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Your Primer on Total Knee Systems
Choose the right implant, cutting guides and instruments to streamline your outpatient joint program.
Kendal Gapinski
Publish Date: June 2, 2016   |  Tags:   Orthopedics
total knee replacement TOOLS OF THE TRADE When it comes to total knee replacement, you have several options for instrumentation and implants.

There are hundreds of total knee systems on the market. That can make choosing and stocking arthroplasty instrumentation, cutting guides, implants and other equipment an overwhelming task if you're just starting out with your total joint program. But to be successful, you need to have a streamlined inventory, especially if you're in a smaller facility that wasn't designed to perform total joint procedures. Here's a look at a few of your total knee system options best suited for outpatient cases.

When you start looking at your options for total knee replacement, it can be helpful to break the systems down into a few larger categories. These groups are broad, but most manufacturers have a system that falls into one of these sets, says Keith R. Berend, MD, an orthopedic surgeon with Joint Implant Surgeons, Inc., and CEO and president of White Fence Surgical Suites in New Albany, Ohio.

  • Standard systems. Most surgeons use a conventional system for a majority of their arthroplasty cases. Standard systems are typically comprised of several trays of reusable instruments and power tools, cutting templates and off-the-shelf implants designed to work with a large range of patients. Within each system, the style of the implant, sizes, materials and more can vary (see "Which Style Implant to Choose?" on p. 48). Most standard total knee systems use anywhere from 7 to 9 large trays per case, though you can work with your vendor to reduce that number. Standard systems are usually more affordable, more accessible and give surgeons more options during the procedure. However, they also can be cumbersome to store and process in smaller facilities.
  • Robotic-assisted systems. These systems use computer navigation and intelligent instruments to help position and fit the implant during surgery. They either use a pre-op CT scan of the patient's knee or specialized handheld instruments to map out the patient's anatomy and create a computerized template. This virtual surgical plan then guides the surgeon as he makes cuts in the bone, eliminating the need for standard mechanical cutting guides. "Robotic-assisted systems may help improve accuracy in some cases, but they may not be of value to high-volume or experienced surgeons, and may also be cumbersome in the outpatient environment," says Dr. Berend.
outpatient total joints
  • Single-use systems. Surgeons using these systems use disposable instrumentation and cutting templates to shape the knee and place an off-the-shelf prosthesis. They tend to be lighter than conventional trays, may ease cleanup after cases and are marketed with claims of limited reprocessing and storage requirements. Still new to the market, there are few options available and evidence supporting some manufacturer claims — like a lower risk of infection — is still limited.
  • Patient-specific systems. These include custom-designed instrumentation that fits each individual patient's anatomy. There are 2 main types of patient-specific technology on the market: patient-specific cutting templates and patient-specific total knee implants. For the cutting guides, patients first undergo a pre-op MRI or CT scan. That is then used to make the custom, disposable cutting jig, and the surgeon then places an off-the-shelf knee implant. For patient-specific implants, patients also receive a pre-op CT scan, but the manufacturer then 3D prints a custom cutting jig and a custom implant. These are delivered to the facility, along with all of the single-use instrumentation needed for the case, in a single box.

Administrators may like that these specialty systems can keep on-the-shelf inventory low, says David J. Raab, MD, CEO and president of the Illinois Sports Medicine and Orthopedic Surgery Center in Morton Grove. However, surgeons may dislike their lack of surgical and technical options, and you might still have to have back-up devices on hand in case the surgeon isn't happy with the options provided, says Dr. Berend. "While they may become the new standard eventually, today single-use, patient-specific and robotic-assisted systems are still relatively new to the market and evidence supporting any advantages of standard equipment is limited," he says.

While some doctors are embracing these new, technology-driven knee systems, Dr. Raab notes that a successful outpatient program takes more than just new instrumentation and implants. "There are some who believe that things like patient-specific cutting blocks make a difference, since in some instances it can minimize the necessity of having other implants or instruments in the room, or possibly help reduce blood loss," he says. "But, a minimally invasive surgical technique, good patient selection and education, and multimodal pain management play a bigger role in your success."

