When considering knee replacement surgery, a common question arises regarding the fate of the anterior cruciate ligament (ACL). Knee replacement procedures involve different approaches, which influence whether the ACL remains after surgery. Understanding these differences can help clarify expectations regarding post-operative knee function.
Understanding the ACL and Knee Replacement
The anterior cruciate ligament, or ACL, is a band of strong connective tissue located within the knee joint. It connects the thigh bone (femur) to the shin bone (tibia), running diagonally across the front of the knee. The ACL’s primary role involves preventing the tibia from sliding too far forward under the femur and limiting excessive twisting of the knee joint. This ligament works with other structures, including the posterior cruciate ligament (PCL), to maintain overall knee stability and guide its motion.
Knee replacement surgery, known as arthroplasty, involves resurfacing damaged bone and cartilage with artificial components, or implants. The extent of this replacement varies, with two main types being total knee replacement (TKR) and partial knee replacement (UKR). A total knee replacement resurfaces all three compartments of the knee, while a partial knee replacement addresses only the diseased portion of the joint. These procedures aim to alleviate pain and restore mobility caused by conditions like osteoarthritis.
ACL Status After Total Knee Replacement
In the majority of total knee replacement (TKR) procedures, the anterior cruciate ligament (ACL) is removed. ACL removal is standard practice, even if healthy. The removal is often necessary to create adequate space for the artificial joint components and to facilitate proper placement of the implants. Prosthetic designs, such as posterior-stabilized (PS) implants, are specifically engineered to function without the ACL, often incorporating a cam-and-post mechanism to replicate its stabilizing role.
While some newer TKR designs aim to preserve the ACL, these are not as widely used as traditional designs. Early attempts at ACL-preserving total knee replacements faced challenges, including premature wear of components. In many cases of severe knee arthritis, the ACL may already be compromised or degenerated, making its removal a practical step during the procedure.
ACL Status After Partial Knee Replacement
Partial knee replacement (UKR), also known as unicompartmental knee arthroplasty, presents a different scenario regarding the ACL. In this less extensive procedure, the surgeon replaces only one of the knee’s three compartments, typically the medial compartment. A significant advantage of UKR is the potential to preserve the patient’s existing ACL, along with other healthy ligaments. This preservation is possible because the surgery is confined to a smaller area of the knee, leaving the undamaged parts intact.
For a patient to be a candidate for UKR with ACL preservation, their ACL must be healthy and fully functional before the surgery. If the ACL is torn or significantly damaged, a partial knee replacement might not be suitable unless combined with an ACL reconstruction. The ability to retain the native ACL in UKR is considered a benefit, as it can contribute to a more natural feeling knee and potentially better knee movement.
Functional Implications of ACL Status
The presence or absence of the ACL after knee replacement has implications for how the knee functions post-surgery. Following a total knee replacement where the ACL is typically removed, the knee achieves stability through the design of the artificial implants and the balance of surrounding soft tissues. Modern TKR designs are highly effective at restoring knee function, allowing patients to regain mobility and reduce pain.
For partial knee replacement, retaining the ACL can offer certain advantages. The preserved ACL can contribute to improved proprioception, which is the body’s sense of joint position and movement. This can lead to better knee kinematics. While some studies suggest benefits in proprioception and kinematics with ACL preservation, other research indicates that maintaining the ACL in UKR may not always translate to a measurable improvement in proprioceptive feedback. Ultimately, both total and partial knee replacement procedures are designed to provide a stable, functional knee, with implant technology continuously evolving to optimize patient outcomes.