Kinematic Alignment

What is Kinematic Alignment (TKA)?

Kinematic alignment (KA) is a customized technique for total knee arthroplasty (TKA) that aims to anatomically position and kinematically align total knee components with the aim of restoring the native, pre-arthritic joint lines and rotational axes of a patient’s knee. The interaction between the ligaments, menisci, and articular surfaces of the femur, tibia, and patella determine the kinematics of the normal knee and are described by three kinematic axes. Total knee replacement, also called total knee arthroplasty, is a surgical procedure in which the worn-out or damaged parts of the knee joint are removed and replaced with artificial knee components called prostheses or implants.

Traditionally, most knee replacements are aligned by way of a philosophy called the mechanical alignment (MA) method. This aims to align every knee replacement the same way in all patients. The goal is a “straight” leg. When we look at the natural alignment of native knees, we see that as with all biological phenomena, there is a variation. Most knees are naturally not “straight”. In fact, only 2 percent of natural knees are straight when measured using the hip-knee-ankle (HKA) method on X-ray. Mechanical alignment seeks to put every patient into a “straight” alignment with a HKA of 0 degrees.

The soft tissues of each knee are designed to rotate around the individual kinematic axes of that knee. In addition to their alignment, each patient has a specific, and different, set of rotational axes. Kinematic alignment of a total knee arthroplasty seeks to replicate these axes and the overall shape of the knee and put the knee into the alignment it was in prior to the development of arthritis and deformity.

Anatomy of the Knee

The knee is made up of the femur (thighbone), tibia (shinbone), and patella (kneecap). The lower end of the femur meets the upper end of the tibia at the knee joint. A small disc of bone called the patella rests on a groove on the front side of the femoral end. The fibula, another bone of the lower leg, forms a joint with the shinbone. The bones are held together by protective tissues, ligaments, tendons, and muscles. Synovial fluid within the joint aids in the smooth movement of the bones over one another. The meniscus, a soft crescent-shaped area of cartilage between the femur and tibia, serves as a cushion and helps absorb shock during motion.

Indications for Kinematic Alignment (TKA)

Kinematic alignment for total knee arthroplasty is usually recommended to prevent the undesirable consequences of abnormal kinematics associated with mechanical alignment such as instability, motion loss, accelerated component wear, and component loosening from uneven load-sharing between compartments. The principle of kinematically aligned TKA is to restore the three kinematic axes of the normal knee. Because the knee moves in a more natural way, patients experience better bending of the knee and a faster return to function. Patients report a more natural-feeling knee. In this technique, the position is customized to each and every knee.

Preparation for Kinematic Alignment (TKA)

The preoperative preparation for kinematic alignment for TKA is similar to traditional knee replacement procedures. But contrary to traditional techniques, kinematic alignment for knee replacement involves careful planning and utilizes a series of CT scans to generate 3D images of an individual’s unique knee anatomy. These images enable the surgeon to design a personalized plan tailored to an individual and help determine the precise bone cuts and implant size prior to performing the surgery.

In addition, preparation for kinematic alignment total knee arthroplasty may involve the following steps:

• A review of your medical history and a physical examination by your doctor to check for any medical issues that need to be addressed prior to surgery.
• Diagnostic tests such as blood work and imaging to help detect any abnormalities that could compromise the safety of the procedure.
• You will be asked if you have allergies to medications, anesthesia, or latex.
• You should inform your doctor of any medications or supplements that you are taking or any conditions you have such as heart or lung disease.
• You may be asked to avoid medications such as blood thinners or anti-inflammatories for a specific period prior to surgery.
• You should refrain from alcohol or tobacco at least a few days prior to the surgery and several days after as they can hinder the healing process.
• You should not consume solids or liquids at least 8 hours prior to surgery.
• You should arrange for someone to drive you home after surgery.
• A signed informed consent will be obtained from you after the pros and cons of the surgery have been explained.

Procedure for Kinematic Alignment (TKA)

Total knee arthroplasty surgery using the kinematic alignment technique is performed under spinal or general anesthesia. Your surgeon will make an incision on the skin over the affected knee to expose the knee joint. The damaged portions of the femur bone are cut at appropriate angles using specialized jigs. The femoral component is attached to the end of the femur with or without bone cement. 

Your surgeon then cuts or shaves the damaged area of the tibia and the cartilage. This removes the deformed part of the bone and any bony growths, as well as creates a smooth surface on which the implants can be attached. Next, the tibial component is secured to the end of the bone with bone cement or screws. 

Your surgeon will place a plastic piece called an articular surface between the implants to provide a smooth gliding surface for movement. This plastic insert will support the body’s weight and allow the femur to move over the tibia like the original meniscus cartilage. 

The femur and the tibia with the new components are then put together to form the new knee joint. To make sure the patella glides smoothly over the new artificial knee, its rear surface is also prepared to receive a plastic component. With all the new components in place, the knee joint is tested through its range of motion.

During kinematic alignment total knee arthroplasty, the knee component is inserted in the exact position that matches the position of the native knee before the patient develops arthritis. Effectively, your surgeon will remove the exact same thickness of bone that matches the thickness of the new metal knee placing the new metal knee in the same position as the original knee. Your surgeon will use pre-operative CT scans to assist with this planning; however, your surgeon may also utilize specialized instruments and measuring devices that allow them to do it in the event a CT scan cannot be done before surgery. Your surgeon literally measures each small cut of bone to the millimeter to ensure an accurate kinematic alignment knee reconstruction.

Finally, the incisions are closed with sutures and sterile dressings are applied.

Postoperative Care and Recovery

In general, postoperative care instructions and recovery after kinematic alignment total knee arthroplasty will involve the following steps:

• You will be transferred to the recovery area where your nurse will monitor your vital signs as you recover from the effects of anesthesia.
• You may experience pain, swelling, and discomfort in the knee area. Pain and anti-inflammatory medications are provided as needed to address these.
• Antibiotics are also prescribed to address the risk of surgery-related infection.
• You are encouraged to walk with assistance as frequently as possible around the hospital bed to prevent the risk of blood clots.
• Instructions on surgical site care and bathing will be provided to keep the wound clean and dry.
• You will be placed on crutches for the first few weeks with instructions on restricted weight-bearing.
• You are advised to keep your leg elevated above the heart level for a defined period while resting to prevent swelling and pain.
• Refrain from strenuous activities and lifting heavy weights for the first few months. A gradual increase in activities over a period of time is recommended.
• An individualized physical therapy regimen will be designed to help strengthen your knee muscles and optimize knee function once you are off crutches.
• You should be able to resume your normal activities in a couple of months, but with certain activity restrictions. Returning to sports or high-intensity activities may take at least 6 months or longer.
• Refrain from driving until you are fully fit and receive your doctor’s consent.
• A periodic follow-up appointment will be scheduled to monitor your progress.

Risks and Complications

Kinematic alignment total knee arthroplasty is a relatively safe procedure; however, as with any surgery, there are risks and complications that can occur, such as:

• Pain
• Bleeding
• Infection
• Knee stiffness
• Blood clots or deep vein thrombosis (DVT)
• Allergic/anesthetic reactions
• Injury to soft-tissue structures, such as nerves and blood vessels