Which Style Implant to Choose?

knee implant IMPLANT DECISIONS After you choose a knee system, your surgeons will need to select an implant.

Within each type of knee system are also several different implant designs. The surgeon chooses the implant style based on his technique and the patient's anatomy, but here's a quick overview of some of the differences.

  • Implant designs. A surgeon can choose from 4 different implant designs, depending on their manufacturer's availability within a particular system: cruciate-retaining (CR), posterior-stabilized (PS), bicruciate-retaining (BCR) and unicompartmental. CR implants let the surgeon preserve the patient's posterior cruciate ligament, if it's still intact. However, PS implants let the surgeon remove the ligament and replace it with a cam-and-post system. BCR designs are relatively new to the market and are designed to save both the anterior and posterior cruciate ligaments. Unicompart-mental knees replace just one side of the joint and work well in outpatient settings, though they are less common than total joint replacement.
  • Fixation. While some implants are attached using fast-curing bone cement, cementless prostheses are made of a material that attracts new bone growth to keep the device in place. Both approaches work well, says Paul W. Manner, MD, a professor at the University of Washington School of Medicine and author of AAOS's OrthoGuide to Knee Replacement Implants, though more surgeons are moving to cementless options since it's an easier operation, takes less time and can be a better fit in younger patients.
  • Tibial components. Most patients get a fixed-bearing implant, where the polyethylene cushion of the tibial component is attached firmly to the metal tray beneath it. Mobile-bearing implants have a cushion that moves freely in this tray, allowing for a few more degrees of rotation. Dr. Manner notes that surgeons may use mobile-bearing implants on younger, more active patients since the devices require more support from surrounding soft tissue.

— Kendal Gapinski

Finding the right fit
Finding the right fit requires close collaboration with your surgeons and materials manager. Dr. Berend notes that his center has embraced a system where surgeons use a conventional total knee system but work collaboratively to "downsize the footprint" of it. "By improving our workflow and pre-op planning, we're able to trim down the standard 7 to 9 trays use in total knee replacements to 2 to 3," he says.

Here's how it works: Surgeons send their pre-op surgical plan to the facility a week ahead of time, and include basic information about the case and the patient. The materials manager takes this information and coordinates with the vendor to decide what equipment needs to be in the trays, and which is optional. Let's say your surgeon informs you that he'll be replacing the left knee of a 5-foot-2 woman. "Using that information, your materials manager can work with your vendor to create 2 customized trays that include instrumentation and cutting templates in a size range suitable for smaller adults and only for the left knee," says Dr. Berend. "This tweak alone can dramatically cut the number of trays used in each case, since many standard systems automatically come with a large range of sizes and instruments used for both the right and left knee."

Lawrence J. Parrish, MBA, administrator and COO of the Illinois Sports Medicine and Orthopedic Surgery Center, says his center has taken a similar approach. When his surgeons started doing outpatient total joints, the center's leadership looked at the large, generic trays the docs were using in their hospital cases and worked to streamline them. "We met with the surgeons and implant reps to go over the tray lists and refine them, specifically targeting the soft-tissue trays," he says. "If any specialty trays are needed, they're brought in for that particular case by the vendor's reps."

By simplifying the system, not only are you making storage and processing easier, you're also boosting efficiency for staff and surgeons. "As a surgeon, these procedures should eventually become routine," says Dr. Raab. "You should be able to cut down on the things that are unnecessary and slowing you down."

Dr. Berend notes that it also means you can take on one-off special cases. "I recently worked on a case where the patient had a femoral nail in place. That meant I needed handheld navigation for the procedure, which isn't something that's routinely kept on the shelf at the surgery center," he explains. "Our materials manager coordinated this request with our vendor, who was then able to ensure I had the equipment I needed without placing an additional burden on the center's inventory." OSM