy.
      • The software sized the femoral and tibial components both to a size 3.
        • The bone quality was good so I felt a press-fit construct was appropriate.
  10. Robotic Osteotomy
      • The order of bone cuts can be set to the surgeon’s preference.
      • The cuts are made within virtual boundaries set by the robot to protect the soft tissues.
        • These boundaries can be expanded if needed.
    1. Dock Robot
    2. Distal Resection
    3. Posterior Chamfer Resection
    4. Anterior Resection
    5. Posterior Resection
    6. Anterior Chamfer Resection
    7. Check and Clean Resections
      • Once the cuts are made, I place a laminar spreader in the joint which allows me to visualize the posterior knee where I remove any meniscus remnants, PCL remnant, and posterior osteophytes.
  11. Tibial Robotic Osteotomy
    1. Medial Resection
    2. Lateral Resection
    3. Inject Marcaine
  12. Implant Trials & Corrections
    1. In this case, the knee was trialed with a 9mm polyethylene insert.
      • The knee had a 10 degree extension lag which I could correct with overpressure to 0 degrees.
      • The knee flexed to 125 degrees with gravity.
      • I felt that overall the varus/valgus stability was tight throughout the arc of motion.
      • I decided to resect an additional 1mm off the tibia.
      • The robotic arm was brought back in to make the additional resection.
        • The arm is able to guide a highly accurate resection, taking off exactly 1 more mm in the same mechanical alignment as the previous resection.
    2. The knee was then trialed again. Now, the mechanics were improved.
      • The knee came to full extension and flexed to 130 degrees with gravity.
      • It was stable to varus/valgus and not overly tight.
      • The patella tracked centrally.
  13. Final Implant Placement & Check Positioning
      • The robotic arm is then removed from the field.
      • The femoral lugholes were drilled and the box cut was made for the posterior stabilized femoral component.
      • The keel punch was used at the rotation of the tibia and the 4 small lugholes were drilled.
    1. Tibial Base Plate Placement
      • The real size #3 tibial baseplate was impacted into place.
    2. Femoral Component Placement
      • The real size #3 PS femoral component was impacted into place.
      • Both components had excellent intrinsic stability with nearly 100% bony contact.
    3. Liner Insertion
      • The 9mm polyethylene liner was deemed appropriate and impacted into place.
  14. Closure
    1. Copious irrigation is carried out.
    2. The tourniquet is deflated and hemostasis is obtained using electrocautery.
    3. Layered Suture Closure
      • I close the arthrotomy with #2 Quill suture.
      • I then use a 0 vicryl suture to close a deep tissue layer.
      • I use 2-0 vicryl subcutaneously.
      • I use 3-0 monocryl subcuticularly.
    4. A sterile bandage is applied and the patient is allowed to awaken from anesthesia.