CUTTING EDGE Dr. James Bates recently added robotic-assisted joint replacement and has improved on his already excellent outcomes.

If you're thinking of launching a total joint program, you should seriously consider adding a navigation-driven robotic-assisted system. The technology lets surgeons customize total knee replacement surgery for individual patients, increasing the precision of implant placement and ultimately improving outcomes. Newer systems have advanced to the point where cuts result in less collateral damage to bone and soft tissues, and less surgical dissection is required.

How it works
Perioperative management of patients is no different than conventional surgery. We haven't created dramatic new protocols just because we're using computers and robotics. This technology helps with the surgical workflow by eliminating steps taken with conventional instrumentation that can damage bone tissue. For example, surgeons traditionally run metal rods through the marrow cavity of the tibia and femur to gauge the angles of needed bone cuts. They often don't think twice about performing this step, even though it causes substantial damage to bone tissue. Working with computer-navigated, robotic-assisted technology eliminates having to use the bone-damaging metal rods.

The robotic system I use requires the insertion of 4 pins — 2 affixed to the tibia and 2 affixed to the femur. They serve as registration posts, which let the robot's computer navigation system produce a 3D map of the joint. The pins affixed to the femur are inserted through the main skin incision; the other 2 are placed through puncture incisions in the skin over the tibia. They create small holes in the bone, but are much less damaging than the rods and jigs needed to determine cutting angles during conventional surgery.

A mobile computer workstation with a small receptor on top receives signals from the pins placed in the patient's femur and tibia. The non-sterile workstation is moved into the room once the patient has been draped and positioned.

Before starting surgery, you must register the pins to tell the computer which reference points you're using. The 4 pins placed earlier act as 2 fixed array systems on the tibia and femur. You first place a probe on points around the knee and ankle as instructed by the computer. To complete the final registration, you rotate the hip in large circles. The computer senses where the center of the rotation occurs around the femur and builds a 3D model that's displayed on the workstation's screen. The entire registration process takes about 10 minutes. Now you're ready to begin the surgery.

The initial tibia bone cut is a basic flat cut, but it has to be done accurately to properly align the tibial component of the implant. That accuracy is aided by placing the robotic system's cutting block at the top of the tibia. The computer senses where the block is placed and, if it's properly positioned, gives you the green light to make the flat cut to remove arthritic bone and cartilage.

Next, after placing a spacing device in the knee, the joint is put through a full range of motion, allowing the computer to assess instability based on ligament laxity or insufficiency. The computer also captures points in time when the knee is straightened and flexed. It uses these points to calculate the anatomical corrections needed to establish a "zero" mechanical axis, which occurs when alignment is in a straight line from the center of the hip, through the knee and to the ankle.

Cuts on the femur have yet to be performed, but the computer has already determined the gaps you'll create with cuts made for a selected implant size for the femur bone. The computer calculates how much to cut off the distal and posterior parts of the femur to create a perfect balance of ligaments and center the mechanical axis.

Once you decide to move forward with the operative plan outlined by the computer, you affix a robotic cutting jig onto the array pins placed in the femur. The robotic arm then spins into position to set up a cutting jig that's used to guide cuts displayed on the 3D bone model.

You then place joint prostheses at the end of femur and on the top of the tibia to determine the accuracy of the cuts. You can use the computer's tracking to confirm how perfectly the mechanical axis has been restored and how stable the joint is through the entire range of motion before cementing in the implant.

Realizing the benefits
You spend additional computer time on the front end mapping out the joint, but you save time during the cutting phase because it's planned out so precisely. I haven't yet had to revise the cuts the computer mapped out. The robotic system is also amazing in its accuracy. For example, notching the anterior cortex of the femur during conventional surgery has a high incidence of periprosthetic fracture. I'm always impressed with how the robot makes that cut perfectly every time. When reviewing post-op X-rays, I'm also amazed that the placement of the implant looks exactly as it did in the 3D model displayed on the screen in the OR.

Even slight variations to the bone cuts made during conventional surgery could overload one part of the knee, which might lead to an early failure of an implant within 20 years. In contrast, the robotic system's increased accuracy in placing implants results in a more exact recreation of the knee's mechanical axis. It also ensures the replacement is perfectly aligned, so the balance of the forces that go through the implant are equivalently balanced on all parts of the knee. I believe increased accuracy in aligning the mechanical axis will increase the long-term survivability of the implants.

EXACT FIT The added precision offered by robotic-assisted surgery improves the long-term survivability of implants.

Robotics doesn't impact the short-term recovery of patients or lead to a faster return to activity. Those factors are influenced by minimally invasive dissection, less aggressive incisions and novel anesthetic techniques. I do, however, believe robotics will improve joint functional outcomes. A more accurate placement of the implant facilitates better range of motion in the joint. I've performed approximately 50 robotic-assisted procedures. Anecdotally, my sense is that the patients gain early motion at 1 week and 1 month post-op faster than they would have had they undergone conventional surgery.

Robotic technology levels the playing field among surgeons. The instant precision it provides is ideally suited for inexperienced surgeons who want to get a joint replacement program up and running. However, prior knee surgeries or joint deformities can make it extremely challenging to determine the true center of the mechanical axis. During those circumstances even the most experienced joint replacement specialist would benefit greatly from using robotic technology.

My robotic-assisted surgery procedures last only approximately 10 minutes longer than it takes to perform conventional surgery. That's an important consideration, because increased time on the table is associated with significant morbidity in joint replacement procedures.

Making the investment
The cost of adding robotic technology to your joint replacement OR is certainly a factor, but isn't as significant as you might expect. Implant manufacturers have teamed with robotics companies to offer the computer guidance at no cost in exchange for purchasing the company's implants. Other than the $220 to $300 the disposable array pins add to each case, robotic joint replacements cost no more than they would with conventional instrumentation. OSM