The knee is much more than a simple hinge. It is the largest joint in the body and provides us with the mobility we usually take for granted. 

The knee joint is made up of three bones: the femur, tibia and patella (the kneecap). These bones are held together by ligaments and tendons, including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), lateral collateral ligament (LCL), medial collateral ligament (MCL) and patella tendon.

In orthopedics, malalignment occurs when the bones and joints are not lined up correctly. As a result, the body’s load (i.e. weight) is not shared evenly, but instead is carried disproportionately by the body’s other joints. Malalignment is typically described as a deviation of greater than 3º from the limb’s mechanical axis, with the mechanical axis defined as an imaginary line that runs from the center of the femoral head (in the hip socket) to the center of the ankle through the knee.

Over time, poorly aligned implants can cause loosening and pain, potentially requiring revision surgery. Poorly aligned implants are estimated to account for approximately 16% of total knee revision surgeries. An estimated 31% of TKA procedures result in poorly aligned knee implants.

Total knee arthroplasty (TKA), or total knee replacement, is a surgical procedure in which the portions of the femur, tibia and (typically) patella that form the knee joint are replaced with plastic and metal surfaces.

In a healthy knee, the ends of the bones that form the joint are covered by cartilage. However, when a surgeon suggests that a total knee arthroplasty is appropriate, the cartilage is typically damaged or worn away, commonly as a result of osteoarthritis, leaving the bone exposed and causing severe pain. Knee replacement is generally the treatment of last resort for osteoarthritis.

The term “conventional instrumentation” refers to the metal guides and cutting blocks that are used in approximately 97% of TKAs. These instruments do not contain computers and are purely mechanical.

In total knee arthroplasty, the term “computer-assisted surgery,” or “CAS,” describes the large computer systems (often the size of a podium) that are sometimes used in the operating room to provide the surgeon with precise information on the angles of the knee bone cuts that the surgeon is making. Large console computer-assisted surgery has been shown to significantly reduce the rate of poorly aligned knee implants as compared to total knee arthroplasty performed using conventional instrumentation.²⁶ However, large console computer-assisted surgery has failed to gain widespread acceptance among orthopedic surgeons for a variety of reasons, including the extended learning curves, longer average procedure times and high product prices they typically entail. It is estimated that currently only 3% of total knee arthroplasty procedures in the United States use computer-assisted surgery.²⁷

The KneeAlign™ system is a surgical navigation system that is equivalent to computer-assisted surgery in precisely measuring tibial cuts in total knee arthroplasty (TKA). The KneeAlign™ system, however, is much lower in cost and far easier for the surgeon to use than large console computer-assisted surgery. The KneeAlign™ navigation unit is slightly larger than a smartphone.

Visit our Products and Technology page for more information about the KneeAlign™ system