The question of whether the Anterior Cruciate Ligament (ACL) remains after a total knee replacement, known as Total Knee Arthroplasty (TKA), is common for patients considering the procedure. TKA involves resurfacing the damaged ends of the thigh bone (femur) and shin bone (tibia) with metal and plastic components to alleviate pain and restore function. The fate of the ACL is a procedural decision that impacts the design of the artificial joint and how stability is achieved. In nearly all standard TKA procedures, the ACL is removed to accommodate the prosthetic components and optimize the long-term mechanics of the new joint.
Function of the Anterior Cruciate Ligament
The Anterior Cruciate Ligament is a band of connective tissue situated deep within the knee joint, connecting the femur to the tibia. Its primary function is to prevent the tibia from sliding too far forward beneath the femur, a motion known as anterior translation. The ACL provides approximately 85% of the restraining force against this forward movement and also limits excessive rotation of the knee joint. Furthermore, the ACL contains specialized nerve endings called mechanoreceptors, which contribute to proprioception—the body’s sense of joint position and movement.
ACL Management During Total Knee Replacement
The standard answer is that the ACL is almost always removed, or “sacrificed,” during Total Knee Arthroplasty. This removal is a deliberate and necessary step for most implant designs, especially since the ACL is often already nonfunctional or frayed in patients with advanced arthritis. The surgical preparation of the tibia requires the bone’s upper surface to be cut flat to accept the metallic tibial tray component. This bone cut fundamentally removes the ACL’s insertion point, making its retention technically impossible with conventional implants. Removing the ligament also creates the physical space required for the proper placement and fit of the prosthetic components.
TKA designs are categorized based on how they manage the posterior cruciate ligament (PCL), but the ACL is still removed in nearly all cases. The two main categories are Cruciate-Retaining (CR) and Posterior-Stabilized (PS) designs. Even in CR designs, which retain the PCL, the ACL is sacrificed to ensure proper tracking of the prosthetic joint surfaces. The majority of TKA procedures utilize designs that sacrifice both the ACL and, in PS implants, the PCL. This deliberate removal allows the surgeon to achieve optimal soft tissue balancing and alignment.
While a few highly specialized implants are designed to preserve both the ACL and PCL—known as bicruciate-retaining designs—these represent a small minority of procedures and are not the standard of care.
Stability in the Prosthetic Knee
When the native ACL is removed, the stability it provided is replaced by the mechanical design and geometry of the artificial components. The implant is engineered to provide the necessary restraint against excessive forward and backward movement. Stability is also achieved by the surgeon balancing the remaining soft tissues, such as the collateral ligaments, which prevent side-to-side instability.
The most common type of implant, the Posterior-Stabilized (PS) design, uses a unique mechanical feature to compensate for the loss of both the ACL and PCL. This mechanism is called the “post and cam” system. The polyethylene insert on the tibia features a vertical projection, or “post,” which engages with a curved surface, or “cam,” on the underside of the femoral component.
As the knee bends, the cam interacts with the post, forcing the femoral component to roll backward on the tibial component. This mechanical engagement physically prevents the tibia from sliding too far forward, replicating the function of the sacrificed ligaments. The result is a mechanically stable joint where movement forces are contained by the prosthetic components.